Code Basics

Jul 8, 2004 1:53 PM, By Mike Holt

A change to 338.10 of the 2002 NEC is meant to clarify that when Type SE service-entrance cable is used for interior wiring it needs to comply with the installation requirements of Parts I and II for NM cable, but not the 60°C conductor ampacity limitations of 334.80. This change simply reverts the text back to the requirements contained in the 1996 NEC. It’s important to note that Type USE cable can't be used for interior wiring because it isn't listed for this application.

Now consider the following example calculation:

Sec. 424.3(B) requires the branch-circuit conductor for electric space heating equipment to have an ampacity of not less than 125% of the total heating load. A 10kW heater with a 3A blower motor must be wired with a conductor that has an ampacity of at least 56A (10,000W ÷ 240V + 3A). Therefore, it's acceptable to use 4 AWG NM cable or 6 AWG SE cable.