200a Meter socket, Main breaker combo.

Merry Christmas
Status
Not open for further replies.

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
In most cases you would be fine with your 4/0 SER
BUT
There are a lot of "depends"
The Code cycle makes a difference, '05,'08;'11 all treat SE cable in a different manner.
Interpretation makes a difference. Some inspectors use 310.15(B)(6) {'08 Reference} as their only guide. Some use 338.10(B)(4) and augment 310.15(B)(6)

The nuances have been discussed here at length. Best to run it by your AHJ
 

guschash

Senior Member
Location
Ohio
Is the cable four wires? House panel would be a sub panel now. I'm taking as the meter/combo is outside and main panel is in the house.
 

Riograndeelectric

Senior Member
Since this is a resi. app. Can you use 4/0 SER from the Main to the sub panel?

so now we have a sub panel? regardless of the wiring method would not 310.15(B)(7) from 2011 NEC.
Handbook comment "section 310.15(B) (7) permitted the main feeder to a dwelling unit to be sized according to the conductor sizes in table 310.15(B) (7). the permission to use this table applies only to conductors carrying 100 percent of the dwelling unit's diversified load." Diversified load?

would the conductors now be required to sized to 310.15 (B) (16) ?
which would be250MCM AL?

what if the main panel is not located on the house and you are running feeders to the house you can derate the conductors and use table 310.15(B) (7)?
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
so now we have a sub panel? regardless of the wiring method would not 310.15(B)(7) from 2011 NEC.
Handbook comment "section 310.15(B) (7) permitted the main feeder to a dwelling unit to be sized according to the conductor sizes in table 310.15(B) (7). the permission to use this table applies only to conductors carrying 100 percent of the dwelling unit's diversified load." Diversified load?

would the conductors now be required to sized to 310.15 (B) (16) ?
which would be250MCM AL?

what if the main panel is not located on the house and you are running feeders to the house you can derate the conductors and use table 310.15(B) (7)?

There has been much discussion to this Table during the last two or three Code cycles and there is still ambiguity in the enforcement.
A old lingering question has to do with some controversy concerning the reduced ampacity of SER in insulated areas.
Some inspectors rule the reduced ampacity conductor can not be used.

A second discussion has center around the situation where some of the load if fed from the service point ahead of the sub-panel. In those situations the sub-panel no longer carries 100% of the load. So you have a situation where an E/C feeds a 60 amp HVAC load from the interior panel and uses 310.15(B)(7) to feed that interior panel. On an identical job, he feeds the HVAC from a combo meter center thus reducing the sub-panel load by 60 amps but how he has to increase his feeder to the interior panel (unless he adds protection)...
There are different interpretations by AHJs
 

ceb58

Senior Member
Location
Raeford, NC
There has been much discussion to this Table during the last two or three Code cycles and there is still ambiguity in the enforcement.
A old lingering question has to do with some controversy concerning the reduced ampacity of SER in insulated areas.
Some inspectors rule the reduced ampacity conductor can not be used.

A second discussion has center around the situation where some of the load if fed from the service point ahead of the sub-panel. In those situations the sub-panel no longer carries 100% of the load. So you have a situation where an E/C feeds a 60 amp HVAC load from the interior panel and uses 310.15(B)(7) to feed that interior panel. On an identical job, he feeds the HVAC from a combo meter center thus reducing the sub-panel load by 60 amps but how he has to increase his feeder to the interior panel (unless he adds protection)...
There are different interpretations by AHJs
Gus has a very valid point and argument on this situation. But I would first ask, dose this meter comb have a built in buss for branch circuits or dose it just have the main?
 
SER isn't allowed up here but I had a job where I had to change meter location because it would have been inside the new addition. By using MBR pedestal I could run EMT across "crawl" space of addition instead of bury rigid way under existing concrete. Of course wires up sized to "feeders" and grounding bushings to use EMT as ECG.
 

kwired

Electron manager
Location
NE Nebraska
It mostly depends on what temperature rating you are allowed to use for the SE cable, which is dependent on which edition of NEC applies.

If you are allowed to use 75C then 4/0 is acceptable either way. 310.15(B)(7) allows 4/0 for a 200 amp circuit, and as long as the calculated load is not over 180 amps 310.15(B)(16) also allows 4/0 because next size standard overcurrent device is 200 amps.
 

ceb58

Senior Member
Location
Raeford, NC
we're on the 2011 NEC so I think it's good to go.

It mostly depends on what temperature rating you are allowed to use for the SE cable, which is dependent on which edition of NEC applies.

If you are allowed to use 75C then 4/0 is acceptable either way. 310.15(B)(7) allows 4/0 for a 200 amp circuit, and as long as the calculated load is not over 180 amps 310.15(B)(16) also allows 4/0 because next size standard overcurrent device is 200 amps.
310.15 B 7 will allow it. But if it were a situation where you used table 310.15 B 16 and it was in contact with thermal insulation it would drop it back to the 60 deg. column which would be 150 amp.
 
Status
Not open for further replies.
Top