Corpus sync: neutrality remakes, note hygiene, datasheet relocation, transformer-split cross-refs
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title: Enclosed Switches and Disconnects
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When to use: Enclosed low-voltage (600V and below) safety and disconnect switches and enclosed molded-case switches applied as service, feeder, and equipment disconnecting means in commercial, institutional, and industrial facilities. Covers fusible and non-fusible switches; heavy-duty and general-duty classes and where each is appropriate; horsepower, ampere, and voltage ratings from 30A through 1200A; short-circuit current rating (SCCR), series ratings, and the role of the upstream current-limiting fuse class (Class R, J, T, L) in establishing a high SCCR; number of poles and solid versus switched neutral; service-entrance-rated switches with neutral bonding and equipment grounding; enclosure selection to NEMA 250 (Types 1, 3R, 4, 4X stainless and nonmetallic, 12) by environment; defeatable and non-defeatable door interlocks; provisions for lockout/tagout per OSHA 1910.147 and line-side isolation; visible-blade indication; and the disconnecting means required at HVAC and rooftop units. Listed to UL 98, with enclosures to UL 50 and UL 50E and construction to NEMA KS 1, and applied per NFPA 70 Articles 404, 408, 430 Part IX, and 440.
− Not intended for: Panelboards (see [[sync/low-voltage-panelboards]]); metal-enclosed switchboards and switchgear; medium-voltage switches and load interrupters above 600V; molded-case circuit breakers applied as branch or feeder overcurrent protection; and automatic and manual transfer switches (see [[sync/automatic-transfer-switches]]).
+ Not intended for: Panelboards (see [[sync/panelboards]]); metal-enclosed switchboards and switchgear; medium-voltage switches and load interrupters above 600V; molded-case circuit breakers applied as branch or feeder overcurrent protection; and automatic and manual transfer switches (see [[sync/automatic-transfer-switches]]).
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### Switches covered by this standard are individually enclosed air switches, manually operable by an external handle, with all current-carrying parts enclosed, rated 600V and below and 1200A and below. {note}
−### For assemblies that subdivide a feeder into branch circuits with individual overcurrent devices, see [[sync/low-voltage-panelboards]]. {note}
+### For assemblies that subdivide a feeder into branch circuits with individual overcurrent devices, see [[sync/panelboards]]. {note}
### For drawout power circuit breaker assemblies and higher fault-duty distribution, the switch is part of switchboard or switchgear scope and is not covered here. {note}
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### Switch procurement shall not proceed until the corresponding submittals are reviewed and returned.
−### The marked SCCR submitted for a fusible switch shall state the specific fuse class and maximum fuse ampere rating, because the assembly SCCR is established only with those fuses installed. {note}
+### The marked SCCR submitted for a fusible switch shall state the specific fuse class and maximum fuse ampere rating, because the assembly SCCR is established only with those fuses installed.
## Closeout Submittals {toc}
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# Environmental and Service Conditions {toc}
−## A switch and its enclosure shall be suitable for the electrical system, ambient conditions, and physical environment at its point of installation. {note}
+## A switch and its enclosure shall be suitable for the electrical system, ambient conditions, and physical environment at its point of installation.
## Installation Environment {toc}
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### Switches installed in locations with sustained ambient temperatures above 40°C shall be derated or an oversized switch shall be specified per the manufacturer's published derating data.
−### Rooftop-mounted switches serving air-conditioning equipment routinely see elevated ambient temperatures from solar gain and shall be rated accordingly. {note}
+### Rooftop-mounted switches serving air-conditioning equipment routinely see elevated ambient temperatures from solar gain and shall be rated accordingly.
# Duty Class {toc}
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## Heavy-duty switches are rated to 600V and up to 1200A, accept current-limiting fuses for a high short-circuit current rating, and are available in the full range of enclosure types; general-duty switches are limited to 240V and 600A and to NEMA Type 1 and Type 3R enclosures. {note}
+## The switch duty class shall be specified for each application, selected to meet the required voltage, ampacity, short-circuit rating, and enclosure type.
+
```datasheet
label: Duty Class
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### A non-fusible switch may be provided where overcurrent protection is supplied by an upstream device and the switch is required only as a disconnecting or isolating means.
−### A non-fusible switch shall be applied only where the upstream overcurrent device protects the conductors and equipment served by the switch. {note}
+### A non-fusible switch shall be applied only where the upstream overcurrent device protects the conductors and equipment served by the switch.
## Fuse Provisions {toc}
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### Class H and Class K fuses shall not be used where the available fault current exceeds 10kA, because a switch fused with non-current-limiting fuses is rated only 10kA SCCR.
−### Rejection-style fuse clips shall be provided so that a current-limiting fuse cannot be replaced with a non-current-limiting fuse of a lower class, which would void the marked short-circuit current rating. {note}
+### Rejection-style fuse clips shall be provided so that a current-limiting fuse cannot be replaced with a non-current-limiting fuse of a lower class, which would void the marked short-circuit current rating.
### Class R, J, and T fuses are current-limiting and establish a switch SCCR of up to 200kA, while Class H and K fuses are not current-limiting and hold the switch to a 10kA SCCR; the fuse class is therefore a short-circuit decision, not only an overcurrent decision. {note}
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### A switched neutral (fourth switched pole) shall be provided where the neutral must be opened together with the ungrounded conductors, such as where the switch isolates a separately derived system or where required by the equipment served.
−### Switching the neutral of a system that is bonded both upstream and downstream of the switch creates objectionable neutral current paths; the neutral shall be switched only where the application requires it. {note}
+### Switching the neutral of a system that is bonded both upstream and downstream of the switch creates objectionable neutral current paths; the neutral shall be switched only where the application requires it.
## Service-Entrance Rating {toc}
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### The neutral bonding jumper of a service-entrance switch establishes the main bonding connection for the service; its omission leaves the service ungrounded and is a serious safety defect. {note}
−### The Contractor shall coordinate the service neutral bond and grounding electrode connection at a service-entrance switch with [[sync/grounding-and-bonding]]. {note}
+### The Contractor shall coordinate the service neutral bond and grounding electrode connection at a service-entrance switch with [[sync/grounding-and-bonding]].
# Construction and Components {toc}
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### The lockout provision shall accept the number of padlocks required by the facility's energy-control program, with multiple-lock hasps provided where more than one worker must lock out the switch.
−### A line-side barrier or shield shall be provided where required so that the line terminals remain guarded when the door is open and the switch is OFF. {note}
+### A line-side barrier or shield shall be provided where required so that the line terminals remain guarded when the door is open and the switch is OFF.
# HVAC and Equipment Disconnects {toc}
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### Working clearance shall be measured from the front of the enclosure or the front of any live parts, whichever is greater, to the nearest obstruction.
−### Working space in front of a disconnecting means shall not be used for storage. {note}
+### Working space in front of a disconnecting means shall not be used for storage.
## Conductor Terminations {toc}
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### The installed fuse class and ampere rating shall match the fuse class on which the switch SCCR and the circuit overcurrent protection were based.
−### A label identifying the required fuse class and maximum ampere rating shall be applied to or within each fusible switch. {note}
+### A label identifying the required fuse class and maximum ampere rating shall be applied to or within each fusible switch.
# Testing {toc}
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## Each switch shall receive an arc-flash warning label in accordance with NFPA 70E prior to energization.
−## Where a fusible switch's fuse class is critical to its short-circuit rating, the required fuse class and maximum ampere rating shall be marked at the switch. {note}
+## Where a fusible switch's fuse class is critical to its short-circuit rating, the required fuse class and maximum ampere rating shall be marked at the switch.
## Where a series-rated combination is relied upon, the switch shall be field-marked to identify the series combination and the required upstream device per NFPA 70 110.22.
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## Switches shall be inspected for damage on delivery, and any damage shall be documented and reported before installation.
−## A switch whose enclosure, operating mechanism, or interlock shows evidence of impact or moisture intrusion shall not be installed. {note}
+## A switch whose enclosure, operating mechanism, or interlock shows evidence of impact or moisture intrusion shall not be installed.
# Warranty {toc}
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## Stocking spare fuses allows a cleared fuse to be replaced promptly, restoring the disconnect to service without waiting on procurement. {note}