minimum service size for dwelling

Paul1955

Member
Location
Trinity, Alabama
Can someone point me where (or if) the 2011 code states the minimum service for a dwelling unit is 100 amps?

Or this this typically a local requirement?

Thanks
Could you be thinking of 230.79(C) or 225.39(C)? "For a one-family dwelling, the service disconnecting means shall have a rating of not less than 100 amperes, 3-wire."
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Electrical Contractor
Could you be thinking of 230.79(C) or 225.39(C)? "For a one-family dwelling, the service disconnecting means shall have a rating of not less than 100 amperes, 3-wire."
Although that section gives the correct answer it just state that the disconnect must be 100 amps. Art. 230.230.42B is what we are after

230.42 Minimum Size and Rating
230.42(B) Specific Installations. In addition to the requirements
of 230.42(A), the minimum ampacity for ungrounded conductors
for specific installations shall not be less than the
rating of the service disconnecting means specified in
230.79(A) through (D).
 

cowboyjwc

Moderator
Staff member
Location
Simi Valley, CA
Since you are in CA, per 110.10(e) of the 2013 Building Energy Efficiency Standards:

1. The main electrical service panel shall have a minimum busbar rating of 200 amps.

2. The main electrical service panel shall have a reserved space to allow for the installation of a double pole circuit breaker for the future solar electric installation.

Now this is for new construction of course.
 
More specifically, here's the dilemma:

Old "motor inn" motel with 10 units was at some point in the last 50 years converted to mini 1 bedroom apts, with small gas range, gas wall heater & gas water heaters, no laundry, (minimal load). Until a month ago, the entire facility was feed by a 50 amp service. The neutral failed on the service entrance, plus the entire service was hanging by a single screw. The DP 50amp fed a small sub-panel 130' away from the main.

I replaced the service with a meter/main 200amp, 20/40 panel, and ran 130' of 1 1/4" with #2 Thhn feed by a DP 100amp to the sub-panel (it was rated for 100 amps). My work was fully permitted and inspected.

The owners asked about individual metering, but had balked at the cost.

I gave the owners a price for rewiring one unit, with the thought of installing a small sub-panel feed by a DP 40amp. A general contractor gave them a cheaper price to do all the work (without a permit)

The general was caught doing the remodel w/o a permit, and the city shut down the entire job. The city inspector has initially taken the position that the unit had to be have a 100amp service. (BTW, this is still possible, my original job will allow for it, just tremendous overkill)

I say the service is already there (my 200amp), and as long as we show the load (which has been calculated per NEC 200 (2011), we can run what ever the appropriate size feeders are to the new panel in the unit. It calculated to roughly 30 amps. (2 small appliance circuits at 1500 watts each= 3000w, 1500w general lighting, dishwasher @ 1188w, garbage disposal @ 1140w, no laundry or other appliances, hood 300w)

Your thoughts?
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
I think that an argument can be made by the inspector that each dwelling unit needs to have a 100 amp feeder and panel, even if all six are compliantly fed from one 200A service based on their calculated load.
 

GoldDigger

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Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
If code requires 100A (or 60A) for a "dwelling unit" it seems to me to require that to be brought all the way to the unit, even if all the units share a larger POCO service. These are individual residences, not even apartments in a single building.
 
If code requires 100A (or 60A) for a "dwelling unit" it seems to me to require that to be brought all the way to the unit, even if all the units share a larger POCO service. These are individual residences, not even apartments in a single building.
And the requirement is for the "service". and for further clarification, I would agree that if they are individually metered,they would likely be required to have 100amp services.
 
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Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Electrical Contractor
I don't believe 100 amps is required at each unit. If that were the case then apartments would be grossly overkill in say small apartment buildings especially where the heat and a/c may be central to all units
 
I don't believe 100 amps is required at each unit. If that were the case then apartments would be grossly overkill in say small apartment buildings especially where the heat and a/c may be central to all units
These are small, @ 500 sq feet. It would be real over kill.

I just wanted to bounce it off the forum to see if they agreed with my position before I argue, err discuss it :), with the city.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
From what I understand is you can have a 100amp disconnect fed from a 50amp source?
Absolutely. As long as the conductors are properly protected by upstream OCPD.
If the disconnect in question is a service disconnect and the 50A source is a 50A service, then no.
 

mbrooke

Batteries Not Included
Location
United States
Occupation
*
Absolutely. As long as the conductors are properly protected by upstream OCPD.
If the disconnect in question is a service disconnect and the 50A source is a 50A service, then no.


I guess I should ask what is classified as a service disconnect? What would be a legal example of a 60amp main in a dwelling be it single or multi?
 

BrianDTC

Member
Location
Hamden CT
I am also confused about the minimum service size for a dwelling unit. 230.79C says 100A, 3W min. but D says 60A for "all others". Is multi-family dwelling covered in "all others"??

Please help. I have a warehouse building converted to a multifamily dwelling and the landlord is giving 30A to each appt. right now. I'm trying to tell him he needs to give atleast 60A or 100A to each tenant.

Please help!!

Thanks.
 

charlie b

Moderator
Staff member
Location
Seattle, WA
Occupation
Electrical Engineer
We are in the wrong article here! :happyyes: 230 is not a player in this discussion. :happyno: The requirement for a minimum 60 amp service disconnecting means (i.e., from 230.29(D) for "all others") has been met by way of the new 200 amp panel. From that point downstream, the utility company is not involved, the word "service" does not apply, and neither does article 230. We are discussing feeders to individual dwelling units, not services to individual dwelling units. I don't know of any requirement for a minimum disconnect rating or a minimum panel rating for dwelling units that are not fed directly from the utility.
 

charlie b

Moderator
Staff member
Location
Seattle, WA
Occupation
Electrical Engineer
230.79C says 100A, 3W min. but D says 60A for "all others". Is multi-family dwelling covered in "all others"??
Yes. For your project, my answer is that the only requirement is that you provide enough capacity for the calculated load. I tend to doubt that 30 amps is enough, unless the "permanent provisions for cooking" is a gas stove, and unless there is no laundry equipment in each unit. Electricguy61's calculation came out close to 30 amps, so it is possible. But I think you need to do a load calculation, before you push for a 60 amp feeder to each unit.

 
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