How do you calculate electrical cable size?

Answer 1

The most common system you will see is in the form:

"xx/y [type] [/w ground]" * xx is the wire size in the AWG system * y is the number of conductors. * Type THHN (for example) is the kind of wire insualtion. Romex (which is a brand name) is the regular plastic sheathed cable used 90% of the time in homes and commercial buidlings. * BX is metal sheathed cable. * /w ground means the cable has a ground wire.

* XX, the size, tells you how much current can flow through the wire, this is the primary consideration when choosing wire. * The voltage rating is also included. (typ 600V) meaning it is suitable for circuits up to 600V. * THHN, THXN, XHHW, etc, is the type of insulation. There are many of these for industrial wiring & should only be a concern if your wiring is outdoors, or installed in non typical environments.

* You will also see a temperature rating stamped in Deg C, 60, 75, & 90. This tells you the operating conditions under which the cable is suitable. Keep in mind that resistivity rises with temperature, so the hotter the area, the lower ampacity. Follow the link for further explanation.

Answer 2

To find required wire size for a certain amperage, use NEC Table 310.16.

Length and # of connections also add to the resistance, hence increasing amp draw; increasing wire size.

Length adds resistance which REDUCES amp draw.

Properly made connections do not add resistance.

Answer 3

You first find the connected amperage to the load. Then go the the electrical code book and look up that amperage and the wire size that is recommended. Then you look up the recommended size of a breaker to safely protect that wire.

Answer 4

standard uses