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[bennie]

After applying the derating factors for temperature, and number of conductors in a conduit, do you reduce the load to match the ampacity or reduce the breaker size, or increase the wire size?

[ July 07, 2003, 10:49 PM: Message edited by: bennie ]

 

[websparky]

Re: Loading

Hi bennie,

OK, I'll bite.

Typically one would increase the wire size and conduit size if necessary.

 

[bennie]

Re: Loading

Hi Web: If you increased the wire size from No.#14 to No.#12 because of derating, could you put the No.#12 on a 20 amp breaker?

 

[pierre]

Re: Loading

Bennie

One could put a 20 amp breaker on the 12 wire after derating, but that would ultimately defeat the reason for derating and be a violation.

Pierre

 

[don_resqcapt19]

Re: Loading

The use of the term "derating" is misleading. The correct code term is "ampacity adjustment". If the ampacity of a conductor is required to be adjusted because there are more than 3 current carrying conductors in a raceway or because of an ambient temperature above or below 30?C, then the "adjusted ampacity" becomes the maximum code permitted ampacity for that conductor and the overcurrent protection device is not permitted to exceed the "adjusted ampacity" in most cases.
Don

 

[bennie]

Re: Loading

I have always been under the impression that load is adjusted to meet the corrected ampacity, or the the size of the conductor is selected to meet the load after correction factors are applied.

The overcurrent device is sized to the ampacity, without the correction factor. 240.4(D)

 

[don_resqcapt19]

Re: Loading

Bennie,

I have always been under the impression that load is adjusted to meet the corrected ampacity, or the the size of the conductor is selected to meet the load after correction factors are applied.

In most cases the load is fixed, so the conductor is sized so that the (adjusted) ampacity of the conductor equals or exceeds the load and the conductor is protected at or below its ampacity.

The overcurrent device is sized to the ampacity, without the correction factor. 240.4(D)

The code section is poorly worded, but I don't read it as saying that you can protect these small conductors with an OCPD that a rating higher than the adjusted ampacity.
Don