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Old 03-16-2010, 08:03 PM   #16
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Originally Posted by Stubbie View Post
You must have a neutral not a grounded leg to have an MWBC.
Huh? Could you explain further?
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Old 03-16-2010, 08:46 PM   #17
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See post #2

Multiwire branch circuits have a shared neutral that serves two hot wires not one. A grounded leg of a 120 volt or 277 volt single phase 2 wire branch circuit carries all the current of the single hot wire and is therefore not a neutral. A mwbc shares a grounded leg that serves to carry the unbalanced current (difference between) two hot legs of opposite ends of the transformer. This makes the grounded leg a neutral wire ...neutrals carry the diffence in current of two or more ungrounded conductors.

Just becasue a branch circuit has multiple wires does not make it an MWBC...

You need this to have a mwbc voltage has nothing to do with it.
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Last edited by Stubbie; 03-16-2010 at 08:49 PM.
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Old 03-16-2010, 08:53 PM   #18
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Very nice, Stubbie. Thanks.
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Old 10-22-2010, 02:36 PM   #19
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Quote:
Originally Posted by kbsparky View Post
277 Volts from a MWBC would involve using a 480 Volt source. Not exactly a DIY project.
Not all that worse than European projects, where originally 240v countries get its power from 415Y/240 sources.

There was a lawsuit somewhere in which someone was hurt when something happened to him involving a leg and a ground on 277v lighting wiring in the state of California. The worker wasn't trained for working over 300v and lawyer argued that 277v is part of 480v, thus exceeding his <300v training, but the judge threw that out.
http://ecmweb.com/mag/electric_dangers_working_hot/
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Old 10-22-2010, 03:07 PM   #20
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480/277
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Old 10-22-2010, 03:10 PM   #21
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Quote:
Originally Posted by Stubbie View Post
A two wire with ground 277 volt branch circuit is no more a MWBC than a two wire with ground 120 volt circuit. You must have a neutral not a grounded leg to have an MWBC.
the neutral is the grounded leg.the ground wire is the grounding wire.per code.
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Old 10-22-2010, 08:19 PM   #22
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One hot wire and one neutral wire (for example standard U.S. 120 volt circuit) -- Not a MWBC.

Two hot wires and no neutral wire (for example a 240 only volt heating circuit in the U.S.) -- Not a MWBC.

In a 277/480 volt symmetric (wye) 3 phase circuit/service, if you are supplying the lights using two or all three of the hot lines along with the neutral, then you ahve a MWBC. If you use just one of the hot wires and the neutral, you do not have a MWBC supplying the lights.
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Old 10-28-2010, 03:50 AM   #23
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Quote:
Originally Posted by AllanJ View Post
One hot wire and one neutral wire (for example standard U.S. 120 volt circuit) -- Not a MWBC.

Two hot wires and no neutral wire (for example a 240 only volt heating circuit in the U.S.) -- Not a MWBC.

In a 277/480 volt symmetric (wye) 3 phase circuit/service, if you are supplying the lights using two or all three of the hot lines along with the neutral, then you ahve a MWBC. If you use just one of the hot wires and the neutral, you do not have a MWBC supplying the lights.
I couldn't remember the name of it, but what about a duplex on opposing poles with shared linkage on neutral side and jumper removed on hot side so that top and bottom are on opposing poles?
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Old 10-28-2010, 05:39 AM   #24
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Originally Posted by HVAC_NW View Post
I couldn't remember the name of it, but what about a duplex on opposing poles with shared linkage on neutral side and jumper removed on hot side so that top and bottom are on opposing poles?
There is no name for that. It is simply a MWBC to a device where two circuits are sharing the same yoke.
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