Pedestal 200 amp house 100 amp what rule here

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kbrandt

Member
Location
arizona
Ok I have read all the threads on 310.15 b 6. But none really apply to my question.

Have a 200 amp pedestal that feeds the house with 100 amp breaker, also feeds from pedestal a shop with 40 amps.

Owner wants to be able to hook a generator up when power goes out, only to the house which is 100 amp. this will be thru a manuel 100 amp transfer switch.

Can I use #4 to the x-fer switch then back to the house? Or is this (the house panel) a sub panel and have to use #3? I read as a sub panel.

Pedestal is away from house. And tried to see what is feeding it now but can't tell.

I have seen 100 amp meter panel on pole to feed mobile home. Underground to 100 amp panel in mobile home feed with #4, I think it should be #3, but they pass everytime. Am I wrong?

Thanks for any help.
 

Twoskinsoneman

Senior Member
Location
West Virginia, USA NEC: 2020
Occupation
Facility Senior Electrician
Here is what you have to consider to qualify for that table...

"the feeder between themain disconnect and the panelboard that supplies, either by
branch circuits or by feeders, or both, all loads that are part
or associated with the dwelling unit"

Does your feeder meet that definition?
My thought is that the "shop" is part of the loads associated with the dwelling and therefore the feeder to the 100A panel does not qualify for use of table 310.15(B)(7)
 

kwired

Electron manager
Location
NE Nebraska
Ok I have read all the threads on 310.15 b 6. But none really apply to my question.

Have a 200 amp pedestal that feeds the house with 100 amp breaker, also feeds from pedestal a shop with 40 amps.

Owner wants to be able to hook a generator up when power goes out, only to the house which is 100 amp. this will be thru a manuel 100 amp transfer switch.

Can I use #4 to the x-fer switch then back to the house? Or is this (the house panel) a sub panel and have to use #3? I read as a sub panel.

Pedestal is away from house. And tried to see what is feeding it now but can't tell.

I have seen 100 amp meter panel on pole to feed mobile home. Underground to 100 amp panel in mobile home feed with #4, I think it should be #3, but they pass everytime. Am I wrong?

Thanks for any help.

The feeder to the house can be sized according to 310.15(B)(6). Is the transfer switch installed "in the feeder"? If so it is just a switch in the feeder line side and load side are still the same feeder - generator side of transfer switch would not need to be larger than 4AWG either. But could be smaller if generator capacity is lower and proper corresponding overcurrent is installed at generator.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
It may end up being an AHJ call due to the facts noted in post #2. Is the shop "associated" with the dwelling. Since they are on one meter, I think most inspectors would say "yes" and require the #3.
 

kwired

Electron manager
Location
NE Nebraska
It may end up being an AHJ call due to the facts noted in post #2. Is the shop "associated" with the dwelling. Since they are on one meter, I think most inspectors would say "yes" and require the #3.

Maybe I am reading it wrong but from what I understand OP is wanting to transfer 100 amp feed to the house. If the transfer switch is located so that is basically breaking the 100 amp feeder to the house then we don't even care that the shop exists as it is not part of anything involved here. If OP is trying to install transfer switch on supply side of pedestal it is a whole different situation.
 

Twoskinsoneman

Senior Member
Location
West Virginia, USA NEC: 2020
Occupation
Facility Senior Electrician
Can I use #4 to the x-fer switch then back to the house?

I think I understand you Kwired. This is an existing installation. I wonder what is run to the 100 amp panel now?
Basically he just wants to splice a x-switch in the existing feed....and wants to know what has to be run from the gen to the x-switch?
 

kwired

Electron manager
Location
NE Nebraska
I think I understand you Kwired. This is an existing installation. I wonder what is run to the 100 amp panel now?
Basically he just wants to splice a x-switch in the existing feed....and wants to know what has to be run from the gen to the x-switch?

And if all it is supplying is a dwelling unit why wouldn't 310.15(B)(6) be allowed to size this conductor? If the existing feeder is smaller than 4AWG there is a problem, if it is larger ...who cares, unless they want to take voltage drop into consideration.
 

Twoskinsoneman

Senior Member
Location
West Virginia, USA NEC: 2020
Occupation
Facility Senior Electrician
My thought is that the "shop" is part of the loads associated with the dwelling and therefore the feeder to the 100A panel does not qualify for use of table 310.15(B)(7)

It may end up being an AHJ call due to the facts noted in post #2. Is the shop "associated" with the dwelling. Since they are on one meter, I think most inspectors would say "yes" and require the #3.

And if all it is supplying is a dwelling unit why wouldn't 310.15(B)(6) be allowed to size this conductor? If the existing feeder is smaller than 4AWG there is a problem, if it is larger ...who cares, unless they want to take voltage drop into consideration.

I think I made my opinion clear of why I don't think it qualifies for use of table 310.15(B)(7). Because IMHO the shop load is part of the associated load. It's just my opinion of the wording. Also I think it is a dumb rule. But it is what is it is.
BTW I consider your opinion valid also and would not argue with the AHJ about it either way because IMO it's somewhat open to interpretation.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
I agree with Post #8, but mine is an opinion also.
The service (for the "shop" and "dwelling" might qualify foe 310.15(B)(6), hut the feeder to the house would not.
The opinion that matters is the AHJ
 

kwired

Electron manager
Location
NE Nebraska
I think I made my opinion clear of why I don't think it qualifies for use of table 310.15(B)(7). Because IMHO the shop load is part of the associated load. It's just my opinion of the wording. Also I think it is a dumb rule. But it is what is it is.
BTW I consider your opinion valid also and would not argue with the AHJ about it either way because IMO it's somewhat open to interpretation.
My understanding is the shop has nothing to do with the conductors that are being asked about, all that it supplied by conductors in question is house - why does that not qualify for 310.15(B)(6)

I agree with Post #8, but mine is an opinion also.
The service (for the "shop" and "dwelling" might qualify foe 310.15(B)(6), hut the feeder to the house would not.
The opinion that matters is the AHJ

Again if the only thing being supplied is the feeder to the house why does not 310.15(B)(6) apply? This is exactly what that section is intended for is conductors supplying entire dwelling units.

Again as I said - maybe I misunderstand what is intended to be supplied, but if it is (all of)the dwelling only I am standing behind what I have already said.
 

Twoskinsoneman

Senior Member
Location
West Virginia, USA NEC: 2020
Occupation
Facility Senior Electrician
My understanding is the shop has nothing to do with the conductors that are being asked about, all that it supplied by conductors in question is house - why does that not qualify for 310.15(B)(6)



Again if the only thing being supplied is the feeder to the house why does not 310.15(B)(6) apply? This is exactly what that section is intended for is conductors supplying entire dwelling units.

Again as I said - maybe I misunderstand what is intended to be supplied, but if it is (all of)the dwelling only I am standing behind what I have already said.


Because the only thing that table is used for is the main power feeder to the dwelling unit. To be considered the main power feeder it must carry all the loads associated with the dwelling unit. IF you consider the shop an associated load then the feeder to the 100a panel is not the main power feeder
 

kwired

Electron manager
Location
NE Nebraska
Because the only thing that table is used for is the main power feeder to the dwelling unit. To be considered the main power feeder it must carry all the loads associated with the dwelling unit. IF you consider the shop an associated load then the feeder to the 100a panel is not the main power feeder

The OP says it is the main power feed to the house and the shop is on a separate 40 amp circuit that is why I am confused by why you keep mentioning the shop .. it has nothing to do with the feeder in question.

add: what the OP did not make clear is where it is intended to install the transfer switch - but he kind of hints at the fact it will be supplying the house only.
 

Twoskinsoneman

Senior Member
Location
West Virginia, USA NEC: 2020
Occupation
Facility Senior Electrician
The OP says it is the main power feed to the house and the shop is on a separate 40 amp circuit that is why I am confused by why you keep mentioning the shop .. it has nothing to do with the feeder in question.

add: what the OP did not make clear is where it is intended to install the transfer switch - but he kind of hints at the fact it will be supplying the house only.

I understand. In your opinion they are not associated. In my opinion they are associated. Because of the nature of the definition of the word "associated" I accept the AHJ's opinion either way. If you end up being my AHJ I would happily accept and encourage your opinion. :happyyes:
 

kwired

Electron manager
Location
NE Nebraska
I understand. In your opinion they are not associated. In my opinion they are associated. Because of the nature of the definition of the word "associated" I accept the AHJ's opinion either way. If you end up being my AHJ I would happily accept and encourage your opinion. :happyyes:

I understand the shop is associated to the dwelling - they are on same property. But electrically in the OP's situation the only association is the fact they are supplied from the same pedestal, but by separate feeders. Once past the two feeder breakers I fail to see any association as far as the electrical installation is concerned. That separate building could easily be another dwelling and a second transfer switch installed - now you have two feeders that are both allowed to be sized by 310.15(B)(6). Put the transfer switch on the supply side of the pedestal and now you need to size conductors to T310.16 - whether the second building is a dwelling or a shop.
 

Twoskinsoneman

Senior Member
Location
West Virginia, USA NEC: 2020
Occupation
Facility Senior Electrician
I understand the shop is associated to the dwelling

For application of this section,
the main power feeder shall be the feeder between the
main disconnect and the panelboard that supplies, either by
branch circuits or by feeders, or both, all loads that are part
or associated with the dwelling unit.

Finally you see things my way! :lol:
I'm kidding.

I understand what your saying, I really do, but you haven't swayed me.
As I said I think it's a dumb rule and should be modified to accommodate ANY dwelling feeders that have reasonable load diversity such as feeders out to a garage or work shop or even a basement sub.
 

kwired

Electron manager
Location
NE Nebraska
For application of this section,
the main power feeder shall be the feeder between the
main disconnect and the panelboard that supplies, either by
branch circuits or by feeders, or both, all loads that are part
or associated with the dwelling unit.

Finally you see things my way! :lol:
I'm kidding.

I understand what your saying, I really do, but you haven't swayed me.
As I said I think it's a dumb rule and should be modified to accommodate ANY dwelling feeders that have reasonable load diversity such as feeders out to a garage or work shop or even a basement sub.

Actually I am starting to see it your way. Where I live many times that shop is not associated with the dwelling - it is just another structure on the farm - and the dwelling is ...the dwelling. In town the shop is associated with the dwelling - usually. Some of what I just said may need taken into consideration and the decision could still possibly go either way.
 

Twoskinsoneman

Senior Member
Location
West Virginia, USA NEC: 2020
Occupation
Facility Senior Electrician
I understand your thinking. Association can be determined by functionality and even vicinity. I think (based solely on personal observation and reading others opinions) most AHJ are going to see any loads on the same service to be associated.
 

kbrandt

Member
Location
arizona
Here it is-- a 200 amp pedestal on property, out of pedestal a 100 amp feeds house and 40 amp to shop. I want come off 100 amp breaker (that feeds house) in pedestal to x-fer switch then to house.

Basically interrupting the line to house. Does it count as a feeder and can I use #4. Since the pedestal is the main panel, I wondered if the house panel is considered a sub panel that would need #3.

Hope this helps.
 

kwired

Electron manager
Location
NE Nebraska
Here it is-- a 200 amp pedestal on property, out of pedestal a 100 amp feeds house and 40 amp to shop. I want come off 100 amp breaker (that feeds house) in pedestal to x-fer switch then to house.

Basically interrupting the line to house. Does it count as a feeder and can I use #4. Since the pedestal is the main panel, I wondered if the house panel is considered a sub panel that would need #3.

Hope this helps.

It is a feeder - it is a subpanel those are kind of the same thing for most conversations - NEC uses the term feeder, and the sub panel is just a panel - that is not service equipment.

Your question is whether or not 310.15(B)(6) can be used for determining size of the feeder conductor. From my point of view yes, from Twoskins point of view no, and I can see his reasoning - now ask your AHJ what his opinion is or just use the 3 AWG and you can't be wrong.
 
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