Conduit sizing

Conduit sizing

The conduit fill is the amount of areas in square inches, of conductors inside section of conduit. Conduits fill is necessary for dissipation of heat, pulling of wires, potential high cost change orders when the conductors that you specified do not fit inside the conduit. We require conduit fill when we installing new conduit & conductors or adding new conductors to existing conduit run. The maximum allowable fill for new conduit is 26% & for old 40%. Some necessary instructions are remember:

·        Always put extra conduit in crossing roads.

·        If the conduit crossing is for illumination or power supply, put in a spare 2” conduit.

·        If the conduit crossing is for signal conduits at an intersection put in a spare 3” conduit. If the crossing is not at the intersection put in a spare 2” conduit.

·        A 2” conduit should be the minimum size used for all crossings.

·        Install a spare 2” conduit into a service cabinet.

·        Install a spare 2” conduit between all transformers and the improvement the transformer is serving.  (ITS cabinet, VMS cabinet, etc.)

·        Always best try to not use too many different sizes of conduits. Stick with even sizes of conduits. (1”, 2”, 3” or 4”).

·        Leave room for future conductors. Running 2” conduit nears the service or where there is potential for future expansion usually provides plenty of future room.

·        The conduit from the luminaries pole to the adjacent junction box  5’–10’  away shall be 1”. This is usually the only place you would ever run a 1” conduit in grade  (except the grounded electrode conductor)

Here two types of conduits are designed with illustrations.

1.     Rigid Metal Conduit: Type RMC

2.     Rigid Nonmetallic Conduit: Type RNC ( PVC schedule 40, PVC schedule 80 & HDPE schedule 40)