What is the correct connections for a Murray MP215AFC breaker for a Split A/C unit

Question

I seem to be running into a never to be found answer on the wiring for this 240 2 pole combination AFC breaker.

I have a Split unit wired L1 & L2 with a ground back to the sub panel not a neutral. The breaker requires a Neutral panel connection for the coiled up white wire. It also requires the L1 & L2 to be hooked up to the breaker. I'm all good with this but, it wants the neutral LOAD from the A/C unit back into the breaker's Load Neutral which i don't have.

I am not using a neutral but i am using a ground return that is tight to the ground bus bar of the panel. I can not see plugging in the ground return to the Load Neutral connection of the breaker. That makes no sense to me.

Murray's information seem to point to leaving the Load neutral connection empty and keep the A/C ground on the panel ground. No one has been able to clarify this. I know the AFCI rules may not apply to 240 V circuits but I want to protect this anyway. I found a similar GE breaker which has NO neutral load return on the breaker but i just want to hear it from an expert.

Answer 1

Use whatever terminals you need. For instance if you were using this breaker on a 120V circuit, hook up neutral and one hot*, and leave the other hot empty. If using on a 240V only circuit, yes - simply hook up the hots and leave neutral empty. 0 current will flow, and the device will correctly compute differential currents (for its GFCI functionality).

There's one asterisk. The AFCI needs neutral to power itself. So you need to hook up the neutral pigtail. We figured this out when helping a Philippine resident set up GFCI protection for some bathroom circuits; they use North American style equipment but with neutral omitted. In that case we had to add a small transformer to synthesize a 120V center-point (quasi-neutral) to power the AFCIs. We couldn't use ground because neutral is not ground.

It is good that you realize not to misuse ground to fill the empty terminal in the breaker. If you had connected ground to both the ground bar and LOAD neutral, it would have tripped. If you had connected ground to ONLY the breaker, fault current would be misrouted through the AFCI causing too high an impedance for prompt breaker trip, and the GFCI section of this AFCI would see that fault current as normal current, breaking GFCI. So I'm glad you had the horse sense not to do that.

For reference, neutral is not ground, they have completely different jobs, and entangling/confusing them breaks their safety jobs. The confusion often arises because people see the neutral-ground equipotential bond in the main panel, and this bond is often done informally e.g. with grounds and neutrals going to the same bar. You'll never see that in a panel I do; I prefer bonds I can put a clamp meter around.

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* wait what? What? Use this breaker on a 120V circuit!?? Yes, you can use a 240V breaker to power one or two independent 120V circuits. In fact, when people have a need for a 30A/120V circuit, I recommend they use a 30A/2-pole breaker, because those have many other applications, and a 30A/1-pole has almost no practical use.

Answer 2

You are correct

For Siemens/Murray (as well as Square D and Eaton) AFCIs, you wire them the same way you would a GFCI breaker, as internally they have significant GFCI heritage, and in fact can and will trip on a gross ground fault.

So, for a 240V-only load like your A/C, wire the neutral pigtail to the neutral bar, the hots to the hot lugs, the ground to the ground bar, and leave the load neutral lug unconnected.