Multi wire circuits

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greg1147

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I am looking into an update in a cubicle area using six monster cables, four # 10s and 1 # 8 all fed from a 400 amp 3 ph 4 wire panel. One of the four phase conductors and one green is identified as an isolated ground even thought the panel is not equipped with a isolated ground bar. Do I need a tie handle for all four breakers. I am leaning toward yes, where are they available? Even though the furniture manufacturer identifies a system with an IG no provisions exist in the panel. The only problem so far is harmonics in on area of ten computers each with its own UPS, this being corrected. I thought facilities was going to easy!!!
Thanks Greg
 
First off is this a fix-type partition or a freestanding type partition?

605.6 for fixed partitions and 605.7 for freestanding type partitions.

Also if you have a freestanding partition that is cord and plug connect take a look at 605.8. This section does not permit multiwire branchcircuits.

Chris
 
You only need to handle tie the 3 hots that make up the multiwire branch circuit. The 4th two wire circuit can be on it's own single pole as it is not a multiwire branch circuit.
 
Dennis Alwon said:
I am reading this as one neutral for all four hot conductors. Is this correct?
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Good question, I have wired a lot of office partitions and have never seen that set up.

With the 3+1 circuit set ups normally you get this.

A Multiwire Circuit

Black 12

Red 12

Blue 12

white 10

Green 12

and a two wire circuit.

Pink 12

Gray 12

Green with yellow 12
 
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So the million dollar question. If this is 4 hots with one neutral is it a multiwire branch cir.? Obviously I believe it should have a 4 gang handle tie but I don't believe they make one.

Branch Circuit, Multiwire. A branch circuit that consists of two or more ungrounded conductors that have a voltage between them, and a grounded conductor that has equal voltage between it and each ungrounded conductor of the circuit and that is connected to the neutral or grounded conductor of the system.
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Dennis Alwon said:
So the million dollar question. If this is 4 hots with one neutral is it a multiwire branch cir.? Obviously I believe it should have a 4 gang handle tie but I don't believe they make one.
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It is not a multiwire branch circuit, two of the conductors will not have a voltage between them. I don't know what it would be, I am betting just a mistake. :smile:

In my experience the whole point of the 3+1 furniture is 3 'dirty power' circuits and 1 'clean power' circuit. Many times they come from separate panels and transformers. That would be interesting on a single neutral. ;)
 
iwire said:
It is not a multiwire branch circuit, two of the conductors will not have a voltage between them.
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So you have 2 - "A" phases and a "B" and "C" phase. Now you do have voltage between one of the "A" phases and "B" & "C" phases as well as the other "A" phase and "B" & "C" phases. What a mess....:D

I think if a common neutral is allowed with 2 conductors on the same phase then the art. 240.15(B)(1) may need to be re written

I don't know what it would be, I am betting just a mistake. :smile:
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:D:D-- definitely
 
The previous wiring method is obviously incorrect the circuit arrangement is three "hot" one neutral, one ground, and one "hot", one neutral, one ground; the later all marked with a orange tracer ID is IG. Then all return to the same panel and are terminated on the same neutral buss and grounding buss as all others which pretty much defeats purpose of the IG provisions. Sorry for misleading in the original post but the continuing repairs and code correction is becoming a second career, talk about overload.
 
greg1147 said:
The previous wiring method is obviously incorrect...
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Not so obvious to me. Actually appears obviously correct to me.

...the circuit arrangement is three "hot" one neutral, one ground, and one "hot", one neutral, one ground; the later all marked with a orange tracer ID is IG. Then all return to the same panel and are terminated on the same neutral buss and grounding buss as all others which pretty much defeats purpose of the IG provisions...
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IMO you are good to go... IF, and only if ...the panel is supplied directly and exclusively by a separately-derived-system (SDS) transformer. IG wire (insulated) goes all the way from green/orange wire to ground bus in panel with no connection to anything else.
 
As Bob stated in an earlier post you will need to handle tie the three circuit breakers feeding the MWBC portion of the partion feed ( 3 Hot conductors sharing the neutral)
210.4(B) &240.15(B)(1)

Joe
 
Smart $ said:
Not so obvious to me. Actually appears obviously correct to me.



IMO you are good to go... IF, and only if ...the panel is supplied directly and exclusively by a separately-derived-system (SDS) transformer. IG wire (insulated) goes all the way from green/orange wire to ground bus in panel with no connection to anything else.
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It will be, as of right now it returns to a JB and terminates with all other grounds. It will be corrected.
 
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