Can I run 2 panels off the same main breaker? Or?

roger

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Fl
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Retired Electrician
Here's the definition from the NEC which controls the use of (2020) 310.12:

"Dwelling Unit. A single unit, providing complete and independent living facilities for one or more persons, including permanent provisions for living, sleeping, cooking, and sanitation."

Would you explain how it's possible to interpret an ADU as other than a second dwelling unit? I'm not seeing it.

Cheers, Wayne
I know the definition and it's not relevant to this conversation. Using your argument would mean a single residence with multiple kitchens is not a single residence, IOWs a single residence can only have one kitchen.
 

JohnDS

Senior Member
Location
Suffolk, Long Island
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Electrician
You can not use the reduction unless the feeder serves the whole load of the dwelling as in singular.
I am still confused what you mean by reduction and 83% rule. Are you thinking I'm suggesting that I'm going to tap from the 2/0 copper and split it into two smaller feeders(1 for each panel)? If so, I'm not suggesting that, I was suggesting 2/0 copper feeder just split into two more 2/0 copper feeders(each running to its own panel).

Remove the disconnect or take the guts out and use it as a j-box for both the apartment and the house.. Make that a "gutter' or j-box set two disconnects beside it. (y)
Don't mess with the meter, unless your in Indiana. Its common to see three or four conduits coming out of a meter base in rual Indiana, no disconnects any where in sight.:oops:
Thank you for that. The reason I was suggesting the option to come out of the meter is because around here an outside disconnect is not required for a panel that is within 5' of the meter. I believe the 2020 code wants disconnects outside regardless, but it's not adopted here yet. The outside disconnect that you see there is only there because the main panel is about 45' away and requires one.

In any event, I appreciate the plan. I may do just what you said, or unless someone can confirm that it is ok to just double tap the meter with 2/O SEU, straight into the 200 amp apartment panel since it has a main breaker in it already.
 

wwhitney

Senior Member
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Berkeley, CA
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Retired
I know the definition and it's not relevant to this conversation.
How can it possibly not be relevant? To apply (2020) 310.12(B), all we need are "feeder conductors supplying the entire load associated with an individual dwelling unit". So we need to know how many individual dwelling units there are.

Using your argument would mean a single residence with multiple kitchens is not a single residence, IOWs a single residence can only have one kitchen.
I said no such thing, nor does it follow logically from what I have said. I'm really having trouble following your logic and figuring out what we disagree on.

Cheers, Wayne
 

wwhitney

Senior Member
Location
Berkeley, CA
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Retired
I am still confused what you mean by reduction and 83% rule.
2/0 Cu has a 90C ampacity of 195A but a 75C ampacity of 175A. Since 175A is a standard breaker size, and since breakers limit you to the 75C ampacity due to their termination limits, 2/0 Cu has to be protected at 175A (at most) unless (2020) 310.12, the 83% rule, applies. Which is for feeders and services carrying the full load of a single dwelling unit.

Cheers, Wayne
 

roger

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Fl
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I am still confused what you mean by reduction and 83% rule. Are you thinking I'm suggesting that I'm going to tap from the 2/0 copper and split it into two smaller feeders(1 for each panel)? If so, I'm not suggesting that, I was suggesting 2/0 copper feeder just split into two more 2/0 copper feeders(each running to its own panel).
2/0 copper THWN is only good for 195 amps under table 310.15(B)16 now, Table 310.15(B)(7) allows you to go down one size for the service conductors or main feeder because of demand factors
 

roger

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Or what Wayne said. Don't pay too much attention to our debate. BTW, 83% basically is saying one size.
 

JohnDS

Senior Member
Location
Suffolk, Long Island
Occupation
Electrician
2/0 Cu has a 90C ampacity of 195A but a 75C ampacity of 175A. Since 175A is a standard breaker size, and since breakers limit you to the 75C ampacity due to their termination limits, 2/0 Cu has to be protected at 175A (at most) unless (2020) 310.12, the 83% rule, applies. Which is for feeders and services carrying the full load of a single dwelling unit.

Cheers, Wayne
Thank you for explaining. So techniclly, since it is two dwelling units or will be, I can't just split the 2/O load wire coming from the meter, i stead I would have to upsize this wire first.......according to NEC at least. Correct?

I was just looking for a temporary solution until I can get a 400 amp multi meter, instead of spending $1k running SER from my main panel to power the apartment panel.
 

Buck Parrish

Senior Member
Location
NC & IN
I am still confused what you mean by reduction and 83% rule. Are you thinking I'm suggesting that I'm going to tap from the 2/0 copper and split it into two smaller feeders(1 for each panel)? If so, I'm not suggesting that, I was suggesting 2/0 copper feeder just split into two more 2/0 copper feeders(each running to its own panel).


Thank you for that. The reason I was suggesting the option to come out of the meter is because around here an outside disconnect is not required for a panel that is within 5' of the meter. I believe the 2020 code wants disconnects outside regardless, but it's not adopted here yet. The outside disconnect that you see there is only there because the main panel is about 45' away and requires one.

In any event, I appreciate the plan. I may do just what you said, or unless someone can confirm that it is ok to just double tap the meter with 2/O SEU, straight into the 200 amp apartment panel since it has a main breaker in it already.
Hardly any body in rual Indiana follows NEC 230.72 "EXCEPT' me. I refuse to let the locals corrupt my electrical installations.
So many so called electricians think that on a 400 amp service, the panel that is 45 feet away needs a disconnect but the one in the house behind the meter does not because it's only 5 feet away.
Well that's wrong - Disconnects must be grouped 230.72 -(They both, up to six must be at the meter ( or service) and labled.
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
Thank you for explaining. So techniclly, since it is two dwelling units or will be, I can't just split the 2/O load wire coming from the meter, i stead I would have to upsize this wire first.......according to NEC at least. Correct?
I would say that you have two dwelling units, so if you divide the wiring after the meter, then:

The wiring that is after the division is just for one dwelling unit so 310.12 applies, and you can use 2/0 Cu (or 4/0 Al) to a 200A service disconnect to a 2/0 Cu feeder (or 4/0 Al).

The wiring before the division does not get to use 310.12, so you need to do a load calculation and size it to the load supplied. If you have existing 2/0 Cu wiring, it's fine if the calculated load for both dwelling units is 175A or less. No need to use a 125% factor for continuous load in that check, as they are just service conductors, no OCPD or feeder conductors involved.

Actually, what is the temperature limit of the meter can terminations? If for some reason that was 90C, and the POCO connection at the service point was 90C, then this would be a rare case that everything is 90C rated, and you could use 195A for the 2/0 Cu before the division.

Cheers, Wayne
 
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JohnDS

Senior Member
Location
Suffolk, Long Island
Occupation
Electrician
Hardly any body in rual Indiana follows NEC 230.72 "EXCEPT' me. I refuse to let the locals corrupt my electrical installations.
So many so called electricians think that on a 400 amp service, the panel that is 45 feet away needs a disconnect but the one in the house behind the meter does not because it's only 5 feet away.
Well that's wrong - Disconnects must be grouped 230.72 -(They both, up to six must be at the meter ( or service) and labled.

Well I never understood or agreed with 5' of unprotected wire entering a house, but cant say I haven't done them like that. I guess every licensed electrician and inspector does it wrong around these parts. I just don't understand why it's allowed then, if thats the case. But then again, why is the local power company allowed to feed a 200 amp service with #4 aluminum conductors. I know they don't follow NEC, but that just gives them the right to do what they want cause it's in the air?
 

Amps

Electrical Contractor
Location
New Jersey
Occupation
Electrical, Security, Networks and Everything Else.
Am I missing something? Is 2/O copper not a 200 amp conductor? That's all that is used for 200 amp services around here.



This is a temporary setup, it's not intended to have the tenant pay for their own electric until the multi position meter is available and installed. For now, electric is included in the rent if it's being done this way.

So with disturbing this service as little as possible, what would be the best course of action for now? Should I tap SEU right out the bottom of the meter from the same load lugs as the main panel and directly feed the apartment panel(has its own main breaker)? Or should I just come out of the load side of this disconnect somehow?
Maybe add a WP trough or large PVC jbox below the meter and do the splicing in that. Two conductors under each load lug may not be a good thing. Or..... can you pull the SER back and run it into the new panel? Temporarily put it on a 100A breaker? Or find double lugs for the new panels main breaker? Then feed the new panel from the meter? Really stretching it here.
 

roger

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Location
Fl
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Retired Electrician
I would say that you have two dwelling units, so if you divide the wiring after the meter, then:



Cheers, Wayne
Note that Wayne's opinion is simply his opinion, my opinion which is simply my opinion is that you do not have two dwellings and you should ask your building authority (which is pretty lax in Indiana from what I hear) for their call.

IMO, you should follow Buck's lead in post #28
 

wwhitney

Senior Member
Location
Berkeley, CA
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Retired
my opinion which is simply my opinion is that you do not have two dwellings and you should ask your building authority (which is pretty lax in Indiana from what I hear) for their call.
I can't argue with the advice above.

But take the duplex floor plan below. Certainly two dwelling units, no question. Now change one side to be half the floor area, no garage, just one bedroom, one bathroom, kitchen, living room. That still meets the NEC definition of dwelling unit, so it's still two dwelling units. Since that dwelling unit is smaller, you might call it an attached apartment, an in-law unit, or an ADU.

Cheers, Wayne 3152850190216e196b1ed42c2c7f7e4f.jpg
 

JohnDS

Senior Member
Location
Suffolk, Long Island
Occupation
Electrician
Where do I find such a thing lol? I could maybe do this on the outside 200 amp disconnect instead, and then run SEU to the new panel. Anyone? This would save me a ton of work lol
I think I found the answer. Look what I managed to scrounge up lol. Although a little over kill, but I can pretty much take a pig tail from the load side of the outside disconnect and just plug the 2 panel feeds in. I haven't used these in a long time, anyone know what the correct name of these are called? And do they sell them in 3ways instead of 9ways? 20220916_212610.jpg 20220916_212558.jpg
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
Pretty sure those are 3 way. For each "tee" of plugs, the middle one is the screw access, and then the wire can come into either of the other two plugs.

Cheers, Wayne
 

Buck Parrish

Senior Member
Location
NC & IN
Where do I find such a thing lol? I could maybe do this on the outside 200 amp disconnect instead, and then run SEU to the new panel. Anyone? This would save me a ton of work lol
You might need SER to your first panel. If it's after your first disconnect. (y)
 

kwired

Electron manager
Location
NE Nebraska
I can't argue with the advice above.

But take the duplex floor plan below. Certainly two dwelling units, no question. Now change one side to be half the floor area, no garage, just one bedroom, one bathroom, kitchen, living room. That still meets the NEC definition of dwelling unit, so it's still two dwelling units. Since that dwelling unit is smaller, you might call it an attached apartment, an in-law unit, or an ADU.

Cheers, Wayne View attachment 2562158
I will say other building codes may factor in on what the building inspection dept might consider separate dwellings, but per NEC alone the mentioned in law units or ADU's are separate dwelling units as long as they fulfill art 100 definition.

Guest suites in any occupancy can fit that definition as well, and is pretty common in many hotels and resorts even if all you have for actual walls leaves you with one main room and a bathroom
 
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