400A service install

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mccayry

Senior Member
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Tennessee
I am installing a 320a cont double lug meter base. My plan is to run one set of 2/0 cu condutors to a 200a MB panel located just behind the meter base. The second set of 2/0 cu conductors will be ran to a 200A disco also behind meter base. From the disco I will run about 75' to a 2nd 200A MB panel located at the opposite end of the home. I guess my question is will a 4/0 AL ser cable be sufficient to feed the second panel as long as the calculated load doesnt exceed 180A. If so are there any thoughts or recommendations that would work better in this situation. This will take place in a finished basement with a drop ceiling. Thanks
 

Little Bill

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Location
Tennessee NEC:2017
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Semi-Retired Electrician
I am installing a 320a cont double lug meter base. My plan is to run one set of 2/0 cu condutors to a 200a MB panel located just behind the meter base. The second set of 2/0 cu conductors will be ran to a 200A disco also behind meter base. From the disco I will run about 75' to a 2nd 200A MB panel located at the opposite end of the home. I guess my question is will a 4/0 AL ser cable be sufficient to feed the second panel as long as the calculated load doesnt exceed 180A. If so are there any thoughts or recommendations that would work better in this situation. This will take place in a finished basement with a drop ceiling. Thanks

A few things IMO, are wrong. I don't think you can use 2/0 to each panel because each panel doesn't serve the entire load on the house, you would need 3/0. Another is, you have to use the 60 deg. column on SE cable and 4/0 Alum. is only good for 150A. You might want to do a load calc. to see what you actually need.
 
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RUWired

Senior Member
Location
Pa.
I am installing a 320a cont double lug meter base. My plan is to run one set of 2/0 cu condutors to a 200a MB panel located just behind the meter base. The second set of 2/0 cu conductors will be ran to a 200A disco also behind meter base. From the disco I will run about 75' to a 2nd 200A MB panel located at the opposite end of the home. I guess my question is will a 4/0 AL ser cable be sufficient to feed the second panel as long as the calculated load doesnt exceed 180A. If so are there any thoughts or recommendations that would work better in this situation. This will take place in a finished basement with a drop ceiling. Thanks
Correct me if i'm wrong, but table 310.15(B)6 doesn't apply when you have more than one feeder to a dwelling. Only one set that carries 100 % of the load is allowed to be derated.

The 2/0 conductors are only rated for 175 amps. The 4/0 al conductors are only rated for 150 amp at 60 degree c. per 338.10(B) and 334.80.

Is the disconnect a fused disconnect?

Rick
 

Dennis Alwon

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Chapel Hill, NC
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Retired Electrical Contractor
I agree with Bill. I believe Tennesse is under the 2008 NEC and that makes se cable run inside a building at 60C not 75C. You may want to put 2- 200 main breaker with provisions to feed a 125 amp at the other end . Take the larger loads from the 200 amp MB panels behind the meter base.
 

marti smith

Senior Member
So if he puts in one disconnect to disconnect both panels, would he then be compliant by 310.15(B) 6 and also the table?
(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.

Am I understanding correctly?
 

Little Bill

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Tennessee NEC:2017
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So if he puts in one disconnect to disconnect both panels, would he then be compliant by 310.15(B) 6 and also the table?
(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.

Am I understanding correctly?

The OP said he had a double lug meter to feed both panels. I guess you could only use 1 of the lugs but that wouldn't help much since the panels are behind the meter inside the house. If he used a disct. he could use the 2/0 to it but would have to go up to the 3/0 from the disct. to the first 200A panel, then treat the other 2 as subpanels.
 

mccayry

Senior Member
Location
Tennessee
A few things IMO, are wrong. I don't think you can use 2/0 to each panel because each panel doesn't serve the entire load on the house, you would need 3/0. Another is, you have to use the 60 deg. column on SE cable and 4/0 Alum. is only good for 150A. You might want to do a load calc. to see what you actually need.

So I guess my best option would be to feed the disco and panel # 1 with 3/0 and feed panel # 2 with either 350 AL or feed panel # 2 with 4/0AL with 150A OCP. All the 400A services that are feeding 2-200A MB panels back to back that I have seen have always been fed with 2/0 cu. I swear I learn something new every day.
 

augie47

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Location
Tennessee
Occupation
State Electrical Inspector (Retired)
So I guess my best option would be to feed the disco and panel # 1 with 3/0 and feed panel # 2 with either 350 AL or feed panel # 2 with 4/0AL with 150A OCP. All the 400A services that are feeding 2-200A MB panels back to back that I have seen have always been fed with 2/0 cu. I swear I learn something new every day.

This is embarrassing, but it points out a major flaw in the TN inspection system.
You need to run this by the AHJ in the area where the job is located. What you have been told here is, IMHO, 100% NEC.
That said, I agree that in many, many areas of TN the 2/0 will be accepted and in many areas you will be fine with the 4/0 AL feeder. This is enforced differently by inspectors throughout TN and we have asked for an official interpretation from our leaders in Nashville for about 3 or 4 years only to be told by each consecutive supervisor that an answer is forthcoming.


I refrain on makiong any comments about adult leadership
 

Little Bill

Moderator
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Location
Tennessee NEC:2017
Occupation
Semi-Retired Electrician
So I guess my best option would be to feed the disco and panel # 1 with 3/0 and feed panel # 2 with either 350 AL or feed panel # 2 with 4/0AL with 150A OCP. All the 400A services that are feeding 2-200A MB panels back to back that I have seen have always been fed with 2/0 cu. I swear I learn something new every day.

This is embarrassing, but it points out a major flaw in the TN inspection system.
You need to run this by the AHJ in the area where the job is located. What you have been told here is, IMHO, 100% NEC.
That said, I agree that in many, many areas of TN the 2/0 will be accepted and in many areas you will be fine with the 4/0 AL feeder. This is enforced differently by inspectors throughout TN and we have asked for an official interpretation from our leaders in Nashville for about 3 or 4 years only to be told by each consecutive supervisor that an answer is forthcoming.


I refrain on makiong any comments about adult leadership

I know there are some 400A services here that are fed by 2/0, to (2) 200A MB panels. The OP's setup differs from that in that he is going to only (1) 200A panel with 1 set of the 2/0, then to a discnt. with the 2nd set of 2/0, then to the other 200A panel. I've seen/heard where the AHJ was fine with the (2) 200A panels alone, but mixing in the disct. makes the 2nd 200A a sub panel which doesn't carry all the load. I'm not saying this is necessarily correct or my opinion but just how the AHJ saw it. I probably would do as Gus suggested and run it by you AHJ first.
 

infinity

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Location
New Jersey
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Journeyman Electrician
This doesn't seem unsafe to me. If you had a 200 amp service with one 200 amp panel fed by #2/0 Cu it would be code compliant and safe. Add the second panel fed with the same #2/0 and it's unsafe? I do agree that according to the NEC it's a violation.
 

augie47

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Location
Tennessee
Occupation
State Electrical Inspector (Retired)
This doesn't seem unsafe to me. If you had a 200 amp service with one 200 amp panel fed by #2/0 Cu it would be code compliant and safe. Add the second panel fed with the same #2/0 and it's unsafe? I do agree that according to the NEC it's a violation.

Pasahwwwww ! A flaw in Code logic ? :D
Same situation.. I have an outside service disconnect with a feeder to my interior panel. The feeder is sized per 310.15(B)(6).
The HVAC condenser is moved to the meter end of the residence and is fed from one of the previously unused spaces in the service disconnect. My now less loaded SE feeder is undersized and not compliant.

Rob, I know you are aware, I'm just pointing out the strange situation.
 

mccayry

Senior Member
Location
Tennessee
All Im trying to is make sure that all my work is safe and is code compliant. Many of the inspectors in my area have no problem with what I stated in my original post. I still very new at this and constantly learning. Here are 2 different situations where the install was approved by the AHJ. The first picture is a 400A Service with 2 sets of 2/0 cu feeding dual 200A MB Panels. Pay no attention to the wiring in the panel on the right. That is the hvac contractors mess. The 2nd picture is a 400A service with 2/0 Cu between disco's and Panel. pics 163.jpg
summertime 049.jpg
 

infinity

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Location
New Jersey
Occupation
Journeyman Electrician
Why the disconnects feeding main breaker panels? And yes the #2/0's are a violation for 200 amps.

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mccayry

Senior Member
Location
Tennessee
Why the disconnects feeding main breaker panels? And yes the #2/0's are a violation for 200 amps.

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This was a job I looked at a few weeks ago. The HO's father had set the meterbase, disco's, and panels. Why he put 2 disco's is beyond me. They were wanting me to bring all the homeruns into the panels. This house was an existing house that had to be moved and was set on a basement foundation. Before I signed on to do so I had both the AHJ and the POCO engineer take a look at it and they had no problem with the setup. Im not saying its right Im just saying it gets done all the time around here and all the AHJ's are fine with it.
 

Little Bill

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Location
Tennessee NEC:2017
Occupation
Semi-Retired Electrician
This was a job I looked at a few weeks ago. The HO's father had set the meterbase, disco's, and panels. Why he put 2 disco's is beyond me. They were wanting me to bring all the homeruns into the panels. This house was an existing house that had to be moved and was set on a basement foundation. Before I signed on to do so I had both the AHJ and the POCO engineer take a look at it and they had no problem with the setup. Im not saying its right Im just saying it gets done all the time around here and all the AHJ's are fine with it.

Can't tell from the pictures, but it appears that the NM is stapled more than 12" from the box and at least 1 of the inspectors here wouldn't pass that. Seems safe enough to me, but I'm not the one inspecting.
Did you use the panel from the house that was moved as a junction box for the new panel?
 
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