700.10(B) - Separation Questions

Status
Not open for further replies.

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
120 foot long string of 12' long LED linear fixtures. Every third one is an egress light. There is an empty chamber (intended for power wiring) that runs the length of each fixture, and that connects to the similar chamber of the next fixture in line. Questions:
  1. If there is a barrier running the length of the chamber, can I take credit for it as providing the independence required by 700.10(B) between the normal circuit wires on one side of the barrier and the emergency circuit wires on the other side of the barrier?
  2. If that answer is "no," and I suspect it is, then can I omit the barrier, run the normal circuit wires within the chamber, and run the emergency circuit wires in the same chamber but using type MC cable?
 

Smart $

Esteemed Member
Location
Ohio
I too was leaning towards "no"... but then I recalled...
410.64 Luminaires as Raceways. Luminaires shall not be
used as a raceway for circuit conductors unless they comply
with 410.64(A), (B), or (C).

(A) Listed.
Luminaires listed and marked for use as a raceway
shall be permitted to be used as a raceway.

(B) Through-Wiring.
Luminaires identified for through-
wiring, as permitted by 410.21, shall be permitted to be
used as a raceway.

(C) Luminaires Connected Together.
Luminaires designed
for end-to-end connection to form a continuous assembly,
or luminaires connected together by recognized
wiring methods, shall be permitted to contain the conductors
of a 2-wire branch circuit, or one multiwire branch
circuit, supplying the connected luminaires and shall not be
required to be listed as a raceway. One additional 2-wire
branch circuit separately supplying one or more of the connected
luminaires shall also be permitted.
So are you saying the barrier is furnished as part of the fixture?

Do the instructions say wiring can be run on either side of the barrier?

Are the fixtures listed or identified per the above?
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
My boss brought this question to me, as it relates to one of his projects. My initial response was to wonder whether the fixtures were listed for having normal and emergency wiring in separate chambers. I tend to doubt that they are. That is what brought the question about using MC cable into the discussion. Assuming the fixture is listed to be used as a raceway, what I want opinions on is whether I can take credit for MC cable as being the way to keep normal and emergency wiring independent of each other.
 

Smart $

Esteemed Member
Location
Ohio
... Assuming the fixture is listed to be used as a raceway, what I want opinions on is whether I can take credit for MC cable as being the way to keep normal and emergency wiring independent of each other.
IMO, no... not when run in the same raceway that contains normal conductors. The emergency load wiring is not "entirely independent of all other wiring and equipment".
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
The emergency load wiring is not "entirely independent of all other wiring and equipment".
That is the essence of the question. If there were a short circuit in the normal circuit wiring internal to the fixture, would the metal that surrounds the emergency circuit wiring internal to the MC cable protect the emergency circuit wiring, and prevent it from being damaged? More to the point, is MC cable listed for such a purpose? I don't see anything in the "uses permitted" or "uses not permitted" that answers this question.

 

steve66

Senior Member
Location
Illinois
Occupation
Engineer
What's wrong with the barrier? It separates the emergency circuit, and that's the intent.

I also believe MC cable would be enough separation. It's a wiring method in its own right.

Of course, with that argument, you could also say a 3 conductor line cord provides enough separation. I'm on the fence with that one.

I don't believe a properly protected 20A lighting circuit could have a short severe enough to damage the emergency wiring on the other side of a barrier, or emergency wiring in a MC Cable.
Not unless the OCP failed at the same time a short occurred, and I think that's pretty unlikely.
 

Smart $

Esteemed Member
Location
Ohio
That is the essence of the question. If there were a short circuit in the normal circuit wiring internal to the fixture, would the metal that surrounds the emergency circuit wiring internal to the MC cable protect the emergency circuit wiring, and prevent it from being damaged? More to the point, is MC cable listed for such a purpose? I don't see anything in the "uses permitted" or "uses not permitted" that answers this question.

I would say in most cases, the armor would protect the EM conductors... but that's just it, "most cases" is not "all cases". Also, it's not a matter of permitted and not permitted uses of MC. More to the point, running the MC in the fixture is not independent of normal wiring and equipment. You would actually have EM wiring included in the normal wiring method and in the normal equipment. That is about as far from independent as it could possibly be. The only thing less independent is using single conductors.
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
More to the point, running the MC in the fixture is not independent of normal wiring and equipment.
Actually, that is the point that I am trying to resolve one way or the other.

You would actually have EM wiring included in the normal wiring method and in the normal equipment.
I'm sorry, but I do not understand what you are saying here. Let's take the light fixture out of the discussion, and talk instead about a surface-mounted raceway (SMR).

  • If I put two runs of MC cable in a length of SMR, one with normal circuit wires and the other with emergency circuit wires, are the two sets of wires independent, in the context of 700.10(B)?
  • If that is a "no," then this issue can be put to bed right now.
  • If that is a "yes," then take the normal wires out of their MC cable and run them as single conductors in the same SMR as the MC cable with its emergency circuit wires. Here again I ask, are the two sets of wires independent, in the context of 700.10(B)?
  • If that is a "no," then this issue can be put to bed right now.
  • If that is a "yes," then how is this different from running single conductors (normal circuit) and MC cable (EM Circuit) within the designated raceway portion on a long light fixture any different?

 

LIM

Member
Location
NC
120 foot long string of 12' long LED linear fixtures. Every third one is an egress light. There is an empty chamber (intended for power wiring) that runs the length of each fixture, and that connects to the similar chamber of the next fixture in line. Questions:
  1. If there is a barrier running the length of the chamber, can I take credit for it as providing the independence required by 700.10(B) between the normal circuit wires on one side of the barrier and the emergency circuit wires on the other side of the barrier?
  2. If that answer is "no," and I suspect it is, then can I omit the barrier, run the normal circuit wires within the chamber, and run the emergency circuit wires in the same chamber but using type MC cable?

If the barrier is present you are fine. Wiremold is done like this on regularly. Same as separating line and low voltage wiring. As far as #2 I would be comfortable with that as long as you had the proper terminations at each emergency fixture to keep the wiring truly separate.
 

iwire

Moderator
Staff member
Location
Massachusetts
I install and work on a ton of linear lighting and I would love to see an example of linear lights with two distinct wiring chambers.

The odd thing is if we wire in the field we have to keep the separation but if we order prewired plug and play fixtures that are a UL listed system they can run EM and normal together.
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
. . . but if we order prewired plug and play fixtures that are a UL listed system they can run EM and normal together.
Let me ask, then, can you get a UL listed system that has ten or more fixtures in a line, with every third one being an EM fixture, and that has "plug and play" connections for both normal and EM wiring from fixture to fixture, and that has one point of connection for the two power sources at one end of the string? That is essentially what the electrical contractor for this project wants to do. The alternative is to run parallel conduits along the ceiling, each run hitting junction boxes along the way, with vertical conduits dropping down at appropriate intervals to hit the normal and EM light fixtures. The owner wants to avoid having all that conduit visible to the people walking by.

 

iwire

Moderator
Staff member
Location
Massachusetts
Let me ask, then, can you get a UL listed system that has ten or more fixtures in a line, with every third one being an EM fixture, and that has "plug and play" connections for both normal and EM wiring from fixture to fixture, and that has one point of connection for the two power sources at one end of the string?

Very common for us to do just that, the latest ones will have a single plug to connect the fixtures together containing normal, emergency and 0-10 volt dimming conductors.

It always struck me odd that a factory could mix them but as you described we would have to jump through hoops to do the same thing.

Honestly, my personal opinion is that mixing them is a bad design but the money savings makes it attractive.
 

Smart $

Esteemed Member
Location
Ohio
Actually, that is the point that I am trying to resolve one way or the other.

I'm sorry, but I do not understand what you are saying here. Let's take the light fixture out of the discussion, and talk instead about a surface-mounted raceway (SMR).

  • If I put two runs of MC cable in a length of SMR, one with normal circuit wires and the other with emergency circuit wires, are the two sets of wires independent, in the context of 700.10(B)? Yes
  • If that is a "no," then this issue can be put to bed right now.
  • If that is a "yes," then take the normal wires out of their MC cable and run them as single conductors in the same SMR as the MC cable with its emergency circuit wires. Here again I ask, are the two sets of wires independent, in the context of 700.10(B)?
    No
  • If that is a "no," then this issue can be put to bed right now.
  • If that is a "yes," then how is this different from running single conductors (normal circuit) and MC cable (EM Circuit) within the designated raceway portion on a long light fixture any different?

Answer within quote.
 
Status
Not open for further replies.
Top