Surge suppressors

Robert G. Brown rgb at
Fri Nov 1 13:52:13 PST 2002

On Fri, 1 Nov 2002, Jim Lux wrote:

> Circuit Rating/Receptacle rating
> 15/not over 15
> 20/15 or 20
> 30/30
> 40/40 or 50
> 50/50

I'm trying to understand that.  Are they saying you can't use a
20A-rated receptacle on a 15A, 14Ga wire circuit?  I'd have thought it
was the exact opposite, that it has to be at LEAST 15 (just like the 40
A circuit needs a receptacle that is at LEAST 40).  

> (B)(2) Total Cord-and-Plug-Connected Load
> Where connected to a branch circuit supplying two or more receptacles or 
> outlets, a receptacle shall not supply a total cord-and-plug-connected load 
> in excess of the maximum specified in table ...
> circuit rating/recep rating/max load
> 15 or 20/15/12
> 20/20/16
> 30/30/24

This makes sense, although the code should provide protection against
any load that doesn't blow the breaker, anywhere or way it is plugged in
(because such a load, sustained, can always occur by accident), max
sustained INTENTIONAL load should be lower by design to allow for things
like poor power factors and different things being plugged into the
different receptacles.

This is why I still just don't understand permitting a 15 A receptacle
on a 20 A branch, where an 19 A sustained accidental overload (caused by
e.g. a partial short circuit) could burn the receptacle without blowing
the breaker.  I also don't understand the "not over" on the 15 A circuit
rating for the same reason -- if 5 A receptacles existed and I used one
on a 15 A circuit, I could critically overload it without blowing the
breaker.  Whereas using a 20 A receptacle on a 15 A breaker, it just
provides a greater margin of safety, the same as using 12 Ga wire for
shorter runs than strictly necessary.

Sigh.  Now I'm puzzled.  Any insight?

BTW, did you find the code online (I'd love the URL) or do you have a
paper copy.  IS the code online?


Robert G. Brown	             
Duke University Dept. of Physics, Box 90305
Durham, N.C. 27708-0305
Phone: 1-919-660-2567  Fax: 919-660-2525     email:rgb at

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