System Furniture - 3PH Circuit Protection?

[ElectDesigner]

Quite often when office spaces are designed system furniture (desk and cabinets with receptacles and data outlets already built in) is specified, so naturally the designer provides either a wall or floor recessed junction box with a certain number of circuits. So on the plans it will be shown as a junction box with CCTS A.1,2,3 etc. The contractor would then connect the feeders from the furniture to the junction box.

Now, the other day I was looking at a design where the designer specified a 3PH connection to the junction box like A.1/3/5 - and on the panel schedule it is protected by a 3pole breaker - im just a bit confused here , I understand he needs three circuits to the jbox, but why from a 3pole breaker? I would have just provide three separate circuits - my reason being say the guy working at a workstation short a circuit, the breaker corresponding to that circuit will trip without affecting the other two circuits (say two other workstations). Im not sure why that specific desinger did this?

 

[infinity]

If it's a MWBC it requires simultaneous disconnect of all three circuits. Here's one such requirement:

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.

 

[Jraef]

... the breaker corresponding to that circuit will trip without affecting the other two circuits (say two other workstations). Im not sure why that specific desinger did this?

So that if one trips it WOULD affect the others. If an island of equipment needs more power than one breaker can provide and one breaker trips, then someone locks it out not realizing there are two more circuits there, they can get hurt. So if you use a 2 or 3 pole breaker (depending on how much power you need), one overloaded circuit causing a trip ensures that the entire island is safe when the breaker is locked off.

Similar to the dishwasher / garbage disposal issue under the sink.

 

[wiigelec]

Ever been shocked by an 'Edison' neutral?

 

[Sir4bz]

Safety and Value Engineering

Safety and Value Engineering

This install yeilds a slight cost savings in regards to copper. But, safety is the main driver of this design. People were still getting injured where additional separate circuits remained energized. Lawyers, lawsuits, settlements, insurance costs and injured employees aren't very cost effective either.

 

[iwire]

This install yeilds a slight cost savings in regards to copper. But, safety is the main driver of this design. People were still getting injured where additional separate circuits remained energized. Lawyers, lawsuits, settlements, insurance costs and injured employees aren't very cost effective either.

It is not about the number of circuits it is about the common neutral.

If the furniture was supplied with 3 two wire circuits a common disconnect would not be required.

 

[Sir4bz]

If the furniture was supplied with 3 two wire circuits a common disconnect would not be required.

I'm not disputing that. The OP was wondering what the designer's intention was regarding the
3-pole breaker, which will probably remain undisclosed. In response to that, since safety is such a major factor today, I based my response on the safety factor alone. I could be wrong, but doesn't the NFPA 70 E require that PPE be worn when working where there is live voltage present, other than voltage checks? I believe it's PPE or LOTO of all live voltage.