Correct grounding of metal junction box w/splices for 3 circuits

[Noah Katz]

I have 3 circuits (microwave, disposal, and dishwasher) entering a metal box where the THHN wire will be spliced to Romex.

I spent half an hour reading 2020 NEC Article 250 but didn't see multiple circuits specifically addressed.

To ground the box do I just need to pigtail off of one circuit's ground wire and attach to the box, or do I pigtail all 3 circuits' ground wires together?

In case you're wondering, the conduit is metal, which I believe is sufficient for grounding, but I don't trust all of the mechanical joints nor the fittings' set screws.

 

[Megawatt]

I'm not talking grounds vs. neutrals.

Two people said there was a hazard in connecting the neutrals from different circuits together.

They're already connected together at the panel neutral bar, so how is the hazard created?

If you have more than 1 circuit sharing neutrals and you turn 1 breaker off to work on it the neutral will still have voltage on it from the other circuits sharing that same neutral. That’s the danger they are talking about

 

[Cookie]

After further thought, I realize I really don't see the hazard in pigtailing all of the neutrals together, since they're all connected together at the neutral bus bar in the panel.

What am I missing?

A neutral that is supposed to be dead, would now be live to whom ever is working on it. This is not to code.

 

[Paul92688]

If the circuits are separate then keep the neutrals separate, joining them all together can create a hazard for anyone working on the circuits if they are not all isolated.

While it is not definitive, his first line is "I have three circuits..." I would take that to mean 3 individual circuits. If not, then I would expect it to be 1 circuit.

Paul

 

[Noah Katz]

Hmm, I didn't get a reply notification; anyway

A neutral that is supposed to be dead, would now be live to whom ever is working on it. This is not to code.

How could a neutral be anything but dead when it's grounded at the panel?

Regardless, the crux of the matter which no one has addressed, is how it can make any difference if the neutrals are tied together at a junction box when they're already tied together at the panel.
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While it is not definitive, his first line is "I have three circuits..." I would take that to mean 3 individual circuits. If not, then I would expect it to be 1 circuit.

I definitized it a bit later on:

These are three separate circuits as required by 2020 NEC, each on it's own breaker, black/white/green THHN runs for each.

 

[davesparks]

Regardless, the crux of the matter which no one has addressed, is how it can make any difference if the neutrals are tied together at a junction box when they're already tied together at the panel.

In a normal circuit if a fault develops in the neutral then the circuit will stop working,someone will notice and get it fixed.
In your proposed arrangement if a fault develops in one of the neutrals the circuit will continue to work due to the other two neutrals being linked to it, however the fault will cause those two neutrals will be overloaded, but nobody will notice due to everything working. This overload could then lead, ultimately, to a fire.

Any GFCI (RCD) installed now or in the future to protect the circuit will trip instantly due to the imbalance caused by the joining of the neutrals.

Anybody working on the installation in the future will be unaware of this arrangement being in place, expecially considering it is specifically prohibited by your electrical code.

 

[Cookie]

Hmm, I didn't get a reply notification; anyway



How could a neutral be anything but dead when it's grounded at the panel?

Open a neutral under load, and it will float up to 120 volts.

 

[Noah Katz]

@davesparks Solid points, thanks very much for taking the time to explain.

@Cookie Hmm, yes it will if it gets disconnected at the ground end; another good point, thanks.

 

[davesparks]

Open a neutral under load, and it will float up to 120 volts.

Yes, normally that would happen on the load side of the break.
However the proposed situation of joining three neutrals together would prevent the voltage rise from occurring, but it would overload the other two neutrals.

 

[Cookie]

Yes, normally that would happen on the load side of the break.
However the proposed situation of joining three neutrals together would prevent the voltage rise from occurring, but it would overload the other two neutrals.

Yup, that is unless someone shut down the microwave circuit un-doing the wire nuts thinking they are all dead. This is why the NEC requires any branch circuit sharing a neutral be equipped with listed handle ties or a multi pole breaker.

 

[Cookie]

Here is a good read on why MWBC need handle ties:

Independent Electrical Contractors

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