SER question

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LarryFine said:
My question is really several parts:

1a. What's the smallest al SER we can use one 200 breaker on (200a svc)?

1b. What's the smallest al SER we can use two 200a breakers on (320a svc)?

2a. What's the largest breaker we can use to protect one 4/0 al SER (200a svc)?

2b. What's the largest breakers we can use to protect two 4/0 al SER's (320a svc)?
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Unfortunately it is going to depend on what Code cycle in use and how the AHJ enforces the "60? rule"

assuming we are speaking of installs which fit the terms of 310.15(b)(6)

1a.
Locally: With interior SER, 300 kcmil AL, 4/0 Cu
Most areas: 4/0 AL, 2/0 Cu

1b. Based on 2 cables to 2 200 amp panles
Locally and some areas: 300 kcmil AL, 4/0 Cu
Some areas: 4/0 AL, 2/0 Cu

2a. Locally with interior runs 150 amp (on Al)
Most areas 200 amp

2b Locally with interior runs 150 amp (on AL)
many areas 200 amp
 
Larry I am confused your questions are mentioning service but you state ser. Do you mean when the ser carries the entire load?
 
augie47 said:
Unfortunately it is going to depend on what Code cycle in use and how the AHJ enforces the "60? rule"
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'05 here in Va.

assuming we are speaking of installs which fit the terms of 310.15(b)(6)
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Yes.

1a.
Locally: With interior SER, 300 kcmil AL, 4/0 Cu
Most areas: 4/0 AL, 2/0 Cu

1b. Based on 2 cables to 2 200 amp panles
Locally and some areas: 300 kcmil AL, 4/0 Cu
Some areas: 4/0 AL, 2/0 Cu

2a. Locally with interior runs 150 amp (on Al)
Most areas 200 amp

2b Locally with interior runs 150 amp (on AL)
many areas 200 amp
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Which is NEC, 'local' or 'many'? :)
 
Dennis Alwon said:
Larry I am confused your questions are mentioning service but you state ser. Do you mean when the ser carries the entire load?
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In the "200a svc" cases, yes, in the "320a svc" cases, no.

It's confusing when you throw in the calculated loads allowing smaller conductors than the breakers alone would.

I'd like to throw together a chart showing calulated load, minimum conductor size, and maximum breaker sizes.
 
LarryFine said:
'05 here in Va.

Yes.

Which is NEC, 'local' or 'many'? :)
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Been the topic of much discussion here and elsewhere.
You can do a search of "338.10" and follow the points of view.
Until there is some clarification in the Code on the relationship of
338.10/310.15(B)(6) and 215.2 I'm afraid you will find as I have that
"Code" on this particular subject is much an interpretation by the AHJ in that particular area.
As stated, in the area I work, the "Code" method varies by driving 30 miles in any direction.
 
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augie47 said:
You can do a search of "338.10" and follow the points of view.
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I have been, believe me.

... "Code" on this particular subject is much an interpretation by the AHJ in that particular area.
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The best bet is to ask the inspector about any subject that's known to be less than clear, but, that can be a double-edged sword: it's good to know before you start, but bad to alert him to a new change we've lived without in our blissful 'ignorance'. :cool:
 
Just to clarify one thing. Let's say you are doing an overhead service on a single family home. You run #2 SE down the wall and hit the meter socket, then out of meter into home but the loadcenter location on the oppisite side of unfinished basement so you install a disconnect right below the meter socket on the OUTSIDE of home. Now we have to run subfeed cable to across the basement to the subpanel.

Can you still run the #2 al subfeed since this is considered service entrance and not branch circuit or feeder?
 
slick 50 said:
Just to clarify one thing. Let's say you are doing an overhead service on a single family home. You run #2 SE down the wall and hit the meter socket, then out of meter into home but the loadcenter location on the oppisite side of unfinished basement so you install a disconnect right below the meter socket on the OUTSIDE of home. Now we have to run subfeed cable to across the basement to the subpanel.

Can you still run the #2 al subfeed since this is considered service entrance and not branch circuit or feeder?
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Once you have hit the service disconnecting means the conductors after that are no longer service entrance conductors, but are now feeders.

Chris
 
repeating what Larry suggest (post 51), for a particular job you might be wise to check with the AHJ.
I many local areas, the #2 AL feeder on the interior of the house will be considered to be 75 amp cable per 338.10(B)(4). I some areas it would be accepted as 1 whole house 100 amp feeders.
Different folks view it different ways.
 
Thanks....If you was to install the service assuming the ser was good at 100amp and the inspector shut you down, would it be feasible to change the breaker feeding the ser to a 70 amp. Especially if the calculated load is less than 50?
 
If the #2 AL was supplying the entire residence and you changed the breaker you would be in violation of 230.79(D)

(sorry, Bill, stepped on you)
 
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