Utility Manholes and Handholes

NOTE This standard governs the below-grade structures that give access to an underground electrical or communications duct system: the manhole or vault a person climbs into to pull, splice, and rack cable, and the handhole that is reached from grade with the cover off. It covers the structure as a product and as set in the ground, from the decision between a manhole and a handhole, through the load rating, the precast sections and the enclosure, the openings in the walls, the frame and cover, the hardware cast or set inside, the drainage, and the grounding provisions, to the excavation and backfill that belong to the structure alone, the field checks, the warranty, and the spares. (1.1)

NOTE The structure is the one part of a duct system that is opened again and again for the life of the site, and it is the part that is wrong most often: a handhole rated for a lawn that ends up in a drive aisle, a manhole with no pulling iron opposite the duct that matters, a sump with nowhere to drain, a cover with no legend over a telecommunications vault, a rack insert that was never cast in. Each of those is decided here, before the structure is cast, so that the cable trade finds the structure ready when the pull begins. (1.2)

NOTE A manhole and a handhole differ in what a person does with them, not in their size alone. A manhole is entered, which makes it a confined space with the work space, the headroom, the access opening, and the entry procedures that NFPA 70 Article 110 Part V and the OSHA confined-space rules require. A handhole is never entered; its depth is the depth a person can reach from grade, and its floor is often open to the soil. The choice between them follows the cable: a splice in medium-voltage cable, a large conductor count, or a change of direction in a heavy feeder needs a manhole, and a pull point in a lighting or communications run needs a handhole. (1.3)

NOTE The following are governed elsewhere and are outside this standard: (1.4)

NOTE A utility that will own and maintain a structure on its side of the service point builds it to its own drawings, inspects it against them, and refuses one it did not approve, so its standard governs those structures whatever this standard says; an Owner-owned structure on the Owner's side of the service point is built to this standard, and the serving utility reviews it only where the utility's cable will pass through it. (1.6)

NOTE The shop drawing is where a manhole is either right or expensive. A duct window on the wrong wall, a pulling iron off the line of the duct it serves, or a rack insert missing from a wall that will carry three circuits is cast into eight tons of concrete before anyone on the site sees it, and the remedy is a core drill or a new structure. The drawing is reviewed against the duct bank drawings and the cable schedule together, not alone. (3.1.2)

NOTE The plant programs audit the same things, mixture control, reinforcement placement, curing, and the record that ties a section to its strength test, and differ in who audits them: the NPCA program is the one most utility-structure producers hold, the ACPA program is the pipe and circular-manhole producers' program, a state DOT approval is what a producer serving public-works jobs holds and is sometimes the only one it holds, and a plant program accepted by the Engineer of Record is the route for a regional producer with none of the three, at the cost of the Engineer's own audit. (4.2)

NOTE A tier rating belongs to the tested assembly of a body and its cover, and a cover from another maker or another product line on a tested body carries no rating; the matched pair is what the test report certifies and what the structure schedule relies on. (4.4)

NOTE A manhole spends its life in the ground, wet for part of every year, loaded by the soil on its walls and by whatever crosses the surface above it, and frozen through its upper sections in a cold climate. Those four conditions, the surface load, the groundwater, the soil chemistry, and the frost, set the load class, the drainage approach and the joint treatment, the concrete exposure class, and the base and backfill of the structure, and each is decided in its own article below against the fact that drives it. (5.1)

NOTE A sealed manhole is a boat: a 6 ft by 8 ft by 7 ft chamber displaces more than 20,000 lb of water, and a structure with a tight floor, sealed joints, and sealed duct windows in a high water table lifts out of its excavation, taking the duct bank with it, unless its own weight and the soil on its base hold it down. An open-bottom handhole and a manhole with weep openings fill instead of floating, which is why the flotation check and the drainage decision are made together. (5.4)

NOTE The ACI 318 exposure classes are the language a producer's mixture is qualified in. A structure in a climate where its concrete never freezes while wet is F0; one that freezes with only rain wetting it is F1; one that freezes saturated, which is the upper part of any structure standing in groundwater in a cold climate, is F2; and F3 adds deicing salt, which reaches the top slab and the upper joint of a manhole in a salted pavement. The sulfate class is read from the soil and groundwater chemistry in the geotechnical report, and it changes the cement type and the water-cementitious ratio of the mixture rather than the structure. (5.7)

NOTE Six feet of headroom is the code floor and leaves a splicer stooped under the roof with a rack of cable at eye level; 7 ft is the height most utility manholes are built to, and it is the height at which four arms of medium-voltage cable and a splice stack on one wall with room for the splicer between them; a taller chamber buys more arms per wall and room for a sheave at a deep duct, at the cost of a deeper excavation, a heavier section, and more water to pump. A manhole that is also the low point of a long duct run gains from the extra depth, because the sump is then below the lowest duct by a useful margin. (6.8)

NOTE Separate structures cost a second excavation and a second casting at every access point and keep the communications contractor out of a chamber with energized power cable, and they are what most serving utilities and campus communications departments require; a shared structure saves the second structure where the site is tight and is lawful only with the partition the code requires, which turns one chamber into two narrower ones and costs most of the saving in a small structure. (6.11)

NOTE The tiers of ANSI/SCTE 77 are written for enclosures off the roadway that meet occasional, non-deliberate vehicle loading, each tier naming a design load that a test load one and one-half times greater proves on the assembled body and cover; the ASTM C857 loadings are highway-derived wheel loads for a buried concrete structure. The two systems describe the same surface in different words, and the load class in the datasheet is written in the words of the surface so that either product can be matched to it. A handhole in a lawn 3 ft from a drive aisle is in the drive aisle the first time a delivery truck cuts the corner, which is why the class is read from the paving plan at the final condition and, where the use of the surface is uncertain, from the heavier of the two surfaces that could end up over it. (7.7)

NOTE A rectangular chamber gives flat walls to rack cable on, square corners for the duct windows, and a floor plan the duct bank drawings can be laid out against, and it is what nearly every electrical and communications manhole is; a circular chamber is the sewer trade's product, stocked by every pipe producer in 48 in. to 96 in. diameters, cheaper where a producer of rectangular vaults is far away, and awkward to rack and window because every wall is curved. A separate top slab lets the base and walls be set and backfilled while the slab is on the truck and is removed later to lower a long splice or a reel of cable into the chamber; a monolithic top saves the perimeter joint and the slab's lifting operation at the cost of that access; a cone on a circular chamber brings the opening to the frame without a slab and needs the vertical room above the highest duct to develop its taper. (8.3)

NOTE Four thousand psi is the strength the product standards require and the strength the producers' mixtures are qualified to, and a structure designed to ASTM C857 at that strength carries its load class without a higher figure; a 5,000 psi or 6,000 psi mixture is specified where the exposure class F2 or F3 or the sulfate class S2 or S3 drives the water-cementitious ratio down and the strength follows, and where the structural design of a deep or a wide-span structure asks for it. (8.6)

NOTE A butyl sealant is laid on the lower section and compressed by the weight of the upper one, forgives a joint face that is not perfectly clean, and seals as long as the sections are brought together within its compression window, which is why it is the joint on most utility structures; a confined rubber gasket in a machined joint profile gives the tightest joint and is the sewer trade's joint, available on circular sections from every pipe producer and on rectangular sections from few; a mortared joint is the cheapest, is sound in a dry site above the water table, and opens with the first settlement or frost movement, after which it leaks. (8.8.2)

NOTE A wrap over a sealed joint is a second barrier that stops the fine seepage a compressed sealant can still pass under a head of water, and it costs a day of access to the outside of the structure before backfill; a wrap on every joint buys that barrier where the structure must stay dry and is pumped by the Owner, a wrap below the groundwater elevation puts it only where there is a head to resist, and no wrap is the usual condition of a structure whose sump drains and whose cable is rated for immersion. (8.8.5)

NOTE A dense precast wall is its own water barrier, and most utility structures are backfilled bare; a bituminous coating is the traditional dampproofing of a utility manhole, cheap, applied at the plant, and worth its cost where the groundwater carries sulfate or chloride that would otherwise work on the concrete; a crystalline coating closes the pores of the concrete itself and does not depend on a film that backfill can tear; a membrane is the tightest and the most expensive, and it is specified for a structure that must stay dry in a high water table and whose joints are also wrapped, because a membrane over an unwrapped joint ends at the joint. (8.8.7)

NOTE Polymer concrete, a resin-bound aggregate with a fiberglass reinforcement, is light enough to set by hand in the smaller sizes, does not corrode, reaches Tier 22 in every catalog, and is the enclosure most site electrical and communications handholes are; fiberglass-reinforced polymer is lighter still, is the enclosure of the telephone and cable plant, and flexes under load, which the tier test allows within a limit; precast concrete is heavy, needs a machine to set, carries highway loading with an iron cover, and costs the least per cubic foot in the larger sizes; a polyethylene or structural plastic box is the lightest and cheapest, tops out at Tier 8 or a stated light-duty rating, and is the enclosure of landscape lighting and irrigation controls rather than of a duct system. (9.2)

NOTE An open bottom lets the water that enters a handhole drain into the stone beneath it, lets a ground rod be driven inside the box, and is how nearly every polymer concrete and fiberglass handhole is furnished; a closed bottom with a drain opening keeps soil and rodents out of a box in a sandy or an organic soil and still drains; a sealed bottom is a box that holds water, chosen where the box sits in a contaminated soil or where the Owner will pump it, and it is the one configuration that puts a splice under water in a high water table. (9.4)

NOTE The matching cover is the one the enclosure was tested with, carries the tier with the body, and is the cover on nearly every non-concrete handhole; an iron frame and cover on a precast concrete handhole carries highway loading and takes the same legend and grade adjustment as a manhole casting; a steel checker-plate cover is light, is lifted by one person, rusts unless galvanized or stainless, and is the cover of an indoor or a canopy-covered box more than of one in the open; a concrete slab with lifting slots is the cheapest cover on a precast box in turf and needs a bar and two people to lift. (9.6)

NOTE A cast-in terminator is a bell end or a terminator fitting set in the form at the plant, one per duct, in the array the duct bank drawings show, so that the duct bank is formed to the wall and no grouting is left for the site; it is the tightest entry and it commits the duct layout at the plant, which is its cost when the duct bank changes. A knockout window is a thinned panel in the wall, the size of the whole duct array, broken out at the site, with the ducts and their end bells entering through it and the window grouted around them; it tolerates a late change in the array and depends on the grout for its seal. A field-cored opening serves a future duct or a duct that the shop drawings missed, one duct at a time, and cuts whatever reinforcement is in its path. (10.2)

NOTE Non-shrink grout to ASTM C1107 fills a window around a duct array completely and is the closure of nearly every window; a hydraulic cement with a waterstop ring around each duct holds against a head of water and is specified on a structure below the groundwater elevation that the Owner wants dry; a modular mechanical seal is a bolted rubber link assembly around each duct in a cored opening, the tightest closure and the one that is removable, and it fits a single cored duct rather than a grouted array. (10.4)

NOTE The end bell or terminator at the mouth of each duct, the sealing of the duct itself after the cable is in, and the slope of the duct bank toward the structure are furnished under Underground DuctbankUnderground Electrical Duct BanksResolves to the current adopted revision.sync/underground-ductbank, and the window, its reinforcement, and its closure around the ducts are furnished here. (10.7)

NOTE Gray iron is the casting of nearly every manhole in a pavement, stiff, heavy enough to stay seated by its own weight, and cheap; ductile iron carries impact and tension that would crack gray iron and is chosen under a wheel load above highway loading, under repeated heavy impact, and where a lighter cover of the same rating is wanted; a composite cover is lighter than iron, does not conduct, and has no scrap value where theft of iron covers is a recurring loss, at a lower impact rating and a higher price; a hatch gives a rectangular opening large enough to lower a splice case or a reel through, suits a vault serviced from above and a chamber in turf or a plaza, and is a trip edge and a snow-plow casualty in a pavement. (11.1.5)

NOTE Twenty-six inches is the code minimum for a person in a harness; 30 in. and 32 in. are the openings most utilities standardize on, large enough for a person with a tool bag and a retrieval tripod over the hole; a 36 in. opening passes a cable reel stand and a splice tent frame and is the opening of a vault where equipment is lowered through the roof; the larger the opening, the heavier the cover and the larger the frame seat the top slab has to carry. (11.1.8)

NOTE The legend is read by a locator with a one-call ticket, by a maintainer looking for the right structure in a row of three, and by the next contractor deciding whether to lift it; ELECTRIC and HIGH VOLTAGE tell the person at the cover what is energized under it, the communications legends tell them it is not, and an Owner with its own convention names the system in its own words, cast at no extra cost when the pattern is ordered. NFPA 70 314.30(D) requires a handhole cover to identify its function, and this standard applies the same rule to every cover. (11.2.3)

NOTE An iron manhole cover of 150 lb to 300 lb is secured by its own weight, is lifted with a hook, and needs no bolt in a pavement where a vehicle on it is the only load it sees; pentagon-head bolts need a socket that is not sold at a hardware store and are the utility industry's deterrent to the casual lifter; hex-head bolts hold a light cover down against a wheel passing over its edge and against frost, and are opened by anyone with a wrench; a cam or bar lock under a hidden bolt is the securing of a structure in a public place where a lifted cover is an open shaft, and it costs a special tool that the Owner has to keep track of. On a handhole, where the cover weighs 40 lb to 90 lb and the code requires a tool, bolts are the usual means and the choice is between the hex head anyone can open and the pentagon head that only the Owner's crew can. (11.3.6)

NOTE Precast concrete rings are stocked in 2 in. to 8 in. heights, carry a wheel load through a mortar bed, and are the adjustment on nearly every manhole in a pavement; polyethylene and rubber rings are light, are set without mortar, and are the adjustment where the frame will be reset every time the pavement is milled, at the cost of a ring that a heavy wheel load can distort; brick courses are the oldest method, are permitted by many jurisdictions and prohibited by others, and depend entirely on the mason; a cast collar fits an odd elevation or an off-center frame and ties the frame to the slab in one piece; a frame set directly on the slab is the stiffest and is possible only where the slab elevation was set to the final grade when the structure was ordered. Every ring adds two joints, and each joint is a hinge under traffic; a tall stack works loose, admits water behind the frame, and settles, taking the pavement with it, which is why the stack has a ceiling and a riser section takes over above it. (11.4.4)

NOTE Steps cast in the wall are always there, cost little, and are what the sewer trade and many municipal electric utilities require; they also corrode at the wall where the encapsulation is cut, they take a wall that could carry cable, and a step that fails under a person who trusted it is the injury most utilities that prohibit them are remembering. A fiberglass ladder does not corrode and does not conduct, which matters in a chamber with energized cable; an aluminum ladder is lighter and cheaper and corrodes in a wet structure with concrete in contact. A portable ladder set by the entrant under the confined-space program is the practice of most electric utilities and of every Owner whose entrants bring a tripod and a retrieval line anyway, and it leaves all four walls for cable. (12.5)

NOTE A nonmetallic rack of glass-reinforced nylon or fiberglass does not corrode, does not conduct, needs no bonding, and carries the arm loads of medium-voltage cable in every catalog, at a higher price per stanchion and a lower load rating per arm than steel; a hot-dip galvanized steel rack is the traditional rack, the strongest, and the cheapest, and it rusts at the arm sockets in a wet structure within the life of the cable and has to be bonded; a stainless rack is the steel rack without the rust at several times the price; an aluminum rack is light and corrosion resistant in a dry structure and pits where it stands in water against concrete. (13.1.2)

NOTE A threaded insert cast into the wall at the plant is set to the shop drawing, cuts no reinforcement, and is what the rack maker's stanchion is punched for; a continuous channel cast into the wall takes a stanchion anywhere along it and suits a structure whose rack layout is not settled when it is cast; a post-installed anchor is drilled into the wall at the site, finds reinforcement by chance, and is the fastening of a rack added to an existing structure or of an insert the plant missed. (13.1.4)

NOTE Three feet is the spacing most utilities rack medium-voltage cable at, and it supports a 1,000 kcmil cable with a splice case between two arms without sag; a closer spacing carries a heavier splice and a tighter training radius, and a 4 ft spacing is the limit at which a large cable still clears the floor between arms. The stanchion at each side of a window carries the cable as it leaves the duct, which is where the training radius starts. (13.1.6)

NOTE A porcelain insulator on each arm supports a medium-voltage cable on a rounded, non-conducting saddle that does not cut the jacket and does not carry a fault current into the rack, and it is the support most utilities put under every medium-voltage cable; a polymer saddle does the same at a lower price and a lower crushing load, and it is the support of a communications structure and of a nonmetallic rack whose arms are already non-conducting; a bare arm with a cable tie is the support of a light cable in a handhole-sized vault and of a communications cable, and it is the arm a heavy cable wears its jacket against. (13.1.11)

NOTE The arrangement of the cable on the arms, one circuit per arm, power opposite communications, the splice supported on an arm at each side, and the slack loop, is governed by Medium Voltage CablesMedium-Voltage CablesResolves to the current adopted revision.sync/medium-voltage-cables and the standard of each other cable in the structure; the racks, arms, and supports they are arranged on are furnished here. (13.1.13)

NOTE The pulling tension of a cable is calculated under its own standard from the conductor size, the route, and the lubricant, and the iron that anchors the sheave or the puller sees that tension and the shock of a stuck cable breaking free; the factor of two covers the shock and the angle of the pulling line, and an iron rated below it is the one that pulls out of the wall with the puller at full load, which is the accident this article exists for. (13.2.3)

NOTE A hot-dip galvanized steel iron is the iron in nearly every structure, strong, cheap, and good for decades in a chamber that drains; a stainless iron is chosen where the structure stands in brackish or corrosive water and the iron will be relied on for the life of the structure; a polymer-coated iron adds a barrier over the zinc and is damaged by the first pulling line that saws across it. (13.2.5)

NOTE A sump pit collects the water the duct bank drains into the chamber at one place a pump can reach, keeps the floor dry between storms, and is the drainage of nearly every electrical manhole, pumped by the Owner's crew before an entry; a floor drain to a gravity outlet keeps the chamber dry without a pump and exists only where a storm sewer or a slope to daylight lies below the floor and the authority permits the connection; weep openings let water pass down into the stone base and up again when the water table rises, and they drain a structure above the groundwater elevation in a free-draining soil for nothing; a sealed floor is the choice where the soil is contaminated, where the structure must not discharge, or where the floor is below groundwater and every opening would be an inlet, and it is the floor that fills from above and is pumped. (14.2)

NOTE A sump pump is not furnished under this standard; where the Owner will keep a manhole dry by a permanent pump, the pump, its power, and its discharge are a project-specific design and the structure under this standard carries only the sump the pump sits in and the sleeve its discharge leaves through. (14.7)

NOTE A sleeve cast through the floor of a manhole lets a rod be driven inside the chamber after the structure is set and keeps the rod and its connection where a person can test them, which is the arrangement in nearly every electrical manhole; a rod driven through the open bottom is the handhole's version of the same thing; a structure with no rod of its own is bonded through the duct bank to the electrode at the next structure or at the equipment, which the grounding standard allows where the run is short, and it saves a rod in a structure that carries only communications cable or low-voltage lighting circuits. (15.2)

NOTE The rod, the ground bar, the bonding conductor, and the bonding of the racks, pulling irons, frame, cover, steps or ladder, and metallic conduits in the structure are furnished under Grounding And BondingGrounding and Bonding for Electrical SystemsResolves to the current adopted revision.sync/grounding-and-bonding, which connects to the sleeve and the inserts furnished here; a handhole's metal cover is bonded there as NFPA 70 314.30(D) requires. (15.5)

NOTE An engraved stainless or laminated plastic tag inside the opening is read by the person who lifts the cover and survives a repaving that replaces the cover; a number cast or stamped in the cover is read without lifting it and is lost when the cover is swapped with the next one down the street; a stencil is the cheapest, is read from the opening, and is repainted every decade or two. The marker is what ties the structure to the record drawings, the circuit schedule, and the confined-space inventory, and a structure without one is identified by counting from the corner. (16.2)

NOTE The identification of the ducts themselves at the wall, including the spare ducts, is furnished under Underground DuctbankUnderground Electrical Duct BanksResolves to the current adopted revision.sync/underground-ductbank, and the tags on the cable are furnished under the standard of that cable. (16.4)

NOTE Damp walls and a seep at a joint that does not run are the condition of most structures in the ground and are not a defect; a stream through a joint, a window that pours when the water table is up, and a floor that does not drain are, because each puts the splice under water and the entrant in it. The vacuum test is for the structure the Owner has decided to keep dry and has paid for the sealed joints and windows of; applied to a structure with weep openings it proves nothing. (17.4)

NOTE The continuity of the bonding and the resistance of the electrode at each structure are tested under Grounding And BondingGrounding and Bonding for Electrical SystemsResolves to the current adopted revision.sync/grounding-and-bonding, and the duct proving is performed under Underground DuctbankUnderground Electrical Duct BanksResolves to the current adopted revision.sync/underground-ductbank. (17.5)

NOTE Six inches of stone levels a firm subgrade and is the bed under most handholes and under a manhole on a sand or gravel; 12 in. bridges a soft or wet clay subgrade and gives a manhole that stands in groundwater a drained bed to sit on; a thicker bed replaces an unsuitable subgrade or a frost-susceptible soil below a shallow structure, and above 24 in. the geotechnical engineer is designing a foundation rather than a bed. (18.1.4)

NOTE Excavated soil put back around a structure costs nothing and settles unless it is compacted in lifts, and it is the backfill of a structure in turf; granular fill compacts to the density a pavement over it needs and drains; crushed stone drains fastest, needs little compaction, and is what the makers of polymer concrete handholes require around their enclosures; a flowable fill needs no compaction at all in a trench too narrow for a compactor, locks the structure in, and floats a light enclosure if it is poured too fast. (18.2.5)

NOTE A handhole cover cracked by a truck and a manhole cover lost to a snowplow or a scrap thief are replaced in a day only if the Owner has one of the same pattern on the shelf, because a cover with the Owner's legend and the right tier is not a stocked item at a supply house; the special tool for a locking cover is the one spare that is needed on the first night call and is missing most often. (21.3)