2-2-2-4 AL SER ampacity

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jetlag said:
I agree with all that , you know a lot of outside disconnects have a few breaker spaces . We use those all the time in rural area for the well pump and storage buildings . I know , that means entire load is no longer on the sub-panel . I have never seen any one get flagged by the inspector for that. I assumed he had a 200 amp main panel and was not connecting a 100 amp sub to a 100 amp main panel , but like you say in that case the ser could be the same for both.
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And depending on the code cycle even with a 200 amp service you may use #2 AL for a sub panel feeder. There are penty of areas on old codes.

This stuff always amazes me.
 
Isnt there an NEC rule that lets you still use the dwelling ampacities if you have a load or two in the main disconnect. IE just 1 15 amp convenience outlet?
 
100 amp sup

100 amp sup

Sierrasparky said:
And depending on the code cycle even with a 200 amp service you may use #2 AL for a sub panel feeder. There are penty of areas on old codes.

This stuff always amazes me.
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Well in my opinion , you should be able to figure the load on a sub panel the same as you do on service entrance , the same as if the sub panel was serving it own mini house . And use the dwelling load calculations for it . As long as the sub panel had a variety of dwelling loads on it and was not running to some designated pieces of equipment only . What if the area served by sub panel had all the same loads as a small house with the same area ? You can downsize the conductors for the small house , whats the difference ?
 
You do not need to justify your reasoning. We all agree that it does not make sense. But it is the code and the CMP has resisted all attempts to change it.
One point in its favor is that it is incredibly simple to state and unambiguous. Just not logical. :)
 
great goldigger

great goldigger

GoldDigger said:
You do not need to justify your reasoning. We all agree that it does not make sense. But it is the code and the CMP has resisted all attempts to change it.
One point in its favor is that it is incredibly simple to state and unambiguous. Just not logical. :)
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I can't resist one last point . The newer codes won't let you downsize the conductors to main dwelling service panel unless it carries the entire load of the dwelling . OK, we use the outside disconnects all the time that have breaker spaces built in and we connect outside loads on that . The inside panel no longer carries the entire load . Also there is a code that says loads like a well pump must have a disconnect in the main panel . I finally asked the inspector why we never get flagged on those things and he looked at me and said "Why would I flag the ser size when all you have done with the out side breakers is take some load off of them ? And why would they sell the outside disconnects with breaker spaces if all the circuits have to originate from the main panel ? " I just said "Good for you"
 
338.10(B)(4) which points you to 334 part II which 334.80 will require you to use the 60? column any ways so in spite of the insulation you would still have to use 75 amps rating for the cable, 240.4 allows the next size up if 75 amps is not a standard breaker or fuse rating and 240.6 does not list 75 amps as a standard rating so yes you can use a 80 amp breaker for it as long as the calculated load does not exceed 75 amps.

Most NM cable and AC cable type wiring methods have the 60? column requirement, MC cable does not have this requirement.
 
mbrooke said:
Isnt there an NEC rule that lets you still use the dwelling ampacities if you have a load or two in the main disconnect. IE just 1 15 amp convenience outlet?
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The 2014 uses a different method for services on a residence. You must take 83% of the service size. For instance if you want a 200 amp service then the wire after derating must be rated for 200 * 83% or 166 amps. It is still the same for a sub panel in that you must carry the full load of the service in order to use the 83% rule.
 
ser amps

ser amps

jumper said:
As crazy as it seems, unfortunately no. Proposals allowing such have not been accepted in the past.
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Thanks jumper I have never seen it put that way before . I sure see why people did the proposals , if the loads you decide to put on the breaker spaces in the outside disconnect have already been put into the dwelling calculations and the ser size has been determined with that included , then all you are doing is taking some load off the ser that has already been designed to carry that load . Maybe someone can word this better if they can figure out what I tried to say !
 
jetlag said:
Thanks jumper I have never seen it put that way before . I sure see why people did the proposals , if the loads you decide to put on the breaker spaces in the outside disconnect have already been put into the dwelling calculations and the ser size has been determined with that included , then all you are doing is taking some load off the ser that has already been designed to carry that load . Maybe someone can word this better if they can figure out what I tried to say !
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Gimme a sec, I will look up a proposal that Mike Holt submitted and was rejected.
 
jetlag said:
I can't resist one last point . The newer codes won't let you downsize the conductors to main dwelling service panel unless it carries the entire load of the dwelling . OK, we use the outside disconnects all the time that have breaker spaces built in and we connect outside loads on that . The inside panel no longer carries the entire load . Also there is a code that says loads like a well pump must have a disconnect in the main panel . I finally asked the inspector why we never get flagged on those things and he looked at me and said "Why would I flag the ser size when all you have done with the out side breakers is take some load off of them ? And why would they sell the outside disconnects with breaker spaces if all the circuits have to originate from the main panel ? " I just said "Good for you"
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Nothing in NEC requires a well pump to be supplied from a specific panel - maybe some local code somewhere does.

Dennis Alwon said:
The 2014 uses a different method for services on a residence. You must take 83% of the service size. For instance if you want a 200 amp service then the wire after derating must be rated for 200 * 83% or 166 amps. It is still the same for a sub panel in that you must carry the full load of the service in order to use the 83% rule.
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End result generally gives you same conductor size as in the past - but what is the bigger change is before you did not have to apply ampacity adjustments and now you do if you have a high ambient temp, or number of conductors in raceway is an issue.

jetlag said:
Thanks jumper I have never seen it put that way before . I sure see why people did the proposals , if the loads you decide to put on the breaker spaces in the outside disconnect have already been put into the dwelling calculations and the ser size has been determined with that included , then all you are doing is taking some load off the ser that has already been designed to carry that load . Maybe someone can word this better if they can figure out what I tried to say !
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Correct the loads in the outside panel are in the total load calc - and the reason the service or main feeder can be sized based on total dwelling load. I agree if you have 100 amp supply in and 100 amp supply out that you have taken some of the load away if there are circuits originating at the outdoor panel, but you have changed the load diversity on the indoor panel, and you are not going to know how much with simple calculations.

Take a situation where you have a 200 amp main supply and a 100 amp sub panel, and it it not quite so simple to say the 100 amp subpanel can have a conductor with less then 100 ampacity supplying it as it could be with the 100 amp main supply and 100 amp subpanel situation.

Does it really cost that much more to increase from 2 AWG to 1AWG or to use a 90 amp breaker instead of a 100 amp breaker?
 
kwired said:
Does it really cost that much more to increase from 2 AWG to 1AWG or to use a 90 amp breaker instead of a 100 amp breaker?
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I haven't found anyplace local that stocks #1 SER cable , but I routinely do use #1/0 SER for subfeed from meter/main to panel nowadays. Honestly haven't paid any attention to the cost difference, it is what is expected at inspection so it is what goes in.
 
macmikeman said:
I haven't found anyplace local that stocks #1 SER cable , but I routinely do use #1/0 SER for subfeed from meter/main to panel nowadays. Honestly haven't paid any attention to the cost difference, it is what is expected at inspection so it is what goes in.
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I can see availability being an issue for something like SE cable. Around these parts SE cable is not all that common so a jump from #2 to #1 for inside a raceway is not that big of a deal.
 
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