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Mike Lamb

Tied Circuit Breakers

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The electrician in this rehab tied random adjacent 120V breakers to each other with a piece of wire.  Any logical reason to do this?

PB030106AA.JPG

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It looks like someone was trying to tie together the halves of multi-wire circuits. 

They missed a few and, of course, it would be better to use real handle ties. 

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I'd write it up.  Someone might come along and not understand why they're there and take them off. At some point later, the breakers of a single MWC end up on the same pole, overloading the neutral and perhaps causing a fire.

Edited by Marc

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12 hours ago, Marc said:

Someone might come along and not understand why they're there ...

Like me. My grasp of electricity is not the greatest.  Many questions here.

So the tied breakers in question are sharing the same neutral? And if one breaker trips you want both to trip so the neutral cannot be overloaded?  And the ties should not be removed?  And tying the two breakers together with something other than electrical wire should be done?

I also had to look up the acronym MWC. Minor Work Certificate?  That would mean someone other than a licensed electrician did the work?

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17 hours ago, Mike Lamb said:

But why?  And is it a bad idea?

With a multi-wire circuit, if you were to cut power to one breaker and not the other (or others in the case of 3-phase systems) and then attempt to work on the circuit, the live neutral could bite you. That's why the 2008 NEC began requiring a simultaneous disconnect at the circuit's breakers. (Before that you only needed a simultaneous disconnect when different parts of the multi-wire circuit fed two receptacles on the same yoke.) 

My guess is that this installation pre-dated the 2008 requirements but someone decided to try to make it safer anyway. (Maybe a home inspector told them to do it.)

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1 hour ago, Mike Lamb said:

So the tied breakers in question are sharing the same neutral? And if one breaker trips you want both to trip so the neutral cannot be overloaded?  And the ties should not be removed?  And tying the two breakers together with something other than electrical wire should be done?

In your picture, each set of tied breakers (and some sets that aren't tied) form "mult-wire circuits" (MWCs). 

These save wire by using 3 wires (instead of 4) to serve 2 circuits. To do this, the 2 breakers must originate on different poles of the system, so their power is 180-degrees apart (for a single-phase system). In this way, the shared neutral only carries the difference in current between the two circuits. Long ago, there was no rule about having a simultaneous disconnect between the two breakers (or fuses). The danger of a system like this is that if you cut power to one half of the circuit you could still be shocked by the current on the neutral from the other half of the circuit. In 1981, MWC breakers had to be tied together only for those circuits where both halves of the circuit delivered power to two receptacles on the same yoke. (Often the dishwasher and disposer.). Then, in 2008, all MWC breakers had to be tied together. The ties are there to ensure a *simultaneous disconnect*, not a *common trip*; its still possible for the breakers to trip independently. 

The danger that Marc referred to is that someone might re-arrange the breakers in the panel, unaware of the presence of MWCs. If you were to move the breakers or wires such that two halves of a MWC originated on the *same* pole, then the shared neutral would not carry the difference in current, but rather the sum of the current. This could overload the neutral and cause it to burn. By installing formal handle ties, you also signal to future amateurs that these two breakers "go together." 

 

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