Agreed.

I've always considered the critical specification of a circuit breaker
to be the highest current it can hold and not trip, assuming standard
test conditions ... such as voltage, temperature, humidity, magnetic
fields, vibration, gravity, orientation, mounting, atmosphere content,
and atmosphere pressure.

What some provincial code then says about it, and how it requires any
relabelling or use, is less interesting than the physics.  But if the
label is required to be different to that specification, that's
something to watch out for.

On Mon, Feb 16, 2015 at 06:40:20PM -0500, Allen Mulvey wrote:
> See:
> http://ecmweb.com/basics/sizing-circuit-breaker
>=20
> "A CB is designed and evaluated to carry 100% of its rated
> current for an indefinite period of time under standard test
> conditions."
>=20
> 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.
>=20
> Allen
>=20
> > -----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
> > View/change your membership options at
> > http://mailman.mit.edu/mailman/listinfo/piclist
>=20
> --=20
> 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
James Cameron
http://quozl.linux.org.au/
--=20
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