Multiwire branch circuits - Fixed type partitions

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deek5

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According to NEC 605.6, Multiwire branch circuits supplying power to the partition shall be provided with a means to disconnect simultaneously all ungrounded conductors at the panelboard where the branch circuit originates.

My question is as follows. Most office furniture is prewired as either 4 circuit/8 wire or 5/circuit, 8 wire. The panelboard manufacturers that I have contacted, Siemens, Cutler-Hammer, Square D, provide handle ties to trip up to (3) individual circuit breakers. Is there a way to simultaneously trip 4 or 5 breakers?

Thanks,
Ken
 
Re: Multiwire branch circuits - Fixed type partitions

You have to realize that what you are describing is more than one Multi-Wire Branch Circuit.

You would need more than one set of breakers for this installation, and Multiple Circuits would not need to be joined together with handle ties, only the ungrounded conductors that made up the individual Multi-Wire Branch Circuits .

Remember a Multi-Wire Branch Circuit is one circuit.

Roger

[ November 03, 2005, 03:13 PM: Message edited by: roger ]
 
Re: Multiwire branch circuits - Fixed type partitions

I would add that if the furniture is wired with separate neutrals for each circuit than you can use all single pole CB's.
 
Re: Multiwire branch circuits - Fixed type partitions

Thank you for the responses.

I don't think I explained my question correctly.

We have a 4 circuit, 8 wire (4 phase conductors, 2 neutral conductors and 2 ground conductors), prewired at the furniture factory, furniture system. We provide (4) individual 20A single pole breakers to that furniture partition. The code requires that all (4) circuit breakers trip simultaneously. Manufacturers can only provide handle ties for up to (3) 20A-1P breakers. How do we trip all (4) circuit breakers simultaneously?

Thanks again, Ken
 
Re: Multiwire branch circuits - Fixed type partitions

Manufacturers can only provide handle ties for up to (3) 20A-1P breakers. How do we trip all (4) circuit breakers simultaneously?
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You don't. If you have 2 separate 3 wire, multiwire branch circuits. Each one would get a 2 pole CB. The code requires each multiwire branch circuit to simultaneously disconnect. Not all of the circuits at once.
 
Re: Multiwire branch circuits - Fixed type partitions

Originally posted by deek5:
We have a 4 circuit, 8 wire (4 phase conductors, 2 neutral conductors and 2 ground conductors), prewired at the furniture factory, furniture system.
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Ken, each neutral is shared by two hot wires, right? That means you have two individual 3-wire (aka multi-wire) circuits. All you need is a 2-pole breaker or handle-tied pair of breakers for each 2-hot-&-1-neutral group.

It is not necessary to disconnect both multi-wire circuits simultaneously. It is important, however, to be able to identify the two hots and single neutral for each group, which you would anyway to make sure the two hots are on opposing phases.
 
Re: Multiwire branch circuits - Fixed type partitions

Another scenario for an 8 wire furniture system would be A-B-C phases with 1 neutral and a fourth circuit with it own neutral. This would require one 3 pole CB for the multiwire and a single pole CB for the dedicated circuit.
 
Re: Multiwire branch circuits - Fixed type partitions

I think my confusion is whether 4 circuit furniture is considered a multi-wire branch circuit.

Per NEC article 100, a branch circuit is the conductors from the over-current protection to the outlet. Per 210.4 multiple circuits serving one piece of equipment (office furniture) is considered a multi-wire branch circuit. Per 605.6 all multi branch circuits supplying furniture shall be simultaneously disconnected. Most major furniture manufacturers provide the 4 circuit furniture. When there are more than three circuits required there is no way to comply with this requirement without using a shunt trip, contactor or relay panel to simultaneously disconnect all 4 poles. It appears to me that 605.6 was modified in the 2005 NEC to protect maintenance personnel. Without intimate knowledge of how the furniture is wired an unsuspecting person might only trip 3 out of the 4 branch circuits. They then proceed to work on the furniture thinking they turned off the power and end up getting electrocuted from the fourth branch circuit. Handle ties are not UL listed for more than two single pole breakers, and therefore can not be used on a 4 circuit furniture feed. Nor can using a combination of 2 pole breakers be used since they can not disconnect the multi-wire branch circuit simultaneously. This change leads me to believe that when we encounter 4 circuit furniture we need to provide a shunt trip, contactor or relay panel and associated control (properly labeled) to comply with 605.6.


Ken
 
Re: Multiwire branch circuits - Fixed type partitions

Ken, you have more that one circuit. You are only required to simultaneously disconnect the ungrounded of each circuit.

605.6 Fixed-Type Partitions
Wired partitions that are fixed (secured to building surfaces) shall be permanently connected to the building electrical system by one of the wiring methods of Chapter 3. Multiwire branch circuits supplying power to the partition shall be provided with a means to disconnect simultaneously all ungrounded conductors at the panelboard where the branch circuit originates.
 
Re: Multiwire branch circuits - Fixed type partitions

If this still baffles you after all the explanations given above, just go outside and turn off the main breaker for the building. Now your 8 circuits are all off simultanously. :D
 
Re: Multiwire branch circuits - Fixed type partitions

Deek,

You're not understanding the requirement. You only need to simultaneously disconnect the circuits that are multiwire branch circuits which by definition are circuits that are sharing a neutral. With a 4 circuit/8 wire furniture partition this would require either two 2 pole CB's or one 3 pole and a single pole. The NEC does not require you to disconnect all of the circuits to the partition at the same time. Only those circuits that sharing a neutral.

Look at these examples:

Circuit A & B sharing a neutral = 2 pole CB
Circuit C & D sharing a neutral = 2 pole CB


Circuit A & B & C sharing a neutral= 3 pole CB
Circuit D separate neutral = 1 pole CB


Hope this helps.

Trevor
 
Re: Multiwire branch circuits - Fixed type partitions

Thank you all for your help.

I understand now what the code requires.

I thought the code wanted all 4 or 5 circuits to trip together so a tech doesn't think he is safe if he trips only one of the breakers for the office furniture.

Thanks,
Ken
 
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