Minimum Residential Electric Size by code ?

[lakee911]

I was having a conversation with a collegue of mine and she informed me that the minimum electric service size is 200A and that is by code. I told her that a utility may require at a minimum size, and I think that is 100A around here, but by code it would depend on the load calc. Who's right?

I just did complete a project with six 100A services (all remote sites) and no one flagged it as too small.

Jason

 

[iwire]

There is no minimum service size required by the NEC, there may be other codes or standards that require a minimum size service.

If you do the Article 220 load calculations and they show a 60 amp service is large enough you could install a 60 amp service.

 

[lakee911]

Thanks! (Some text to exceed the minimum)

 

[RICK NAPIER]

NEC 230.79(D) For a one family dwelling, the service disconnecting means shall have a rating of not less than 100 amps, 3 wire.

 

[shepelec]

Doesn't 230.79(c) require a minimum of 100A for a residential single family?:-?

 

[lakee911]

NEC 230.79(D) For a one family dwelling, the service disconnecting means shall have a rating of not less than 100 amps, 3 wire.

Doesn't 230.79(c) require a minimum of 100A for a residential single family?:-?

It only states that the disconnecting means must be rated for 100A. This doesn't mean that the service is rated for 100A ... however, if one were to install a 60A service, for example, then it would need seperate overcurrent protection.

I guess it loosely implies 100A minimum service.

 

[RICK NAPIER]

My error it is (C)

 

[iwire]

It only states that the disconnecting means must be rated for 100A. This doesn't mean that the service is rated for 100A ...

That is correct.

however, if one were to install a 60A service, for example, then it would need seperate overcurrent protection.

A 100 amp fused disconnect with 60 amp fuses would do it.

I guess it loosely implies 100A minimum service.

From a practical standpoint I agree.

 

[cowboyjwc]

If I remember correctly, the code used to require a minimum 60 amp service, but pleased don't ask me when that was.

 

[480sparky]

If I remember correctly, the code used to require a minimum 60 amp service, but pleased don't ask me when that was.

230.79 goes back to at least 1975. It may go further back, but under another number. It was 100 for a SFD back then.

 

[iwire]

If I remember correctly, the code used to require a minimum 60 amp service, but pleased don't ask me when that was.

230.79 goes back to at least 1975. It may go further back, but under another number. It was 100 for a SFD back then.

Disconnect size not necessarily the service size.

 

[LawnGuyLandSparky]

If I remember correctly, the code used to require a minimum 60 amp service, but pleased don't ask me when that was.

iWire could tell you, as he probably installed the last one...

 

[Volta]

As a FPN, it goes back at least to 1937.

It is recommeded that the service switch have, in all cases, a rating not less than 60 amperes, and the circuit-breaker not less than 50 amperes.

It was probably 1951 that the general requirement started.

. . . In general the service disconnecting means shall have a rating of not less than 60 amperes if a switch is used,and not less than 50 amperes if a circuit-breaker is used: however for installations consisting of not more than two 2-wire branch circuits a switch or circuit-breaker of 30-ampere minimum rating may be used.

 

[cowboyjwc]

Disconnect size not necessarily the service size.

You are correct, maybe what it was was that the smallest service entrance conductors you could have were #8's.

Give a guy a break, I can't hardly remember what I had for breakfast this morning.

 

[LarryFine]

Give a guy a break, I can't hardly remember what I had for breakfast this morning.

Breakfast?

 

[Volta]

I was having a conversation with a collegue of mine and she informed me that the minimum electric service size is 200A and that is by code. I told her that a utility may require at a minimum size, and I think that is 100A around here, but by code it would depend on the load calc. Who's right?

I just did complete a project with six 100A services (all remote sites) and no one flagged it as too small.

Jason

As you are local, be aware that Upper Arlington has passed an ordinance requiring (generally) not less than a 150 amp service.

?1301.01 ELECTRICAL SERVICE EQUIPMENT
The minimum size of a permanently installed new electrical installation shall be one hundred fifty (150) amperes. Existing electrical service panels less than one hundred fifty (150) amperes may be replaced to equal the existing service capacity, but shall not be less than one hundred (100) amperes in any case. During electrical service upgrades, the existing service equipment shall be replaced with new, or previously unused, electrical service equipment, shall be replaced at the time the electrical service is upgraded and shall be done prior to energization by the electrical utility.

Some exceptions apply.

 

[jxofaltrds]

As you are local, be aware that Upper Arlington has passed an ordinance requiring (generally) not less than a 150 amp service.


Some exceptions apply.

That is in violation of the RCO (Residential Code of Ohio).

 

[kwired]

100 amps

100 amps

230.42 Minimum Size and Rating.

(A) General. The ampacity of the service-entrance conductors before the application of any adjustment or correction factors shall not be less than either (A)(1) or (A)(2). Loads shall be determined in accordance with Part III, IV, or V of Article 220, as applicable. Ampacity shall be determined from 310.15. The maximum allowable current of busways shall be that value for which the busway has been listed or labeled.
(1) The sum of the noncontinuous loads plus 125 percent of continuous loads
(2) The sum of the noncontinuous load plus the continuous load if the service-entrance conductors terminate in an overcurrent device where both the overcurrent device and its assembly are listed for operation at 100 percent of their rating
(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).

230.79 Rating of Service Disconnecting Means.

The service disconnecting means shall have a rating not less than the calculated load to be carried, determined in accordance with Part III, IV, or V of Article 220, as applicable. In no case shall the rating be lower than specified in 230.79(A), (B), (C), or (D).
(A) One-Circuit Installations. For installations to supply only limited loads of a single branch circuit, the service disconnecting means shall have a rating of not less than 15 amperes.
(B) Two-Circuit Installations. For installations consisting of not more than two 2-wire branch circuits, the service disconnecting means shall have a rating of not less than 30 amperes.
(C) One-Family Dwellings. For a one-family dwelling, the service disconnecting means shall have a rating of not less than 100 amperes, 3-wire.
(D) All Others. For all other installations, the service disconnecting means shall have a rating of not less than 60 amperes.

 

[Volta]

That is in violation of the RCO (Residential Code of Ohio).

Care to share?

 

[Smart $]

...

230.79 Rating of Service Disconnecting Means.

The service disconnecting means shall have a rating not less than the calculated load to be carried, determined in accordance with Part III, IV, or V of Article 220, as applicable. In no case shall the rating be lower than specified in 230.79(A), (B), (C), or (D).
(A) One-Circuit Installations. For installations to supply only limited loads of a single branch circuit, the service disconnecting means shall have a rating of not less than 15 amperes.
(B) Two-Circuit Installations. For installations consisting of not more than two 2-wire branch circuits, the service disconnecting means shall have a rating of not less than 30 amperes.
(C) One-Family Dwellings. For a one-family dwelling, the service disconnecting means shall have a rating of not less than 100 amperes, 3-wire.
(D) All Others. For all other installations, the service disconnecting means shall have a rating of not less than 60 amperes.

That's fine, but the OP question did not state there be a dwelling, only that it be residential... so s-t-r-e-t-c-h-i-n-g that technicality, the answer would be 15A :roll: