See:
http://ecmweb.com/basics/sizing-circuit-breaker

"A CB is designed and evaluated to carry 100% of its rated
current for an indefinite period of time under standard test
conditions."

The important part is "under standard test conditions." In
the real world the circuit breaker is likely to heat up
above "standard" test temperature. The 1996 NEC code
compensates for this by requiring you to use breakers rated
at least 20% higher than the anticipated load.

Allen

> -----Original Message-----
> From: piclist-bounces@mit.edu [mailto:piclist-
> bounces@mit.edu] On Behalf Of Richard R. Pope
> Sent: Monday, February 16, 2015 6:15 PM
> To: Microcontroller discussion list - Public.
> Subject: Re: [EE] Insulation testing
>=20
> James, Allen,
>      We have to be careful here. What I am talking about
is the
> rated
> trip current. A circuit breaker with 20 amps on the handle
> which is the
> rated trip current will trip under two different
conditions. The
> first
> condition is if a sudden current of 20 amps or more is
drawn by
> the
> circuit. The second is if a current of 80% of the rated
trip
> current,
> which is 16 amps for a 20 amp breaker is drawn for an
> extended time
> period. This has nothing to do with what the contacts are
rated
> at. This
> only deals with the circuit conditions.
>      You can go to the manufacturers website and find out
what
> all of
> the ratings are. Yes, if the voltage were to go very high
for
> some
> reason the breaker would trip if the fuse on the primary
side of
> the
> transformer didn't blow first. In the US we have two
different
> voltages
> available in most of our homes. It is single phase 120 and
240
> volts.
> Thanks,
> rich!
>=20
> On 2/16/2015 4:25 PM, Allen Mulvey wrote:
> > If the breaker pops at a higher current the wire will
get
> > hotter than it should and could cause a fire. I agree
all
> > components should be able to handle at least 20% more
than
> > required but this cannot apply to the point where
breakers
> > pop. The breaker contacts, etc. should be able to handle
> > more, you want it to pop before it self destructs.
> >
> > Allen
> >
> >> -----Original Message-----
> >> From: piclist-bounces@mit.edu [mailto:piclist-
> >> bounces@mit.edu] On Behalf Of James Cameron
> >> Sent: Monday, February 16, 2015 5:00 PM
> >> To: Microcontroller discussion list - Public.
> >> Subject: Re: [EE] Insulation testing
> >>
> >> My ambiguity detector fired ...
> >>
> >> On Mon, Feb 16, 2015 at 03:36:48PM -0600, Richard R.
> Pope
> >> wrote:
> >>> Robert,
> >>>       It is ok for a breaker to trip at less than what
> > the NEC
> >>> specifies but not at a higher current.
> >> I'd really want a breaker to trip at a higher current
than
> > it is
> >> specified for.
> >>
> >> --
> >> James Cameron
> >> http://quozl.linux.org.au/
> >> --
> >> http://www.piclist.com/techref/piclist PIC/SX FAQ &
list
> >> archive
> >> View/change your membership options at
> >> http://mailman.mit.edu/mailman/listinfo/piclist
>=20
> --
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list
> archive
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> http://mailman.mit.edu/mailman/listinfo/piclist

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