How do you know a new circuit breaker is protecting the circuit properly?

[Terry]

http://groups.google.com/group/alt....c74/a542c9b51e25efaf?lnk=arm#a542c9b51e25efaf

Anyone want to provide a definitive answer for this question?

It was posted at alt.home.repair

The guy has a new oven that is 30A.
He wants to change the existing 50A breaker to 30A.
Is this required?

 

[Nobody]

What do you want to protect? The wire or the equipment?

 

[Bill Kaszeta / Photovoltaic Resources]

http://groups.google.com/group/alt....c74/a542c9b51e25efaf?lnk=arm#a542c9b51e25efaf

Anyone want to provide a definitive answer for this question?

It was posted at alt.home.repair

The guy has a new oven that is 30A.
He wants to change the existing 50A breaker to 30A.
Is this required?

The usual USA situation is that the panel circuit breaker is intended to
protect the wiring and the wire size determines the circuit breaker
ampacity. You need to determine the gauge of the wire and the termperature
rating of the wire. Then consult Table 310-16 of the National Electrical Code.
Temperature derating may apply. Because most circuit breakers have
a 75C terminal rating, you are usually limited to the 75C rating column of
the table. #8 AWG wire is required for 50A at 75C copper wire.

Ovens should load the circuit to only 80% of its capacity. A minimum fuse
would be 30 x 1.25 = 37.5A, rounded up to the next standard of 40A.

Best to consult a local electrician.
Bill Kaszeta
Photovoltaic Resources Int'l
Tempe Arizona USA
[email protected]

 

[[email protected]]

| Ovens should load the circuit to only 80% of its capacity. A minimum fuse
| would be 30 x 1.25 = 37.5A, rounded up to the next standard of 40A.

Can you cite the specific NEC rule that applies to circuits with only
one outlet (as opposed to the rules, like 210.23(B), that only apply to
multiple outlets) that says no more than 80% for non-continuous loads?

 

[Bud--]

The usual USA situation is that the panel circuit breaker is intended to
protect the wiring and the wire size determines the circuit breaker
ampacity. You need to determine the gauge of the wire and the termperature
rating of the wire. Then consult Table 310-16 of the National Electrical Code.
Temperature derating may apply. Because most circuit breakers have
a 75C terminal rating, you are usually limited to the 75C rating column of
the table. #8 AWG wire is required for 50A at 75C copper wire.

Ovens should load the circuit to only 80% of its capacity. A minimum fuse
would be 30 x 1.25 = 37.5A, rounded up to the next standard of 40A.

Best to consult a local electrician.

Residential ovens are not likely to be considered a continuous load. For
minimum circuit rating US-NEC 220.55 can be used, which accounts for the
non-continuous nature and "diversity" if multiple units are connected.
NEC 210.19-A-3 also has minimum rating rules (and has a rule on tapping
cooktops to heavier circuits that include an oven).


The breaker also protects the oven. Maximum breaker ratings for an oven
are in NEC 422 and in general can not exceed a maximum, if marked on the
oven, or 150% of the rated oven current (or next larger standard size).
If the oven (or associated literature) is marked "maximum 30A" the
breaker size must be reduced to 30A. Otherwise it depends on the oven
rating.