Using a shared neutral for two or three circuits

[TWX]

I'm in the process of planning my power to my backyard shed. I have a single phase 120V subpanel on the wall of the house about 40' from the shed that can handle either six or eight circuits, some of which will be used for house-related things, but I want to run at least two circuits to my shed, and possibly a third circuit later over to the gazebo.

Because of this I'm considering burying some flexible conduit from the subpanel to the shed, filling it with five wires- black 12awg, red 12awg, blue 12awg, bare 12awg or 14awg, and white 8awg. The black, red, and blue will be hot, and the thick white would be neutral for all three circuits. At the shed itself I'd split off neutrals to each of the two circuits used in the shed itself and later when I run either conduit or direct-burial cable to the gazebo I'd also tie the neutral there into the big neutral wire.

Is this acceptable? I don't anticipate actually drawing all three circuits heavily constantly (one will be for lighting, and the one to the gazebo will be for lighting and one receptacle for yard work) I'd rather not have to pull three 12awg white neutral wires in addition to the other four conductors in the 3/4" conduit I plan on using...

 

[nehog]

I'm in the process of planning my power to my backyard shed. I have a single phase 120V subpanel on the wall of the house about 40' from the shed that can handle either six or eight circuits, some of which will be used for house-related things, but I want to run at least two circuits to my shed, and possibly a third circuit later over to the gazebo.

Only one circuit allowed to the detached building.

Because of this I'm considering burying some flexible conduit from the subpanel to the shed, filling it with five wires- black 12awg, red 12awg, blue 12awg, bare 12awg or 14awg, and white 8awg. The black, red, and blue will be hot, and the thick white would be neutral for all three circuits. At the shed itself I'd split off neutrals to each of the two circuits used in the shed itself and later when I run either conduit or direct-burial cable to the gazebo I'd also tie the neutral there into the big neutral wire.

Use a sub-panel in the shed. They are not expensive, and will be much easier to install.

Is this acceptable? I don't anticipate actually drawing all three circuits heavily constantly (one will be for lighting, and the one to the gazebo will be for lighting and one receptacle for yard work) I'd rather not have to pull three 12awg white neutral wires in addition to the other four conductors in the 3/4" conduit I plan on using...

Acceptable? Not really. Generally a bad idea, one circuit to the building, a sub-panel, and branch out from there.

 

[MrMark]

shared neutral only can have two hots (on opposite phases). Otherwise you will overload the shared neutral.

 

[Gooch]

shared neutral only can have two hots (on opposite phases). Otherwise you will overload the shared neutral.

Unless he's got a 3 phase service at his house(unlikely, but you never know)

 

[TWX]

shared neutral only can have two hots (on opposite phases). Otherwise you will overload the shared neutral.

Even with an 8awg wire? I thought 8awg was rated to something like 46A at 120V...

 

[TWX]

Unless he's got a 3 phase service at his house(unlikely, but you never know)

I wish! Though many of the postwar neighborhoods here through about 1960 are 3ph because the air conditioners at the time needed it. My neighborhood is twenty years too new unfortunately.

 

[Gooch]

Even with an 8awg wire? I thought 8awg was rated to something like 46A at 120V...

doesn't matter.

one phase per neutral.

 

[Norcal]

shared neutral only can have two hots (on opposite phases). Otherwise you will overload the shared neutral.

The OP has a single phase service, so there is not more then one phase, the correct term would be opposite legs, not phases.

 

[MrMark]

I say phases. You can say what you want. I think I am correct. Don't make this like the HVAC forum. There are already enough assholes on here.

 

[AussieDan]

Seems like we've drifted off the original question a little here...

My understanding is that in this situation a multiwire branch circuit (2 hots on opposing legs/phases sharing a common neutral and fed from a single 2-pole breaker) is allowed, though 3 hots would not be due to the aforementioned risk of overloading the neutral.

It is certainly a better idea to just run a 4-wire feeder to a subpanel in the garage to allow for future expansion, but if you only need 2 "circuits" then a multiwire branch circuit would be legal per NEC 2008 section 225.30.

 

[TWX]

Just to clarify,

There is only one phase.

The subpanel has 50A, 120V service. It's wired hot, neutral, ground only. The panel used to be hot-hot-ground, but I needed a neutral, so one of the hot wires got repurposed to Neutral. A single-pole breaker in the main panel feeds this subpanel. and the two different halves of the subpanel will be bridged into one phase as soon as I get around to finishing it this morning.

That's why I figured, since any new circuits for lighting and 20A outlets fed from this circuit would be in-phase to each other, a single, LARGE wire could function for neutral for them.

 

[Alchymist]

The OP has a single phase service, so there is not more then one phase, the correct term would be opposite legs, not phases.

I say phases. You can say what you want. I think I am correct. Don't make this like the HVAC forum. There are already enough assholes on here.

Just to clarify,

There is only one phase.

The subpanel has 50A, 120V service. It's wired hot, neutral, ground only. The panel used to be hot-hot-ground, but I needed a neutral, so one of the hot wires got repurposed to Neutral. A single-pole breaker in the main panel feeds this subpanel. and the two different halves of the subpanel will be bridged into one phase as soon as I get around to finishing it this morning.

That's why I figured, since any new circuits for lighting and 20A outlets fed from this circuit would be in-phase to each other, a single, LARGE wire could function for neutral for them.

Hold on a minute, guys, I didn't get my popcorn yet.....

 

[TWX]

Okay, since there seems to be confusion, is the term I want "Single Wire Earth Return"?

One hot conductor, pulling and pushing electrons against the Neutral, which is ultimately Earthed via grounding rod?

 

[Grumpy365]

Even with an 8awg wire? I thought 8awg was rated to something like 46A at 120V...

You can downsize the neutral. It falls under the grounded conductor chart in the NEC, I would call out the chart number, but I am not near my book.

 

[Stuart in MN]

You can downsize the neutral. It falls under the grounded conductor chart in the NEC, I would call out the chart number, but I am not near my book.

You can do that in some circumstances on a three phase system, but it doesn't apply to a 120vac single phase system like what is being discussed here.

 

[Grumpy365]

You can do that in some circumstances on a three phase system, but it doesn't apply to a 120vac single phase system like what is being discussed here.

Yes, by code, you can apply it to a single phase system. I just went thru this, I am positive you can do this, at least when feeding a sub panel.

 

[Charles (in GA)]

Okay, since there seems to be confusion, is the term I want "Single Wire Earth Return"?

One hot conductor, pulling and pushing electrons against the Neutral, which is ultimately Earthed via grounding rod?

Common mis conception, it does not return to earth. It has an earth to help balance the neutral with earth, but the neutral goes all the way back to the power plant, and so does the current.

Charles

 

[Charles (in GA)]

Simply put, you can have only one feeder to a detached building. It can be a simple 120v circuit, one hot/one neutral/one ground, or it can be a multi-wire (defined by code, two hots on opposing bus'es of the panel and a neutral) or a true 240v circuit, with or without a neutral, but no more.

Charles

 

[Charles (in GA)]

The subpanel has 50A, 120V service. It's wired hot, neutral, ground only. The panel used to be hot-hot-ground, but I needed a neutral, so one of the hot wires got repurposed to Neutral. A single-pole breaker in the main panel feeds this subpanel. and the two different halves of the subpanel will be bridged into one phase as soon as I get around to finishing it this morning.

I hope the wire was white to start with, or is larger than AWG 6. #6 and smaller neutral (grounded conductors) MUST be white or gray full length, you are not allowed to remark the ends of a different color to "make" it a neutral. NEC 200.6.

Charles

 

[Alchymist]

I hope the wire was white to start with, or is larger than AWG 6. #6 and smaller neutral (grounded conductors) MUST be white or gray full length, you are not allowed to remark the ends of a different color to "make" it a neutral. NEC 200.6.

Charles

True with one exception, I think. I believe if the conductor is part of a cable, ie, not individual wires, it can be remarked white. No? I know that the white can be remarked to indicate a power conductor, but can't remember if the reverse is true. Anyone have a copy of Nec 200 handy? Concerns only manufactured (bundled) cable with #4 conductors or smaller.

 

[Zeke]

I'd like to settle the "phasing" issue once and for all. Since it does pertain here to the neutral in question being used for multiple circuits. OK, the power supply is single phase. The 2 hot legs provide alternating current with opposing sine waves. I'm not an electrician, so correct mu assumptions.

Looking at the sine waves, they cross over at the same point. I think some are considering this phasing as it would be out of phase in 2 DC currents, like you stereo speakers.

So, what is the precise word for the opposing sine waves?

That, gentlemen, should solve the issue and stop the bickering.

Unless I need to be corrected.

 

[Alchymist]

Single phase, center tapped opposing waveforms.

 

[Falcon67]

And since they run as opposing wave forms, the single neutral is OK since it does not get overloaded.

For the OP - sounds like no, your panel is 120V so you can run one circuit out there, or pull a 4 wire feed from another panel.

 

[Zeke]

Thank you. I will now make sure when I load a panel I balance my "wave forms."

 

[Alchymist]

Thank you. I will now make sure when I load a panel I balance my "wave forms."

Cute! When I do it, I balance the "loads" on each leg - I have a scale reading in KG that I hang from the ceiling.

Seriously, I think there is no way to ever settle this - here or on many another forum. There will always be some in each camp, regardless.

 

[Charles (in GA)]

True with one exception, I think. I believe if the conductor is part of a cable, ie, not individual wires, it can be remarked white. No? I know that the white can be remarked to indicate a power conductor, but can't remember if the reverse is true. Anyone have a copy of Nec 200 handy? Concerns only manufactured (bundled) cable with #4 conductors or smaller.

Doesn't matter if it is bundled in a cable or not, 200.6 doesn't allow the use of a "non-white" wire as a neutral unless it is larger than AWG6.

It is acceptable, many times necessary, to remark the ends of a white wire to some other color, when it is in a cable (romex). loose wires in conduit must be proper color/markings full length.

Charles

 

[brewchief]

Doesn't matter if it is bundled in a cable or not, 200.6 doesn't allow the use of a "non-white" wire as a neutral unless it is larger than AWG6.

It is acceptable, many times necessary, to remark the ends of a white wire to some other color, when it is in a cable (romex). loose wires in conduit must be proper color/markings full length.

Charles

Slight hijack, can a "non-green" wire be marked green for use as a ground?

On occasion I've had to make up a longer A/C whip then the premade ones and have marked a colored wire green with green tape, inspector has never made a fuss but I'm wondering if it meets code.

 

[TWX]

Doesn't matter if it is bundled in a cable or not, 200.6 doesn't allow the use of a "non-white" wire as a neutral unless it is larger than AWG6.

It is acceptable, many times necessary, to remark the ends of a white wire to some other color, when it is in a cable (romex). loose wires in conduit must be proper color/markings full length.

Charles

Any idea when 200.6 was introduced into code? I ask because if anyone ever asks, the house was built in '79 and this is the way I found it... *grin*

 

[ishiboo]

Any idea when 200.6 was introduced into code? I ask because if anyone ever asks, the house was built in '79 and this is the way I found it... *grin*

Have you run the #s? I am not so sure that doing it correctly and the "safest" way is much more expensive than doing it your way.

Yes, electrically you can run all 3 hots back on the same neutral. But to be safe, it'd need to be large enough to accommodate the sum of the 3 breakers you have, i.e. if they are 3 20A breakers you need a neutral capable of carrying 60A safely. This is not permitted by code, however.

Now, your misunderstanding seems to be that you would have to pull 3 neutrals, this is not the case... the case is the 3 separate feeds alone is not allowed. To do it properly, you would pull a single hot, neutral and ground from your sub panel to a sub panel in the shed, and then split up your circuits there with breakers. You could do this inexpensively with aluminum cable and a small panel.

 

[TWX]

At this point I'll probably just bury three 12-2 outdoors/direct-bury bundles- two for the shed, and one for later expansion further out to the gazebo. I'll probably go buy 200' or more of it since I can use it for other things too, and it can be used in the workshop or the like if needed. I'll run the circuits as regular 12awg wire in conduit down to a box mounted about six inches from the ground, transition to the direct-burial cables there, run the cables, and come in to another box mounted on the shed a few inches from the ground. wirenut off the bundle set up for future expansion, and switch to armor cable for the wiring inside of the shed since the walls are not finished inside. Eventually either come through the shed with more armor cable to another box for more direct-burial cable across to the gazebo, or else come right out at the original box on the shed again back into the ground with more direct-burial cable over to the gazebo.

This way I don't have to deal with water getting into the conduit, I don't have to worry about keeping track of neutrals, etc.

Only remaining question- would I need to run a higher gauge ground from the subpanel down to the box where the wiring transitions to the various direct-bury circuits, or would 14 or 12awg be adequate?

 

[AussieDan]

The usual understanding is that this setup would also not be legal:

225.30 Number of Supplies. Where more than one building or other structure is on the same property and under single management, each additional building or other structure that is served by a branch circuit or feeder on the load side of the service disconnecting means shall be supplied by only one feeder or branch circuit unless permitted in 225.30(A) through (E).

You might be able to make an argument for why it falls under the exceptions, but the advice you got already to just put a small subpanel in the garage will result in a much simpler job with more expansion capability regardless.

 

[Aceman]

This thread is RIDICULOUS.

Remark one wire WHITE in your existing cable at both ends, if you don't already have a white wire. Then run some #8 to your outbuilding(h,n,g). Set a panel, jump the buss together(for 120v), drive some rods. Call for inspection. DONE.

 

[TWX]

Heh.

Did I mention that this is an 8' by 8' tuffshed? The only reason I want a separate circuit for lights as compared to receptacles is so that if I ever have to operate a saw, a battery charger, or something else yard related, if I trip the breaker for the receptacles I don't want the lights going out.

At this point guys, don't worry about it anymore. It'll get done and it'll be safe.

 

[Aceman]

Did I mention that this is an 8' by 8' tuffshed

Doesn't matter, I've wired 4 small sheds in one guys backyard a couple years ago. Each one had it's own panel with rods driven. It could be a doghouse or mansion, it still gets a grounding electrode system when you run a feeder out there.

At this point guys, don't worry about it anymore. It'll get done and it'll be safe.

Definitely get it inspected. Since you're so confident, you shouldn't have anything to worry about...

 

[MrMark]

And what exactly do you think that "grounding electrode system" (I guess that's a couple rods) on the doghouse or shed will do for you in terms of safety?

 

[PanamaExpat]

I know this is my first post but how many of you quoting code and pontificating on this poor guys problem are actually licensed electricians or as I am an electrical engineer? I do not have time to explain what he needs to do at the moment or the reason ground rods are needed but when I get back in I will elucidate on the topic.

 

[Alchymist]

I know this is my first post but how many of you quoting code and pontificating on this poor guys problem are actually licensed electricians or as I am an electrical engineer? I do not have time to explain what he needs to do at the moment or the reason ground rods are needed but when I get back in I will elucidate on the topic.

Electronics background 50+ years, + industrial electrician for several years.
Which is pretty irrevelant - don't have nor claim to have all the answers - or current copy of the code handy. Heres the info, grounding starts on about pg 15:
http://www.pfeiffereng.com/Principals of Electrical Grounding.pdf

Free download, .....

Note that this does not incorporate later code changes (2008), but the ground explanations are accurate.

 

[MrMark]

I know this is my first post but how many of you quoting code and pontificating on this poor guys problem are actually licensed electricians or as I am an electrical engineer? I do not have time to explain what he needs to do at the moment or the reason ground rods are needed but when I get back in I will elucidate on the topic.

This should be good. Ground rods can be explained in about 10 seconds and it has already been done in this thread. They are for lightning and to reference the neutral. Let's see you elucidate on that.

 

[gatchel]

Elucidate:
transitive verb
: to make lucid especially by explanation or analysis


(For anyone else who has never heard that word or was curious to it's exact definition)

 

[Alchymist]

This should be good. Ground rods can be explained in about 10 seconds and it has already been done in this thread. They are for lightning and to reference the neutral. Let's see you elucidate on that.

Ah, yes - a plethora of explanations forthcoming...