# disagreement on main lug vs main breaker



## n175h (Oct 12, 2009)

I have a disagreement with my electrician. He is installing a 400amp 3phase disconnect on the wall outside my business. POCO specd out 2x2/0 CU wire for each phase and 2x2/0 CU for the neutral on the 120/208v service and required the disconnect to have double lug capability for each wire pair. POCO's load calculation total was 320 amps. 

Inside the building he wants to hang 2 separate 200 amp 3 phase load centers to feed all the circuits. I like this idea because one 400amp 3 phase load center costs as much as 4 200 amp 3 phase load centers. 

My disagreement is he wants to use main lug for the inside panels. I think they should have main breakers. Seems to me since they are 200 amps and the fuses in the disconnect are 400 amp one or both panels could possibly be overloaded and not be protected. Each panel has 42 spaces. 

The cost difference is $300, but after reading on this forum for a couple of months, I don't think it is the best way.

David


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## plummen (Jan 10, 2010)

I dont see any harm in having main breaker panels installed,depending on how the outside disconnect or disconnects are wired/installed it would make it easier to isolate things inside building for repairs without affecting the other panel :thumbsup:


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## rrolleston (Oct 17, 2011)

I think it would be best to have a disconnect inside for each panel for maintenance also. It don't make sense to shut everything to do work inside one panel. Also I think OSHA requires it. And I am almost sure MSHA requires it.


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## zappa (Nov 25, 2011)

Breakers would be a very nice convenience.


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## Stubbie (Jan 7, 2007)

n175h said:


> I have a disagreement with my electrician. He is installing a 400amp 3phase disconnect on the wall outside my business. POCO specd out 2x2/0 CU wire for each phase and 2x2/0 CU for the neutral on the 120/208v service and required the disconnect to have double lug capability for each wire pair. POCO's load calculation total was 320 amps.
> 
> Inside the building he wants to hang 2 separate 200 amp 3 phase load centers to feed all the circuits. I like this idea because one 400amp 3 phase load center costs as much as 4 200 amp 3 phase load centers.
> 
> ...


It is much more common to have disconnects on the outside of a commercial building than inside....unless an electrical room is provided. I don't like the idea of one disconnect for both panels. I'd check with poco to see if they would permit a double lugged meter socket and then you could feed two outside 3 phase 200 amp service disconnects grouped by the meter.


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## rrolleston (Oct 17, 2011)

Having the disconnects outside would work I guess but seems inconvenient to have to go outside.


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## busman (Nov 7, 2008)

Your electrician is wrong. If the OCPD is outside (fuses), then the conductors to the inside are feeders and have to be protected at their ampacity. The easiest way to do your service would be to dispense with the outside disconnect and use to 200A main panels inside, unless these panels are not right at the location where the conductors enter. If the panels are some ways into the building, then I would mount two 200A disconnects outside (grouped) and use two MLO panels inside.

Mark


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## n175h (Oct 12, 2009)

busman said:


> Your electrician is wrong. If the OCPD is outside (fuses), then the conductors to the inside are feeders and have to be protected at their ampacity. The easiest way to do your service would be to dispense with the outside disconnect and use to 200A main panels inside, unless these panels are not right at the location where the conductors enter. If the panels are some ways into the building, then I would mount two 200A disconnects outside (grouped) and use two MLO panels inside.
> 
> Mark


That's what I told him, but he is the electrician, not me. I just read the forums. POCO requires a 400a disconnect adjacent the meter socket outside. 

I'll go ahead and buy the two 200 amp panels with the breaker and have them ready for install when POCO and the electrician get together for the 3 phase change over.

David


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## busman (Nov 7, 2008)

BTW, a lot of times MCB panels are cheaper than MLO because of quantities sold. Also if your electrician can cite code for unprotected feeders, I'm all ears. Taps are what you'll have with what you are proposing and that's fine.

Mark

Btw, is the poco requiring the 400a disco or just a disco outside. If the latter, I would ask them about two 200a discos outside. You can also learn a lot abuut what the poco allows by looking at other services in your area.


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## mpoulton (Jul 23, 2009)

Even if you can get away with running "taps" from the 400A disco to each 200A panel, the panels will then be limited to a total of 200A worth of breakers in each since there is no other appropriately sized overcurrent protection for the feeder taps or the panel busses. This may be a problem. Having 200A main breaker panels would fix this.

EDIT: Nevermind - this is not an allowable installation.


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## zappa (Nov 25, 2011)

mpoulton said:


> Even if you can get away with running "taps" from the 400A disco to each 200A panel, the panels will then be limited to a total of 200A worth of breakers in each since there is no other appropriately sized overcurrent protection for the feeder taps or the panel busses. This may be a problem. Having 200A main breaker panels would fix this.


Very interesting..... Are there codes that would allow this configuration, like maybe a sticker placed on the panel.


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## busman (Nov 7, 2008)

zappa said:


> Very interesting..... Are there codes that would allow this configuration, like maybe a sticker placed on the panel.


There is no code that allows multiple OCPDs to protect a feeder. The six disconnect rule is only for services. The taps would have to be protected by a MCB panel.

Mark


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## n175h (Oct 12, 2009)

I did drive around town to see various installations. I did see a couple of places with two disconnects and one meter. So, I'm going to see if POCO will allow two 200 amp 3 phase disconnects to feed two 200amp subs. I found this:

http://www.mrsupply.com/cutler-hammer-disconnect-switch-dg324nrk.html

This should work fine. A 400amp disconnect is outrageously expensive. 

http://www.grainger.com/Grainger/SQUARE-D-Safety-Switch-2CR22?Pid=search

David


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## plummen (Jan 10, 2010)

Well Id say its your call,youre writing the check


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## jimmy21 (Jul 2, 2008)

unless im missing something here. Even if you had a 200amp main breaker at each panel, the feeders for each panel would still not have proper over current protection.


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## frenchelectrican (Apr 12, 2006)

jimmy21 said:


> unless im missing something here. Even if you had a 200amp main breaker at each panel, the feeders for each panel would still not have proper over current protection.


More likey not proper protection unless they sized the feeder from the main OCPD from meter location aka 400 amp fuse or breaker and sized that and go to the raceway and split it there due it will have very short run to main breaker(s) but I have to take a look at the NEC code to see if that legit.

Merci,
Marc


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## zappa (Nov 25, 2011)

jimmy21 said:


> unless im missing something here. Even if you had a 200amp main breaker at each panel, the feeders for each panel would still not have proper over current protection.


I always seem to put my foot in mouth when trying to interpret code, and maybe this is the same thing Marc is saying, but I think it sounds legit under one of the tap rules if the distance is not too great.


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## n175h (Oct 12, 2009)

Distance will be about 36 inches.

David


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## Techy (Mar 16, 2011)

from the lugs in the outside disconnect to the lugs in the panel?


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## busman (Nov 7, 2008)

OK. There are several code compliant ways to install this service.

1) Install a 400A service disconnect (fuses) outside. If you do this, the following conductors after the disconnect are feeders and require their own OCPD which can be inside at the two panels by virtue of the tap rules.

2) Install two 200A service disconnects outside using the grouped disconnect rule for services. You could then use MLO or MCB panels inside.

3) Install no disconnect outside and two 200A panels inside using the grouped service disconnect rule. This is only allowed if the panels are at the closest point of entry of the service entrance conductors to the building.

Regardless of the method chosen, the conductors and OCPD must be sized based on load calculations. There are load calculation methods for services, feeders and branch circuits. It seems that some here think that OCPD devices are meant to be activated. The intent of the code is to design electrical systems using load calculations such that the tripping of an OCPD is the protection of last resort due to an unusual coincidence of loads being on at the same time. Because the load calculations are statistical in basis, OCPD is required. With that said, you cannot just build a 400A service and then put any amount of load in either panel just because there is a 200A CB protecting the wires.

The only real exception to the ability of a load calculation to restrict OCPD tripping is in the case of multiple receptacle branch circuits where it is impossible to know what loads will be plugged in. In this case, it's up to the system designer to attempt to anticipate the loads and install the right power capacity. The code helps with this by requiring minimum size circuits at some locations - bathrooms, kitchens and laundry for examples.

I hope this helps,

Mark


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## n175h (Oct 12, 2009)

Thanks Mark.

David


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## n175h (Oct 12, 2009)

*Finally got the 3 phase gear installed*

It's been since February that we started this remodel. I thought I would bring it back to the top to show how it turned out. All inspected and approved and waiting on AEP to plug in the meter. Hopefully tomorrow.

All sub panels with isolated neutrals, bonding at the 400 amp disco only. I pulled ground wires through all my EMT and bonded all my J boxes. I don't like using pipe for the ground. AEP and AHJ only requires one ground rod here. Both subs have 200 amp mains. The 400 amp disco has lugs that accept 2 wires under one screw, but AEP won't accept that type of lug. We had to put double barrel lugs in the meter socket as shown. They also required a bypass. Total load per AEP engineer is about 310 amps, which did not require a CT. That saved us a bunch of $$$

We decided to use 208/120 3phase instead of 240v delta.

David


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## n175h (Oct 12, 2009)

and more


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## brric (Mar 5, 2010)

Just curious, what size are those service conductors to the disco?


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## n175h (Oct 12, 2009)

brric said:


> Just curious, what size are those service conductors to the disco?


They are 2/0


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## k_buz (Mar 22, 2012)

2/0 AL? 

Those would need to be 4/0 for 200A MBs.

The next thing I would double check is the lugs on the disco. They have two wires under one lug. USUALLY, those would need to be double lugs.


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## n175h (Oct 12, 2009)

k_buz said:


> 2/0 AL?
> 
> Those would need to be 4/0 for 200A MBs.
> 
> The next thing I would double check is the lugs on the disco. They have two wires under one lug. USUALLY, those would need to be double lugs.


My bad, it is 4/0

As I posted the lugs were designed to accept 2 wires under one screw. I verified that with the electrician as soon as I saw the switch and opened the door on it.

David


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## k_buz (Mar 22, 2012)

n175h said:


> My bad, it is 4/0
> 
> As I posted the lugs were designed to accept 2 wires under one screw. I verified that with the electrician as soon as I saw the switch and opened the door on it.
> 
> David


Had me worried there for a minute :thumbsup:

Looks like you did your homework, and they did a clean, professional job.


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## k_buz (Mar 22, 2012)

After looking at the pictures a second time...

How did they leave the disco with one conduit, and hit each panel with a separate conduit? Is there a J-Box or Tee somewhere not shown?


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## jbfan (Jul 1, 2004)

k_buz said:


> After looking at the pictures a second time...
> 
> How did they leave the disco with one conduit, and hit each panel with a separate conduit? Is there a J-Box or Tee somewhere not shown?


Trough above the panels.


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## k_buz (Mar 22, 2012)

I see the trough, but the feeders come into the bottom of the panel...that's why I didn't think the trough had the feeders in it.


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## frenchelectrican (Apr 12, 2006)

That look good there with that set up and it better to use 208Y120 than 240D120 system so you can able use all of them without issue at all.

Just make sure the equiment that do required 240 volts that are listed to run on 208 without issue ( some case you may call the manufacter for the details)

Merci,
Marc


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## busman (Nov 7, 2008)

Two things. I can't see the Main Bonding Jumper in the photos, is there one? Also the ground wire looks way too small for a 400A service. Lastly, I wouldn't take the electricians word on the double lugging, I'd want to see it in the manufacturer's instructions. Very few lugs are listed for doubles.

Mark


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## kbsparky (Sep 11, 2008)

I saw the main bonding jumper .... look again:


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## rrolleston (Oct 17, 2011)

Was going to say small ground too but metal pipe so it's just a in addition to the pipe. But was really interested on what size pipe you used from the disconnect to the trough looks a little tight and how long is the run?


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## rrolleston (Oct 17, 2011)

I would have used the same double barrel lugs that you used on the meter socket for the disconnect I don't like double tapping. Those must be some decent size lugs to accept 2 4/0 wires.


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## n175h (Oct 12, 2009)

busman said:


> Two things. I can't see the Main Bonding Jumper in the photos, is there one? Also the ground wire looks way too small for a 400A service. Lastly, I wouldn't take the electricians word on the double lugging, I'd want to see it in the manufacturer's instructions. Very few lugs are listed for doubles.
> 
> Mark


Neutral lug is screwed to the cabinet, so the bond is lug to cabinet to ground lug. Ground wire is #6. Pipe for feeders to sub gutter (trough) inside is 3" diameter and is 10" long.


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## brric (Mar 5, 2010)

rrolleston said:


> I would have used the same double barrel lugs that you used on the meter socket for the disconnect I don't like double tapping. Those must be some decent size lugs to accept 2 4/0 wires.


They are designed and listed to accept two conductors.


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## n175h (Oct 12, 2009)

brric said:


> They are designed and listed to accept two conductors.


They were huge. I don't think he could have landed just one conductor in the lug without fragmenting the wire strands into a big mess.

David


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