1 Scope
NOTE This specification covers stationary battery systems consisting of a battery (one or more series strings of cells), one or more battery chargers, a DC distribution panel, and the associated monitoring, alarms, room ventilation, and spill containment, intended to supply 24, 48, 125, or 250 nominal volts DC to critical control and protection loads. (1.1)
1.2 Equipment and installation shall comply with the referenced IEEE standards for the selected chemistry and with NFPA 70 Article 480 for the storage battery installation.
1.3 Where the project is a substation or generating station under the exclusive control of an electric utility, the utility's adopted edition of IEEE C2 (National Electrical Safety Code) governs and the present standard shall be applied in a manner consistent with that code.
1.4 Basis of Design
NOTE A DC battery system is a continuously available source whose first job is to operate switchgear protective relays, trip and close coils, and emergency control loads when the AC supply is disturbed or absent. (1.4.1)
1.4.2 The system shall be designed for the worst-case duty cycle that can occur during an AC outage — including momentary inrush from breaker close coils — and not for an average load.
1.4.3 The Contractor and the Engineer shall treat the duty cycle, not the steady float current, as the basis of design.
1.5 Lithium-Ion Exclusion
1.5.1 This standard does not cover lithium-ion energy storage systems intended for grid-side or behind-the-meter energy applications; those systems trigger the full NFPA 855 / UL 9540 code stack and shall be specified separately.
1.5.2 Where a utility-style lithium chemistry is proposed as a direct replacement for a VRLA control battery, the requirements of NFPA 855 and UL 9540 / UL 1973 shall be applied in addition to this standard.
1.5.3 The Engineer of Record shall confirm the listing and the local AHJ position before procurement of any proposed lithium-ion control battery.
1.6.1 Grounding of the DC system and bonding of the battery rack and enclosures shall be in accordance with Grounding And Bonding. 2 Referenced Standards
2.1 Equipment, materials, and installation shall comply with the latest adopted edition of the following standards and codes.
2.2 Where the contract documents, the adopted building code, or a referenced standard conflict, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.
2.3 Standards List
| Standard |
Title |
| NFPA 70 |
National Electrical Code (Article 480 — Stationary Standby Batteries) |
| NFPA 70E |
Standard for Electrical Safety in the Workplace |
| NFPA 855 |
Standard for the Installation of Stationary Energy Storage Systems |
| IEEE C2 |
National Electrical Safety Code |
| IEEE 450 |
Recommended Practice for Maintenance, Testing, and Replacement of Vented Lead-Acid Batteries for Stationary Applications |
| IEEE 484 |
Recommended Practice for Installation Design and Installation of Vented Lead-Acid Batteries for Stationary Applications |
| IEEE 485 |
Recommended Practice for Sizing Lead-Acid Batteries for Stationary Applications |
| IEEE 946 |
Recommended Practice for the Design of DC Power Systems for Stationary Applications |
| IEEE 1106 |
Recommended Practice for Installation, Maintenance, Testing, and Replacement of Vented Nickel-Cadmium Batteries for Stationary Applications |
| IEEE 1115 |
Recommended Practice for Sizing Nickel-Cadmium Batteries for Stationary Applications |
| IEEE 1187 |
Recommended Practice for Installation Design, Installation, and Maintenance of Valve-Regulated Lead-Acid Batteries for Stationary Applications |
| IEEE 1188 |
Recommended Practice for Maintenance, Testing, and Replacement of Valve-Regulated Lead-Acid (VRLA) Batteries for Stationary Applications |
| IEEE 1491 |
Guide for Selection and Use of Battery Monitoring Equipment for Stationary Applications |
| IEEE 1578 |
Recommended Practice for Stationary Battery Electrolyte Spill Containment and Management |
| IEEE 1635 / ASHRAE 21 |
Guide for the Ventilation and Thermal Management of Batteries for Stationary Applications |
| UL 1973 |
Standard for Batteries for Use in Stationary, Vehicle Auxiliary Power and Light Electric Rail Applications |
| UL 1989 |
Standby Batteries (chargers and stationary battery products) |
| UL 924 |
Emergency Lighting and Power Equipment (where applicable) |
| IBC |
International Building Code (stationary storage battery system provisions) |
| IFC |
International Fire Code (stationary storage battery system provisions) |
| ASCE 7 |
Minimum Design Loads and Associated Criteria for Buildings |
| ANSI/NETA ATS |
Standard for Acceptance Testing Specifications for Electrical Power Equipment and Systems |
3 Submittals
3.1 Action Submittals
3.1.1 Contractor shall submit the following for the Engineer's review prior to fabrication and procurement.
3.1.2 No portion of the DC system shall be ordered or installed before the corresponding submittals are reviewed and returned.
3.1.3 Contractor shall submit the following action submittals
- Battery sizing calculation per IEEE 485 (lead-acid) or IEEE 1115 (Ni-Cd), showing the assumed duty cycle, end-of-discharge voltage, design margin, aging factor, and temperature correction factor
- Charger sizing calculation per IEEE 946, showing the assumed continuous DC load, recharge current, and recharge time
- Product data for the cells or monoblocs, the charger(s), the DC distribution panel, the battery rack, the battery monitor, and the spill containment system
- Shop drawings showing the battery rack elevation, cell or jar arrangement, charger and DC panel locations, conduit and cable routing, and clearances in the battery room or cabinet
- One-line diagram of the DC system showing the battery, the charger(s), the DC distribution, downstream protective devices, and all monitoring and alarm points
- Cable sizing calculations including ampacity, voltage drop, and short-circuit withstand for the battery cables and DC feeders
- Ventilation calculation per IEEE 1635, showing the assumed hydrogen evolution rate, the required dilution airflow, and the air-change rate or sustained ventilation rate
- Seismic certification documentation for the battery rack and the charger, where required by the applicable building code
- Manufacturer's installation instructions for the cells, the rack, and the spill containment system
☑ Battery sizing calculation (IEEE 485 or IEEE 1115)
☐ Charger sizing calculation (IEEE 946)
☐ Product data for cells, charger, DC panel, rack, monitor, containment
☐ Battery room / cabinet shop drawings with clearances
☐ DC system one-line diagram
☐ DC cable sizing calculations (ampacity, voltage drop, short-circuit)
☐ Ventilation calculation (IEEE 1635)
☐ Seismic certification for rack and charger
☐ Manufacturer installation instructions
3.2 Closeout Submittals
3.2.1 Contractor shall provide the following at substantial completion before the DC system is accepted into service:
- Operation and maintenance manuals for the battery, the charger, the DC panel, and the monitoring system
- Acceptance test reports per IEEE 450 or IEEE 1188 (lead-acid) or IEEE 1106 (Ni-Cd), signed by the testing technician
- Initial commissioning test report including the load test or modified performance test, charger functional test, and alarm verification
- As-built drawings reflecting the installed battery configuration, cell numbering, polarity, and cable terminations
- A baseline record of intercell connection resistances, individual cell or monobloc float voltages, and individual cell or monobloc internal resistance or conductance
- Warranty documentation from the cell manufacturer and the charger manufacturer
- A recommended maintenance schedule keyed to IEEE 450, IEEE 1188, or IEEE 1106 as applicable
- A copy of the safety data sheet for the electrolyte
☑ Operation and maintenance manuals (battery, charger, DC panel, monitor)
☐ Acceptance test reports (IEEE 450 / 1188 / 1106), signed
☐ Initial commissioning test report (load/performance, charger, alarms)
☐ As-built drawings (configuration, cell numbering, polarity, terminations)
☐ Baseline record (intercell resistances, float voltages, internal resistance)
☐ Warranty documentation (cells and charger)
☐ Recommended maintenance schedule (IEEE 450 / 1188 / 1106)
☐ Electrolyte safety data sheet
4 Quality Assurance
4.1 Manufacturer Qualifications
4.1.1 Cells, chargers, and racks shall be supplied by manufacturers regularly engaged in the production of stationary battery systems for utility, substation, or industrial control applications, with a minimum of five years of documented experience in the specified chemistry.
4.1.2 The cell manufacturer shall publish performance data — capacity versus discharge rate, capacity versus temperature, float current, and expected service life — for the specific cell type proposed.
4.2 Source Limitations
4.2.1 The cells of a single battery shall be from a single manufacturer, of a single type and design, and of a single date code or production lot to the extent practical.
4.2.2 Mixing of cell types, ages, or capacities within a single battery is not permitted.
NOTE Cells with different characteristics in series will not share the load uniformly, and the weakest cell will dictate the battery's performance and life. (4.2.3)
4.3 Testing Personnel Qualifications
4.3.1 Acceptance and performance testing shall be performed by a firm regularly engaged in testing stationary batteries, employing technicians trained in the test procedures of IEEE 450, IEEE 1188, or IEEE 1106 as applicable to the chemistry.
4.3.2 Testing personnel shall demonstrate experience with the discharge load bank, the cell-voltage data acquisition system, and the manufacturer's specific procedures for the cells being tested.
4.4 Listing and Labeling
4.4.1 The charger shall be listed and labeled to UL 1989 by a Nationally Recognized Testing Laboratory.
4.4.2 The DC distribution panel and DC overcurrent devices shall be listed for DC service at the system voltage.
4.4.3 Cells and monoblocs shall be listed to UL 1973 where required by the AHJ or the applicable code.
4.4.4 In traditional substation control applications the AHJ commonly accepts cells designed and manufactured to the relevant IEEE recommended practice without separate UL listing, and the Engineer of Record shall confirm the local position before procurement.
5 Environmental and Service Conditions
NOTE Battery performance is strongly dependent on temperature. (5.1)
5.2 The Engineer shall establish the design ambient temperature range of the battery room or cabinet, and the Contractor shall apply the corresponding temperature correction factor in the sizing calculation.
5.3 The room or cabinet shall be conditioned and ventilated to keep the battery within the temperature range used for sizing and for service-life prediction.
5.4 Design Ambient Temperature
25°C (77°F) — conditioned battery room (reference)
20°C–25°C (68°F–77°F) — conditioned
5°C–40°C (41°F–104°F) — unconditioned interior
Outdoor cabinet, full ambient range — site specific
NOTE The reference temperature for stationary battery capacity ratings is 25°C (77°F); capacity decreases at lower temperatures and increases (with accelerated aging) at higher temperatures. (5.4.1)
NOTE A battery sized at 25°C and installed in an unconditioned space that routinely operates at 10°C may deliver substantially less than its rated capacity at the time it is most needed; conditioning the battery space to the reference temperature is, in most cases, less expensive over the life of the system than the cell oversizing required to compensate for cold operation. (5.4.2)
5.5 Temperature Correction Factor
25°C (no correction)
21°C (1.04 multiplier, typical conditioned space minimum)
15°C (1.11 multiplier)
10°C (1.19 multiplier)
5°C (1.25 multiplier)
0°C (1.30 multiplier)
5.5.1 The Contractor shall apply a temperature correction factor in the sizing calculation, taken from the cell manufacturer's published data or from the tables in IEEE 485 (for VLA) or IEEE 1115 (for Ni-Cd).
5.5.2 The temperature correction shall be applied to the minimum expected battery temperature during a discharge, not the average.
5.5.3 A 125 VDC station battery sized for a 25°C room but allowed to drop to 0°C during a winter outage will see roughly a 20–25 percent capacity reduction at the moment of discharge and shall be sized accordingly.
5.5.4 The multipliers above are representative of vented lead-acid cells discharged at moderate rates; the Contractor shall use the cell manufacturer's published correction factor for the specific cell type, discharge rate, and end-of-discharge voltage of the project duty cycle.
5.6 Maximum Battery Temperature
5.6.1 Battery space cooling shall keep the maximum continuous cell temperature at or below 25°C where the published design life is to be achieved.
NOTE Lead-acid float current and the rate of grid corrosion roughly double for every 10°C above 25°C, so a VRLA battery operated continuously at 35°C will reach end of life in approximately half the service hours of one operated at 25°C. (5.6.2)
5.7 Altitude and Humidity
NOTE Stationary battery performance is not strongly altitude-dependent within the range of typical installations. (5.7.1)
5.7.2 Charger output ratings shall be confirmed for the installation altitude per the charger manufacturer's data.
5.7.3 Battery rooms shall be kept dry.
NOTE Standing water or persistent high humidity accelerates corrosion of intercell connections and of the rack itself. (5.7.4)
5.8 Seismic Requirements
Not required
IBC/ASCE 7 — Importance Factor 1.0
IBC/ASCE 7 — Importance Factor 1.5 (essential facility)
OSHPD pre-approval required (California healthcare)
5.8.1 Where required by the applicable building code, the battery rack and the charger shall be seismically certified by shake-table testing per ICC ES AC156 or by analysis per ASCE 7.
5.8.2 The rack shall be designed to retain the cells during a seismic event without damaging the intercell connectors or the cell jars.
5.8.3 Site-specific anchorage shall be designed by the Engineer of Record and shown on the contract drawings.
6 Battery Selection
6.1 Chemistry
○ Vented lead-acid (VLA, flooded)
● Valve-regulated lead-acid (VRLA, AGM or gel)
○ Vented nickel-cadmium (Ni-Cd, pocket plate or fiber plate)
○ Lithium-ion (NFPA 855 / UL 9540 applies)
6.1.1 The Engineer shall make the chemistry selection early in design.
NOTE The chemistry decision drives almost every downstream requirement in this standard — cell sizing method, charger float voltage, ventilation, spill containment, room layout, monitoring strategy, maintenance interval, and design life. (6.1.2)
NOTE Vented lead-acid (VLA) cells offer the longest published design life (commonly 20 years), the most predictable end-of-life behavior, and the longest history of utility service, at the cost of higher ventilation requirements during charging and equalize, mandatory electrolyte maintenance, and the largest room footprint per kilowatt-hour of stored energy. (6.1.3)
NOTE Valve-regulated lead-acid (VRLA) cells eliminate routine electrolyte maintenance and produce far less hydrogen under normal float operation, allowing more compact installations and use in cabinets rather than dedicated rooms; they are less tolerant of high temperatures than VLA, more difficult to assess by float voltage alone, and have a shorter published design life — typically 10 to 15 years for long-life telecom-grade product, and as short as 5 to 8 years for general-purpose VRLA installed in poorly conditioned spaces. (6.1.4)
NOTE Vented nickel-cadmium (Ni-Cd) cells tolerate a wider temperature range, tolerate deep discharge and partial-state-of-charge operation without measurable harm, and resist thermal runaway in service; they are more expensive per kilowatt-hour, require a higher number of cells for a given nominal voltage, and require different charger float and equalize voltages, and are the conventional choice for outdoor cabinets in extreme climates and for installations where occasional deep discharge is expected. (6.1.5)
NOTE Specifying lithium-ion brings NFPA 855 and UL 9540 into scope and is outside the typical control-battery application. (6.1.6)
6.1.7 Lithium-ion in this application shall not be selected without explicit AHJ confirmation and a separate hazard mitigation analysis where required.
6.2 Nominal Voltage
○ 24 VDC
○ 48 VDC
● 125 VDC
○ 250 VDC
6.2.1 Nominal DC voltage shall be dictated by the connected protective relays, breaker close and trip coils, communications equipment, and any inverter loads.
NOTE 125 VDC is the predominant voltage for medium-voltage and large low-voltage switchgear control in North American utility and industrial practice; 250 VDC is used at larger generating stations and where long DC cable runs to remote switchyards make a higher voltage economical; 48 VDC is the predominant voltage for telecommunications, smaller distribution substations, and packaged equipment; 24 VDC is used for small local control applications. (6.2.2)
6.3 End-of-Discharge Voltage
1.75 V/cell (lead-acid, typical short-duration duty)
1.81 V/cell (lead-acid, longer duty, higher EOD)
1.67 V/cell (lead-acid, deep discharge, severe duty)
1.00 V/cell (Ni-Cd, typical)
1.14 V/cell (Ni-Cd, higher EOD)
6.3.1 End-of-discharge (EOD) voltage shall be agreed with the Engineer before sizing, set by the lowest-voltage-tolerant load in the DC system — typically a protective relay, an inverter, or a breaker close coil.
NOTE A lower EOD allows a smaller battery (because more of the cell's capacity is usable) but increases the risk that a load drops out before the duty cycle ends; a higher EOD is conservative but increases cell count and size. (6.3.2)
6.3.3 The EOD set in the sizing calculation shall be the same EOD used to determine the minimum system voltage at the end of the duty cycle, accounting for cable voltage drop between the battery terminals and the most distant load.
7 Battery Sizing
7.1 The battery shall be sized to supply the specified duty cycle, at the end-of-discharge voltage, at the minimum design temperature, at end of life, with the specified design margin.
7.2 Sizing shall follow IEEE 485 for lead-acid (VLA or VRLA) and IEEE 1115 for Ni-Cd.
7.3 The Contractor shall submit the calculation showing each factor explicitly.
7.4 Duty Cycle Development
NOTE The duty cycle is a time-versus-load profile that begins at the loss of charger output and continues through the longest expected period without recharge. (7.4.1)
7.4.2 The duty cycle shall include three load classes per IEEE 946
- Continuous loads that are present throughout the duty cycle — indicating lamps, relay holding currents, communications power, supervisory relays
- Noncontinuous loads energized for a defined portion of the duty cycle — emergency lighting transfers, motor-operated valves, recloser operations, alarm pickup
- Momentary loads, with a duration not exceeding one minute, that produce a sharp inrush — circuit breaker trip and close coils, lockout relay coils, SCADA contactor pickups
7.4.3 The duty cycle shall explicitly include at least one breaker close operation at the end of the discharge.
NOTE The momentary load at the end of the duty cycle is typically the sizing driver for a control battery, because the cell voltage is lowest then and the inrush is highest. (7.4.4)
7.4.5 Duty Cycle Duration
1 hour (typical attended substation)
4 hours
8 hours (typical unattended substation)
24 hours (remote / isolated site)
Per drawings
7.4.5.1 The Engineer shall set the duty cycle from the facility's operating concept, not from a table default.
NOTE Eight hours is the predominant duty cycle for unattended distribution substations because it brackets the time to dispatch a repair crew and restore station service; attended generating stations and stations with redundant station service may use shorter cycles, and remote sites with long restoration times use longer cycles. (7.4.5.2)
7.5 Design Margin
10% (minimum, well-defined loads)
15%
20% (typical)
25% (loads not fully developed)
7.5.1 A new substation with a fully developed relay and control schedule may use 10 percent; a battery in a building where future loads are likely to be added to the DC panel shall use 20 to 25 percent.
7.5.2 Design margin shall be applied to the calculated cell size, not to the cell quantity.
NOTE The design margin accounts for load growth and for inaccuracies in the load tabulation. (7.5.3)
7.6 Aging Factor
1.25 (standard IEEE 485 — sized to 80% of rated capacity at end of life)
1.10 (Ni-Cd per IEEE 1115)
1.00 (replacement-on-demand strategy — not recommended)
7.6.1 Sizing without an aging factor presumes the battery will be replaced at the first sign of capacity loss; this is operationally impractical for utility-style installations and shall not be used.
NOTE IEEE 485 defines end of life as the point where the cell delivers 80 percent of its rated capacity; the corresponding aging factor of 1.25 (1.00 / 0.80) ensures the battery still supplies 100 percent of the design duty cycle at end of life, while Ni-Cd cells age more gradually and IEEE 1115 commonly uses 1.10 to 1.15. (7.6.2)
7.7 Temperature Correction
7.7.1 Temperature correction shall be applied per the manufacturer's published data or per IEEE 485 / IEEE 1115 tables, using the minimum design temperature of the battery space during a discharge.
NOTE See the Environmental and Service Conditions section above for representative multipliers. (7.7.2)
7.8 Design Life
10 years (VRLA, general purpose)
15 years (VRLA, long-life telecom-grade)
20 years (VLA, utility station)
20+ years (Ni-Cd, pocket plate)
7.8.1 The Engineer shall coordinate the design life with the Owner's asset-management horizon.
NOTE Published design life is achieved at the reference temperature (25°C) under recommended float charge with the manufacturer's recommended maintenance; actual service life depends on the operating temperature, the cycling history, and the quality of maintenance, and a 20-year design life is undermined by a maintenance program that cannot survive the first ownership change. (7.8.2)
8 Battery Construction
8.1 Cells and Monoblocs
Flooded lead-acid, lead-antimony grids
Flooded lead-acid, lead-calcium grids
Pure lead, flat plate (long-life telecom)
VRLA, absorbent glass mat (AGM)
VRLA, gelled electrolyte
Ni-Cd, pocket plate
Ni-Cd, fiber plate / sintered plate
NOTE Lead-calcium grids reduce gassing and water loss compared to lead-antimony, making them the conventional choice for modern stationary VLA cells, while lead-antimony is more tolerant of cycling and is sometimes specified for batteries that see frequent discharge. (8.1.1)
NOTE AGM and gel are both VRLA constructions; AGM is the predominant choice for substation control and has better high-rate performance, while gel is sometimes preferred for hot environments because of its lower water loss. (8.1.2)
NOTE Pocket-plate Ni-Cd is the conventional substation choice in cold climates; fiber- and sintered-plate Ni-Cd offer higher energy density at higher cost. (8.1.3)
8.2 Cell Jars and Containers
8.2.1 Cell jars shall be transparent or translucent where electrolyte level is to be inspected visually (VLA, vented Ni-Cd).
8.2.2 VRLA monobloc containers shall be flame-retardant per the cell standard.
8.2.3 All jar materials shall be resistant to the electrolyte and to the cleaning agents recommended by the manufacturer.
8.3 Intercell Connections
8.3.1 Intercell connectors shall be sized to carry the maximum discharge current at the rated short-circuit fault duration without exceeding the manufacturer's allowable connector temperature rise.
8.3.2 Connectors shall be lead-plated copper, copper-clad lead, or solid lead, selected for compatibility with the cell post material.
8.3.3 Bolts shall be stainless steel or as supplied by the cell manufacturer.
8.3.4 Each intercell connection shall be installed with the manufacturer's specified anti-corrosion compound on the contact surfaces and shall be torqued to the manufacturer's specified value using a calibrated torque tool.
8.3.5 Intercell connection resistance shall be measured and recorded after installation.
NOTE The baseline intercell connection resistance values are the reference for all subsequent maintenance testing. (8.3.6)
8.4 Cell Numbering and Polarity
8.4.1 Every cell or monobloc shall be permanently numbered in series order from the positive terminal of the battery.
8.4.2 Polarity markings on the positive and negative terminals shall be permanent and unambiguous.
8.4.3 A cell numbering and polarity diagram shall be posted at the battery.
9 Battery Charger
9.1 The charger shall be a constant-voltage, current-limiting type, suitable for the specified chemistry, listed to UL 1989, and sized to carry the full continuous DC load while simultaneously recharging the battery from a fully discharged state to approximately 95 percent of rated capacity within the specified recharge time.
9.2 Charger Sizing
Continuous load + recharge in 12 hours
Continuous load + recharge in 24 hours
Continuous load + recharge in 8 hours (rapid)
Site-specific per IEEE 946 calculation
NOTE The IEEE 946 sizing formula for a lead-acid charger is approximately: (9.2.1)
Charger output (A) = 1.1 × (continuous DC load in amperes) + (battery capacity in ampere-hours × K / recharge time in hours)
NOTE where K is the manufacturer's published recharge factor (often 1.10 to 1.15 for lead-acid). (9.2.2)
9.2.3 The Contractor shall submit the charger sizing calculation showing each term.
NOTE The 1.1 multiplier on the continuous load accounts for charger derating and load growth, and a 12-hour recharge time is the predominant value for utility station applications because it leaves substantial margin for a second discharge within the same day. (9.2.4)
9.3 Charger Output Voltage Modes
Float only
Float and equalize (manual initiation)
Float and equalize (automatic, time-initiated)
Two-rate float (temperature-compensated only)
9.3.1 Equalize shall not be applied to a VRLA battery unless specifically permitted by the manufacturer, because the higher voltage increases recombination heat and accelerates dry-out.
NOTE The float voltage maintains the battery at full charge with minimal water loss and minimal grid corrosion; for VLA at 25°C this is approximately 2.20 to 2.25 V/cell, depending on the manufacturer, while the equalize voltage is a higher setting (approximately 2.30 to 2.40 V/cell for VLA) used periodically to bring lagging cells back into balance after a discharge or to recover from a maintenance event. (9.3.2)
9.3.3 Temperature compensation of the float voltage is recommended for installations where the battery temperature varies more than ±5°C from the reference temperature.
9.3.4 The temperature-compensation slope shall be set per the cell manufacturer's published data; an arbitrary slope can drive the battery into chronic undercharge or chronic overcharge.
9.4 Charger Redundancy
Single charger
Two chargers, one operating, one standby (manual transfer)
Two chargers, parallel operation with automatic load sharing
Two chargers per battery, redundant feeds from independent AC sources
9.4.1 Redundant chargers should be specified for installations where the battery duty cycle is short relative to the worst-case charger repair time, or where the AC source for the charger may be lost in the same event that triggers the DC duty cycle.
9.4.2 Where two chargers are specified, they should be fed from independent AC circuits so that a single AC outage cannot disable both.
NOTE A single charger is acceptable for installations where the loss of a single charger is operationally tolerable for the time required to replace it, recognizing that the battery itself continues to supply the loads. (9.4.3)
9.5 Charger Output Filtering and Ripple
2% RMS of nominal DC (general)
1% RMS (sensitive electronic loads)
0.5% RMS (high-end communications)
30 mV RMS (telecom 48 VDC)
9.5.1 Charger output ripple shall be measured at the charger output terminals with the battery connected.
NOTE Excessive AC ripple at the charger output accelerates battery grid corrosion and may interfere with sensitive electronic loads; the 2 percent RMS limit is the conventional general-purpose target, with lower limits applying where solid-state relays, communications equipment, or sensitive monitoring share the DC bus. (9.5.2)
NOTE Ripple measured with the battery disconnected is not representative of normal operation, because the battery acts as a filter. (9.5.3)
9.6 Charger Alarms and Indications
- AC input loss
- High DC voltage
- Low DC voltage
- Ground fault (positive and negative, where the system is ungrounded)
- Charger fail / DC output loss
- Battery on discharge (current flowing out of the battery)
☑ AC input loss
☐ High DC voltage
☐ Low DC voltage
☐ Ground fault — positive bus
☐ Ground fault — negative bus
☐ Charger fail
☐ Battery on discharge
☐ Charger in equalize
☐ High battery temperature
10 DC Distribution
NOTE The DC distribution panel takes the charger output and the battery in parallel and distributes them through individually fused or breaker-protected branch circuits to the protective relays, breaker control circuits, inverters, and other DC loads. (10.1)
10.2 DC Panel Configuration
Single bus, single charger, single battery
Single bus, redundant chargers, single battery
Dual bus with tie, redundant chargers, single battery
Dual bus, fully redundant (two chargers, two batteries)
10.2.1 The dual-bus topology shall be reflected on the DC one-line diagram and shall be coordinated with the redundancy of the loads themselves.
NOTE A single-bus arrangement is acceptable for installations where the DC system can be taken out of service to address a fault, while dual-bus arrangements are used at large generating stations and critical substations where DC must remain available during maintenance of any single element. (10.2.2)
10.3 DC Overcurrent Protection
● DC-rated molded case circuit breakers
○ DC-rated fuses with disconnects
○ Combination — breakers for major feeders, fuses for branches
10.3.1 DC overcurrent devices shall be listed for DC service at the system voltage.
10.3.2 AC-rated devices applied to DC service do not extinguish the arc reliably and shall not be used.
10.3.3 The interrupting rating shall equal or exceed the maximum short-circuit current available from the battery.
10.3.4 Battery short-circuit current shall be calculated using the manufacturer's published cell short-circuit data and the battery cable impedance.
NOTE Battery short-circuit current can substantially exceed the steady-state load current. (10.3.5)
10.4 Battery Disconnect
● Two-pole DC breaker at battery terminals
○ Fused disconnect with DC-rated fuses
○ Knife switch with separate DC-rated fuses
10.4.1 A disconnecting means shall be provided in the battery main DC circuit, located within sight of the battery, and shall open both the positive and negative leads, in accordance with NFPA 70 Article 480.
10.4.2 The battery disconnect shall be capable of interrupting the maximum short-circuit current available from the battery.
10.5 System Grounding
● Ungrounded (with ground fault detection)
○ Solidly grounded (positive or negative)
○ High-resistance grounded
10.5.1 Ungrounded systems shall be equipped with a continuous ground fault detector that alarms on the presence of a fault to ground on either bus.
10.5.2 The ground fault detector shall not draw enough current to be itself a hazard if it should fail.
10.5.3 Solidly grounded DC systems shall be specified explicitly where used.
10.5.4 DC system grounding shall be coordinated with Grounding And Bonding for the bonding of the battery rack, the cabinet, the conduit, and the enclosures of the charger and the DC panel. NOTE Substation control DC systems are conventionally ungrounded so that a single ground fault on either bus does not cause a misoperation of a protective relay or a breaker control circuit, and so that an undetected ground fault does not propagate into a phase-to-phase fault inside the control circuits. (10.5.5)
11 Battery Monitoring
None — manual periodic measurement only
String-level — total voltage, current, ambient temperature
Per-cell or per-monobloc — voltage and ambient temperature
Per-cell — voltage, temperature, and internal resistance / conductance
11.1 The monitor shall be wired to the facility's annunciator or SCADA with, at minimum, common-alarm contacts for "battery alarm" and "monitor system fail."
11.2 Where granular alarming is supported, individual cell-level alarms shall be reported as data points rather than aggregated, so that a developing single-cell failure is visible before it cascades.
NOTE Battery monitoring is recommended for any unattended installation and is essential for VRLA installations, because VRLA cells provide no visual cues to a developing fault and float voltage alone is a weak indicator of state of health; per-cell monitoring with periodic internal-resistance measurement is the most reliable way to identify a failing cell before it fails an in-service discharge, and IEEE 1491 provides guidance on selection of battery monitoring equipment. (11.3)
11.4 Float Current Monitoring (VRLA)
11.4.1 The monitoring system for a VRLA installation should report float current and should alarm on float current exceeding the manufacturer's recommended threshold.
NOTE For VRLA installations, float current is a leading indicator of thermal runaway: as a VRLA cell dries out, its internal resistance rises and its float current decreases, and as a VRLA cell approaches thermal runaway, internal heating accelerates recombination and float current rises sharply. (11.4.2)
12 Ventilation and Room Requirements
NOTE Hydrogen is evolved by all lead-acid and vented Ni-Cd batteries during charging, in proportion to the overcharge current. (12.1)
12.2 The hydrogen concentration in the battery space shall be kept below 25 percent of the lower flammable limit, which is 4 percent by volume in air.
NOTE The conventional design target is 1 percent hydrogen by volume, with 2 percent as the alarm threshold per IEEE 1635. (12.3)
12.4 Ventilation Method
Natural ventilation (sized per IEEE 1635 / IBC)
Continuous mechanical ventilation
Mechanical ventilation initiated by hydrogen detector
Sealed cabinet with internal recombination (small VRLA only)
12.4.1 Where natural ventilation is used, the Engineer shall confirm that the natural-ventilation airflow at the worst-case wind and temperature condition is sufficient to keep hydrogen below the design target.
12.4.2 A sealed cabinet without forced ventilation is acceptable only for small VRLA installations, where the cabinet design has been evaluated for hydrogen accumulation per IEEE 1635 and the manufacturer's published guidance.
12.4.3 Sealed cabinets shall not be used for VLA or vented Ni-Cd installations.
NOTE For VLA batteries and for vented Ni-Cd batteries, mechanical ventilation is the predominant approach in modern installations because the airflow can be sized to a known evolved-hydrogen rate and verified during commissioning, while natural ventilation is acceptable for small VLA installations and for VRLA installations where the hydrogen evolution rate is low and the room volume is large. (12.4.4)
12.5 Ventilation Rate
Per IEEE 1635 calculation (engineered)
Continuous airflow producing one air change per hour (small VRLA)
5 cfm per square foot of floor area
Per IBC / IFC table value for stationary storage battery
12.5.1 Rule-of-thumb ventilation values may be used for small installations but shall not be substituted for the IEEE 1635 calculation in any installation where the AHJ requires a calculation submittal.
NOTE The IEEE 1635 calculation determines the required airflow from the charger output current, the cell finishing current (the fraction of charger current that produces gas at the end of charge), the number of cells, and the room volume, and gives a defensible engineered result. (12.5.2)
12.6 Hydrogen Detection
● Provided — alarm at 1% H₂ by volume, initiate ventilation if not continuous
○ Provided — alarm only, no ventilation actuation
○ Not provided — continuous mechanical ventilation is the sole control
12.6.1 A hydrogen detector should be provided in every battery room and battery cabinet where the hydrogen evolution is non-negligible.
12.6.2 The hydrogen detector shall be located near the highest point of the space, because hydrogen is lighter than air and accumulates at the ceiling.
12.6.3 The detector's response time and recovery time shall be confirmed against the calculated rate of hydrogen accumulation.
12.7 Room Construction
Dedicated battery room within electrical room
Dedicated standalone battery room
Walk-in outdoor enclosure
Outdoor cabinet adjacent to switchgear
Indoor cabinet within electrical room
12.7.1 The battery room shall be constructed of materials compatible with the electrolyte and with hydrogen accumulation.
12.7.2 Walls and ceiling shall be sealed where necessary to prevent hydrogen leakage into adjacent spaces.
12.7.3 Light fixtures, switches, and any other potential ignition sources in the battery room shall be located outside the immediate cell area, or shall be rated for the classified area where the AHJ classifies the space.
12.7.4 Electrical conduit shall be sealed at penetrations into the battery room to prevent hydrogen migration into other electrical equipment per NFPA 70.
12.7.5 The room or cabinet layout, including cell arrangement, charger and DC panel locations, working clearances, and ventilation routing, shall be as shown on the battery room layout. 13 Spill Containment
Built-up curb with sealed, electrolyte-resistant floor coating
Drip pans under each cell row, drained to neutralization sump
Modular containment trays integral to the rack
Not required — VRLA, no free electrolyte
13.1 VLA and vented Ni-Cd installations contain free liquid electrolyte and shall be provided with spill containment per IEEE 1578 and the applicable building and fire codes.
13.2 The containment shall be sized to hold the volume of electrolyte from the largest single cell and shall be of materials compatible with the electrolyte.
13.3 A neutralization material (sodium bicarbonate for lead-acid sulfuric acid electrolyte; boric acid for Ni-Cd potassium hydroxide electrolyte) shall be stored adjacent to the battery in a clearly labeled container.
13.4 A spill kit appropriate to the chemistry shall be provided in the battery room.
13.5 Eye-wash and emergency drench shower shall be provided where required by the applicable workplace safety code.
13.6 The eye-wash shall be located within 10 seconds of unobstructed travel from any point in the battery work area.
NOTE For VLA installations, a built-up curb is the conventional method and provides the most reliable long-term containment, while modular containment trays integral to the rack are acceptable where the rack is so configured and the trays are listed for the electrolyte. (13.7)
14 Installation
14.1 Coordination and Sequencing
14.1.1 The Contractor shall sequence the work so that the battery rack is installed and anchored, and the ventilation system is operational, before cells are placed on the rack.
14.1.2 Cells shall not be left on a temporary surface or on the floor before installation.
NOTE Handling damage to jars and posts is a common cause of premature cell failure. (14.1.3)
14.2 Rack Assembly
14.2.1 The battery rack shall be assembled per the manufacturer's instructions on a level floor.
14.2.2 Rack steel shall be electrically isolated from the cells by the manufacturer's supplied insulators.
14.2.3 The rack itself shall be bonded to the building grounding electrode system per Grounding And Bonding. 14.2.4 Seismic anchorage shall be installed as shown on the seismic certification.
14.3 Cell Installation
14.3.1 Cells shall be inspected on receipt for jar cracks, terminal damage, and shipping discharge below the manufacturer's threshold.
14.3.2 Cells outside the acceptable shipping voltage shall be set aside for the manufacturer's freshening charge before installation.
14.3.3 Cells shall be installed in series order with consistent polarity per the cell numbering diagram.
14.3.4 Intercell connectors shall be installed and torqued per the manufacturer's specification using a calibrated torque tool.
14.3.5 Anti-corrosion compound shall be applied to the contact surfaces per the manufacturer's instructions.
14.3.6 After all cells are installed and connected, the total string voltage and the polarity at the battery main terminals shall be verified before the battery is connected to the charger.
14.4 Initial Charging and Freshening
14.4.1 Before the battery is placed in service, the Contractor shall apply the manufacturer's recommended initial charge or freshening charge.
14.4.2 After the initial charge, the battery shall be allowed to stabilize at float for the manufacturer's recommended period before acceptance testing.
NOTE For VLA cells the initial charge is conventionally an extended charge at the equalize voltage; for VRLA cells it is typically a constant-current limited charge followed by a float period; for Ni-Cd cells the initial charge follows the manufacturer's specific procedure for the plate construction. (14.4.3)
14.5 Working Clearances
14.5.1 Working clearance at the battery, the charger, and the DC distribution panel shall comply with NFPA 70 Article 110.26 based on the system voltage.
14.5.2 The aisle in front of the battery rack shall be at least 36 inches wide and shall accommodate the cell installation tool and the testing equipment.
14.6 Labeling
14.6.1 Permanent, durable labels shall be applied to the battery, the charger, the DC distribution panel, and the battery disconnect, identifying the following
- The system designation (e.g., "125 VDC Station Battery No. 1")
- The nominal voltage and the ampere-hour rating
- The chemistry and cell quantity
- The date of installation
- The connected load (at the charger and the DC panel)
- DC arc flash warning per NFPA 70E
14.6.2 A laminated single-line diagram of the DC system shall be posted at the DC distribution panel.
15 Testing
15.1 Factory Tests
○ Witnessed factory capacity test (complete battery)
○ Unwitnessed factory capacity test with certified report
● Cell-level certificate of conformance only (no complete battery test)
15.1.1 The cell manufacturer shall perform routine production tests on every cell, including capacity verification on a statistical sample basis, and shall provide a certificate of conformance for the cells supplied.
15.1.2 Where witnessed factory testing of a complete battery is specified, the cells shall be assembled and discharged at the manufacturer's facility per IEEE 450 or the equivalent test for the chemistry.
15.1.3 The charger shall receive the manufacturer's standard production test, including output voltage and current verification, ripple measurement, and functional check of all alarms.
15.2 Field Acceptance Tests
15.2.1 Contractor shall engage a qualified testing firm to perform acceptance testing per ANSI/NETA ATS and per IEEE 450 (VLA), IEEE 1188 (VRLA), or IEEE 1106 (Ni-Cd) as applicable to the chemistry.
15.2.2 Field acceptance testing shall occur after installation and initial charging are complete and before the battery is placed in service.
15.2.3 Field acceptance tests shall include as a minimum the following
- Visual inspection of every cell, the rack, the intercell connectors, and the spill containment
- Measurement and recording of total float voltage and current
- Measurement and recording of individual cell or monobloc float voltage
- Measurement and recording of every intercell and intertier connection resistance, with comparison to the manufacturer's specified value and to the average of the string
- Measurement and recording of baseline internal resistance or conductance for each cell or monobloc, where the monitoring system or the cell manufacturer provides the equipment
- Ground continuity verification from the battery rack and the cabinet to the building grounding electrode system
- Charger functional test, including output voltage and ripple measurement, current limit verification, and operation of each alarm and indication
- Battery monitor functional test, including alarm and trend verification
Performance test (full duty cycle to EOD voltage)
Modified performance test (combined performance and service test)
Service test (project duty cycle at the project EOD)
Not required at acceptance — periodic test only after warranty
15.2.4 The Engineer shall not waive the acceptance capacity test on the grounds of cost.
NOTE A performance test or modified performance test at acceptance establishes the as-installed capacity of the battery and is the baseline against which all future performance is judged; IEEE 450, IEEE 1188, and IEEE 1106 each describe the corresponding test for their chemistries, and a battery whose installed capacity was never measured cannot be defended at any later point in its life. (15.2.5)
15.3 Re-Test After Repair
15.3.1 Any cell that fails the acceptance test, and any connection that fails the resistance check, shall be repaired or replaced and the affected portion of the battery shall be re-tested.
15.3.2 The test report shall record both the initial result and the post-repair result.
16 Maintenance Requirements
16.1 The Contractor shall provide a recommended maintenance schedule and shall train the Owner's personnel in the periodic inspection and test procedures before substantial completion.
16.2 The recommended maintenance schedule shall be keyed to the IEEE recommended practice for the chemistry: IEEE 450 for VLA, IEEE 1188 for VRLA, IEEE 1106 for Ni-Cd.
16.3 Maintenance Intervals
16.3.1 The following maintenance intervals are representative and shall be tailored to the installation by the Owner:
- Monthly — total float voltage, total float current (where measured), ambient temperature, visual inspection for leaks or unusual conditions, electrolyte level (VLA), pilot cell specific gravity (VLA)
- Quarterly — every cell float voltage, every cell temperature (or representative sample), connection resistance check on a rolling basis
- Annually — every cell internal resistance / conductance measurement, every intercell connection resistance, full visual inspection, electrolyte level top-up to specified level (VLA), pilot cell specific gravity (VLA), confirmation of charger float and equalize voltages, ventilation system functional check, ground continuity check, alarm function test
- Every 2 years (VRLA) or as recommended (other) — service test or performance test per the IEEE recommended practice
- Every 5 years and after any unusual event — full performance test per IEEE 450 / 1188 / 1106
16.4 A pilot cell shall be designated for VLA batteries.
16.5 The pilot cell shall be rotated periodically (typically annually) so that each cell is, over time, treated as the pilot.
NOTE The pilot cell is the cell whose temperature and specific gravity are measured at the monthly interval as a representative of the string. (16.6)
17 Warranty
1 year full / 4 year prorated (general VRLA)
2 year full / 18 year prorated (long-life VRLA)
2 year full / 18 year prorated (VLA)
Manufacturer's standard for Ni-Cd
1 year from substantial completion
2 years from substantial completion
5 years from substantial completion
17.1 The warranty for cells shall be from the cell manufacturer directly to the Owner, transferable from the Contractor at substantial completion.
17.2 The Engineer shall confirm that the prorated terms of the cell warranty are commercially reasonable and clearly stated before accepting the submittal.
17.3 Achieved capacity at the acceptance test shall be at least the manufacturer's published rated capacity adjusted for temperature.
17.4 Cells delivering less than 100 percent of rated capacity at acceptance shall be replaced by the manufacturer under warranty.
NOTE The prorated portion of the cell warranty is conventional in the industry and reflects the long published life of stationary cells. (17.5)
☐ One complete spare cell or monobloc per cell type installed
☐ Spare intercell connectors and hardware (10% of installed quantity)
☐ Spare DC fuses (one set of each rating installed)
☐ Spare charger control board or critical subassembly
☑ Spill kit (one per battery room)
☐ Calibrated torque wrench for intercell connections
☐ Cell-handling lifter (where cells exceed 50 lb)
18.1 Spare cells, where provided, shall be stored on a level surface, kept in float charge or freshened on the manufacturer's recommended interval, and labeled with the installation-ready date.
NOTE A spare cell that has been allowed to sit on the shelf for years without freshening is not a spare; it is a failed cell that the Owner does not yet know is failed. (18.2)