750 MCM AL service

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mdshunk

mdshunk

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About what "size" would you call a service done with one set of 750 MCM aluminium conductors? I'm speculating that it's about 550 amps. :-?
 
Just thought I should add that this is an existing dwelling, from that late 70's, done with a CT service. I'm just trying to figure out where we're at, so I can see where to go.
 
Conductor size doesn't determine the amperage of the service, it's only a function of it. That starts with the main disconnect/overcurrent size. If your main is 60 amps, you have a 60 amp service. Run 6 parallel sets of 2,000kcmils to it, it's still a 60 amp service.
 
480sparky said:
Conductor size doesn't determine the amperage of the service, it's only a function of it. That starts with the main disconnect/overcurrent size. If your main is 60 amps, you have a 60 amp service. Run 6 parallel sets of 2,000kcmils to it, it's still a 60 amp service.
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That sounds good until you get to a service with more than one service disconnect. :smile:

You might have five 100 amp service disconects all supplied with a single run of 4/0 CU.

What size service is that?
 
mdshunk said:
There's a mess of 100 amp panels tapped from a gutter.
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Wow, that is a weird coincidence. :cool:

Given that situation IMO your service 'size' is really the 310.16 rating of your service conductors, 385 amps @ 75 C
 
iwire said:
Wow, that is a weird coincidence. :cool:

Given that situation IMO your service 'size' is really the 310.16 rating of your service conductors, 385 amps @ 75 C
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I'm just scratching my head over the 310.15(C) calculation, and making my 550 amp guess by continuing the logical progression from Table 310.15(B)(6)
 
That big a service in a dwelling..... back in the 70's... must have been a helluva house.
I'm going to back to my '70s Codes to see if there's any help there.
 
mdshunk said:
I'm just scratching my head over the 310.15(C) calculation, and making my 550 amp guess by continuing the logical progression from Table 310.15(B)(6)
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I was wondering if that was how you came up with 550.

Not saying what your thinking would not work I just don't see anything in the NEC allowing it unless you are an EE.

Can you get an EE to bless this?

Would it be worth it?
 
480sparky said:
That big a service in a dwelling..... back in the 70's... must have been a helluva house.
I'm going to back to my '70s Codes to see if there's any help there.
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It is a pretty nice place. All concrete block walls and concrete span deck floors. I've been to this place doing work many times, and every time is a new adventure. It's a real "treat" to work on. The simplest things are sorely complicated by the unusual construction type and the use of unusual wall and ceiling finish materials.
 
mdshunk said:
About what "size" would you call a service done with one set of 750 MCM aluminium conductors? I'm speculating that it's about 550 amps. :-?
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I'm sure you asked HO if they had plans around from the service installation or upgrade. I'd like to see that load calc.
Sounds like you need add something to this.
Where did you get 550A?
 
chris kennedy said:
Sounds like you need add something to this.
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Yup. One hot tub and possibly a sauna box. That's their wish, anyhow. Matter of fact, the hot tub is sitting there, "ready to be hooked up", as the spa salesman probably told them.
 
Ah, an early version of a McCastle.

If I trace the ancestry of Table 310.15(B)(6) [our infamous 'cheat table'], it was born in 1975 as #3 in the Notes to Tables 310-16 through 310-19. It lists wire sizes up to 200 amp, so there was no relief in wire sizes back then on any service larger than that. Could the service be newer than the house?
 
480sparky said:
Could the service be newer than the house?
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Doubt it. It probably was engineered, but back then, no plan review was required in this jurisdiction and the occupants are not the original owners.
 
480sparky said:
It lists wire sizes up to 200 amp, so there was no relief in wire sizes back then on any service larger than that. Could the service be newer than the house?
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But, that service as he describes it is 'legal' today due to 230.90(A) Exception 3. Which allows the total of the service disconnects to exceed the ampacity of the service conductors. However the calculated load would have to be below the rating of the conductors.

In your 75 NEC was there is similar exception or rule?
 
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