Furniture Systems - 605

[ASG]

I'm do a lot of commercial office design and they are leaning more and more to open office spaces and furniture clusters. Due to 210.4(B), the office I am working at has a standard for using 2P breakers if it is a 2+2 furniture system. I was looking through the forum archives and 605 was brought up. I see in 605.9 it says that if it is a cord-and-plug connected system but I don't really run into those. But then 605.7 and 605.8 just say to use the wiring methods of Chapter 3. Which wiring methods are they referring to? Is this what we should be doing (multipole breakers instead of breaker ties) or is just personal preference?

 

[infinity]

The 2008 NEC said this regarding MWBC's:

605.7 Freestanding-Type Partitions. Partitions of the freestanding type (not fixed) shall be permitted to be connected to the building electrical system by one of the wiring methods of Chapter 3. Multiwire branch circuits supplying power to permanently connected freestanding partitions shall be provided with a means to disconnect simultaneously all ungrounded conductors at the panelboard where the branch circuit originates.

Since the requirement became redundant with the addition of the requirement in Article 210 it was removed from later code versions.

 

[ASG]

So does that mean we should be using 2 pole breakers or 4 pole breakers?

 

[GoldDigger]

So does that mean we should be using 2 pole breakers or 4 pole breakers?

I am not sure what you mean by 2+2. The applicable rule applies to MWBCs, in which two or more line conductors share a common neutral for line to neutral loads.
It does not apply to "branch" wiring which combines multiple circuits in a single set of ducts and connectors.
If there are several branch circuits, MWBC or not, in one partition wiring cable and duct system it may be a desirable design feature to use handle tires across all the supply circuits, but IMHO it is not required by code.

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[infinity]

I would guess that the 2+2 would be two MWBC's. Only the circuits sharing a single neutral are required to have a simultaneous disconnecting means.

This would be two MWBC's:

 

[GoldDigger]

I would guess that the 2+2 would be two MWBC's. Only the circuits sharing a single neutral are required to have a simultaneous disconnecting means.

This would be two MWBC's:

As a practical matter, though, I would turn off both circuits when working in the cubicle wiring.

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[infinity]

As a practical matter, though, I would turn off both circuits when working in the cubicle wiring.

Good practice but not (yet anyway) required by the NEC.

 

[ASG]

I am not sure what you mean by 2+2. The applicable rule applies to MWBCs, in which two or more line conductors share a common neutral for line to neutral loads.
It does not apply to "branch" wiring which combines multiple circuits in a single set of ducts and connectors.
If there are several branch circuits, MWBC or not, in one partition wiring cable and duct system it may be a desirable design feature to use handle tires across all the supply circuits, but IMHO it is not required by code.

Sent from my XT1585 using Tapatalk

Furniture systems are most typically 2+2 which means there are 4 circuits and 2 of them share a neutral(2 hots on one neutral, 2 hots on the other). The second most common is 3+1 (3 hots on one neutral, one with a dedicated neutral).

 

[GoldDigger]

Furniture systems are most typically 2+2 which means there are 4 circuits and 2 of them share a neutral(2 hots on one neutral, 2 hots on the other). The second most common is 3+1 (3 hots on one neutral, one with a dedicated neutral).

That confirms infinity's analysis that you have two independent MWBCs, and the code lets you use two independent two pole breakers OR two pairs of single breakers with a handle tie for each pair.

I am guessing that the 3+1 came up in reaction to computer loads of old which were very non-linear. It also would have to be fed from a three phase panel.

 

[GoldDigger]

I would guess that the 2+2 would be two MWBC's. Only the circuits sharing a single neutral are required to have a simultaneous disconnecting means.

This would be two MWBC's:

Does that diagram really mean what it seems to show, namely that the two neutrals and two grounds are internally connected in the system? I sure hope not!
Bad, evil drawing. Sad.

 

[infinity]

Does that diagram really mean what it seems to show, namely that the two neutrals and two grounds are internally connected in the system? I sure hope not!
Bad, evil drawing. Sad.

I think that the portion to the left of the line of vertical dots is at the source.