Feed for sub panel

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SiddMartin

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In a reason thread, it was pointed out that to feed a 100A subpanel w/ SER, you have to use T310.16.... and you see that #2 it is only rated for 90A. Now, if you are taking it to a MB Panel, and since you can only load the MB of the sub at 80% (duty rating of CBreaker), then you would be okay using #2 SER rated at the 90A for a 100A Subpanel. Am I correct in thinking this?
 
Actually, that main lug panel is likely 125 amp rated at its maximum. Any overcurrent protection at the head end of the feeder 125A or less is just fine. The cable and the gauge you choose, for the most part, will dictate that overcurrent protection size.
 
Lets say I'm feeding a 100A sub in a detached garage. I would have a 100A breaker in the Main protecting #2 SER to a 125A rated MB Sub. This would work?
I guess my main question was use of T310.16, #2 SER is good for 90A, but you can use it for 100A since the breaker protecting it can only be loaded at 80% (100A Breaker protecting it).
 
SiddMartin said:
then you would be okay using #2 SER rated at the 90A for a 100A Subpanel. Am I correct in thinking this?
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IMO not really.

You could use the 90 amp breaker with the 2 AWG AL SER and you could supply any size panel rated at least 90 amps.


However if it supplies a 100 amp panel the rating of the feeder is 90 amps non-continuous or 72 amps continuous.

If you want to use a 100 amp panel to its maximum rating you would need 1 AWG AL SER and a 100 amp breaker.

Then the feeder and the panel would have a legal capacity of 100 amps non-continuous or 80 amps continuous.

Did that make sense? :)
 
Let's keep in mind if you are using the 2008 code that #2 Ser cable is now rated 60C inside a building and is now only rated 75 amps.
 
SiddMartin said:
In a reason thread, it was pointed out that to feed a 100A subpanel w/ SER, you have to use T310.16.... and you see that #2 it is only rated for 90A. Now, if you are taking it to a MB Panel, and since you can only load the MB of the sub at 80% (duty rating of CBreaker), then you would be okay using #2 SER rated at the 90A for a 100A Subpanel. Am I correct in thinking this?
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I'm not sure about a duty rating but I believe if its not a continuous load you can go 100% of the breaker. Also I believe you could go to the next highest standard rating 100 amp. 2005 . Good point dennis
 
iwire said:
IMO not really.

You could use the 90 amp breaker with the 2 AWG AL SER and you could supply any size panel rated at least 90 amps.


However if it supplies a 100 amp panel the rating of the feeder is 90 amps non-continuous or 72 amps continuous.

If you want to use a 100 amp panel to its maximum rating you would need 1 AWG AL SER and a 100 amp breaker.

Then the feeder and the panel would have a legal capacity of 100 amps non-continuous or 80 amps continuous.

Did that make sense? :)
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yes & no... I understand the cont. & non-cont, but when would you consider a panel and being non-continuous? If your sizing a panel load, wouldn't you only load it 80%?

Are you saying, to be safe that you should size the wire for 100% of the breaker, in the event that all the load is continuous? I thought that you would assume that the loads are non-cont. unless you knew otherwise.

Please...clear my head:)
 
Dennis Alwon said:
Let's keep in mind if you are using the 2008 code that #2 Ser cable is now rated 60C inside a building and is now only rated 75 amps.
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excellent observation, code ref? .. too lazy to grab the book
 
and someone clarify for me, if a CB has a duty rating of 80%, how could you ever load at 100%. Whether its cont, or non-cont.
 
Anybody got any bright ideas on the next cheapest way to connect subpanels with a nonmetallic jacketed cable system? I guess we'll just have to get the supply houses to start stocking a couple other new gauges of SER.
 
mdshunk said:
Anybody got any bright ideas on the next cheapest way to connect subpanels with a nonmetallic jacketed cable system? I guess we'll just have to get the supply houses to start stocking a couple other new gauges of SER.
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Ive never actually needed a 100amp panel, its just something I do...
 
SiddMartin said:
but when would you consider a panel and being non-continuous? If your sizing a panel load, wouldn't you only load it 80%?
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In a dwelling unit the entire panel will never be a 'continuous load' not going to happen.

Lets make up a sub-panel in a commercial building.

It has to supply 80 amps of lighting running 10 hours a day.

It also has to supply a machine that uses 20 amps for 2 hours at a time.

That is 80 amps of continuous load and 20 amps of non-continuous load for a combined total of 100 amps when the machine runs.

I could use a 100 amp feeder and panel for this.
 
stickboy1375 said:
Ive never actually needed a 100amp panel, its just something I do...
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I have a local rule that requires that the minimum electrical service permitted to a dwelling unit be 100 amps. If I need to remotely mount the panel, and I've put a 80 amp breaker in the service disconnect to feed that remote panel, I'm not so sure I can call it a 100 amp service.
 
iwire said:
In a dwelling unit the entire panel will never be a 'continuous load' not going to happen.

Lets make up a sub-panel in a commercial building.

It has to supply 80 amps of lighting running 10 hours a day.

It also has to supply a machine that uses 20 amps for 2 hours at a time.

That is 80 amps of continuous load and 20 amps of non-continuous load for a combined total of 100 amps when the machine runs.

I could use a 100 amp feeder and panel for this.
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I should have been more clear, I am talking solely about resi sub panels... sorry, for the mis-understanding
 
SiddMartin said:
I should have been more clear, I am talking solely about resi sub panels... sorry, for the mis-understanding
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Size it off the "calculated load" Articles 220 III, 215-2, Annex D2(a) is a good example
 
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