# 400 amp commercial service



## morg123452000 (Nov 4, 2013)

HelloAll ..I am installibg a 400 amp service single phase 240/120 I have never done one before so I want to makee sure im lookibg at it correcty.. I am from the state of Maine usuibg a 320 metre Enclosure top fed 3 inch steel mastComing into the top with a mast 3" rigid steel ...wire four 250MCM AL paralleled each phase of the ungrounded ...Using table 250.102(c)(1) grounded conductor for this service I can use two 1/0 AL paralleled.....I am going straight through the back of the metre enclosure to 21/2" PVC T (i cant. Find any 2 1/2 inch Ts around here so ill end up using a PVC jbox)to feed two 200 amp main breaker panels..the nipple from the back is less the 24 inches..from 310.16 i can use 3/0 CU for my paralleled un grounded condutors and 1/0 CU for the grounded conductors (250.102(C)(1)to feed the two 200 amp panels..#6 for my grounding electrodes....thanks all


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## Kevin (Feb 14, 2017)

Hello @morg123452000 , I know you've been here since 2013, however I would appreciate it if you followed the link below on how to fill out your profile. It's required. Thank you.









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As for your questions, I'm not a NEC expert so someone else will have to help with that.


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## morg123452000 (Nov 4, 2013)

Kevin_Essiambre said:


> Hello @morg123452000 , I know you've been here since 2013, however I would appreciate it if you followed the link below on how to fill out your profile. It's required. Thank you.
> 
> 
> 
> ...


Just did it sorry thought i akready had it


Kevin_Essiambre said:


> Hello @morg123452000 , I know you've been here since 2013, however I would appreciate it if you followed the link below on how to fill out your profile. It's required. Thank you.
> 
> 
> 
> ...


An addition to this post... If the wires leaving the meter to the panel are connected together at the meter but no the panelboards is it still considered paralleling and is 1/0 the minimum?


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## oldsparky52 (Feb 25, 2020)

morg123452000 said:


> HelloAll ..I am installibg a 400 amp service single phase 240/120 I have never done one before so I want to makee sure im lookibg at it correcty.. I am from the state of Maine usuibg a 320 metre Enclosure top fed 3 inch steel mastComing into the top with a mast 3" rigid steel ...wire four 250MCM AL paralleled each phase of the ungrounded ...Using table 250.102(c)(1) grounded conductor for this service I can use two 1/0 AL paralleled.....I am going straight through the back of the metre enclosure to 21/2" PVC T (i cant. Find any 2 1/2 inch Ts around here so ill end up using a PVC jbox)to feed two 200 amp main breaker panels..the nipple from the back is less the 24 inches..from 310.16 i can use 3/0 CU for my paralleled un grounded condutors and 1/0 CU for the grounded conductors (250.102(C)(1)to feed the two 200 amp panels..#6 for my grounding electrodes....thanks all


I read that twice, and ... my eyeballs are crossed and smoke is coming out of my ears, lol.


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## morg123452000 (Nov 4, 2013)

oldsparky52 said:


> I read that twice, and ... my eyeballs are crossed and smoke is coming out of my ears, lol.


Sorry..is my description that messy?I could rewrite it


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## morg123452000 (Nov 4, 2013)

morg123452000 said:


> Sorry..is my description that messy?I could rewrite it


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## oldsparky52 (Feb 25, 2020)

Some punctuation would be nice. 

1st, I'm not sure but I think I've seen an external disconnect is required on services now, are you required to have this?

2nd, from what you described you are not paralleling your conductors you have two separate sets feeding two separate panels, and that is allowed. So you don't have to be concerned going below 1/0. 

Does your box comply with 314.28?


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## morg123452000 (Nov 4, 2013)

oldsparky52 said:


> Some punctuation would be nice.
> 
> 1st, I'm not sure but I think I've seen an external disconnect is required on services now, are you required to have this?
> 
> ...


I dont need a External disconnect ive asked the inspector i can go right from the meter to feed the two panels..the feed to the meter is top fed..i want to parallel 250 AL beacause of derating and 1/0 AL paralleled FOR MY NEUTRAL..IS THAT OK?..GOING FROM THE METER TO THE DISCONNECTS I DONT NEED TO DERATE BECAUSE ITS A NIPPLE..SO I WAS THINKING 3/0 COPPER PARRALLED FOR MY HOTS WHAT SIZE NEUTRAL CAN I USE?


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## oldsparky52 (Feb 25, 2020)

morg123452000 said:


> I dont need a External disconnect ive asked the inspector i can go right from the meter to feed the two panels..the feed to the meter is top fed..i want to parallel 250 AL beacause of derating and 1/0 AL paralleled FOR MY NEUTRAL..IS THAT OK?..GOING FROM THE METER TO THE DISCONNECTS I DONT NEED TO DERATE BECAUSE ITS A NIPPLE..SO I WAS THINKING 3/0 COPPER *PARRALLED* FOR MY HOTS WHAT SIZE NEUTRAL CAN I USE?


You are not paralleling in your example.


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## morg123452000 (Nov 4, 2013)

oldsparky52 said:


> You are not paralleling in your example.


You mean from the meter to the panels..thats my question..its not considered paralleling..so i dont need to use 1/0 minimum i could use #2?


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## morg123452000 (Nov 4, 2013)

oldsparky52 said:


> You are not paralleling in your example.


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## oldsparky52 (Feb 25, 2020)

morg123452000 said:


> You mean from the meter to the panels..thats my question..its not considered paralleling..so i dont need to use 1/0 minimum i could use #2?


That would be the minimum size, but *what do the load calculations call for*? With that short of a run, I typically would just install the same size conductor for the grounded conductor as the ungrounded conductors. 

Around here the AHJ would want a set of drawings for permitting and that information would be on it.


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## morg123452000 (Nov 4, 2013)

oldsparky52 said:


> That would be the minimum size, but *what do the load calculations call for*? With that short of a run, I typically would just install the same size conductor for the grounded conductor as the ungrounded conductors.
> 
> Around here the AHJ would want a set of drawings for permitting and that information would be on it.


Most if the loads are 240 volt no neutral...but ill take your advise..just looking at my options


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## Dennis Alwon (May 9, 2009)

2 things
1) You neutral can be sized as low as T. 250.102 allows. For 2- 250kcm that is equal to 500 kcm so #2 copper would be allowed if your calculated load would allow it.
A general rule of thumb around here is to use 2 sizes smaller than the ungrounded conductors so 1/0 would be used.

2) As Old sparky stated you are not paralleling when two sets of wire begin at the same point and end up separated.

Here is what I would do.. I would come out of the back of the meter directly into a panel with 2" pipe. I would then LB out the side of the meter and into the back of the second interior panel.

Run 2 sets of 3/0 copper with a 1/0 neutral. No 6 to the rod is good however a #1/0 would be needed to bond any copper water line or whatever.


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## Dennis Alwon (May 9, 2009)

Btw, I would use aluminum not copper-- 4/0 will work if the calculated load is not more than 180 amps in each panel.


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## morg123452000 (Nov 4, 2013)

Dennis Alwon said:


> 2 things
> 1) You neutral can be sized as low as T. 250.102 allows. For 2- 250kcm that is equal to 500 kcm so #2 copper would be allowed if your calculated load would allow it.
> A general rule of thumb around here is to use 2 sizes smaller than the ungrounded conductors so 1/0 would be used.
> 
> ...


Its going through a cement wall and the hole is already bored from an old service so id like to use that hole for one nipple to a T


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## oldsparky52 (Feb 25, 2020)

morg123452000 said:


> Its going through a cement wall and the hole is already bored from an old service so id like to use that hole for one nipple to a T


314.28 has some things to say about the sizes of that box you want to use between the panels.


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## morg123452000 (Nov 4, 2013)

oldsparky52 said:


> 314.28 has some things to say about the sizes of that box you want to use between the panels.


Coming into the back if the box 2 1/2 pipe 6 4/0 ...3 to the left 3 to the right in 2" pipe...if im reading 314.28 right fir 4/0 ..a 12x12x6..should be good fir a back entry..what do you think?


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## kb1jb1 (Nov 11, 2017)

Instead of the T use a properly sized pull box. The T might not give you the bending radius plus you might have to fight with the conductors with a T.


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## morg123452000 (Nov 4, 2013)

kb1jb1 said:


> Instead of the T use a properly sized pull box. The T might not give you the bending radius plus you might have to fight with the conductors with a T.


I planned on using a box 2 1/2 T is non exsistint right now what size box do you recommend...


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## oldsparky52 (Feb 25, 2020)

Morg, did you read 314.28?

2nd paragraph of 314.28(A)2


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## morg123452000 (Nov 4, 2013)

kb1jb1 said:


> Instead of the T use a properly sized pull box. The T might not give you the bending radius plus you might have to fight with the conductors with a T.


I think i going with a gutter easyer all the way around...


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## oldsparky52 (Feb 25, 2020)

morg123452000 said:


> I think i going with a gutter easyer all the way around...


366.58{B}


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## morg123452000 (Nov 4, 2013)

oldsparky52 said:


> 366.58{B}


Reading it now


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## Forge Boyz (Nov 7, 2014)

Dennis Alwon said:


> 2 things
> 1) You neutral can be sized as low as T. 250.102 allows. For 2- 250kcm that is equal to 500 kcm so #2 copper would be allowed if your calculated load would allow it.
> A general rule of thumb around here is to use 2 sizes smaller than the ungrounded conductors so 1/0 would be used.
> 
> ...


Slightly off topic question:
In #1 you say that according to Table 250.102 you could use a #2 copper for the nuetral. At the the end of your post you say that you need 1/0 to a water line or other grounding electrode. Don't you use the same table for sizing both?

Sent from my SM-G970U using Tapatalk


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## Dennis Alwon (May 9, 2009)

Forge Boyz said:


> Slightly off topic question:
> In #1 you say that according to Table 250.102 you could use a #2 copper for the nuetral. At the the end of your post you say that you need 1/0 to a water line or other grounding electrode. Don't you use the same table for sizing both?
> 
> Sent from my SM-G970U using Tapatalk


Yes you do.. My mistake..It should be 1/0...

When I do 400 amp services they are always underground from the power company. If you use 2 disconnects then you can use #2 but his overheads are large so IMO he needs to go to 1/0


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## Dennis Alwon (May 9, 2009)

This is what you need-- use Table 312.6(A)


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## morg123452000 (Nov 4, 2013)

Thinks all for your help yesterday I need to get my nose in the code book more often..morg


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## oldsparky52 (Feb 25, 2020)

Dennis Alwon said:


> ... If you use 2 disconnects then you can use #2 but his overheads are large so IMO he needs to go to 1/0


Isn't the OP using 2 disconnects?


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## Dennis Alwon (May 9, 2009)

oldsparky52 said:


> Isn't the OP using 2 disconnects?


 Yes but I believe you need to use the conductors in the mast as they are service conductors..


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## oldsparky52 (Feb 25, 2020)

Dennis Alwon said:


> When I do 400 amp services they are always underground from the power company. If you use 2 disconnects then you can use #2 but his overheads are large so IMO he needs to go to 1/0


I need to understand this better. You seem to be saying that the overhead service conductors are driving the 2 panel 400-amp installation to use a 1/0 GEC but your 2 panel 400-amp underground service conductors are small enough to allow you to use a #2 GEC?


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## Dennis Alwon (May 9, 2009)

Okay, this is confusing so let me see if I can explain it better. Forget the example for a minute and look at a meter main 200 amp panel. Based on 250.66 Notes 2 listed below. In a meter main there are no service conductors so you would have to look at t.310.15(B)(16) and choose a 75C rated conductor for 400 amps and that would be a minimum 500 kcm. T. 250.66 says 1/0 for the grounding electrode conductor.

Now lets look at a service where we are not responsible for the overhead riser or mast or the underground lateral. It's 400 amp meter with 2- 200 amp panels being feed with 3/0 copper. Table 8 in Chapter 9 for 3/0. It states the cir mil is 167800. Since we have 2 service conductors Note 1 would apply. 167800*2= 335,600 which would be 400 kcm. Back to T. 250.66 the grounding electrode conductor only needs to be #2

Now the op has parallel 250 kcm in the mast. Since these are the largest service conductors they are equivalent to 500 kcm (250 * 2) thus bringing us back to 250.66 which says 1/0



> Notes:
> 1. If multiple sets of service-entrance conductors connect directly to a
> service drop, set of overhead service conductors, set of underground
> service conductors, or service lateral, the equivalent size of the largest
> ...



@oldsparky52


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## oldsparky52 (Feb 25, 2020)

Dennis Alwon said:


> Okay, this is confusing so let me see if I can explain it better. Forget the example for a minute and look at a meter main 200 amp panel. Based on 250.66 Notes 2 listed below. In a meter main there are no service conductors so you would have to look at t.310.15(B)(16) and choose a 75C rated conductor for 400 amps and that would be a minimum 500 kcm. T. 250.66 says 1/0 for the grounding electrode conductor.
> 
> Now lets look at a service where we are not responsible for the overhead riser or mast or the underground lateral. It's 400 amp meter with 2- 200 amp panels being feed with 3/0 copper. Table 8 in Chapter 9 for 3/0. It states the cir mil is 167800. Since we have 2 service conductors Note 1 would apply. 167800*2= 335,600 which would be 400 kcm. Back to T. 250.66 the grounding electrode conductor only needs to be #2
> 
> ...


The OP (I believe) was talking about 250kmil Al. That changes things and allows a #2 cu GEC (and thereby a #2 cu neutral neutral as the minimum size allowed) the way I read Table 250.66. What am I missing?


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## oldsparky52 (Feb 25, 2020)

Dennis Alwon said:


> In a meter main there are no service conductors


I don't understand this statement at all and actually would argue against it. You are more knowledgeable than I ever will be so could you school me a little on how you got to this statement?


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## Dennis Alwon (May 9, 2009)

oldsparky52 said:


> The OP (I believe) was talking about 250kmil Al. That changes things and allows a #2 cu GEC (and thereby a #2 cu neutral neutral as the minimum size allowed) the way I read Table 250.66. What am I missing?



I thought he was talking copper since he had 3/0 copper I assumed the 250 was copper.... My bad


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## Dennis Alwon (May 9, 2009)

oldsparky52 said:


> I don't understand this statement at all and actually would argue against it. You are more knowledgeable than I ever will be so could you school me a little on how you got to this statement?



Most of the meter mains are connected with buss bars so there are no service conductors. Even the ones that have conductors they wouldn't be considered service conductors since they are part of a listed piece of equipment. That is what I was told. I had a 400 amp CH meter main which only had one set of 3/0 compact conductors between the meter part and the panel section. Our state dept says that they are not service conductors because it is part of the listed equipment. How they got by with 3/0 for 400 amps is beyond me but we have no resource on changing that. There equipment was tested that way
@oldsparky52


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## oldsparky52 (Feb 25, 2020)

Dennis Alwon said:


> Most of the meter mains are connected with buss bars so there are no service conductors. Even the ones that have conductors they wouldn't be considered service conductors since they are part of a listed piece of equipment. That is what I was told. I had a 400 amp CH meter main which only had one set of 3/0 compact conductors between the meter part and the panel section. Our state dept says that they are not service conductors because it is part of the listed equipment. How they got by with 3/0 for 400 amps is beyond me but we have no resource on changing that. There equipment was tested that way
> @oldsparky52


Interesting.


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