On Aug 4, 7:30 pm, "Eigenvector" wrote:
"Doug Miller" wrote in message

...





In article k.net,
"David Martel" wrote:
RBM,

60 is fine

Is the OP wrong that the #6 line is rated for only 55 amps or are you
saying that a 60 amp breaker is safe with wire that will fail at 55 amps.
Something is wrong here.

Nothing is wrong at all. The NEC specifically permits going up to the next
higher standard breaker size when the rated ampacity of the wire (55A in
this
case) does not correspond to any standard breaker size.

--
Regards,
Doug Miller (alphageek at milmac dot com)

That doesn't make sense to me at all.

Why allow the breaker to trip at a higher rating than the wire? Conceivably
the wire would fail without the breaker ever tripping. That presumes the
wire rating of 55 A means it is only capable of carrying 55A at 120V- Hide quoted text -

- Show quoted text -

A couple of the posts here seem to make the assumption that a wire
with a 'rated safe' ampacity of 50 amps (i.e. that it can carry 50
amps under normal conditions of voltage drop and length of run etc.)
will immediately heat up and burn off if it is made to carry 55 amps
for intermittent periods of time.
Not so. A 50 amp rated wire (say #6AWG) can probably carry twice that
even if getting a bit warm and with a certain amount of voltage drop.
And anyone who has ever dealt with an emergency situation where one
presses into service whatever reasonable size conductors are available
and has a good feel for the basics of electrical resistance, current
flow and voltage drop will understand that.
In this case we are discussing 'normal' domestic workshop conditions
to meet safety and code requirements.
With only one or two people working a maximum home workshop load is
unlikely to be close to the rated capability.
The statement "is only capable of carrying 55 amps" is probably only
true in regard to maximum current that could be carried continuously.
The reference 'is only capable of carrying 55 amps "at 120V", is
superfluous. We are considering current here, not voltage.
For example: Today we had two people working on a friends personal
vehicle in our domestic garage; the maximum load at any one time was,
intermittently;
1) A small wire welder maximum about 20 amps (@230 volt)
2) A sander/grinder or hand drill, maximum 5 amps (@120 volt).
3) A halogen lamp. 2.5 amps (@ 120 volt)
Total (intermittently) 27.5 amps, plus maybe another light that was
on. Maximum 30 amps say all fed from a panel wired with #6AWG and a
50 amp (Square D) breaker from the main house panel about 40 cable
feet distant. Nothing blinked or went dim etc. Caught fire or popped a
breaker.