# class 320 service panel



## BBQ (Nov 16, 2010)

tmelectric said:


> What size service entrance conductors would you use for a single phase 240 volt class 320 meter main with 2 200 amp sub feed breakers?


What is the calculated load?

If you know the calculated load you can size the conductors based on that, if not you will have to size them based on 400 amps (200x2)


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## Tom45acp (Sep 6, 2011)

Service entrance conductors must be able to carry the sum of the noncontinuous load plus 125% of the continuous load. Can't answer your question accurately unless you state the load. At this point, my guess would be 600 kcmil thwn.


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## McClary’s Electrical (Feb 21, 2009)

tmelectric said:


> What size service entrance conductors would you use for a single phase 240 volt class 320 meter main with 2 200 amp sub feed breakers?


 
Dwelling or commercial?


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## BBQ (Nov 16, 2010)

mcclary's electrical said:


> Dwelling or commercial?


The calculated load maters either way ....... assuming he wants to use the smallest conductor he can.


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## McClary’s Electrical (Feb 21, 2009)

BBQ said:


> The calculated load maters either way ....... assuming he wants to use the smallest conductor he can.


Oh yeah, but still affects the answer.


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## tmelectric (Sep 2, 2011)

The customer anticipates a load of 120 amps on one of the 200 amp breakers and the other one is for future, somewhere, someday, down the road. Since it is the service entrance im not sure if it needs to be sized for the whole 400 amp potential. Just lazy I guess! Thanks!


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## McClary’s Electrical (Feb 21, 2009)

tmelectric said:


> The customer anticipates a load of 120 amps on one of the 200 amp breakers and the other one is for future, somewhere, someday, down the road. Since it is the service entrance im not sure if it needs to be sized for the whole 400 amp potential. Just lazy I guess! Thanks!


 
How is the customer performing a NEC load calc?


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## BBQ (Nov 16, 2010)

mcclary's electrical said:


> Oh yeah, but still affects the answer.


If he has to match the breaker sizes it will mater, if he has the calculated load info (done the correct way) it will not matter if it is dwelling or not.


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## BBQ (Nov 16, 2010)

tmelectric said:


> The customer anticipates a load of 120 amps on one of the 200 amp breakers and the other one is for future, somewhere, someday, down the road. Since it is the service entrance im not sure if it needs to be sized for the whole 400 amp potential. Just lazy I guess! Thanks!


Unless you have a the true calculated load per Article 220 you will have to size for the 400.


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## McClary’s Electrical (Feb 21, 2009)

BBQ said:


> If he has to match the breaker sizes it will mater, if he has the calculated load info (done the correct way) it will not matter if it is dwelling or not.


 
I have two buildings, one is commercial, and one is a residence. They both have the exact same calculated load of 170 amps. What size wire is needed for each?


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## 3xdad (Jan 25, 2011)

tmelectric said:


> The customer anticipates a load of 120 amps on one of the 200 amp breakers and the other one is for future, somewhere, someday, down the road. Since it is the service entrance im not sure if it needs to be sized for the whole 400 amp potential. Just lazy I guess! Thanks!


Customers load calc. is moot.

First of all, i would like to see this 400A meter main with two 200 service disco's. Please post link or pic.

IMO, if all of this is in one enclosure, then the meter is probably listed/rated 400A. If you are designing and building a 320 meter can with tandem lugs to two 200 disco's, your inspector might require a 320 meter can that is specifically listed 400 max.

Either way, if this is resi., then use table 310.15(B)(6). 400cu SEC's. :thumbsup:


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## 3xdad (Jan 25, 2011)

mcclary's electrical said:


> I have two buildings, one is commercial, and one is a residence. They both have the exact same calculated load of 170 amps. What size wire is needed for each?


What the hey, i'll take a crack at it.:thumbup: Table 310.16 75deg. column. If you are using 200 ocpd for both and they are SEC's in raceway, 3/0cu (commercial) 2/0cu (resi. because of table 310.15(B)(6)?


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## BBQ (Nov 16, 2010)

mcclary's electrical said:


> I have two buildings, one is commercial, and one is a residence. They both have the exact same calculated load of 170 amps. What size wire is needed for each?


Is there one main or two?

If it is two mains with a total calculated load of 170 amps you could use 2/0 copper or 4/0 AL for both buildings regardless of the breaker sizes.


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## McClary’s Electrical (Feb 21, 2009)

BBQ said:


> Is there one main or two?
> 
> If it is two mains with a total calculated load of 170 amps you could use 2/0 copper or 4/0 AL for both buildings regardless of the breaker sizes.


Spin:

Single mains, interior load center, se cable


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## BBQ (Nov 16, 2010)

mcclary's electrical said:


> Spin:
> 
> Single mains, interior load center, se cable


With a single main it will make a difference if it is a dwelling unit or not.


230.90(A)


> Exception No. 3: Two to six circuit breakers or sets of fuses
> shall be permitted as the overcurrent device to provide the
> overload protection. *The sum of the ratings of the circuit
> breakers or fuses shall be permitted to exceed the ampacity
> ...


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## Dennis Alwon (May 9, 2009)

BBQ said:


> Is there one main or two?
> 
> If it is two mains with a total calculated load of 170 amps you could use 2/0 copper or 4/0 AL for both buildings regardless of the breaker sizes.


How does 2/0 work? 2/0 is good for 175 amps which is a standard size breaker. IMO T 310.15(B)(6) will not apply with 2 mains. Seems the OP has a meter main- one panel..


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## BBQ (Nov 16, 2010)

Dennis Alwon said:


> How does 2/0 work? 2/0 is good for 175 amps which is a standard size breaker. IMO T 310.15(B)(6) will not apply with 2 mains. Seems the OP has a meter main- one panel..


I am not using that table at all. 

If you have two or more service disconnects, the conductors supplying those disconnects can be rated entirely by the calculated load and not by the breaker sizes.

So if you had two 200 amp panels each with a service disconnect and total calculated load of 170 amps the conductors supplying the meter would only have to be rated 170 amps even though they would have 400 amps of OCP.


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## Dennis Alwon (May 9, 2009)

BBQ said:


> I am not using that table at all.
> 
> If you have two or more service disconnects, the conductors supplying those disconnects can be rated entirely by the calculated load and not by the breaker sizes.
> 
> So if you had two 200 amp panels each with a service disconnect and total calculated load of 170 amps the conductors supplying the meter would only have to be rated 170 amps even thought they would have 400 amps of OCP.


Gotcha-- I thought you were saying the wire between the meter and the two 200 amp panels. :thumbsup:


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## BBQ (Nov 16, 2010)

Dennis Alwon said:


> Gotcha-- I thought you were saying the wire between the meter and the two 200 amp panels. :thumbsup:


Yeah that get part gets sketchy. :blink:


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## AFOREMA1 (Nov 23, 2009)

BBQ said:


> I am not using that table at all.
> 
> If you have two or more service disconnects, the conductors supplying those disconnects can be rated entirely by the calculated load and not by the breaker sizes.
> 
> So if you had two 200 amp panels each with a service disconnect and total calculated load of 170 amps the conductors supplying the meter would only have to be rated 170 amps even though they would have 400 amps of OCP.


In that case don't you also need to tag the panels with a not to exceed calculated load of xxxx amps per the NEC?


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## McClary’s Electrical (Feb 21, 2009)

AFOREMA1 said:


> In that case don't you also need to tag the panels with a not to exceed calculated load of xxxx amps per the NEC?


No the next guy needs to calculate before adding load.


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## AFOREMA1 (Nov 23, 2009)

mcclary's electrical said:


> No the next guy needs to calculate before adding load.


Thanks. Thought I had read something about labeling it just want to be sure.


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## sbrn33 (Mar 15, 2007)

BBQ said:


> I am not using that table at all.
> 
> If you have two or more service disconnects, the conductors supplying those disconnects can be rated entirely by the calculated load and not by the breaker sizes.
> 
> So if you had two 200 amp panels each with a service disconnect and total calculated load of 170 amps the conductors supplying the meter would only have to be rated 170 amps even though they would have 400 amps of OCP.


I learn something everyday here.


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