208Y/120V/200A service comes into meter, then to main 200A fused safety switch, then to a distribution panel that feeds existing 150A panel via breaker. We are adding a 2nd breaker to feed new 200A panel. This is a commercial setting: warehouse.

Is AL 4/0-4/0-4/0-4/0 with 2/0 bare ground SER wire from breaker to new panel OK?

Can SER be run in this commercial warehouse setting:
-Stapled to the walls?
-Stapled/attached to the bottom of joists?
-Inside walls? If yes, what size hole in the studs is required?
-Inside conduit? If yes, is 2" conduit OK?
-And is it normal to strip the covering off of the lengths of the cable that will be inside conduit?

 

Is the new panel 3P or 1P? You would likely need 250kcmil aluminum conductors, what's the distance? Rigid steel pipe or EMT would be required in most commercial zoned buildings, but there are a lot of details in commercial zoning and construction class of the building. Probably 2.5 or 3" off the top of my head without doing the calculation. You would never strip SER, this would be THHN or XHHW conductors. Does your transformer have the capacity for the additional load?

Are you hiring an electrical contractor? Most states do not allow any electrical work in commercial buildings without a license...

 

Yes, we are hiring an electrician but I need to spec wall sizes and floor plan TODAY and it takes a few days to a few weeks to get an electrician in around here. I need to know what is allowed so I can figure out where to frame everything so that an appropriate path will exist.

New panel is 3 pole. Run is only about 20' from distribution panel to new one, though one wood-framed wall minimum (maybe 2, depending on what I decide), and takes 2 right angle turns.

So it DEFINITELY has to be inside conduit? SER cannot be exposed? I probably would put anything outside a wall in conduit anyway, just asking. But can it be run inside walls without conduit?

I was thinking about SER in conduit mounted on wall for about 3', then NOT in conduit inside of a wall for about 9' then back into conduit along a wall for about 6'. Not OK?

 

No.... not ok. The run needs to be in EMT.

 

Fully assembled conduit raceway is almost certainly required. Some commercial sites could use SER under some circumstances, but the strong odds are pipe is required. I'd plan for 3" pipe. The inspector might want threaded rigid steel if there is vehicle traffic (fork lifts) near this run.

 

I'm a little confused on your setup there. You have the service into a 200A fused disconnect and then it feeds an existing 150A panel. Now you are going to add another breaker to feed a 200A sub panel.

So that would mean that your existing 150A sub panel has little to no load on it.
Otherwise you may have difficulties with a 150A panel and a 200A panel on a 200A service.

 

OK, please indulge me to just probe and double-check that I know the rules:

Does it absolutely have to be in conduit all the way? No way we can run SER in walls? No forklift traffic could reach it; short entrance hallway through wall into small computer/utility room with framed-in shelves along the wall through which it comes, then around the corner to the panel. Any way it could run through the studs above the shelves without any conduit? Conduit is going to be too big for the studs.

The chart I found said 4 x 4/0 conductors could go in 2" conduit. Space is tight, is 2" OK? Is 4/0 OK?

And EMT is OK in this situation, right? Even if we have to run it along the wall surface?

 

The existing 150A panel has like maybe 30A max. Reconfig of the building is moving load around. All the 3 phase motors at that end that originally dictated the service and panel there were removed years ago. They want to add the 200A panel to preserve maximum options for how things may be distributed in the future. It may well be that the 150A panel remains with small load on it and the new panel needs 150A or 160A. Or there may be a time when it switches back and the 150A panel needs more juice.

Any harm in preserving the option in both panels just in case it is needed in the future as long as the sum doesn't exceed 200A? There are multiple tenants and they can (will) change over time so requirements may change.

 

What is the construction type of the building?

You need 5 conductors, not 4 that will probably need to be 250kcmil, not #4/0. No 2" pipe is not big enough.

Surface mounted EMT is very likely to be ok.

 

Cinder block shell with wood-framed walls inside.

5 conductors? I was working off the assumption of 4 +ground and that ground is not considered a conductor. Is that not correct?

 

It's possible SER could be allowed; however it would require 15 min finish and physical protection. Many states outright ban plastic cables in commerical which would make this a dealbreaker. Another complication is that I don't think anyone makes 5 conductor SER that big. Even 250 SER would be limited to 170A at 60C whereas you could get 200A with conductors in pipe. Furthermore, if you could source it are you going to special order a 500' spool of it for a 20' run? I don't see it working.

The ground is a conductor which must run in or be part of the same raceway as the other conductors.

 

SER is not allowed in the ceiling spaces of commercial.

4/0 is only good for 200 amps in a residential usage. Commercial uses different sizing rules.

 

Agree, 4/0 aluminum is too small for 200 amps, I believe it is good for 180 amps. I'd use MC cable for this job.

 

I was wondering why nobody suggested MC yet....

 

Cost. 250MCM AL MC cable would be very expensive compared to running a raceway and pulling in conductors.

 

OK, 250 is the cable that is required but that presents a puzzling situation. The cable going from the meter socket to the meter socket to the safety switch and them from there to the distribution panel is 4/0 AL. The safety switch is fused with 200 amp fuses. Right now the distribution panel has only 1 panel connected to it and that has a 150A main but I know that in the past there was another panel connected to it and that had a 200A main and was also connected via 4/0 AL XHHW. Hmmmm, does this sound wrong? And could this be due to the original wiring being done under older versions of the code?

 

Cable ampacity is different than individual conductor ampacity. Was the XHHN in conduit?

 

Could 250MCM be run through walls and/or joists? If so then the framing/building savings might offset the extra cost of the cable.

 

Ah ha! I never thought of that. I guess that's why you guys get the big bucks! All the connections between the meter socket, safety switch, distribution panel, and the former 200A panel were done in a 6 x 6 wireway with 4/0 AL XHHW main conductors and I think they used 1/0 for the neutrals....have to check on that.

 

Individual conductors need to be run in a raceway or cable tray. They cannot be in free air.

 

So is 4/0 AL XHHW in a wireway or conduit OK for 200A? Also, the chart I am looking at says that it is OK to run 4 conductors of 4/0 in a 2" conduit. Does a bare ground count as a "conductor"? In other words, is it OK to run 4 x 4/0 AL XHHW + 2/0 bare ground in a 2" conduit?

 

The 250 MCM MC cable is only more expensive till you factor in labor. This isn't a DIY project.

 

A 2x6 wall should be deep enough. If in doubt deeper is better.

 

I understand that the wiring is not a DIY project and we are not trying to do that. The framing/building IS a DIY project for us.....because that is what we do.

I need to decide how this has to be framed ASAP and the sticking point is where the feed for the panel is gong to run. We are working Saturday AND Sunday on this one. If it can be run through walls then it saves some construction cost and yields a better layout but I need to know how big the holes in the framing for the cable need to be. If conduit has to be run outside walls all the way then we have to modify the shelving to leave room for it and I need to know how much room to leave. If we can do it with 2" conduit then we can get away with 2x8's. If it must be 2.5" conduit then we have to go to 2x10's which is gong to present other challenges. Those are the questions that I am trying to answer.

So, what I need to know is:
1. Will 250MCM work and can it be run both inside walls AND on the surface of walls?
2. If no to #1 then will 250MCM work and can it be run both inside walls and then inside conduit?
3. If yes to #2 then what size conduit must it be?
4. If no to #2 then will 4 x 4/0 conductors plus 2/0 bare ground inside 2" conduit work?
5. If no to #4 then will 2.5" conduit work? (assuming 4/0+2/0 or 250+4/0 XHHW...but I'll let the electrician decide later which one)

I appreciate all the help on this and I think we are close. If i can just get the answers to these scenarios then i can get it built. Thanks.

 

@pcboss: OK, so are you saying that 250MCM will be OK and that it can go through a 2x6 inside a wall? What size hole does it need?

Also, can it be run outside the wall, attached to the surface? That will be in a location where there is no way any forklift is near it; inside a computer room and a narrow hallway.

 

I don't have access to my book today, However the 4/0 or 250 cm is going to need to be in conduit. You cannot run it like a cable.

 

I'd run it with MC cable over the top of the walls and then down a computer room wall and under the computer room floor to where ever it needs to go. If I were using conduit I'd route it the same way and not try to run it inside wood framed walls.