UF-B wire to shed for two circuits - two 14/2 or one 14/3?

[garya505]

I'm putting in UF-B cable to my shed. I want to circuits, one switched (for lights) and one unswitched. Would it be better to use two 14/2 cables or a single 14/3 cable? I know the cost will be a little more for the two 14/2 runs but that is not a big concern. With the single 14/3 they would share a common neutral and ground wire so I suspect there would be a code issue doing that.

 

[wwhitney]

An outbuilding may only be supplied by one circuit or one feeder. And if a feeder, you needs to install a grounding electrode system connected to the EGC in the outbuilding panel. But if a circuit, that may be an MWBC, which you can use as two 120V circuits.

So if you don't want a panel and 2 ground rods at your shed, use a single MWBC, probably better to run 12/3 protected by a 20A double pole breaker (depending on distance). And read up on the MWBC rules if you aren't familiar with them. The circuit will still need a disconnect at the shed, I believe on the exterior or nearest the point of entry. That could be a simple 20A double pole switch that disconnects both ungrounded conductors.

Make sure you comply with the NEC 300.5 cover depth for any buried wiring.

Cheers, Wayne

 

[Sponsor]

 

[garya505]

Oh, I think I found the answer. To do this to code with 14/3 I would have to wire the two circuits out of phase so that the load on the neutral isn't doubled. I don't have that option since I'm coming off a single 15A breaker (and GFCI). I'll have to put in two runs of 14/2.

Did I just answer my own question?

 

[wwhitney]

What's the distance to the shed?

My comment about one feeder or one circuit omitted an important exception, which is that a separate circuit is allowed for something like switched control of some loads. So what are you trying to accomplish?

Apparently you've determined 15A is sufficient for all your shed loads. So if you just want to run hot, neutral, and switched hot you can use a 14/3 where the hot and switched hot are from the same circuit and protected by the same 15A breaker and GFCI. No need for a redundant neutral for that scenario.

Cheers, Wayne

 

[garya505]

An outbuilding may only be supplied by one circuit or one feeder. And if a feeder, you needs to install a grounding electrode system connected to the EGC in the outbuilding panel. But if a circuit, that may be an MWBC, which you can use as two 120V circuits.

So if you don't want a panel and 2 ground rods at your shed, use a single MWBC, probably better to run 12/3 protected by a 20A double pole breaker (depending on distance). And read up on the MWBC rules if you aren't familiar with them. The circuit will still need a disconnect at the shed, I believe on the exterior or nearest the point of entry. That could be a simple 20A double pole switch that disconnects both ungrounded conductors.

Make sure you comply with the NEC 300.5 cover depth for any buried wiring.

Cheers, Wayne

Thanks for the reply.

Given this information ...

I wanted to use two circuits from the house to the shed, but I could get by with one. The backyard has a wall-mounted flood light wired into the backyard outside outlet (through metal conduit) which is on a single 15A GFCI-protected circuit. There were some yard lights coming off that light that were wired using UF-B buried in the dirt, but I removed them.

I was just going to run the UF-B to the shed off that circuit, for an outlet in the shed. I might put a light in there too.

I was hoping to use the NEC 300.5 column 4 option for 12-inch burial of the UF-B.

 

[AlfredeNeuman]

The NEC - 12" rule for depth with GFI is limited to 120V circuits only. Since you have a MWBC (with 240V between conductors) it would not qualify

 

[wwhitney]

The NEC - 12" rule for depth with GFI is limited to 120V circuits only. Since you have a MWBC (with 240V between conductors) it would not qualify

That would be correct for an MWBC, but the OP clarified that both legs will be supplied by the same single pole breaker, so it will be a single 120V branch circuit.

Cheers, Wayne

 

[AlfredeNeuman]

Then why doesn't just use a single 14-2?
If a tandem breakers is used then the 2 circuits will overload the neutral (against the Code)

 

[wwhitney]

Then why doesn't just use a single 14-2?
If a tandem breakers is used then the 2 circuits will overload the neutral (against the Code)

Agreed that a single position tandem is not suitable for an MWBC. I believe the OP wants both constant hot and a switched hot to control a garage load from the house, hence the 14/3.

Cheers, Wayne

 

[Stuff]

I see this as a single circuit connected to a GFCI breaker. 14/2 from panel to a box with a snap switch. Neutral passes through. Hot gets spliced so feeds switch and pass-through. 14/3 from switch box to shed. One circuit. Less than 150v to ground and GFCI protected so only needs 12" burial.