Doug Miller wrote:
In article , Chris Friesen wrote:

16A is the limit for general-use 20A circuits.

This is incorrect.

16A is the limit for a continuous load (explicitly defined by the NEC as
maximum current for 3 hours or more) on a 20A circuit.

As far as I can find out, this is because most fuses or circuit breakers
may trip at less than 100% if the load is over 3 hours, but will not
trip at 80% or less. I believe the reason is heat buildup. Far as I know
it is not a safety limitation.



16A is also the limit for any *single* cord-and-plug-connected load on a 20A
circuit.

There were multiple proposals to change the relevant NEC section several
code cycles ago. One of the arguments is that UL allows equipment (like
hairdryers??) to have a 20A plug and have a load of over 16A (or it
might have been the equivalent 15A plug with load over 12A). Under this
code section it is a code violation to use that UL listed equipment. The
code panel response - 'we're right, they're wrong'.

(Another rationale to change the code was this is a restriction on how
the wiring is used after installation and inspection - there aren't many
of those restrictions in the NEC, and it is essentially unenforceable.
The 3rd argument was that 80% is applied elsewhere in the code to
continuous loads, as above. The code panel's response was 'the code is
the way we want it.')

[To dpb - I was not impressed with the action of the code making panel
on this; an aberration?.]



The limit for noncontinuous loads on 20A circuits is 20A.

(I agree with everything you said Doug.)

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bud--