83% Allowance

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Some feeders in a dwelling also get special consideration. A feeder in a dwelling is not required to have an ampacity greater than the service or feeder to the dwelling. So if you have a dwelling with a 200A service, and that dwelling has a 200A feeder, that feeder can have an ampacity of 166A.

Note that this _DOES NOT_ apply to residential feeders in general, only to ones that are as large as the service.

Where this might come into play is if you have a 200A service with an external disconnect, and a 200A feeder to an interior panel, and an HVAC load is connected at the external disconnect. The 200A feeder can use the 83% sizing.

-Jon
 
winnie said:
Some feeders in a dwelling also get special consideration. A feeder in a dwelling is not required to have an ampacity greater than the service or feeder to the dwelling. So if you have a dwelling with a 200A service, and that dwelling has a 200A feeder, that feeder can have an ampacity of 166A.

Note that this _DOES NOT_ apply to residential feeders in general, only to ones that are as large as the service.

Where this might come into play is if you have a 200A service with an external disconnect, and a 200A feeder to an interior panel, and an HVAC load is connected at the external disconnect. The 200A feeder can use the 83% sizing.

-Jon
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The other place this applies is when the feeder in question carries the entire load of the dwelling unit. One example would be from an outside main breaker or fused disconnect to a single interior panel or to two or more panels in parallel. It could, for whatever reason, be sized smaller than the service in that case. It is only when there is a load connected upstream of the feeder that it no longer carries the entire load of the dwelling unit and you lose the ability to directly apply the 83% factor.
 
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