MWBC Disconnect

Status
Not open for further replies.
N

Npstewart

Senior Member
I have a small exterior structure that requires (3) circuits. I was going to run a MWBC to the structure. The MWBC will be fed from a existing panel in another structure. Technically I don't need a fused disconnect. How would this work? Is there a such thing as a device rated as service equipment (225.36) that can be used to disconnect the whole MWBC? Am I correct in thinking it doesen't have to be fused? Dont have my NEC at home so any help would be appreciated.
 
The OCPD at the circuit origination is all you need for your protection. However, you would need a disconnect at the separate structure. You can use (2) SP switches or (1) SPDT switch.

225.33 (B)
 
Can you define SPDT switch? Is this just a snap switch? I have (3) circuits by the way, not two.

So I guess I would start at the panel with my MWBC, terminate in a junction box and feed the snap switches, then feed the loads. Then, because this is a MWBC supplying one structure I wouldn't need a GEC, just a EGC.


Just to clarify, this is commercial.
 
Unless the whole installation falls under Exception 1 to 225.32 (establish switching procedures and monitored by qualified personnel), 225.33(B) would allow you to use a 3 pole switch** or 3 single pole switches with handle-tie. No GEC is required as long as we are talking about a MWBC.
(emphasizing branch circuit)

** Edwards post shows the most common method I see
 
augie47 said:
Unless the whole installation falls under Exception 1 to 225.32 (establish switching procedures and monitored by qualified personnel), 225.33(B) would allow you to use a 3 pole switch** or 3 single pole switches with handle-tie. No GEC is required as long as we are talking about a MWBC.
(emphasizing branch circuit)

** Edwards post shows the most common method I see
Click to expand...

And if it a 3 phase MWBC.
If single phase MWBC you can't do it because it is gonna be 2 circuits. 2 hots and a neutral and 1 hot and a neutral.
 
qcroanoke said:
And if it a 3 phase MWBC.
If single phase MWBC you can't do it because it is gonna be 2 circuits. 2 hots and a neutral and 1 hot and a neutral.
Click to expand...

agreed... I assumed :D He said it was commercial and from the quality of his posts he is most likely familiar with the definition of a MWBC.
 
225.31 Disconnecting Means.

Means shall be provided for disconnecting all ungrounded conductors that supply or pass through the building or structure.
Click to expand...

225.36 Suitable for Service Equipment.

The disconnecting means specified in 225.31http://code.necplus.org/document.ph...s:70-2011:id02011002562#70-2011:id02011002562 shall be suitable for use as service equipment.

Exception: For garages and outbuildings on residential property, a snap switch or a set of 3-way or 4-way snap switches shall be permitted as the disconnecting means.
Click to expand...

I don't see that a snap switch is acceptable other than for outbuildings on residential property, disconnect must be suitable for use as service equipment.
 
I am supplying (3) 120v loads total; two receptacles circuits and a lighting circuit. I am certain that the switch has to be rated for service equipment. Is that Leviton switch suitable for service equipment?
 
kwired said:
I don't see that a snap switch is acceptable other than for outbuildings on residential property, disconnect must be suitable for use as service equipment.
Click to expand...

Yes, and I agree. While we don't know if the OP is talking of a residential application, no matter how you cut it based on needing 3 circuits he will need to treat this as a feeder. That in turn will require a feeder with an EGC, GES at the out building and a main disco.
 
texie said:
Yes, and I agree. While we don't know if the OP is talking of a residential application, no matter how you cut it based on needing 3 circuits he will need to treat this as a feeder. That in turn will require a feeder with an EGC, GES at the out building and a main disco.
Click to expand...
OP stated it was not residential.

If you had three phase service to a residential application, I don't see why you couldn't use a 3 pole snap switch as disconnect for an outbuilding if fed with a 4 wire MWBC.

Note the exception says "residential property" and does not use the word "dwelling". So does that mean a property with a dwelling or dwellings? Or does it mean residential as in how zoning laws see it? NEC does not define "residential"
 
kwired said:
OP stated it was not residential.

If you had three phase service to a residential application, I don't see why you couldn't use a 3 pole snap switch as disconnect for an outbuilding if fed with a 4 wire MWBC.

Note the exception says "residential property" and does not use the word "dwelling". So does that mean a property with a dwelling or dwellings? Or does it mean residential as in how zoning laws see it? NEC does not define "residential"
Click to expand...

First, I missed the OP's second post that it is not "residential". That said, I don't it changes anything-it is a building/structure that needs to be fed by a feeder and must comply as such.

Even if it was "residential", show me a residence that is supplied with a 208/120 Y service that would allow this to happen. Yes, I've seen many residences supplied with 240/120 3 phase 4 wire, but that still would not allow 3 circuits without making it a feeder.:)
 
texie said:
First, I missed the OP's second post that it is not "residential". That said, I don't it changes anything-it is a building/structure that needs to be fed by a feeder and must comply as such.

Even if it was "residential", show me a residence that is supplied with a 208/120 Y service that would allow this to happen. Yes, I've seen many residences supplied with 240/120 3 phase 4 wire, but that still would not allow 3 circuits without making it a feeder.:)
Click to expand...

I have worked on some pretty moderate residences when it comes to $500K to maybe around $1 million, but never on a really large multimillion dollar residence. If I ever do, I would think 120/208 would probably be considered as a lot of the time it is easier to balance loads on this type of system when majority of loads are 120 volts. But then we may even be looking at enough mechanical loads that 480 volts is considered for service voltage in some cases. I would still probably use 120/208 for lighting panels though if service were 480 volts.
 
texie said:
no matter how you cut it based on needing 3 circuits he will need to treat this as a feeder. That in turn will require a feeder with an EGC, GES at the out building and a main disco.
Click to expand...

texie said:
First, I missed the OP's second post that it is not "residential". That said, I don't it changes anything-it is a building/structure that needs to be fed by a feeder and must comply as such.

Even if it was "residential", show me a residence that is supplied with a 208/120 Y service that would allow this to happen. Yes, I've seen many residences supplied with 240/120 3 phase 4 wire, but that still would not allow 3 circuits without making it a feeder.:)
Click to expand...

A MWBC is a single circuit and would not need a GES

225.30 Number of Supplies.Where more than one building or other structure is on the same property and under single management, each additional building or other structure that is served by a branch circuit or feeder on the load side of the service disconnecting means shall be supplied by only one feeder or branch circuit unless permitted in 225.30(A) through (E). For the purpose of this section, a multiwire branch circuit shall be considered a single circuit.
Click to expand...

250.32 Buildings or Structures Supplied by a Feeder(s) or Branch Circuit(s).(A) Grounding Electrode. Building(s) or structure(s) supplied by feeder(s) or branch circuit(s) shall have a grounding electrode or grounding electrode system installed in accordance with Part III of Article 250. The grounding electrode conductor(s) shall be connected in accordance with 250.32(B) or (C). Where there is no existing grounding electrode, the grounding electrode(s) required in 250.50 shall be installed.

Exception: A grounding electrode shall not be required where only a single branch circuit, including a multiwire branch circuit, supplies the building or structure and the branch circuit includes an equipment grounding conductor for grounding the normally non?current-carrying metal parts of equipment.
Click to expand...

Roger
 
Ok. So it seems as though a snap switch will work to terminate the 3 conductors + a neutral into and from what it looks like a MWBC is considered a single circuit therefore I dont need a GEC, just a EGC.

Does anyone know of a snap switch that is rated as service equipment that I can use for this installation?
 
I have been looking through catalogs and have not found one. I did note that some of the air-conditioner pull out fusible disconnects are service rated. That might be an option or, of course, just a 3 pole fusible safety switch.
 
Npstewart said:
Ok. So it seems as though a snap switch will work to terminate the 3 conductors + a neutral into and from what it looks like a MWBC is considered a single circuit therefore I dont need a GEC, just a EGC.

Does anyone know of a snap switch that is rated as service equipment that I can use for this installation?
Click to expand...

You are not going to find such a thing. A switch that is rated as service equipment means that it has provisions to bond the neutral to the enclosure (main bonding jumper).

The requirement for the switch to be rated for service equipment should have been removed when they removed the exception that allowed bonding the neutral at the separate structure instead of running an EGC.
 
What if I went from 3 ungrounded + neutral to 2 ungrounded conductors + a neutral. Would I have any more options? I would like to have (3) 120v circuits out there but if I have to install a whole panel out there then its not worth it.
 
Status
Not open for further replies.
Top