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Old 02-03-2009, 03:38 PM   #1
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Question 400-amp service

I am replacing a residential 200-amp service to a 400-amp service with a 320-amp meter socket. What size conductors should I use co and or al? Can I undersize the neutral conductor like service cable? What size ground to cold water?

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Old 02-03-2009, 04:38 PM   #2
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Quote:
Originally Posted by BIGRED View Post
I am replacing a residential 200-amp service to a 400-amp service with a 320-amp meter socket. What size conductors should I use co and or al? Can I undersize the neutral conductor like service cable? What size ground to cold water?
Can we assume you have 2- 200 amp disconnects or panels next to the meter? If that is the case 3/0 copper is required with a #2 to the water pipe. Of course there could be variation of that. Let us know.

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Old 02-03-2009, 08:05 PM   #3
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There is one new existing 200-amp panel inside that I am going to re-feed. I am going to add a 200-amp, 2 circuit panel next to it for a sub panel in another location in the basement.
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Old 02-03-2009, 08:39 PM   #4
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Since T. 310.15(B)(6) does not apply here you must use T. 310.16 for your conductors. As I said before 3/0 copper if you are using conduit with 75 or 90 C wire. If you are using SE cable you will be limited to the 60C col. in which case it would be 4/0 copper if you loads don't exceed 195 amps in either panel.
The GEC would be #2 in this case.
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Old 02-04-2009, 10:39 AM   #5
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I am going to run 2 200-amp cables from the meter to inside. I wanted to know the size conductors from the taps to the meter socket.
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Old 02-04-2009, 03:31 PM   #6
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Originally Posted by BIGRED View Post
I am going to run 2 200-amp cables from the meter to inside. I wanted to know the size conductors from the taps to the meter socket.

I got you now-- you are talking about the riser wires. Correct?

I believe the riser only needs to be as large as the calculated load but I would use T. 310.15 and use 400 KCM copper or 600 MCM alum.

You could parallel the riser with 4/0 copper or 300KCM alum.-- (assumed one riser with derating and 90 C wire.

Hope this helps-- someone correct me if I am off base here.
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Old 02-04-2009, 05:14 PM   #7
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Originally Posted by electricista View Post
Since T. 310.15(B)(6) does not apply here you must use T. 310.16 for your conductors.
How do you figure? This is a residential service.
Do you know something we don't?
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Old 02-04-2009, 05:16 PM   #8
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Originally Posted by electricista View Post

I believe the riser only needs to be as large as the calculated load but I would use T. 310.15 and use 400 KCM copper or 600 MCM alum.

You could parallel the riser with 4/0 copper or 300KCM alum.-- (assumed one riser with derating and 90 C wire.
Not just the riser. The whole service entrance.


For 320/400 you can use parallel 4/0AL (2/0CU) or 500AL (350CU).
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Old 02-04-2009, 05:29 PM   #9
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Originally Posted by Speedy Petey View Post
Not just the riser. The whole service entrance.


For 320/400 you can use parallel 4/0AL (2/0CU) or 500AL (350CU).
How are you applying 2/0 copper in this scenario? 2/0 copper is good for a 200 amp service but t. 310.15(B)(6) cannot be used for two 200 amp panels. The se conductors must carry the entire load of the service for T. 310.15(B)(6) to be used.
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Old 02-04-2009, 09:22 PM   #10
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Originally Posted by electricista View Post
How are you applying 2/0 copper in this scenario? 2/0 copper is good for a 200 amp service but t. 310.15(B)(6) cannot be used for two 200 amp panels. The se conductors must carry the entire load of the service for T. 310.15(B)(6) to be used.
I completely don't understand this logic.

You are saying 2/0cu is good for one 200A service, but it is not good for two 200A panels in parallel??? I am very curious as to how you come to this interpretation.

A 320/400A service, using 500mcm AL (or 350mcm CU) on the line side of the meter, and TWO sets of 4/0, 4/0, 2/0 AL (or the CU equiv) on the load side run to two 200A panels, is a VERY typical installation.

What am I missing here?
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Old 02-04-2009, 10:53 PM   #11
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Originally Posted by Speedy Petey View Post
I completely don't understand this logic.

You are saying 2/0cu is good for one 200A service, but it is not good for two 200A panels in parallel??? I am very curious as to how you come to this interpretation.

A 320/400A service, using 500mcm AL (or 350mcm CU) on the line side of the meter, and TWO sets of 4/0, 4/0, 2/0 AL (or the CU equiv) on the load side run to two 200A panels, is a VERY typical installation.

What am I missing here?
It use to be very typical here also. Where in T. 310.15(B)(6) des it allow you to use 2 sets of 2/0 for a 400 amp service. The table shows 400 amps 400KCM. Nowhere does the table allow for your install because this table is base on the diversity of the load for residential units. When you split the loads then the diversity is skewed.

There is a reason why the calculation for a service is different for a residence. I understand why you don't get this because it is a bit odd but, for one, I did not come with with it. It is clear to me and many others that this would be non compliant.

Other then assuming that because 2/0 is good for 200 amps then two 200 amp panels must be good for 400 amps, can you support your reason for 2- 200 amps being compliant.

Quote:
Originally Posted by NEC 2008 Art. 310.15(B)(6)
120/240-Volt, 3-Wire, Single-Phase Dwelling Services and Feeders. For individual dwelling units of one-family, two-family, and multifamily dwellings, conductors, as listed in Table 310.15(B)(6), shall be permitted as 120/240-volt, 3-wire, single-phase service-entrance conductors, service-lateral conductors, and feeder conductors that serve as the main power feeder to each dwelling unit and are installed in raceway or cable with or without an equipment grounding conductor. For application of this section, the main power feeder shall be the feeder between the main disconnect and the panelboard that supplies, either by branch circuits or by feeders, or both, all loads that are part or associated with the dwelling unit. The feeder conductors to a dwelling unit shall not be required to have an allowable ampacity rating greater than their service-entrance conductors. The grounded conductor shall be permitted to be smaller than the ungrounded conductors, provided the requirements of 215.2, 220.61, and 230.42 are met.
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Old 02-05-2009, 07:01 AM   #12
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Your argument that only the lateral or riser is allowed to use this table holds no water. Clearly as shown below the "main power feeder" is included, which is what feeds the service panel.

NEC 2008 Art. 310.15(B)(6) 120/240-Volt, 3-Wire, Single-Phase Dwelling Services and Feeders. For individual dwelling units of one-family, two-family, and multifamily dwellings, conductors, as listed in Table 310.15(B)(6), shall be permitted as 120/240-volt, 3-wire, single-phase service-entrance conductors, service-lateral conductors, and feeder conductors that serve as the main power feeder to each dwelling unitand are installed in raceway or cable with or without an equipment grounding conductor. For application of this section, the main power feeder shall be the feeder between the main disconnect and the panelboard that supplies, either by branch circuits or by feeders, or both, all loads that are part or associated with the dwelling unit. The feeder conductors to a dwelling unit shall not be required to have an allowable ampacity rating greater than their service-entrance conductors. The grounded conductor shall be permitted to be smaller than the ungrounded conductors, provided the requirements of 215.2, 220.61, and 230.42 are met.


Quote:
Other then assuming that because 2/0 is good for 200 amps then two 200 amp panels must be good for 400 amps, can you support your reason for 2- 200 amps being compliant.
I NEVER said I though it was good for "400 amps". I said it was good for two separate 200A amp panels in parallel.
To answer your question, no I can't. I also can't find any specific wording disallowing it either.




Now I see in 2008 there is a supposed change supporting your claim, but I do not see where it is written. All I can see is the handbook commentary.
I am new to the 2008 NEC changes, and do not even use the NEC for residential.
Here is the handbook commentary, but can you point to the exact text they are referring to?

Section 310.15(B)(6) permits the main feeder to a dwelling unit to be sized according to the conductor sizes in Table 310.15(B)(6). For the 2008 Code, the panel clarified that this permission to use this table applies only to conductors carrying 100 percent of the dwelling unit's diversified load.
Provided a single set of 3-wire, single-phase, service-entrance conductors in raceway or cable supplies a one-family, two-family, or multifamily dwelling, the reduced conductor size permitted by 310.15(B)(6) is applicable to the service-entrance conductors, service-lateral conductors, or feeder conductors that supply the main power feeder to a dwelling unit. The feeder conductors to a dwelling unit are not required to be larger than its service-entrance conductors.
Exhibits 310.8 and 310.9 illustrate the application of 310.15(B)(6). In Exhibit 310.8, the reduced conductor size permitted is applicable only to the service-entrance conductors run to each apartment from the meters. In Exhibit 310.9, the reduced conductor size permitted is also applicable to the feeder conductors run to each apartment from the service disconnecting means, because these feeders carry the entire load to each apartment.



Last edited by Speedy Petey; 02-05-2009 at 07:04 AM.
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Old 02-05-2009, 07:21 AM   #13
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Originally Posted by Speedy Petey View Post
Your argument that only the lateral or riser is allowed to use this table holds no water. Clearly as shown below the "main power feeder" is included, which is what feeds the service panel.


I am sorry that you thought I said this but I did not. I said the riser was allowed to be sized to the calculated load of the service but I have heard that and would need to double check that.

You are correct that the main power feeder is included and that's is why I said 2/0 cannot be used in this situation.

Yes the change in the 2008 is really a clarification of what was meant in the past, IMO.

Quote:
I NEVER said I though it was good for "400 amps". I said it was good for two separate 200A amp panels in parallel.
To answer your question, no I can't. I also can't find any specific wording disallowing it either.
The op is installing a 400 amp service using 2- 200 amp panels. T. 310.15(B)(6) is not allowed-- that is a 400 amp service. By the way I don't believe 2- 200 amp panels are considered a parallel install. To be parallel they must begin and terminate together.

In either case I must disagree that 2/0 is allowed for the 200 amp panels when used to have a 400 amp service. Around here we consider 2- 200 amp panels a 400 amp service.
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Old 02-05-2009, 02:28 PM   #14
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I guess it is a locational difference.

I agree that two panels is not technically a parallel run. I use that term more as a descriptive term. The two panels are basically in parallel. They start and end in the same locations.

Also, this is not considered a true "400A" service here. We can use the calculated load which is why 350cu or 500al is accepted as they are rated for 350A in 310.15(B)(6).
Taking this into consideration, each half of the service (each 200A panel) could then be considered 160A continuous, so then even 310.16 agrees that 2/0cu is fine being that it rated for 175A.
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Old 08-28-2009, 08:44 AM   #15
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Default 400 amp parallel service

I see this a lot. A 400 amp meter pan with 2, 4/0 service cables feeding 2 200 amp panels. This does not constitute a 400 amp service in parallel. Parallel conductors must be terminated in the same manner at both ends!
you would have to bring both service cables into a trough, bug them and then feed each 200 amp panel from the NOW paralled service conductors.
So, If an inspector was having a bad day he could knock this down as a violation of the parallel conductor rule. Andrew
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Old 02-14-2012, 03:00 PM   #16
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Default Black/Yellow/Blue Phasing

Came across a 277/480V service today in Northern Central NJ, PSEG territory that was phase taped Black/Yellow/Blue for 277/480V.

New combination for me, should I just assume incompetence?
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Old 02-14-2012, 03:57 PM   #17
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Originally Posted by NY Inspector View Post
I see this a lot. A 400 amp meter pan with 2, 4/0 service cables feeding 2 200 amp panels. This does not constitute a 400 amp service in parallel. Parallel conductors must be terminated in the same manner at both ends!
you would have to bring both service cables into a trough, bug them and then feed each 200 amp panel from the NOW paralled service conductors.
So, If an inspector was having a bad day he could knock this down as a violation of the parallel conductor rule. Andrew
I agree with the parallel definition however 4/0 conductors are allowed to feed 2- 200 amp panels. The 320 amp meters have double lugs so there is no need for a trough.
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Old 02-14-2012, 07:04 PM   #18
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Here in Missouri we build a "400" amp service as the load side of meter base is 2/0 copper to each 200 amp panel
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Old 02-15-2012, 03:57 AM   #19
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Originally Posted by Speedy Petey View Post
I guess it is a locational difference.

I agree that two panels is not technically a parallel run. I use that term more as a descriptive term. The two panels are basically in parallel. They start and end in the same locations.

Also, this is not considered a true "400A" service here. We can use the calculated load which is why 350cu or 500al is accepted as they are rated for 350A in 310.15(B)(6).
Taking this into consideration, each half of the service (each 200A panel) could then be considered 160A continuous, so then even 310.16 agrees that 2/0cu is fine being that it rated for 175A.
I can see it pretty clear when you use the 2/0 CU THHN's that I have no issue for long time when we do the twinner 200's panels for 320 service but once we hit a true 400 amp the bet is out of the window due our state of Wisconsin codes did change a little ( they did tweak it more to commercal side )

I know one city in Wisconsin really did nail my rear end due their city code change and they fail to inform few EC's whom they don't go in that city often but I did show the art #'s and they seems back off a little but they inform me next time I did show up in that city better prepared for larger conductor sizeing.

But in France we have a bit of leeway for 360 amp service we do simair to your set up in stateside.

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Old 02-15-2012, 05:58 AM   #20
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Pete, any service conductor that does not carry the entire load of the home must use 310.16.

So picture this

Utility > weatherhead > riser > 400 meter socket > two 200 amp panels.

In my above example only the riser could be sized per 310.15(B)(6).

The two runs from the meter to the panels are required by the NEC to be sized per 310.16 becuse those runs do not carry the entire load of the home. I understand you may have local rules but what I am saying is what the NEC requires and actually has for many years.

(By the way, I am using old section numbers, they numbers have changed in the 2011)


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