Sub-panel

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Oldmaster2

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Master Electrician
I see that the 83% percentage conductor size as it applies to feeders serving a sub panel is only viable if the panel serves the entire load.
Regarding a sub panel, how can it not be the entire load? The argument is that the service panel does not carry the entire load because of the sub panel ? My response is the breaker that feeds the sub panel is located in the main service panel, thus the service panel serves the entire load. Maybe I'm just confused?
 
Oldmaster2 said:
I see that the 83% percentage conductor size as it applies to feeders serving a sub panel is only viable if the panel serves the entire load.
Regarding a sub panel, how can it not be the entire load? The argument is that the service panel does not carry the entire load because of the sub panel ? My response is the breaker that feeds the sub panel is located in the main service panel, thus the service panel serves the entire load. Maybe I'm just confused?
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83% for a feeder to a sub panel is not code compliant.
 
You have two panels. The first panel has an OCPD and a feeder to the second panel. The sub-panel is not carrying the entire load if the first panel has other breakers supply other loads.
 
xformer said:
83% for a feeder to a sub panel is not code compliant.
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Unless (a) the feeder carries the entire load of a dwelling unit (e.g. the service supplies two separate dwelling units) or (b) the feeder is the same size as an upstream feeder than does carry the entire load of a dwelling unit (e.g. a 100A feeder on a 100A service for one dwelling unit).

Cheers, Wayne
 
Oldmaster can you explain the exact installation that you have with all the conductor and OCPD sizes?
 
100 amp service . 2/2/4 seu .
Feed to sub panel 1/1/2/4 Ser
Inspector insists service entrance conductor is must be #1. Since in his mind it does not carry the full load because of the sub,?
 
Oldmaster2 said:
100 amp service . 2/2/4 seu .
Feed to sub panel 1/1/2/4 Ser
Inspector insists service entrance conductor is must be #1. Since in his mind it does not carry the full load because of the sub,?
Click to expand...
The fact that the sub is fed by #1's is irrelevant. The service conductors to the service panel are properly sized according to the 83% rule because they are carrying the entire load. Not sure why the inspector is missing that. Maybe he needs to see a one line diagram.
 
Oldmaster2 said:
100 amp service . 2/2/4 seu .
Feed to sub panel 1/1/2/4 Ser
Inspector insists service entrance conductor is must be #1. Since in his mind it does not carry the full load because of the sub,?
Click to expand...
He's wrong, the service conductors DO carry the full load. How could they not?

And your feeder conductors need not be larger than the service conductors.
 
wwhitney said:
Unless (a) the feeder carries the entire load of a dwelling unit (e.g. the service supplies two separate dwelling units) or (b) the feeder is the same size as an upstream feeder than does carry the entire load of a dwelling unit (e.g. a 100A feeder on a 100A service for one dwelling unit).

Cheers, Wayne
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Wouldn't your first example be actually two services? One for each structure or separate dwelling unit?
 
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