Backfeeding MBR sub panel.

[DaveTap]

I have an unusual theatre installation with a 200A portable dimmer rack and circuits for chain-motors installed to lift lighting trusses. The portable dimmer racks are to be connected using cam-locks and welding type cables to a fancy UL approved box that requires a disconnect for simultaneous opening and OCP. I also have to connect several chain-motors used for lifting the lighting truss that need to run while the racks are not powered. Wall space is limited and we have a SquareD 200A 3phase MBR lug through panel that I would like to use by connecting my feeders to the lugs and backfeeding the 200A MBR as the disconnect for the cam-locks while still keeping the bus live for the chain-motors.
If everything is clearly marked are there any NEC issues with this?

 

[mdshunk]

Forgive me, but what does MBR stand for? Master bedroom is the only thing that comes to mind for me.

EDIT... crap. Main breaker. Sorry.

 

[DaveTap]

Forgive me, but what does MBR stand for? Master bedroom is the only thing that comes to mind for me.

EDIT... crap. Main breaker. Sorry.

Don't feel bad Marc... I thought same thing when I first started in the forums.
But my question still stands... Is there anything wrong with backfeeding it this way?

 

[mdshunk]

110.3(B) seems to be the only thing that applies. I did look up what I could find on the Square D site, and there seems to be no special instruction that you must feed a feed through panel through the main. Therefore, I see no 110.3(B) violation. It would seem that as long as the feed connected to the bottom lugs has the appropriately sized OCPD, and what you connect to the 200 amp main can handle being fused at 200 amp, you have no problem.

I see what you propose as being no different than putting a 200 amp breaker in an MLO panel to feed that load. In your case, the 200 amp breaker seems to already be installed conveniently by the factory!

 

[LarryFine]

It's also important that the terminals of the breaker are not specifically identified with 'line' and 'load' or similar. Check the panel documentation, too.

Of course, another possible source for more info is Square D itself. If you need evidence that this would be NEC- and/or UL-compliant, that's where I'd look.

 

[mdshunk]

It's also important that the terminals of the breaker are not specifically identified with 'line' and 'load' or similar.

That sorta is the standard response. I did research Square D's breakers some time back when I got (wrongly) red-tagged for feeding the "bottom" of a molded case breaker type disconnect. It seems that the only one's they market at present that are labeled "Line" and "Load" are the one's that you install the rating strips into. My red tag was taken back.

 

[DaveTap]

Thanks Marc... I think you just saved me a dozen phone calls.

In your case, the 200 amp breaker seems to already be installed conveniently by the factory!

Not to mention free... since it was the panel I removed upgrading to a donated 400A panel which will now feed this one.

 

[don_resqcapt19]

Dave,

The portable dimmer racks are to be connected using cam-locks and welding type cables to a fancy UL approved box...

The use of welding cable would be a code violation.
Don

 

[DaveTap]

Dave,

The use of welding cable would be a code violation.
Don

I know... thats why I said welding type cables... They are individual stranded wires rated 600 VAC, but I'm not sure what type... Typically used for connecting large generators, rock concerts or in this case rented Syncrolites http://www.syncrolite.com/index.html DL's, XSpots http://www.highend.com/products/ and so on for temporary concerts and shows, under the supervision of EEs and electricians on their staff.

 

[don_resqcapt19]

Dave,
It may be Type W portable power cable, but in many cases welding cable is used in violation of the code. The portable cable provided with every large generator that I have ever rented was welding cable.
Don

 

[edamico11]

Dave

Dave

I use 2/0 awg sc-105c 600v, oil res, 60c water res per NEC Table 400-5(B) for 90C (this is printed on the cable) we call it Stage lighting cable, (also printed on the cable it says PPC-Stage lighting Cable.) Does this not fall under Article 590? BTW we use it in a 3 phase 5 wire @200amp situation..


oops I mean Article 520.. sorry

 

[DaveTap]

Dave,
It may be Type W portable power cable, but in many cases welding cable is used in violation of the code. The portable cable provided with every large generator that I have ever rented was welding cable.
Don

Yeah didn't know what else to call it that others would recognise, although I've seen a lot of welding cable used also. Its for my church and we're very safety conscious... so didn't want the cables running down through the trap door or stairs again.

I use 2/0 awg sc-105c 600v, oil res, 60c water res per NEC Table 400-5(B) for 90C (this is printed on the cable) we call it Stage lighting cable, (also printed on the cable it says PPC-Stage lighting Cable.) Does this not fall under Article 590? BTW we use it in a 3 phase 5 wire @200amp situation...
oops I mean Article 520.. sorry

I think thats what we have also... but when someone tells me stage lighing cable I picture SO cord with stage pins.

 

[Ronald Fenger]

Type of dimmers?

Type of dimmers?

Are the dimmers you are using high density dimmers? If they are is the panel you are hooking them up to have enough ampasity on the neutral? High density dimmers require doubling up on the neutral because of the 3rd order harmonics of a dimmer at a less than 100% output. If you dont have a properly sized neutral you will run into trouble.

 

[zbang]

Yeah didn't know what else to call it that others would recognise, although I've seen a lot of welding cable used also.[ /QUOTE]

Many people I know in the lighting trade still call it welding cable even though they replaced that stuff years ago. Otherwise it's "entertainment" cable or simply "feeder". Are contractor rental places still supplying real welding cable for power? The big outfits I've worked with (Kohler, Aggreko) don't.

I think thats what we have also... but when someone tells me stage lighing cable I picture SO cord with stage pins.

My problem there is that when someone says "stage plug", I think of the really old flat-contact jobbers, not the pin-type (AKA Bates) connectors. The old ones were fun. Came in half and full width versions, often with internal fuses and loose contacts .

(Side note: Some really old stages had floor connectors labeled "ARC". They were usually 125a DC feeds for portable arc lamps.)

 

[don_resqcapt19]

Are contractor rental places still supplying real welding cable for power? The big outfits I've worked with (Kohler, Aggreko) don't.

They do around here, at least one of the above does, because that is where I last rented generators from.
Don