Grouping Neutrals?
Grouping Neutrals?
(OP)
Why is it not code to group neutrals according to the corresponding phases. 1,3&5 should have a seperate neutral as should 2,4&6 ect.. How can I be sure which breakers to shut off if I have to work on circuit#24 if it could be grouped with neutral#1?
RE: Grouping Neutrals?
If you shut off circuit #24, how would it get power from the neutral of another circuit?
RE: Grouping Neutrals?
This may be of some help, but you could check with the engineering department at Square-D or one of the companies that make distribution panels.
RE: Grouping Neutrals?
A common trip breaker would prevent this problem, but may cause other problems because all of the hots will be opened when there is a fault on any one of them. I think the best solution would be a code rule that requires the OCPDs that serve multiwire circuits be identified and that the grounded conductors be identified in the panel as to which hots they are associated with. I believe there are some proposals for the 2005 code that address this problem. The code making panel's action on these proposals is not available yet, but you can read the proposals at:
http://www.nfpa.org/nec/TheNEC/ROPsROCs/2003ROP/2003ROP.asp
Don Ganiere
RE: Grouping Neutrals?
Understand that this is being posted by a canadian electrician..I'm not sure of American colour codes. Red, black, and blue are all phases of a three phase system that can be grouped with one neutral but there are no requirements for proper groups of say 1,3&5 to be a specific group sharing the same neutral.
How does one know which red, black, blue is on a specific neutral if it is need a code requirement?
RE: Grouping Neutrals?
YOU DON'T
If the system was installed by a qualified electrician, the neutral should be properly marked at the neutral bus in the panel with all 3 numbers.
Get a cheap amprobe and clip it on ALL the wires under the wirenut of the neutral you are working on. If there is a current and your circuit is off, it is a shared neutral and treat it as such.
As for a code requirement, no there should not be one for the way we group circuits but i believe it would not be a bad idea to require all branch circuits be marked with their circuit numbers along with their neutrals in the panel and in all jboxes. Personally I mark them all including the neutrals and i also try to group them 1,3,5 but that only works on new construction.
RE: Grouping Neutrals?
If what resqcapt19 says is what you are actually working with, then you must open all the single-phase C/Bs associated with that neutral to be de-energized.
An important point: the recommendation by SteveHuck about checking with an amprobe is not safe. Just because there is no current flow, don't assume that there is no voltage. It just means that there is no load connected.
As far as a code requirement, for the NEC, I thought that this type of system was no longer used for branch circuits and individual neutrals were required because of harmonic loads.
RE: Grouping Neutrals?
Multiwire branch circuits are still in common use. Not all loads are nonlinear. In some cases the grounded conductor of a multiwire circuit is inscreased in size over that of the ungrounded conductors for nonlinear loads.
Steve,
Your comment about a "qualified electrican" marking the neutrals is not a common practice in my area. I do it and think that it is a good idea just for the reasons brought up in the original post, but it is not a code rerquirement and therefore many installers do not tag the neutrals.
Don
RE: Grouping Neutrals?
"In some cases the grounded conductor of a multiwire circuit is inscreased in size over that of the ungrounded conductors for nonlinear loads."
This is what we faced when wiring a new server room. SMPS's (in the servers and other computer equipment) are highly non-linear and can lead to substantial heating of the grounded conductor. We used MC with a "Superneutral" wire, where the three phases were 12ga wire and the neutral was 10ga.
Foxfur
RE: Grouping Neutrals?