Minimum Service Size

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rookie4now

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I have a 6 unit building where the insurance co. is requiring fuses to be replaced with CB. There is a 125a service disconnect then a gutter to 6 meters with 30a disconnects. Theses are fed to a 2 circuit panel in each unit. There is one 15a circuit and one 20a circuit in each unit. There is 240v at the main disco but each unit has only 120V.

Here is the problem. There is currently only two #12 wires running to each unit. This is the feed from the disconnect to the 2 circuit sub panel which each unit has. They are currently protected with a 30a fuse. When we change the disconnects over, it is my understanding that 230.77(b) will require a minimum of 30a service as the units have 2 circuits. Since the wiring from the disco to the unit is #12, this will be a problem.

Am I correct about the 30 amp requirement? Is there a requirement that each unit has to have 240? Is the existing installation grandfathered in even if we change the disconnect to each unit? (notice how I am grasping at straws).

Amazingly, there are no tenant issues regarding blown fuses etc. as the units are very small. the owner just wants to do what the insurance co. is requiring and has not had any luck looking at other insurance companies.

Any thoughts, suggestions?
 
rookie4now said:
There is a 125a service disconnect then a gutter to 6 meters with 30a disconnects. Theses are fed to a 2 circuit panel in each unit.
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It sounds like you have your 30 amp discos at the service after the meters.

Every jurisdiction is going to have their own rules on what you must do once you get into panel work.

I would think since it is an existing situation that they can't make you change everything. I would definitely check with the inspection department.
 
circuits

circuits

I may be out of line posting an answer for a "student", the moderator can decide, but in the interst of furthering your education I thought I would comemnt on your statement:

"They are currently protected with a 30a fuse"

You will find in many "replace the fuse panel" situations that the reason no one is haveing trouble with the circuits is the improper, oversized fuse. Once you provide proper overcurrent protection, the problems arise and YOU ARE THE CAUSE (according to them).

Alwon is correct. IMHO, This a situation to be reviewed with the local AHJ.
 
I do a fair number of these jobs as you describe, in year's time.

The minimum service size for a dwelling (each apartment) is 100 amps.

My normal approach to your situation would be as follows... Install a 6 gang meter/main meter stack, which would have 6 meters and 6 tennant breakers at 100 amps each. Feed SER or conductors in conduit from each tennant breaker in that meter stack to each tennant subpanel. In your case, each tennant subpanel would have two branch circuit breakers serving the two existing branch circuits in each dwelling unit. Install service grounding as required to the meter stack. Job done.

These people will start to trip those two branch breakers, since they were formerly fused at 30 amps. These trouble calls will be your inviation to do more work in the future. I can see an inspector requring work on the branch circuits along with the service upgrade, but luckily for me, that doesn't happen in my area. They're happy with whatever upgrades they can get done in an old apartment building.

I can also see the IEBC or the IPMC coming into play, requiring you to install a meter and panel for house loads. This would make a 7th disconnect, which would make you have one main disconnect for the whole service, and have you do cold sequence metering.
 
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First your NEC 'Service' ends at the 125 amp service disconect, the conductors on the load side of the service disconnect are feeders.

That being the case nothing in Article 230 applies to the conductors and disconnects on the load side of the service disconnect.

Being feeders we have to look at the rules in Article 215, I do not find anything in Article 215 that prohibits a 120 volt 20 amp 'feeder'. The feeder must be large enough to supply the calculated load.

However, how far do you have to go anyway?

IMO changing the service has nothing at all to do with the feeders or the wiring in the units.

If you did also up grade the feeder would you than have to upgrade the units to fully comply with todays code, GFCIs, AFCIs, small appliance branch circuits, lighting outlets and switches?

In my opinion the answer is no.

I was once involved with changing the services of 12 - 30 unit apartment buildings. In each building the riser to each of the 30 units was a single 14 AWG K&T circuit. We installed new modular meter stacks with 15 amp single pole breakers for each units riser.

This was a big disappointment to the tenants as all these 14 AWG risers had been protected with 30 amp Edison base fuses, once we switched to the properly sized 15 amp breaker they started tripping them fairly regularly.

I don't know what ever became of it, we did what we where paid to do, we got it inspected and passed.

IMO, what we did was legal and was still a significant increase in safety from the original services with the 30 amp fuses protecting 14 AWG K&T.

Now all that said, I would talk to the inspection department first to see how they feel and I would make very clear in writing to the person paying the bill that the price and work is for a service change, not an entire upgrade.

I would make clear to the owner that only changing the service will likely end up with nuisance tripping of the units feeders and other work for an additional charge will need to be done to fix it.
 
rookie4now said:
Here is the problem. There is currently only two #12 wires running to each unit. This is the feed from the disconnect to the 2 circuit sub panel which each unit has. They are currently protected with a 30a fuse. When we change the disconnects over, it is my understanding that 230.77(b) will require a minimum of 30a service as the units have 2 circuits. Since the wiring from the disco to the unit is #12, this will be a problem.
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230.79(B) seems to address the "problem".

There is NO 230.77(B) in either the '02 or '05 editions of the NEC ~ what edition are you referenceing?

mdshunk said:
The minimum service size for a dwelling (each apartment) is 100 amps.
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Is that a local code?
I read 230.79(C) and (D) slightly different.
 
iwire said:
First your NEC 'Service' ends at the 125 amp service disconect, the conductors on the load side of the service disconnect are feeders.

That being the case nothing in Article 230 applies to the conductors and disconnects on the load side of the service disconnect.
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I see what you're saying
 
mdshunk said:
I do a fair number of these jobs as you describe, in year's time.

The minimum service size for a dwelling (each apartment) is 100 amps.

.
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Do you have a code reference? I previously misquoted the code section I was referring to, it was supposed to be 230.79(b). It reads:

"Two circuit installations. For installations consisting of not more than 2 2-wire circuits, the service disconnecting means shall have a rating of not less than 30 amps."
 
rookie4now said:
Do you have a code reference? I previously misquoted the code section I was referring to, it was supposed to be 230.79(b). It reads:
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Read art. 230.79 (C)(D). I think that's where the 100 amp came from.
 
rookie4now said:
I previously misquoted the code section I was referring to, it was supposed to be 230.79(b). It reads:

"Two circuit installations. For installations consisting of not more than 2 2-wire circuits, the service disconnecting means shall have a rating of not less than 30 amps."
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Let me try again. :grin:

ARTICLE 230 DOES NOT APPLY TO FEEDERS

THE CONDUCTORS RUNNING TO THE UNITS ARE FEEDERS NOT SERVICE CONDUCTORS.

THE JOB YOU DESCRIBE HAS ONE SERVICE DISCONNECT AND IT IS MORE THAN 100 AMPS
 
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iwire said:
THE JOB YOU DESCRIBE HAS ONE SERVICE DISCONNECT AND IT IS MORE THAN 100 AMPS
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Indeed. I substituted the equipment I'd replace it with for the equipment that presently exists on the job. I always viewed a 6 unit apartment building as six, one family dwellings in the same building, requiring a 100 amp service disconnect (tennant breaker) for each (six service disconnects). I never questioned that until just now, reading the responses. It seems that 'dwelling, one family' has a code definition. Thanks for clearing that up, everyone. I've overkilled a lot of stuff in the past, so it would seem.
 
mdshunk said:
I always viewed a 6 unit apartment building as six, one family dwellings in the same building,
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IMO it is six dwelling units.

I don't see how that makes a difference here.:smile:

requiring a 100 amp service disconnect (tennant breaker) for each (six service disconnects).
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It does, if you build the service without a main.

For some reason this service has a 125 amp service disconnect supplying six 30 amp feeder disconnects.

Many times this service would not have a 125 amp service disconnect, it would have six service disconnects and in that case they would have to be 100 amps each.


I've overkilled a lot of stuff in the past, so it would seem.
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But I bet you made money doing it. :)
 
iwire said:
Many times this service would not have a 125 amp service disconnect, it would have six service disconnects and in that case they would have to be 100 amps each.
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Well, I think they could legally be 60's. Reason being, this occupancy type is not a one family dwelling in accordance with the article 100 definition. It is a multifamily dwelling. In that case the 100 amp requirement of 220.79(C) may not apply. It seems like you could apply 230.79(D) "All others", and give each unit a 60 amp service disconnect in the meter stack.
 
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