Section 126.32 - Underground Conduit SystemsNote: While it is often the practice to use "duct" and "conduit" interchangeably, "duct," as used in 220 CMR 126.32, is a single enclosed raceway for conductors or cable; "conduit" is a structure containing one or more ducts; and "conduit system" is the combination of conduit, conduits, manholes, handholes, and/or vaults joined to form an integrated whole.
(1)Location.(a)Routing -- General. 1. Conduit systems should be located so as to be subject to the least disturbance 410 practical. Conduit systems extending parallel to other subsurface structures should not be located directly over or under other subsurface structures., If this is not practical, the rules on "Clearances" (see 220 CMR 126.32(1)(g)) should be followed.2. Conduit alignment should be such that there are no protrusions which would be harmful to the cable.3. When bends are required, the minimum radius shall be sufficiently large to prevent damage to cable being installed in the conduit.(b)Routing -- Natural Hazards. Routes through unstable soils such as mud, shifting soil, etc., or through highly corrosive soils, should be avoided. If construction is required in these soils, the conduit should be constructed in such a manner as to minimize movement and/or corrosion.(c)Routing -- Highways and Streets. When conduit must be installed longitudinally under the roadway, it should be installed in the shoulder or within the limits of one lane of traffic if practical.,(d)Routing -- Bridges and Tunnels. The conduit system shall be located so as to minimize the possibility of damage by traffic. It should be located to provide safe access for inspection or maintenance of both the structure and the conduit system.(e)Routing -- Crossing Railroad Tracks. 1. The top of a conduit system should be located not less than 36 inches below the top of the rails of a street railway or 60 inches below the top of the rails of a railroad. Where unusual conditions exist or where proposed construction would interfere with existing installations, a greater depth than specified above may be required. Exception: Where this is impractical, or for further other reasons, this clearance may be reduced by agreement between the parties concerned and the Department. In no case, however, shall the top of the conduit or any conduit protection extend higher than the bottom of the ballast section which is subject to working or cleaning.
2. All crossing under railroads, manholes, handholes, and vaults should not, where practical, be located in the road bed.(f)Routing -- Submarine Crossings. Submarine crossings should be routed and/or installed so they will be protected from erosion by tidal action or currents. They should not be located where ships normally anchor.(g)Clearances from Other Underground Installations. 1.General. The clearance between a conduit system and other underground structures paralleling it should be as large as necessary to permit maintenance of the system without damage to the paralleling structures. A conduit which crosses over another subsurface structure shall have a minimum clearance sufficient to prevent damage to either structure. These clearances should be determined by the parties involved. Exceptions: When conduit crosses a manhole, vault or subway tunnel roof, it may be supported directly on the roof with the concurrence of all parties involved.
2.Separations Between Supply and Communication Conduit Systems. Conduit systems to be occupied by communication conductors shall be separated from conduit systems for supply conductors by: three inches of concrete, or four inches of masonry, or 12 inches of well-tamped earth. Exception: Lesser separations may be used where the parties concerned concur.
3.Sewers. Sanitary and Storm. If conditions require a conduit to be installed parallel to and directly over a sanitary or storm sewer, it may be done provided both parties are in agreement as to the method. Where a conduit run crosses a sewer it shall be designed to have suitable support on each side of the sewer to prevent transferring any direct load onto the sewer.4.Water Lines. Conduit should be installed as far as is practical from a water main in order to protect it from being undermined if the main breaks. Conduit which crosses over a water main shall be designed to have suitable support on each side as required to prevent transferring any direct loads onto the main.5.Fuel Lines. Conduit shall have sufficient clearance from fuel lines to permit the use of pipe maintenance equipment. Conduit and fuel lines shall not enter the same manhole.6.Steam Lines. Conduit should be so installed as to prevent detrimental heat transfer between the steam and conduit systems.(2)Excavation and Backfill. (a)Trench. The bottom of the trench should be undisturbed, tamped, or relatively smooth earth. Where the excavation is in rock, the conduit should be laid on a protective layer of clean tamped backfill.(b)Quality of Backfill. All backfill should be free of materials that may damage the conduit system. Recommendation: Backfill within six inches of the conduit should be free of solid material greater than four inches in maximum dimension or with sharp edges likely to damage it. The balance of backfill should be free of solid material greater than eight inches in maximum dimension. Backfill material should be adequately compacted.
(3)Ducts and Joints. (a)General. 1. Duct material shall be corrosion-resistant and suitable for the intended environment.2. Duct material and/or the construction of the conduit shall be designed so that a cable fault in one duct would not damage the conduit to such an extent that it would cause damage to cables in adjacent ducts.3. The conduit system shall be designed to withstand external forces to which it may be subjected by the surface loadings set forth in 220 CMR 126.32(4) except that impact loading may be reduced 1/3 for each foot of cover, so no impact loading need be considered when cover is three feet or more.4. The internal finish of the duct shall be free of sharp edges or burrs which could damage supply cable.(b)Installation. 1.Restraint. Conduit, including terminations and bends, should be suitably restrained by backfill, concrete envelope, anchors or other means to maintain its design position under stress of installation procedures, cable pulling operations and other conditions such as settling and hydraulic or frost uplift.2.Joints. Ducts shall be joined in a manner sufficient to prevent solid matter from entering the conduit line. Joints shall form a sufficiently continuous smooth interior surface between joining duct sections so that supply cable will not be damaged when pulled past the joint.3.Externally Coated Pipe. When conditions are such that externally coated pipe is required, the coating shall be corrosion-resistant and should be inspected and/or tested to see that it is continuous and intact prior to backfill. Precautions shall be taken to prevent damage to the coating when backfilling.4.Building Walls. Conduit installed through a building wall shall have a seal (or seals) intended to prevent the entrance of gas or water into the building insofar as practical. The use of seals may be supplemented by gas venting devices in order to minimize building up of positive gas pressures in the conduit.5.Bridges. Conduit installed in bridges shall include the capability to allow for expansion and contraction of the bridge. Conduits passing through a bridge abutment should be installed so as to avoid or resist any shear due to soil settlement;
Conduit of Conductive material installed on bridges shall be effectively grounded.
6.In Vicinity of Manholes. Conduit shall be installed on compacted soil, or otherwise supported when entering a manhole to prevent shear stress on the conduit at the point of manhole entrance.(4)Manholes, Handholes, Vaults. (a)Strength. Manholes, handholes and vaults shall be designed to sustain all expected loads which may be imposed upon the structure. The horizontal and/or vertical design loads shall consist of dead load, live load, equipment load, impact, load due to water table, frost and any other load expected to be imposed upon and/or occur adjacent to the structure. The structure shall sustain the combination of vertical and lateral loading that produces the maximum shear and bending moments in the structure. 1. In roadway areas, the live load shall consist of the weight of a moving tractor -- semi trailer truck illustrated in 220 CMR 126.32 Figure 1. The vehicle wheel load shall be considered applied to an area as indicated in 220 CMR 126.32 Figure 2. In the case of multilane pavements, the structure shall sustain the combination of loadings which results in vertical and lateral structure loadings which produce the maximum shear and bending moments in the structure. Note: Loads imposed by equipment used in road construction may exceed loads to which the completed road may be subjected.
2. In designing structures not subject to vehicular loading, the minimum live load shall be 300 pounds per square foot.3. Live loads shall be increased by 30% for impact.4. When hydraulic, frost or other uplift will be encountered, the structure shall be of sufficient weight or so restrained as to withstand this force: The weight of equipment installed in the structure is not to be considered as part of the structure weight.5. Where pulling iron facilities are furnished, they should be installed with a factor of safety of two based on the expected load to be applied to the pulling iron. Click to view image
V = Variable spacing -- 14 feet to 30 feet. Spacing to be used is that which results in vertical and lateral structure loading which produces the maximum shears and bending moments in the structure. Click to view image
(b)Dimensions. Manholes shall meet the following requirements: A clear working space sufficient for performing the necessary work shall be maintained. The horizontal dimensions of the clear working space shall be not less than three feet. The vertical dimensions shall be not less than six feet except in manholes where the opening is within one foot, horizontally, of the adjacent interior side wall of the manhole.
Exception 1: Where one boundary of the working space is an unoccupied wall and the opposite boundary consists of cables only, the horizontal working space between these boundaries may be reduced to 30 inches.
Exception 2: In manholes containing only communications cables and/or equipment, one of the horizontal dimensions of the working space may be reduced to not less than two feet, provided the other horizontal dimension is increased so that the sum of the two is at least six feet.
(c)Manhole Access Openings. 1. Round access openings in a manhole containing supply cables shall be not less than 26 inches in diameter. Round access openings in any manhole containing communication cables only or manholes containing supply cables having a fixed ladder which does not obstruct the opening, shall be not less than 24 inches in diameter. Rectangular access openings should have dimensions not less than 26 inches by 22 inches.2. Openings shall be free of protrusions which will injure personnel or prevent quick egress.(d)Covers. 1. Manholes and handholes, when not being worked in, shall be securely closed by covers of sufficient weight or proper design so they cannot be easily removed without tools.2. Covers should be suitably designed or restrained so that they cannot fall into manholes or protrude into manholes sufficiently far to contact cable or equipment.3. Strength of covers and their supporting structure shall be at least sufficient to sustain the applicable loads of 220 CMR 126.32(4)(a).(e)Access. 1. Vault or manhole openings shall be located so that safe access can be provided. When in the highway, they should be located outside of the paved roadway when practical. They should be located outside the area of street intersections and crosswalks whenever practical to reduce the traffic hazards to the men working at these locations.2. Personnel access openings in vaults or manholes should be located so that they are not directly over the cable or equipment. Where these openings interfere with curbs, etc., they may be located over the cable if one of the following is provided: A conspicuous warning sign,
A protective barrier over the cable,
A fixed ladder.
In vaults, other types of openings may be located over equipment to facilitate work on this equipment.
(f)Access Doors.1. Where accessible to the public, access doors to utility tunnels and vaults shall be locked unless qualified persons are in attendance to prevent entry by others.2. Such doors shall be designed so that a person on the inside may exit when the door is locked from the outside. Exception: 220 CMR 126.00 does not apply where the only means of locking is by padlock and the latching system is so arranged that the padlock can be closed on the latching system to prevent unauthorized locking from the outside.
(g)Ladder Requirements. Fixed ladders shall be painted or otherwise treated to resist corrosion when location demands.(h)Drainage. Where drainage is into sewers, suitable traps or other means should be provided to prevent entrance of sewer gas into manholes, vaults or tunnels.(i)Ventilation. Adequate ventilation to open air shall be provided for manholes, vaults and tunnels, having an opening into enclosed areas used by the public. Where such enclosures house transformers, switches, regulators, etc., the ventilating system shall be cleaned at necessary intervals. Exception: This does not apply to enclosed areas under water or in other locations where it is impractical to comply.
(j)Mechanical Protection. Supply cables and equipment should be installed or guarded in such a manner as to avoid damage by objects falling or being pushed through the grating.(k)Identification. Manhole and handhole covers should have an identifying mark which will indicate ownership or type of utility.