Best way to wire two circuits of outlets in a workshop?

dw1256

Hi,

I am rewiring a shop in my garage (detached) with two separate circuits for outlets. Does it make sense to wire the outlets so that every other one is on a different circuit? Or, would you just put the first five on one circuit and the next five on the other circuit?

Hope that makes sense.

Thanks.

jbfan

Depends on how you are using the shop and what goes into the receptacles.

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curiousB

I think a more important consideration is to run 12-3 cable from home panel and install a 20A 2P breaker for a MWBC in the shop. At the first box install a (20A T slot) GFCI (yes you must use GFCI in garage) for one phase. Continue the unused phase and neutral to the next box and put in another GFCI (again a 20A T Slot type) for that bank of plugs. Then run as many receptacles you like off the load side of each GFCI.

The 20A circuit will give you a little more cushion for high draw power tools like table saws. The heavier wire (12 AWG) will lessen the voltage drop as well.

jbfan

Unless he is in Canada, then a 20amp receptacle is not required.

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dw1256

I am not sure if I understand exactly what you are saying. Just a little confused when you said "from home panel". I have a sub-panel in the garage already. I was considering the 20A 2P breaker, and running 12-3 from the sub-panel to the first box. From there, I would alternate between the two phases at each outlet using 12-3 wire.

Does that make sense?

Jim Port

That plan would be fine as long as you GFI protect both the circuits.

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Answers based on the National Electrical Code. Local amendments may apply. Check with your local building officials.

k_buz

If you are going to alternate like that using 12-3, I would install a 2P 20A GFI breaker, otherwise you will need a GFI receptacle at every outlet.

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dw1256

Correct. The first outlet on each phase would be a GFI. However, what if you have more than 5 outlets on the circuit? I remember hearing that they will only protect up to a certain amount, right?

curiousB

If you have a sub panel already you really don't need to mess around with 12-3 MWBC. That made more sense if you had a longer run to the main panel from garage. The wire saving of 12-3 to the first outlet is probably inconsequential (making a MWBC not really worth it).

I would still use 12 AWG wire. I'd just run two single pole 20A breakers at the sub-panel. As an aside one downside of MWBC is that if one side trips the other is shut down too. So further makes case for two independent circuits.

You decide if you go with GFCI at the breaker or at the first outlet in the run. It has to be GFCI though.

frenchelectrican

The number of receptales do not affect but the distance that will useally do it.

However I am not sure if someone mention if you run in MWBC format the only way you can have GFCI protection is use the two pole GFCI breaker you can NOT run a GFCI receptale at starting point and go downstream if you use two GFCI receptale at starting point.

The reason why due you will have shared netural and it will trip as soon you put a load on it. The two pole GFCI breaker will handle it just fine but not the GFCI receptales itself unless you put convental GFCI receptales on line side only and the cost can go up real fast due the numbers of GFCI receptales vs two pole breakers.

My prefered way is run it own circuits so that way you only can use a convental GFCI receptale or single pole GFCI breaker.

Note: Genrally GFCI receptale is about 12 to 15 Euros vs 30 to 60 Euros for single pole breaker mais two pole GFCI breaker will typically hit 60 to 100 Euros. ( the price will varies depending on brandname of breaker or GFCI receptale )

Merci,
Marc

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The answer will be based on NEC ( National Electrical code ) or CEC ( Cananda Electrical code ) or ECF ( Electrique Code France )

AllanJ

For the detached building you must come in with either one multiwire branch circuit (red/white/black) with 240 volts red to black, or one 120 volt circuit (white/black). A subpanel is needed if white/black will provide more than 20 amps total (or if white/red 120 volts will provide more than 20 amps total).

My preference is to alternate between the "phases" but it does not have to be one for one even/odd. For example you could do double alternates with boxes #1, #2, #5, #6, and #9 for the black feed and #3, #4, #7, #8, and #10 for the red feed if you wanted to.

Regarding coming in with a multiwire branch circuit and alternating with 12-3 among the receptacles:

If you put a GFCI receptacle at box #1 expecting it to serve 4 more boxes with plain receptacles and put a GFCI receptacle at box #2 expecting it to serve 4 more boxes with plain receptacles, then you must use two 12-2's instead of one 12-3 from box #1 onward. Each 12-2 should leapfrog over the boxes served by the other rather than go through with extra wire nuts and splices inside.

The neutral connected to the load terminal set of a GFCI unit may not be commingled with the incoming feed neutral or the neutral connected to the load terminal set of another GFCI unit.

If you come in with 8-3 or 6-3 wire expecting to use more amperes later, you can procrastinate on installing the subpanel as long as the breaker back at the house is just 20 amps.

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dw1256

Allan J,

I already have a sub-panel in the garage wired from the house with 6/3 copper on a 60 amp breaker. All of my new wiring will run from the sub-panel.

I like the idea of leap frogging rather than using wire nuts in every other box that isn't using that phase. However, what size hole do I need in the studs to accommodate 2 12/2 cables?

Thanks.

jbfan

A 3/4 hole will work.

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