Inspecting multiwire circuits in the panel

Status
Not open for further replies.
D

Dan Smith

New member
Dear Mike,

Is there an easy method for inspecting 15- and 20-amp residential multiwire branch circuits in the panel to insure that if they require a handle tie, they have one and that they're not on the same phase? With red and black conductors running all over the place in some panels, I'm concerned that I'm missing these two problems.

Regards,
Dan Smith
 
Well, first I think you need to wait until the 2008 NEC comes into force in your area. Until then, unless your local jurisduction has special rules of its own, there is no requirement for handle ties on a MWBC. As to having a MWBC for which each phase conductor originates from the same phase, I do not know an easy way to detect that situation.
 
If you have a multiwire branch circuit supplying a device on the same yoke, i.e. a dishwasher/disposal outlet, you would be required to simultaneously disconnect both circuits. See 210.4(B). A 2-pole breaker or approved handle tie would work.
 
Dan Smith said:
Dear Mike,

Is there an easy method for inspecting 15- and 20-amp residential multiwire branch circuits in the panel to insure that if they require a handle tie, they have one and that they're not on the same phase? With red and black conductors running all over the place in some panels, I'm concerned that I'm missing these two problems.

Regards,
Dan Smith
Click to expand...

The handle tie issue isn't critical enough to lose sleep over. . If you catch it, you catch. . If you don't, you don't.

But the phasing issue is very important to prevent doubled neutral currents.

For residential single phase multis, intercept each red at the breaker and pull it out of the wire maze until you find it entering a cable. . Grab the black from the same cable and trace it back the other way to its breaker.

If you're dealing with piped HRs, there's no good way that I know of to independently verify properly wired multis. . Communication with the specific installor [not just the contractor] is the only way.

I think that's the best you can do.

David
 
barbeer said:
Why 2008 code? will there be a new requirement?
Click to expand...

Yes,

210.4(B) Disconnecting Means. Each multiwire branch circuit shall
have a means to simultaneously disconnect all ungrounded
conductors at the point where the branch circuit originates.

Chris
 
Esthy said:
In think 2008 requires ALL multiwiring circuits be in a double pole breaker
Click to expand...

This section doesn't require a double pole breaker only means to simultaneously disconnect all ungrounded conductors. You can use a identified handle tie on multiple single pole breakers and meet the requirements of this section.

Chris
 
inspecting MWBC

inspecting MWBC

When I can't trace the panel wiring down to my satisfaction, I usually use my "clamp-on" on the neutral (assuming we have some loads connected) and switch the questionable breakers to see if the neutral loads react accordingly.
 
Dan Smith said:
With red and black conductors running all over the place in some panels, I'm concerned that I'm missing these two problems.
Click to expand...


my advice is the same to everyone, whenever possible put the monkey on someone else.

When you look in a panel that appears to be a mess just make a suggestion that they have it checked out by a qualified electrician.

I have worked with several home inspection companies and the only time I have ever seen them get in trouble is when they try to do things themselves.

Pass the buck it's the American way.
 
raider1 said:
This section doesn't require a double pole breaker only means to simultaneously disconnect all ungrounded conductors. You can use a identified handle tie on multiple single pole breakers and meet the requirements of this section.
Click to expand...

This is correct. The requirement is for manual de-energization, not over-current protection.
 
There will also be a requirement that you tape (or similiar) the nuetral to the ungrounded conductors of a multiwire circuit in the panel, unless the grouping is obvious. Obvious would include a single cable, or a single MWBC in a raceway.
 
raider1 said:
Yes,

210.4(B) Disconnecting Means. Each multiwire branch circuit shall
have a means to simultaneously disconnect all ungrounded
conductors at the point where the branch circuit originates.

Chris
Click to expand...
So then when that goes into effect, no more using 3 single pole 20amp breakers sharing a neutral. Has to be a 3 pole 20amp? Is this what you are saying??
 
chevyx92 said:
So then when that goes into effect, no more using 3 single pole 20amp breakers sharing a neutral. Has to be a 3 pole 20amp? Is this what you are saying??
Click to expand...

That's pretty much it. You can still use 3 single poles if you install an approved handle tie to connect all 3.
 
kpepin said:
That's pretty much it. You can still use 3 single poles if you install an approved handle tie to connect all 3.
Click to expand...
IMO that change isn't a very good one. We have been doing good all these years without it and now all of a sudden they want to change it? So now instead of shutting 1 breaker to work on a few rows of lighting, you will be shutting 3 breakers at a time shutting more than needs be and causing more potential problems.
 
raider1 said:
Yes,

210.4(B) Disconnecting Means. Each multiwire branch circuit shall
have a means to simultaneously disconnect all ungrounded
conductors at the point where the branch circuit originates.

Chris
Click to expand...


Is it just me or does this new requirement really stink?
 
Has the change been made with the issue of personnal safety in mind.
If you break a neutral splice with the shared circuit you wont get shocked or even electrocuted.
 
This is just another unnecessary requirement, kind of like reidentifying a white conductor in a cable assembly.

Roger
 
Status
Not open for further replies.
Top