Shared Neutral Question

[LarryFine]

As far as MWBC's go, I guess it really depends on the application. In my HT system, I have a normally-wired 50a sub-panel in my closet, and six 15a circuits supplying the various electronics.

I did make sure most of the audio components are on the same phase, though. On phase A: two future lighting circuits, the projector, and the subwoofer amps. On phase B: all of the audio electronics.

My system is quiet with no signal. There's no hiss or hum with zero signal. There are two 14ga speaker wires, a shielded cable, and a 14-2 NM in a stud space for each subwoofer amp, and they're very quiet.

To me, there's no difference between two individual circuits that originate in a panel supplied by a shared neutral, and two circuits that share a neutral. Only the lengths of the BC conductors are different.

 

[Power Tech]

In the Costco's IG panels I have serviced.

The branch 120V, 20 amp circuits feeding the cash registers all have #10 dedicated neutrals.

Have no idea if this is related to the OP.

 

[LarryFine]

The branch 120V, 20 amp circuits feeding the cash registers all have #10 dedicated neutrals.

Dedicated, as in no MWBC's, and they still upsized the groundeds? And then, only them? That's weird.

 

[76nemo]

Took me two pages to catch on:roll: Rehearsal rooms,...I was thinking dressing rooms. Yeah, I'd of ran more than one 20A to a rehearsal room for sure. I didn't see what the fuss was about, but the key word was rehearsal IDIOT.

Not easy being simple:roll:

 

[iwire]

Simple, the magic is the lower impedance of the neutral bus and feeder as opposed to the comparatively "wimpy" #12 or #10 wire. Lower impedance = less resistance to harmonics and noise.

That is hardly true as the neutral in MWBC carries less current and therefore less voltage drop then the grounded conductor in a two wire circuit.

As per our earlier debates, I offer over 20+ years of experience in audio systems wiring, and so far IN EVERY CASE I've encountered with MWBC's there were problems of noise, early equipment failures and other issues which were SOLVED by pulling in dedicated neutrals.

And I am saying that is absolutely imposable unless there where other issues.

Draw it out on paper and try to explain how the location of the OCPD in relation to the point where the neutral 'splits' changes anything as far as hum.

As I have also conceded before, there are times and places that MWBC's are perfectly acceptable..but audio installations are NOT one of them!! :grin:

And other than your personal opinion you have provide no facts to prove that to be true. Don't get upset about this, it is only truth.

LOL did you read what the OP is up against? I have spent a lot of time working with bands and they NEVER have enough power available, if there is an empty socket somewhere they're gonna stick something in it. :grin:
And guitar and bass amps are power hogs.

OK, here I will surprise you and agree, in this case where we can not predict or control circuit loading MWBCs might not be the best way to go. It is remotely possible that all legs of the MWBC could all be loaded to the max with non-linear loads and in that case the current on the neutral might exceed the branch circuit rating. Of course it would not exceed the actually 310.16 rating of the conductor.

But if I was supplying a permanent rack of power amps I would have no problem supplying it with MWBCs.

Tony, I know you have already made up your mind but it appears you have made up your mind based on your gut and not on science.

Show me some proof and I will back off.

 

[Power Tech]

Dedicated, as in no MWBC's, and they still upsized the groundeds? And then, only them? That's weird.

No MWBC. I am assuming it was a spec. when the stores were built.

I only serve 4 so I don't know if it is all of them.

The Walmart I service is an ex Broadway. Nothing dedicated there. Most of the wiring is original (1050's).

I am constantly pulling Coke machines, fans etc. from the critical circuits on the UPS.

 

[iwire]

Most of the wiring is original (1050's).

Thats an old Walmart.:grin:

 

[Power Tech]

Thats an old Walmart.:grin:

Now that I think about it. It may be 1964, steel flex, EMT, and TW.

I say this because the FD wrote them up for no light in the stairwell. An old magnetic ballast stamped 1964. Put lamps in and they struck.

Spooky on the 4th floor, its like going back in time.

Old mogul base bulbs and ("T-14"?) fluorescent fixtures.

 

[iwire]

1050.

 

[Power Tech]

1050.

Just caught that.

I can still see clear in my shooting eye.