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-   -   Line to line load on a MWBC? (http://www.diychatroom.com/f18/line-line-load-mwbc-125858/)

rjniles 12-07-2011 08:52 AM

Line to line load on a MWBC?
 
I am in the process of replacing my existing 120 volt,3/4 HP well pump with a 240 volt, 1HP pump. The pump is is a small pump house about 60 feet from the house (and the sub panel that powers it). The power is supplied by #12 THWN wire in PVC conduit (black, white and green conductors). I also have a light and a receptacle in the pump house; the pump is hard wired.

I am considering pulling in a red #12 THWN conductor, installing a 2 pole 20 amp breaker in the sub and creating a 20 amp MWBC. The pump would be hard wired as a line to line load and the light & receptacle connected as line to neutral loads.

Looking at NEC 210.4 (C), I am not sure this is allowed. The article says a MWBC shall have only line to neutral loads but the exception seems to allow a line to line load if there is only 1 piece of using equipment (the pump). The 20 amp circuit has more than enough capacity for the intended loads.

The question is can I use my MWBC for both my 240 volt pump and the 120 volt light & receptacle?

SD515 12-07-2011 09:22 AM

210.4(C) Exception No. 2: Where all ungrounded conductors of the multiwire branch circuit are opened simultaneously by the branch-circuit overcurrent device.

I read that as yes, you can, though I would pull 2 more wires for the pump only and add the 2-pole 20A. Then the light & recpt can be independent, so you can shut down the pump to work on it, and still have light and power for tools.

SD515 12-07-2011 09:23 AM

Edit to above post: No different than a modern stove or dryer using 240V for the heating elements and 120V for the timers, etc.

rjniles 12-07-2011 10:51 AM

Quote:

Originally Posted by SD515 (Post 788082)
210.4(C) Exception No. 2: Where all ungrounded conductors of the multiwire branch circuit are opened simultaneously by the branch-circuit overcurrent device.

I read that as yes, you can, though I would pull 2 more wires for the pump only and add the 2-pole 20A. Then the light & recpt can be independent, so you can shut down the pump to work on it, and still have light and power for tools.

SD515,

Thanks for the conformation. The problem with pulling in 2 more conductors and having the pump on its own circuit is that I violate the requirement not to have more than 1 circuit or feeder to an outbuilding.
I plan on haviong 2 disconnects in the pump house. 1 to cut off all power and a 2nd to isolate the pump for maintence while keeping the light and receptacle working.

SD515 12-07-2011 11:01 AM

Oops…you’re right about the outbuilding. Good idea with the 2 discos.

Missouri Bound 12-07-2011 12:22 PM

Is the sub-panel in the pump house?..If so you can just feed it with a larger circuit and go from there. You will need to replace the feeder with appropriate size wiring for the circuit amperage you choose.

rjniles 12-07-2011 04:18 PM

Quote:

Originally Posted by Missouri Bound (Post 788200)
Is the sub-panel in the pump house?..If so you can just feed it with a larger circuit and go from there. You will need to replace the feeder with appropriate size wiring for the circuit amperage you choose.

No sub in the pump house, just a 20 amp 120 volt branch circuit that I will upgrade to a 20 amp MWBC. I will never need more capacity than that will provide.

frenchelectrican 12-08-2011 03:31 AM

The key issue you may snag is the pressure switch location if you have the pressure switch at the pump house then the plain jane MWBC will work very well with your plans but if you have the pressure switch in the house that can change a bit so let us know what you have there.

Merci,
Marc

rjniles 12-08-2011 06:14 AM

Marc,
Thanks for your concern but the pressure switch is mounted on the pump (in the pump house).

AllanJ 12-08-2011 06:14 AM

The 20 amp MWBC is a standard feed between two buildings where a MWBC is the most efficient way of bringing the power to the outbuilding.

I don't have the NEC handy at this moment but I never read that a subpanel is needed for a 20 or fewer amp feed just because there are both 120 and 240 volt loads out there.

But you might want to run heavier feed wires in case a future owner of the property wants more power out there (and installs a subpanel out there before upping the main panel breaker set).

frenchelectrican 12-09-2011 06:57 AM

Quote:

Originally Posted by rjniles (Post 788796)
Marc,
Thanks for your concern but the pressure switch is mounted on the pump (in the pump house).

A simple single MWBC will do the job just fine and get a A/C pullout switch that will serve as your disconnect source { the NEC code did mention it have to be simuationed to be disconnected } I think there is other ways to do it but I will have to take a closer look at the codes to see what else to be workable to your situation.

Merci,
Marc

rjniles 12-09-2011 07:21 AM

Planning on using 2 of these:

http://www.homedepot.com/catalog/pro...6afa58_300.jpg

60 amp non-fused pull out.

One as the MWBC enters the pump house and the second to isolate just the pump.

As for adding more capacity, this is a 6' by 6' shed about 5' high at the ridge. It contains the jet pump and the pressure tank. I live in coastal South Carolina so any freezing concerns are covered by the 60 watt light bulb. I don't see a me or any future owner doing anything else with this structure.

frenchelectrican 12-09-2011 07:25 AM

:yes:

That will work very well and they are cheaper than two pole switch btw but only one part is you have to watch out is the netural at the first pullout switch so you will have to make a floating connection for netural while the ground { bare } will be allready landed to the bussbar on the top of it { If I recall the Midwest pullout are in that fashion while Milbank pullout verison is floating verison }

Merci,
Marc

rjniles 12-09-2011 08:09 AM

Marc,
Again thanks for the feedback. I realize I will have to float the neutral (wire nut white to white) in the pullout.

I prefer to use a pull out for a disconnect as I can put it my pocket and no one can flip it back on.


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