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Panels for bigger homes or homes with higher electrical loads are described as 320/400A. Why the "dual" designation? Which one is it, 320 or 400A that they support?

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Structures and RVs follow NEC (National Electrical Code).

Utilities follow NESC (National Electrical Safety Code).

In the structure/NEC way of thinking, continuous loads put excessive strain on the system, and require a 125% disfavorable derate which is then included in the rating. For instance a 3800W water heater derates to 125% of that or 4750W, which is just under the 4800W of a 240V/20A circuit. So we treat that in all respects as a 20A water heater even though it's really 16A.

So in NEC, a load which is 80A continuous yet 100A intermittent is given the nomenclature of a "100A load".

In the utility/NESC way of thinking, you spec the continuous rating of the thing, and are tolerant of a 125% intermittent overload. So in their nomenclature, that same 80A continuous/100A intermittent is deemed an 80A load and they're fine with that having a 100A breaker.

So it's a difference in nomenclature and nothing more.

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  • And that is fine. However when I go buy a 200A panel everybody calls it 200A panel, not 160 (200)A. That is why I had confusion Commented Jul 27, 2023 at 17:58
  • @AlessioSangeli Yeah, there aren't a lot of retail shops who sell utility type gear. They'd only have one customer :) Commented Jul 27, 2023 at 18:14
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320 amp continuous

80% of 400 = 320.

https://forums.mikeholt.com/threads/320amp-vs-400amp.127202/

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