Floating Neutrals

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Old 02-22-19, 08:23 PM
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Floating Neutrals

I'm in the process of renovating my very first restaurant.

A background of my experience (at least for the electrical aspect), I have installed full Lutron Lighting systems from Radio Ra2 where you replace individual light switches/dimmers, to Lutron Homeworks Panels. I've also installed/retrofit new electrical outlets and I've added new breakers into panels (though never replaced a breaker panel from scratch).

Most of my electrical work, since I'm not a Journeyman Electrician, and am more focused on the Audio/Video/Programming side, has been residential grade with an occasional retrofit to add an Electrical Outlet for a TV on a wall in a commercial building.

My current project has a 600 amp, 3 phase, 4 wire Main with 3-200 amp 4 wire panels, 1-60 amp 4 wire panel, and 1-100 amp 4 wire sub panel.

My question is; in Southern California, where codes are extremely strict, what are the guidelines on sharing a neutral between more than one breaker on the same panel in a 110 application? I have multiple locations that have 3-5 circuits and only a couple of neutrals in the conduit. From my understanding, floating a neutral on a 3 phase panel can cause voltage issues on the neutral if both circuits aren't balanced with each other, and one shorts to neutral, thus causing damage, or a fire in the other side of the circuit. That said, even if I balance the loads properly, this is a Restaurant. I may be running a Coffee Machine at one moment, a Toaster another, and there is no guarantee that both will be running simultaneously when a short occurs.

Any time I've done commercial lighting, I've had a dedicated Neutral on each circuit. In this situation, I'm trying to avoid having to pull all existing conduit runs back that have more than one circuit, and add additional neutrals, as well as the larger pulls. In addition, depending on the run, there is the possibility that the conduit may not be rated for the additional neutral conductors I would need.

I asked my inspector, and rather than him telling me what he wanted to see, he basically said that if I don't know the answer to that, I need to hire an electrical engineer. Considering this job went from a simple $100k and we are open, to now close to $600k due to the mickey mouse bull**** the prior tenants pulled, and I'm perfectly capable of safely performing the work, I just need the proper direction to know if something like sharing the neutral will meet code or not, I'm not about to spend another $50k+ for an Electrical Engineer to do what I can do. As it is, I'm already having to re-load balance the panel, as my ******* of an Architect ignored the information I gave him and decided to redo the panels as though this is new construction, directing circuits that are in conduits to the kitchen from Panel A to places like the bathrooms, and circuits in Panel C that are in the bathrooms, to the kitchen.

I understand electricity. I respect electricity. The Architect threw in my face that I'm not an Electrical Engineer, so I need to follow HIS load balanced panel configs.. I kicked back at him that HE is ALSO not an Electrical Engineer, and while he draws **** out on paper, I actually perform the tasks and make them work in the real world, so he shouldn't talk down to me like I'm some novice. I'm sure the guy couldn't even wire a standard NEMA 15 outlet.

Anyways, I digress. While I will admit that I don't know all codes, I've been in the technical industry for 20+ years, and have been on more construction site projects than I can count. This is why I'm here asking for some more details on shared Neutrals, as I'm not afraid to ask if I don't know, rather than just doing and crossing my fingers. Help me to do it right, without telling me to hire an electrician, please?
 
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Old 02-22-19, 08:49 PM
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When done properly it is code to share a neutral.
In a home split phase panel the neutral can shared between two circuit on opposite legs of the service with a double pole breaker.
I am no 3 phase expert but the same principal applies. I am pretty sure you can do it with a triple breaker on all three phases and one neutral. I am less sure but I think it is ok to do with a double pole breaker on two phases.
 
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Old 02-22-19, 09:01 PM
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A double pole breaker would be a 220 circuit. Of course this would share a single neutral as it's a single circuit.

I'm talking about doing 2 single pole circuits sharing a single neutral line. For example, Outlet A: Plugged into a Toaster is in slot 1 of Panel A, and Outlet B: Plugged into a Waffle Iron is in slot 3 of Panel A. Since both circuits are running through the same conduit, I'd have a black, red, white, and green wire. Green for Ground of course, Black for Slot 1 of Panel A. Red for Slot 3 of Panel A, and Neutral shared between both circuits.

I have quite a lot of these conduit runs in half inch conduit throughout the building. I'd hate to have to backpull every one of these and add a second neutral to each line. I know I can share the ground, but I'm not so sure that it's code to share the Neutral on these lines anymore.
 
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Old 02-22-19, 09:21 PM
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A double pole breaker would be a 220 circuit. Of course this would share a single neutral as it's a single circuit.
Is the same thing as
I'm talking about doing 2 single pole circuits sharing a single neutral line.
If you only connect to one hot and neutral it is a 120 volt circuit. You still need the double pole breaker setup so that you have 240 between the hots. A shared neutral circuit is required to have the two breakers tied to trip together.

If you want a more detailed description search 'multi wire branch circuit' or MWBC.
 
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Old 02-23-19, 03:54 AM
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You are looking at shared neutrals, not floating neutrals. Properly installed on. 3 phase system like you are dealing with saved two neutrals in the conduit.
 
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Old 02-23-19, 07:30 AM
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in Southern California, where codes are extremely strict
If codes are so strict, are you sure you can do the electrical work? Many states you are required to be a licensed electrical contractor to do electrical work in a commercial building.

he basically said that if I don't know the answer to that, I need to hire an electrical engineer
No, you would need an electrician. An EE would only be able to lay it out on paper and they do not do the work and are not licensed.

Loads do not need to be balanced on a multiwire circuit. The neutral only carries the unbalance of the load between each ungrounded conductor.

I will also mention that pretty much all receptacles (120v, 208-204v, single phase, three phase) require GFCI protection is a commercial kitchen. The easiest way around this is to hardwire the larger equipment if you can.
 
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Old 02-23-19, 07:40 AM
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A double pole breaker would be a 220 circuit.

This is a 3-phase 4-wire service so it is more likely that you are referring to a 208 volt circuit, not 220. Sharing neutrals as in multiwire branch circuits is quite common in commercial work and with a 120/208 volt system it's actually more common to have one neutral for three circuits and it does not violate the NEC. Also quite common is to find six circuits with two neutrals in one conduit.


Many states you are required to be a licensed electrical contractor to do electrical work in a commercial building.

Excellent point! The areas I am familiar with required a licensed contractor just to take out the permit.
 
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Old 02-23-19, 10:45 AM
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Joed,

I didn't realize it was legal to use a 220v breaker for 2- 110v circuits. This was done in various locations at this restaurant (as well as a 208 3 phase breaker using 2 of the 3 phases for 2 110v outlets, and third output was abandoned). That too, I was under the impression was illegal.

Tolyn,

I had wondered about that. The architect did not call for any GFCI in the kitchen. That said, the outlets under the hood will be connected to the fire suppression system so they are disabled if the system trips.

There currently is not a GFCI circuit in the building. Unfortunately my panels are the old Zinsco screw down terminal type, so I doubt I can get a GFCI breaker for them, considering the only breakers I can get are refurbs. If GFCI is mandatory in the kitchen, is using GFCI breakers acceptable, or would they require the entire circuit and not just the outlet be GFCI? That unfortunately also makes it so any change of sharing neutrals is lost, as you can't share neutrals on a GFCI, and the kitchen is where my conduit runs are that are sharing neutrals at the moment.
 
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Old 02-23-19, 10:54 AM
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A shared neutral and gfi protection is possible.
 
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Old 02-23-19, 12:48 PM
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Only the receptacle is required to have GFCI protection, not the entire circuit. GFCI receptacles are fine.

I didn't realize it was legal to use a 220v breaker for 2- 110v circuits
You can use either a multipole breaker or 2/3 single pole breakers with handle ties.

Side note: Voltages are 120, 208 or 240. There is no 110 or 220.
 
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Old 02-23-19, 05:27 PM
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Double check your voltages. On a 120/208 volt 3 phase system, three hots, (one from each phase) can share a neutral. On a 120/240 volt 3 phase system, only two hots, usually the A phase and C phase, can share the neutral to provide 120 volt power. The other leg may not be used with the neutral (if there is one), shared or not,.and is often marked with orange tape. Its hot to neutral voltage is 208.

Shared neutrals (multiwire branch circuits) can be used with ground fault circuit interrupter receptacles if the latter have their load terminals left empty or a non-MWBC subcircuit (2 wire) comes off of the load terminals.
 

Last edited by AllanJ; 02-23-19 at 05:43 PM.
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Old 03-04-19, 06:39 PM
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Thanks for the suggestions everyone! Allanj, I will definitely check voltages on the 3 phases to see if they are all the same. I was under the impression that for 120v, it didn't matter what phase you grabbed, because the position of the peak/0 point doesn't matter with the neutral. Only in correlation with other phases. Checking voltage across any Phase and Neutral should always net you close to 120v whereas checking voltage across Phase 1 and 2, or Phase 2 and 3 will give you 208 due to phase cancellation. Any one of those phases to neutral will give you 120, as there isn't any phase cancellation happening.
 
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Old 03-05-19, 05:12 AM
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It depends on the type of three phase service your building has. There are some older configurations with a different hot-to-neutral voltage on the high phase, and you have to watch out for it, especially doing remodel work.

If you have the more modern 208Y120 service, then you can use any phase-to-neutral for 120V, any phase-to-phase for 208V single phase, or all three phases for a full three phase 208V motor.
 
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