Hypothetical 400a service

[mark32]

Let's say you are wiring a large dwelling and would like to install two 200a panels, one at the service and another on the other side of the house. Tell me if you like the following setup. From the ct meter you go underground and (Back of meter would place it a number of feet below the grade in the garage) enter a 400a disconnect (All GEC's would terminate here) mounted in the adjacent garage, you then nipple into a metallic trough mounted below it. Out of the top of the trough you nipple into a MLO 200a panel, out of the back of trough you enter with 4/0 AL ser which runs to the other 200a panel 75' away. In the trough you splice the conductors using those insulated taps and bolt an uninsulated distribution block to the trough for the EGC's. Sound good?

 

[Cow]

Let's say you are wiring a large dwelling and would like to install two 200a panels, one at the service and another on the other side of the house. Tell me if you like the following setup. From the ct meter you go underground and (Back of meter would place it a number of feet below the grade in the garage) enter a 400a disconnect (All GEC's would terminate here) mounted in the adjacent garage, you then nipple into a metallic trough mounted below it. Out of the top of the trough you nipple into a MLO 200a panel, out of the back of trough you enter with 4/0 AL ser which runs to the other 200a panel 75' away. In the trough you splice the conductors using those insulated taps and bolt an uninsulated distribution block to the trough for the EGC's. Sound good?

You're tapping a 400A disconnect and running to a panel 75' away?

Can you instead use a 400A metermain with two 200A breakers to feed each panel? I believe they also make 400A combo panels that have 30 spaces in them and also a 200A breaker to feed a remote panel. Then you can ditch the trough and insulated taps/distribution blocks. That should save a good bit of money.

 

[busman]

The only change I might make would be to use one 200A MCB panel and a 200 disconnect in the garage and avoid the costly 400A disconnect. It would still meet the grouped 6 disconnect rule.

 

[iwire]

Code wise I do not see overcurrent protection for the panels or conductors.

I would do all I could to void the 400 amp disco $$$

Maybe the 400 amp meter socket outside, come inside to two 200 amp main breaker panels, at least one with a sub feed kit to feed the remote panel.

 

[Dennis Alwon]

I agree that a 400 amp disco is a mistake. I also would not use a CT unless the poco made me.

Use a 400 amp meter base- they have double lugs, and then run 2 pipes under the slab to 2- 200 panels and as Bob said one would be a feed thru lug panel. Now the problem--- 4/0 ser alum. is only rated 150 amps. I would do everything I could to pipe from the main feed thru panel to the remote 200 amp subpanel so I could use 4/o alum., or I would just install a 125 amp subpanel and add some of the larger circuits to the feed thru panel.

Remember that 4/0 alumin. in conduit is only rated 180 amps but is allowable for 200 cb if the calculated load is not more than 180 amps.

 

[mark32]

Thank you for the replies. In actuality, this was a service I assisted in many years ago when I was still quite green. I drove by the house the other day and the question just popped into my head as to how it was done and how I would do it now. I do know a trough was installed and I know that ser was used to feed the remote sub but it could have been 150a panel now that you mention it Dennis. The poco must have required the ct because I remember that was installed and nothing else outside, equipment wise. That's all I can remember with certainty. If I were to do it I really like the idea of using a meter main combo with 2 200a mains. Aside from that, I now have two questions.

Bob, in your scenario three panels would be involved correct? At the service one of the 200a main breaker panels would exist as one normally would but how would the second panel be used? In other words, as Dennis clarified, there would be feed through lugs installed (Is that what the sub feed kit is?) so inside that panel you'd have just the main and that's it? A 200a disconnect could be used as well here correct?

Dennis, I mentioned using 4/0 AL for the sub but from what you are saying you don't consider it to be a main feeder even though, in this scenario, it originates at service. I don't necessarily disagree, I just never would have looked at it that way. If a panel is located a good distance from the meter a main disconnect (With an OCPD) would be used to protect the feeder but the ampacity would still be sized using table 310.15(b)(6) no?

 

[Dennis Alwon]

The main feeder would have to carry the entire load of the dwelling. That is not possible if you feed 2-200 amp panel.

 

[mark32]

Okay Dennis or anyone else, after some thought here are a few possible scenarios used to do this install, please correct me where I make a wrong turn.

As Cow first mentioned, use a 400a meter with two 200a mains. Here I would have to feed both panels with 3/0 cu in pipe or 4/0 cu SER

Cow also mentioned the use of a 400a combo panel that would have 30+ spaces plus house a 200a main for the remote panel. Here the combo panel would need to be fed with 500 cu

Busman stated using a 200a main panel grouped next to a 200a main disc for the remote panel, same conductors as first scenario

Electrical guru Bob and Dennis mentioned a 400a double lugged meter feeding two 200a main panels, one having feed through lugs to feed remote sub. This one is similar to Busman's suggestion whose idea I think I like better. Any edge, aside from having an extra panel available, to installing a main panel instead of the disconnect? Again, 3/0 cu in pipe or 4/0 cu SER

I've also read, I believe, about a meter with main(s) that would have a few spaces for outdoor loads, another cool idea.

Any thoughts, preferences or corrections?

 

[Dennis Alwon]

As Cow first mentioned, use a 400a meter with two 200a mains. Here I would have to feed both panels with 3/0 cu in pipe or 4/0 cu SER.

I agree- good luck with the 4/0 copper ser--wow

Cow also mentioned the use of a 400a combo panel that would have 30+ spaces plus house a 200a main for the remote panel. Here the combo panel would need to be fed with 500 cu

No the combo meter panel is an all in one. There are usually buss bars from the meter to the panel.

Busman stated using a 200a main panel grouped next to a 200a main disc for the remote panel, same conductors as first scenario

I think he was talking about the main panels not the sub panels.

Electrical guru Bob and Dennis mentioned a 400a double lugged meter feeding two 200a main panels, one having feed through lugs to feed remote sub. This one is similar to Busman's suggestion whose idea I think I like better. Any edge, aside from having an extra panel available, to installing a main panel instead of the disconnect? Again, 3/0 cu in pipe or 4/0 cu SER

I always like having the extra spaces and around here a 200 amp panel is as cheap or cheaper than a 200 amp disconnect.

I've also read, I believe, about a meter with main(s) that would have a few spaces for outdoor loads, another cool idea.

Yes some meter combo panels have 2- 200 amp breakers in them to feed the remote panels. I am sure there are some with other spaces.

 

[mark32]

Ok, sounds good Dennis, yeah that 4/0 cu ser would be costly but I was just trying to make sure I understood what was going on. Since we're on the topic of multi panel installs, if one were to use two main breaker panels; I like the idea of doing what the installer in this link did.

http://forums.mikeholt.com/showthread.php?t=119184

Dennis, you commented on this one and I agree with you but wondered if others agree with jumping panels in such a manner. I see nothing different from doing that to tapping off a full sized gec with split bolts and running a tap into each panel. Visually I thinking jumping panels would look better than just leaving a conductor stapled up above the panels with two split bolts hanging off it.

 

[jaylectricity]

New page!

Why do you need to feed both panels with ridiculously oversized wire? 2/0 to each, right? Double lugs at the load side of the 400A meter.

 

[busman]

Ok, sounds good Dennis, yeah that 4/0 cu ser would be costly but I was just trying to make sure I understood what was going on. Since we're on the topic of multi panel installs, if one were to use two main breaker panels; I like the idea of doing what the installer in this link did.

http://forums.mikeholt.com/showthread.php?t=119184

Dennis, you commented on this one and I agree with you but wondered if others agree with jumping panels in such a manner. I see nothing different from doing that to tapping off a full sized gec with split bolts and running a tap into each panel. Visually I thinking jumping panels would look better than just leaving a conductor stapled up above the panels with two split bolts hanging off it.

That setup is the one I have used and was suggesting. Nice pics.

Mark

 

[Dennis Alwon]

New page!

Why do you need to feed both panels with ridiculously oversized wire? 2/0 to each, right? Double lugs at the load side of the 400A meter.

2/0 would not be legal for a 400 amp service with 2-200 amp panels.

 

[jaylectricity]

Why do you need to feed both panels with ridiculously oversized wire? 2/0 to each, right? Double lugs at the load side of the 400A meter.

2/0 would not be legal for a 400 amp service with 2-200 amp panels.

Are we thinking of the same thing? I'm talking about one set of 2/0 feeding one 200 amp panel, and a second set of 2/0 feeding the other 200 amp panel, both terminating at the load side of the meter. The two sets would be in their own raceway.

Is there some rule that changes this?

 

[Dennis Alwon]

Yes, since the service conductors do not carry the entire load of the service thenT.310.15(B)(6) does not apply. Where in the table does it allow for 2 sets of 2/0? It doesn't because you cannot control the diversity that is in dwellings when the load is split. 3/0 is needed.

 

[jaylectricity]

Yes, since the service conductors do not carry the entire load of the service thenT.310.15(B)(6) does not apply. Where in the table does it allow for 2 sets of 2/0? It doesn't because you cannot control the diversity that is in dwellings when the load is split. 3/0 is needed.

Oh, I believe you, I just figured that as long as each panel's OCPD was sufficient to protect the conductors feeding it, all would be OK. I'll have to check out the code to see where I went wrong.

 

[Dennis Alwon]

Jay if you look at 310.16 2/0 is only good for 175 amps so you cannot protect it with 175 amp OCPD. Now if this was a residence with a 200 amp service then T.310.15(B)(6) would allow 2/0 but not for 2-200 amp panels as in a 400 amp service.

 

[mark32]

Ok, back to the link I provided. How do you feel about the jumping of the disconnect and panel with the #4 as shown in the pics.

 

[Dennis Alwon]

Ok, back to the link I provided. How do you feel about the jumping of the disconnect and panel with the #4 as shown in the pics.

Well, if you look at 250.64(D)(1) as mentioned by Gus one might think you cannot use the busbar, however the 2011 NEC has rewritten this section and specifically allows it.
So, it is my opinion that that was the intent all along.

A grounding electrode conductor tap shall extend to the inside of each service disconnecting means enclosure. The grounding electrode conductor taps shall be sized in accordance with 250.66 for the largest service-entrance conductor serving the individual enclosure. The tap conductors shall be connected to the common grounding electrode conductor by one of the following methods in such a manner that the common grounding electrode conductor remains without a splice or joint:
(1) Exothermic welding.
(2) Connectors listed as grounding and bonding equipment.
(3) Connections to an aluminum or copper busbar not less than 6 mm ? 50 mm (1⁄4 in. ? 2 in.). The busbar shall be securely fastened and shall be installed in an accessible
location. Connections shall be made by a listed connector or by the exothermic welding process. If aluminum busbars are used, the installation shall comply with 250.64(A).

 

[jxofaltrds]

Well, if you look at 250.64(D)(1) as mentioned by Gus one might think you cannot use the busbar, however the 2011 NEC has rewritten this section and specifically allows it.
So, it is my opinion that that was the intent all along.

Not sure if I am following but I agree with Gus and with Larry's post #7:
http://forums.mikeholt.com/showthread.php?t=119184

250.64(D)(1) ****** "Note 1. A tap conductor shall extend to the inside of each service disconnecting means enclosure."

Not expaining this well so help me out.