Control/Dimming Shared Neutral

[Aaron S.]

Good morning everyone. Let me ask an opinion and advice.

I'm working a show set in an apartment on a turn table. We have practicals throughout the house. Wall sconces, recessed lighting, and wall outlets.

I have soca running to the turntable that powers some lepi packs.

My main issue right now is this: The wall outlets want to be 2 cir each. Top and Bottom. The shop that built the set only ran 1 - 12/3 cable through the walls. Some of the outlets want both of the cir to go to the lepi packs, while others want 1 cir to a lepi pack and the 2nd to a Non dim.

Can I/is there a better solution - Have 2 hots running through the 12/3 and share the neutral? If so, what would that look like at the lepi pack side? Would I just "2-fer" the neutral between the 2 connectors going into the dimmer pack?

I know this will leave me with ungrounded circuits. I'm just not seeing another option at this point.

Thanks for your help.

 

[SteveB]

Grounding is a code requirement and as far as I can remember, you cannot share neutrals on single phase branch circuits.

Run a 2nd 12/3 cable and be done with it.

 

[BillConnerFASTC]

The ground is required so you're stuck with that but if the dimmer pack is a single 15 or 20 amp feed - as some leprecon packs are - I don't see a problem with a shared neutral - code wise.

If just one or two that need separate dimmed and non-dim at one outlet, I'd probably look for a dimmer that could be used at the outlet and just feed constant power, of course that depends on a lot of other "ifs" like concealing the dimmer, data, etc.

 

[RonHebbard]

Good morning everyone. Let me ask an opinion and advice.

I'm working a show set in an apartment on a turn table. We have practicals throughout the house. Wall sconces, recessed lighting, and wall outlets.

I have soca running to the turntable that powers some lepi packs.

My main issue right now is this: The wall outlets want to be 2 cir each. Top and Bottom. The shop that built the set only ran 1 - 12/3 cable through the walls. Some of the outlets want both of the cir to go to the lepi packs, while others want 1 cir to a lepi pack and the 2nd to a Non dim.

Can I/is there a better solution - Have 2 hots running through the 12/3 and share the neutral? If so, what would that look like at the lepi pack side? Would I just "2-fer" the neutral between the 2 connectors going into the dimmer pack?

I know this will leave me with ungrounded circuits. I'm just not seeing another option at this point.

Thanks for your help.

@aaron S. Hoping against hope. By any chance did your shop run metal-clad 12/3 cable where you can legally use the metal cladding as your ground conductor? In Canada, we called the cable BX and its waterproof version was called BXL (Lead) prior to the demise of lead sheathing within the metal cladding. I believe on your side of Donald's walls you have "Metal Clad" where we have BX, no longer being conversant with your NEC I could be wrong.
Toodleoo!
Ron Hebbard

 

[SteveB]

The ground is required so you're stuck with that but if the dimmer pack is a single 15 or 20 amp feed - as some leprecon packs are - I don't see a problem with a shared neutral - code wise.

If just one or two that need separate dimmed and non-dim at one outlet, I'd probably look for a dimmer that could be used at the outlet and just feed constant power, of course that depends on a lot of other "ifs" like concealing the dimmer, data, etc.

As a re-read, is a “lepi” pack a Leprecon ?. Than as Bill noted, some of these can run on 208v. Big caveat is you need a 120/208 supply with a 2 pole breaker feeding and should use a 12/4 - hot, hot, neutral, ground

 

[RonHebbard]

@SteveB Back in 1996 our shop in Oakville, Ontario, Canada built two modular decks approximately 120' wide by 60' by two feet thick intended to leap-frog their way across North America with an international tour of Andrew Lloyd Webber's "Sunset Boulevard". The designers specified three Leprecon six or eight dimmer packs with each pack powered by dual line cords via dual magnetic breakers. The dimmers were to tour and be plugged into their niches within the touring decks where they were to power only practicals within the mansion proper. In theory the cast could close in one city after a Saturday evening performance, rest Sunday, travel Monday and open Tuesday evening in a new city. Most of the set, including a touring version of the mansion (built to 80% scale and 50% weight) was to be dealt with by a separate advance crew who'd spend a week setting up the alternate deck in the new theatre then return to the previous venue to strike and truck their other deck. The last I saw of the two decks, we shipped them to Denver where the cast were to hold final rehearsals before commencing their tour. In reality, the EXPENSIVE modular aluminum decks with their 3/4" or 1" thick Arburon modular surfaces were warehoused in Denver when critics upset Mr. Webber by having the gall to pooh pooh another of his productions, "Whistle Down The Wind" I believe, during its out of town previews in Boston causing Mr. Webber to pull his plans to tour "Sunset Boulevard" and close all of his North American productions for a period of time.
To drag this back to the Leprecon dimmer packs, we replaced all of their dual 20 Amp parallel blade males with four contact Hubbell twist-locks such that each pack was powered by two phases of three phase 120 / 208 power distributed within the decks with the internal distro's fed by 3 phase 5 wire 125 amp mini-cams. To this moment I still have a red T shirt presented to me by the head carpenter of the tour's advance crew. Those two decks were MASSIVE, EXPENSIVE and comprised one of the best touring sets our shop ever built.
Toodleoo!
Ron Hebbard

 

[JD]

Often, 12/3 refers to a 4 conductor cable if Romex or metal clad. 12/3 in portable S/SO would usually mean 3 conductors. For whatever reason, in the US the term 12/2 with ground became the standard for 3 conductor Romex/BX (as compared to 12/2 without.) At some point the "with ground" was dropped as all Romex/BX had a ground run. Therefore 12/2 = 3 conductors, 12/3 = 4 conductors.

 

[Aaron S.]

Often, 12/3 refers to a 4 conductor cable if Romex or metal clad. 12/3 in portable S/SO would usually mean 3 conductors. For whatever reason, in the US the term 12/2 with ground became the standard for 3 conductor Romex/BX (as compared to 12/2 without.) At some point the "with ground" was dropped as all Romex/BX had a ground run. Therefore 12/2 = 3 conductors, 12/3 = 4 conductors.

12/3

 

[BillConnerFASTC]

Image not showing for me.

 

[RonHebbard]

Often, 12/3 refers to a 4 conductor cable if Romex or metal clad. 12/3 in portable S/SO would usually mean 3 conductors. For whatever reason, in the US the term 12/2 with ground became the standard for 3 conductor Romex/BX (as compared to 12/2 without.) At some point the "with ground" was dropped as all Romex/BX had a ground run. Therefore 12/2 = 3 conductors, 12/3 = 4 conductors.

@JD Up here north of Donald's walls oldsters still refer to BX and Romex although younger folk no longer refer to Romex and speak of NMD7 which appears to be nylon jacketed equivalent.
Lead jacketed three conductor 13K8 and 27K6 now THOSE were cables worthy of respect. During my apprenticeship I was part of a crew pulling literally miles of 13K8 lead jacketed and 27K6 TEK or TEC, I've forgotten the precise abbreviation, through 4" underground fiber duct between poured concrete manholes, or person holes if you prefer.
Toodleoo!
Ron Hebbard

 

[RonHebbard]

Often, 12/3 refers to a 4 conductor cable if Romex or metal clad. 12/3 in portable S/SO would usually mean 3 conductors. For whatever reason, in the US the term 12/2 with ground became the standard for 3 conductor Romex/BX (as compared to 12/2 without.) At some point the "with ground" was dropped as all Romex/BX had a ground run. Therefore 12/2 = 3 conductors, 12/3 = 4 conductors.

@JD What about HPN appliance cord typically found on toasters and kettles? Up here north of the walls two conductor HPN contained two conductors with one conductor having colored threads next to the copper and a ridge molded along one outside edge of the jacket. This qualified as the "identified conductor", or neutral. Three conductor HPN was similar with a thinner gauge green jacketed conductor molded down the centre in between the other two conductors.
Toodleoo!
Ron Hebbard

 

[JD]

@JD What about HPN appliance cord typically found on toasters and kettles? Up here north of the walls two conductor HPN contained two conductors with one conductor having colored threads next to the copper and a ridge molded along one outside edge of the jacket. This qualified as the "identified conductor", or neutral. Three conductor HPN was similar with a thinner gauge green jacketed conductor molded down the centre in between the other two conductors.
Toodleoo!
Ron Hebbard

The ridged neutral on appliance cord is the same down here. As the old instructions go, the ridge should be connected to the wider pin on parallel plugs (presumed neutral) and connected to the shell of the lamp socket. Yea, don't bet on that one!

 

[Jay Ashworth]

What JD said: when you tell me 12/3, I assume you have a cable with 4 wires in it, unless you tell me "no ground". I, too, got it from Romex work, and I don't know if the practice carries over to the SO we use on a stage or not, but it's always good to specify "w/g" or "n/g", to avoid confusion.

 

[SteveB]

What JD said: when you tell me 12/3, I assume you have a cable with 4 wires in it, unless you tell me "no ground". I, too, got it from Romex work, and I don't know if the practice carries over to the SO we use on a stage or not, but it's always good to specify "w/g" or "n/g", to avoid confusion.

I’ve never seen any SO or SJ refered to as 12/2 with ground and I’ve never seen any SO or SJ indicated as “12/3” and having 4 wires inside. The actual jacket label states “12/3” and means H, N & G.

 

[BillConnerFASTC]

I’ve never seen any SO or SJ refered to as 12/2 with ground and I’ve never seen any SO or SJ indicated as “12/3” and having 4 wires inside. The actual jacket label states “12/3” and means H, N & G.

I agree. It's the difference between portable cables and building wire. If the set had been (and could be by code) 12/3 NM (romex) would provide three conductors plus a bare ground wire. SO and similar portable cables are not labeled that way. (The nomenclature works if you only count insulated conductors.)

 

[SteveB]

I agree. It's the difference between portable cables and building wire. If the set had been (and could be by code) 12/3 NM (romex) would provide three conductors plus a bare ground wire. SO and similar portable cables are not labeled that way. (The nomenclature works if you only count insulated conductors.)

Curious as when NM is allowed on a temporary set ?. Installed in enclosed walls maybe ?. Never seen that, not even on a double sided and finished set wall

 

[BillConnerFASTC]

That's why I added if it could be by code - meaning if it could be.

Now, I'm sure it's been done, as in "ground be damned I need two hots and a neutral on a 12/3 SO."

Just trying to explain nomenclature.

 

[Jay Ashworth]

Indeed; "uninsulated ground" is almost certainly the code trigger there.

 

[Dover]

Both building wire and portable cord are actually described the same way. The leading numbers refer to the gauge and number of full voltage insulated conductors in the assembly, the suffix "w/ ground" denotes the inclusion of an un-insulated non-voltage rated grounding wire of adequate size for the maximum current of the insulated wires. The description "12/3 SOOW" only states that there are 3 12ga voltage rated wires in the cable, it does not guarantee that one of the wires is green, the reverse is also true for Romex, 12/3 Romex could be describing a cable with black, white and green.
There are exceptions in the code that would allow for a cable with out a ground or for the green wire to be used as a current carrying wire but these generally only apply to industrial machinery and none are not applicable here.

 

[Les]

12/3 Romex could be describing a cable with black, white and green.

Anything I've known to be 12/2 Romex to be black/white/bare, with black/white/red/bare being called 12/3 (and their #14 variants in residential use).

I use the term Romex loosely of course, since I'm really just referring to Thermoplastic-sheathed cable.