Electrical conduit, whether it be metal (EMT), plastic (PVC), or flexible conduit, each have their own maximum number of electrical wires allowed in the conduit. Their fill capacities are different, even though they may be the same sized conduit. Fill capacities will differ as we examine the different sizes of wires that may be pulled in the conduit. Obviously, the smaller the wire size, the more wires that can fit within the conduit.
PVC is a plastic conduit that is often used for underground installations and in wet areas. This conduit comes in ten foot lengths and comes with a coupling formed on one end, called the female side.. PVC can be combined by gluing the male end of one stick of conduit to the female end of another using PVC glue. Before gluing the joint, it also can be cleaned by using a can of cleaner. Since PVC is thicker than metal conduit, it holds fewer wires. Also remember that a ground wire is required in PVC piping, as the plastic conduit does not have any grounding properties like the metal conduit does.
PVC conduit comes in different grades for uses outside for underground installation, depending on the area that it will be used and purpose. Schedule 40 PVC is a thinner-walled conduit that is used for most simple underground installations, like running a feed through the yard to feed an outlet on a shed.Then there is the other style PVC that sports a thicker-walled conduit, labeled schedule 80, used for high traffic areas, parking lots, and driveways.
The thick wall conduit protects the contents. Because of the thickness, less wires are able to fit within. For toughness, this is the PVC conduit of choice and well worth the investment. On the job, we use both kinds of these conduits.
EMT conduit is a metal thin-walled conduit. EMT (Electrical Metallic Tubing) can act as the ground connection when connected to electrical boxes where the connections are made.
This conduit comes in ten foot lengths and usually bundled in groups of ten. These sticks have no couplings on the ends.
Couplings can be added to connect to the next piece. These couplings come in setscrew and compression types. Setscrew couplings have two screws, one for each piece of conduit which holds the conduits together and also bonds the ground connection between the conduits. Compression couplings have retainer rings and screw on fitting ends that tighten down on the conduit for a tight connection.
Connectors can be added to attach the conduit to electrical boxes and devices. Complete with locknuts, can they are attached for a tight connection and secure electrically conductive connection.
Flexible conduit (armor-clad) is normally made of twisted metal and is very flexible and can be formed around corners and other obstacles. This conduit is used for devices that may need to be moved around easily. A good example is drop-in fluorescent lighting. Because of its unique ability to bend, shape and move at ease, flexible conduit has a huge advantage over the stiff rigid metal and PVC conduit.
This type comes in rolls and can be cut to the proper length needed to compete the job. By adding special connectors to the ends of the flexible conduit, you can make your connections with ease. Check with your loacl code as to where it is allowable for use.
The table below gives you some typical conduit sizes used around the home and the allowable number of electrical wires allowed in each.
Allowable Conduit Fill Capacities
|Size and Type Of Conduit||#14 Wire||#12 Wire||#10 Wire|
|1 1/2" EMT||84||61||38|
|1 1/2" PVC||80||58||36|