Calculating Fixed Electric Space Heating
Fixed Electric Space Heating Equipment
Per 424.4(B), fixed electric space heating equipment is a continuous load. To determine the current of the conductors, multiply the total current of the equipment by 125%. Once the current of the conductors is found in amps, use Table 310.16 to size the conductors.
The procedure for determining overcurrent protection for fixed electric space heating equipment is also found in 424.4(B). Overcurrent protection for fixed electric space heating equipment is determined by multiplying the total current of the equipment by 125%. If the OCPD does not correspond to a standard size, then go up to the next standard-size OCPD as found in 240.6.
- 424.4(B) Branch-Circuit Conductor Sizing. The branch-circuit conductor(s) ampacity shall not be less than 125 percent of the load of the fixed electric space-heating equipment and any associated motor (s).
When doing service calculations do not forget 220.51, as it addresses how to take those Fixed Electric Heating Loads.
220.51 Fixed Electric Space Heating. Fixed electric space heating loads shall be calculated at 100 percent of the total connected load. However, in no case shall a feeder or service load current rating be less than the rating of the largest branch circuit supplied.
There is an exception to be aware of:
Exception: If reduced loading of the conductors results from units operating on duty-cycle or intermittently, or from all units not operating at the same time, the authority having jurisdiction shall be permitted to grant permission for feeder and service conductors to have an ampacity less than 100 percent if the conductors have an ampacity for the load so determined.