Continuity and Handle Ties- Fun with multiwire branch circuits.

Continuity and Handle Ties- Fun with multiwire branch circuits.

I have stated this before that I am not a big fan of multiwire branch circuits (MWBC) in residential wiring. But it is an approved practice and as home inspectors we need to be aware of them and some of the unique characteristics of this wiring method.

Multiwire branch circuits (MWBC) need special attention. The NEC has recognized this and made changes to the codes to reflect some of it.

In the 2008 NEC it became required that all MWBC need to have a simultaneously disconnect (i.e. handle ties or single handle double pole breaker). This was a change from previous version where this was only required for MWBC on a single yoke such as a duplex receptacle.

2008 NEC-

210.4 Multiwire Branch Circuits. (B) Disconnecting Means. Each multiwire branch circuit shall be provided with a means that will simultaneously disconnect all ungrounded conductors at the point where the branch circuit originates.

From the 2005 NEC-

210.4 (B) Devices or Equipment Where a multiwire branch circuit supplies more than one device or equipment on the same yoke, a means shall be provided to disconnect simultaneously all ungrounded conductors supplying those devices or equipment at the point where the branch circuit originates.

This requirement was due to the fact that MWBC circuits can be dangerous and can result in shock if all of the ungrounded conductors (hots) are not de-energized when working on equipment or devices supplied by a multiwire branch circuit.

I recommend handle ties for all MWBC no matter what the age is as a matter of safety.

Another issue is the grounded conductor or more commonly called the neutral. Special care is needed to ensure that continuity is always present for the neutral. If for some reason the neutral becomes severed where the MWBC diverges into individual circuits this can turn the MWBC into in a 240v circuit. So if the continuity of the neutral conductor of a MWBC is interrupted (opened), the resultant of which will be an over- or under voltage than can cause fire and/or destruction of electrical equipment.  

I was doing a little research to find out when a pigtail was first required for the neutrals.  A pigtail connection consists of an electrical wire used to connect two or more wires that will feed a device such as a receptacle that will maintain continuity of the circuit before the device. The National Electric Code requires that you have a minimum of six inches of wire.

So the answer for the pigtail requirement goes all the way back to 1971.

Now as home inspectors we may not know of this has been done but you should be aware of this.

I think it is prudent to let your clients know of these circuits are present and that due care is needed. I know this is outside of the standards but to me the standards are a place to start not stop.

“If you think it's expensive to hire a professional to do the job, wait until you hire an amateur.”

Red Adair

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