This is probably a foolish question but here goes: 230.79 talks about service size requirements. Say a 3200 square foot storage building is to be built about 100 feet away from an existing building. This is a cold storage building with very few electrical requirements. Four CFL highbay fixtures, one garage door opener, and one general purpose outlet. The calculated load is under 10 amps. This building is to be powered from the service on the main building because the owner wants it on the same meter. So, 230.79d states 'All Others' to have a service rating of not less that 60 amperes. Is this considered a 'service'? Does the panel need to be FED with 60a or greater, or just equipment rated at that, and then the conductors could be sized smaller and protected at the source by the coresponding breaker? We would probably just feed it with #2 aluminum, install a main breaker panel on the outside of the building, drive (2) ground rods and be done. It just seems a little overkill. What do you think?
Service Size
- Thread starter torcho
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It depends on how the wire gets from the existing building to the new one. If in front of the main building disconnect (e.g. double lugged meter), then the new building is a service (NEC 230). If it is fed from a breaker in the main building (or anything past the main disconnect), then you have an outside feeder to that new building and you follow NEC 225.
It doesn't really matter though, as the disconnect size rules are the same for both. A difference though is the service entrance conductors for a service must be sized to match the building disconnect. For a feeder, you could put a 15A breaker in the main building and have that feed a 60A disconnect at the remote building. Done all the time, but some inspectors question it and may think the feeder must be sized to the disconnect. I think this has come up here enough times with substantiation that the rule applies to the size of the remove building disconnect and not its feeder.
The size I'd install depends on the odds of future expansion, and the cost of wire/breakers relative to all the other work costs (trenching or running it overhead to the building, panelboard and grounding system install, etc). If you're installing a raceway, I'd at least go large enough that you could have 100A of capacity (1.25" to 1.5"). If cost is an issue, a 30A to 60A feeder would probably be the least cost and still provide more than the minimum requirements.
It doesn't really matter though, as the disconnect size rules are the same for both. A difference though is the service entrance conductors for a service must be sized to match the building disconnect. For a feeder, you could put a 15A breaker in the main building and have that feed a 60A disconnect at the remote building. Done all the time, but some inspectors question it and may think the feeder must be sized to the disconnect. I think this has come up here enough times with substantiation that the rule applies to the size of the remove building disconnect and not its feeder.
The size I'd install depends on the odds of future expansion, and the cost of wire/breakers relative to all the other work costs (trenching or running it overhead to the building, panelboard and grounding system install, etc). If you're installing a raceway, I'd at least go large enough that you could have 100A of capacity (1.25" to 1.5"). If cost is an issue, a 30A to 60A feeder would probably be the least cost and still provide more than the minimum requirements.
cadpoint
Senior Member
- Location
- Durham, NC
I don’t think you can get around Article 230.79.
I guess my first question is how common is a double lug meter? Nice thought but wouldn't that be an additional expense now?
My second question is don’t you need six circuits for receptacles, for this size building? Maybe I need another cup of coffee.
If you’re going underground, I would also run another conduit for telephone or fire or for security.
This “cold building” to me opens up a lot of questions in my mind, I realize the client might just have only that in mind but the first thing you know their adding additional equipment, or heat then an office.
I think I’d gently question the whole ball of wax. It just seems to cut and dry and as previous implied seems you’ll need more circuits later.
Nothing is so plan to the local AHJ anymore they might have something to say as well. I’d certainly get them in the game.
I guess my first question is how common is a double lug meter? Nice thought but wouldn't that be an additional expense now?
My second question is don’t you need six circuits for receptacles, for this size building? Maybe I need another cup of coffee.
If you’re going underground, I would also run another conduit for telephone or fire or for security.
This “cold building” to me opens up a lot of questions in my mind, I realize the client might just have only that in mind but the first thing you know their adding additional equipment, or heat then an office.
I think I’d gently question the whole ball of wax. It just seems to cut and dry and as previous implied seems you’ll need more circuits later.
Nothing is so plan to the local AHJ anymore they might have something to say as well. I’d certainly get them in the game.
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- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
It doesn't matter if it is a service. Art. 230 is for services but art. 225.39 is for feeders.
It basically says the same as 230.79.
225.39 states the rating of the disconnect. Many here believe the disconnect must have a rating of 60 amps and the wire & OCPD does not. Go figure.
It basically says the same as 230.79.
225.39 states the rating of the disconnect. Many here believe the disconnect must have a rating of 60 amps and the wire & OCPD does not. Go figure.
mcclary's electrical
Senior Member
- Location
- VA
Dennis, so in your opinion a 30 amp breaker feeding a 10/3 that goes outside to a remote building to a 60 amp disconnect is illegal? Because I don't agree.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Opps......................
mcclary's electrical
Senior Member
- Location
- VA
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I do not understand the reasoning behind this so I do run a #6-- for other reasons also. I do not think it is illegal since the wording is pretty clear.
I wonder if 60 amp disconnects have some magical things in it that warrants this. It would be hard to find a panel that was rated less than 60 amps but you certainly can find a disco rated 30 amps--- even the a/c discos I used are rated 60 amps.
Are you creating branch circuits at the second building? if so how many??
Branch Circuits
Branch Circuits
Yeah, we had planned on (3) branch circuits for now: one for the lights, one for the receptacle and one for the door opener. And when I say 'cold' storage, I just mean it is an unheated, uninsulated building. Thanks for the replies.
Branch Circuits
Yeah, we had planned on (3) branch circuits for now: one for the lights, one for the receptacle and one for the door opener. And when I say 'cold' storage, I just mean it is an unheated, uninsulated building. Thanks for the replies.
- Location
- Massachusetts
The CMP have said that rule is only about the disconnect size, not the conductors.
- Location
- Massachusetts
Here it is from the report on proposals for the 2008 NEC.
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
Unless there is something magical about a 60 amp disconnect, as Dennis said, this rule seems silly to me. Why do I need a 60 amp disconnect if I have a 30 amp feeder?
- Location
- Massachusetts
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Here is the part that is troublesome to me.
Maybe this doesn't confuse things to you but it does to me. I see the cmp's answer but why do they use OCPD's to determine the disco rating? It makes me think that the rating is based on breaker size.
Example -- I have a 4 cir 60 amp panel and I install 2- 50 amp breakers in it. Is my disco now rated 100 amps or am I reading this incorrectly?
Maybe this doesn't confuse things to you but it does to me. I see the cmp's answer but why do they use OCPD's to determine the disco rating? It makes me think that the rating is based on breaker size.
Example -- I have a 4 cir 60 amp panel and I install 2- 50 amp breakers in it. Is my disco now rated 100 amps or am I reading this incorrectly?
mcclary's electrical
Senior Member
- Location
- VA
No,,,it would still be 60 amps,
IMO it means if you have a 100 amp ML panel, with (3) 20 amp breakers in it,you have met the 60 amp disco requirement
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I would tend to agree but I am not sure the words are there to defend it. I probably just need to let it go. Bob's post clears it up.
juptonstone
Member
- Location
- Lady Lake, FL
re cold storage building
re cold storage building
just out of curiosity, if you are running a sub-panel then you need a ground and neutral run from the main panel. Why would you re-ground an already grounded system. This would throw off the potential.
re cold storage building
just out of curiosity, if you are running a sub-panel then you need a ground and neutral run from the main panel. Why would you re-ground an already grounded system. This would throw off the potential.
mcclary's electrical
Senior Member
- Location
- VA
When you say re-ground, are you referring to the seperate GES required?
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