House panel size

D

Deno4

Member
Location
Sarasota , Florida
We are working on a townhouse and have a disagreement with the engineer over the unit panel sizes.
Regular residential units, single-phase 120/240V, with AC, washer-dryer, etc., no outside circuits, solar, and chargers.
The unit's calculated load is 126A, and we wanted to use 150A house panels and main breakers outside. The engineer wants us to upgrade to 200A.
He used the 125% rule, 126 x1.25 = 157.5A
As far as I know, the calculated load can be equal to or less than the service size / main breaker because the service load calculation factors in continuous loads.
Who is right here?
 
The '125% rule' applies for continuous loads. IMHO the NEC doesn't say that the calculated load for a residence isn't continuous, but a) we all know it isn't continuous and b) the NEC clearly implies that it isn't continuous with the '83%' rule for service conductors.

If a residence that calculates at 200A requires a 250A breaker and panelboard, why does the NEC permit this to be served with 166A conductors?

With that said, 'working on a townhouse' and 'the engineer wants' leave me a bit confused. If the customer is upscale, the cost difference between a 150A install and a 200A install is tiny and you can just charge for it. Is this wiring multiple places for a developer?
 
There no code requirment to provide for future expansion so the 150 amp feeder and panel is code compliant. Nothing says that the person paying the bill can't ask for more headroom than required.
 
winnie said:
The '125% rule' applies for continuous loads. IMHO the NEC doesn't say that the calculated load for a residence isn't continuous, but a) we all know it isn't continuous and b) the NEC clearly implies that it isn't continuous with the '83%' rule for service conductors.

If a residence that calculates at 200A requires a 250A breaker and panelboard, why does the NEC permit this to be served with 166A conductors?

With that said, 'working on a townhouse' and 'the engineer wants' leave me a bit confused. If the customer is upscale, the cost difference between a 150A install and a 200A install is tiny and you can just charge for it. Is this wiring multiple places for a developer?
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We have 8 units here, but the same engineer is hired for our next project, 202 units of apartments, and his "upgrade " could significantly raise the cost. That's why I want to settle this matter now, but unfortunately, I cannot point to anything in the codebook that would prove I'm right.
 
Deno4 said:
We have 8 units here, but the same engineer is hired for our next project, 202 units of apartments, and his "upgrade " could significantly raise the cost. That's why I want to settle this matter now, but unfortunately, I cannot point to anything in the codebook that would prove I'm right.
Click to expand...
That makes perfect sense. You bid one thing (what the code requires), the engineer wants to get more without paying more.

IMHO have the engineer prove that the house (as a whole) meets the requirements of a continuous load. The NEC doesn't say that a residence is a continuous load, but as you note it also doesn't explicitly say that a residence isn't a continuous load. But it _defines_ what a continuous load is.

The _average_ home uses about 30 kWh per day, or about 5A on average. No reasonably typical home will operate anywhere close to 150A for a period of 3 hours. I bet the utility will set a single 50kVA (or smaller) transformer for all 8 units.

-Jonathan
 
winnie said:
MHO the NEC doesn't say that the calculated load for a residence isn't continuous,
Click to expand...
Not a blanket residential thing but In its round-about, over edited over 100 years way, I do interpret the NEC that way if you agree the 'rating of the service' is the same thing as the 'rating of the service disconnect' as defined in 230.79 (the only other place rating of a service is mentioned)
'rating of the service disconnect' is just the calculated load per whatever section you choose (220.83)
and then and only if 310.12 can apply to the dwelling unit, 310.12(A) says a service rated 100a - 400a .... shall be permitted to have an ampacity not less than 83% of the service rating.
Then 310.12 (C) allows the feeder ampacity to be the same as the service ampacity.
Or something like that, depending on your code cycle, those are 2023 refs.
 
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