[Stickdude]

Is fixed electric space heating considered a continuous load according to the NEC?

[tkrussell]

Yes, so the branch circuit conductors must be rated at 125% of the actual load.

Is this a test your taking?

If so, you may be interested in finding all your answers in the actual code:
NFPA 70: National Electrical Code®

[tkrussell]

OK, I never heard of Snapz. Can you give or show some examples of errors?

[Stickdude]

In reviewing the Study guide and the NEC I now think maybe the study guide is not in error (at least on this topic). If I understand correctly the 125% is applied only the branch circuit rating and not the feeder and service load calculations, except where 220.51 applies, which states, in part, ' in no case shall a feeder or service load current rating be less than the rating of the largest branch circuit supplied'. Am I on track here?

[tkrussell]

Note that 220.51 is for Fixed Electric Heat, and only pertains to heat feeders/services. The 100 percent pertains to adding of loads for feeder and service calculations, it is not subjected to any derating, such as lighting, appliance loads, etc.

Next,since this is fixed heat, then refer to 424.3(B), fixed heat is to be considered as a continuous load.

Next, refer to 210.19(A)(1), where continuous load is required to be 125% of the load to size branch circuit conductors, or 215.2, feeders, again wire size is to be 125% of load.

Then refer to 230.42, for services, again the wire size is to be 125% of continuous load

Isn't this fun?

The 80% rule, (AKA 125% nowadays, but us older guys will continue to use the former) is inbred into the code in many ways, some by tradition.

The 125% rule now allows for non-continuous load to be at 100%.and be added to the 125% continuous load. For example, if a 15 amp lighting circuit in a home is loaded to 15 amps, less than 3 hours, derating is not needed.

Back an edition or two ago, there was a steadfast rule of 80& for anything.

Quite frankly, some electricians like myself that only deal with commercial and industrial, everything is continuous, so guys like me tend to ignore the non-continuous load rule. We like the 80%, for everything, period.

But someone like yourself just learning, really needs to get your mind wrapped around this, as you will come across it more often, until all the older electricians, engineers, inspectors, etc all die off.

[tkrussell]

Forgot to mention, this all is ignored if the equipment is rated to operate at 100 %. This is not common in most installations, large commercial, industrial, or critical applications, and believe me you pay dearly for this rating.

[Stickdude]

Thanks, this helps clarify things. So, calculating the loads as per Parts III, IV, and V in article 220 is just that, calculating loads. Then, we apply those load calculations in sizing of Branch circuits, feeders, and services, taking into consideration non-continuous and continuous portions of those loads.