240 & 120 Question

[LimitedReality]

First, I want to thank everyone on this community for the wealth of knowledge this site has already. I've designed and built a 27x27 two story garage with the knowledge and helpful suggestions that I've obtained from this site. I'm about to begin closing in the walls now and am trying to make sure I've accounted for everything in-wall before I do.

When I mapped out the electrical, I placed a metal quad box with 2 20 amp circuits and 2 outlets on every 3rd stud. I ran 10 outlets total per circuit and put 2 gfci outlets on each circuit, each protecting 4 outlets upstream as per my local inspectors requirements (even though the gfci outlet was rated for more). Since these two circuits are in the same box I used tandem breakers to wire them up. Now comes the question.

It's been over a year since I planned the lighting and electrical to get my permit and I can't remember for certain, but I THOUGHT one of the benefits of this design was not only that I had 2 20 amp circuits available at each drop (to run two higher amperage devices concurrently) but also so I'd have the ability to wire a 240 device at any location while maintaining 120v access at all other outlets on the circuit. Does the fact that these are protected by separate GFCI cause an issue? Does the tandem breaker?

I'd love for someone smarter than me to help confirm if this is true, and if it's isn't, why. I've run dedicated 240 circuits for my welder, table saw and compressor but I want to ensure my understanding before I close up the walls and make things harder on myself in the future since I'm not aware of what will or won't be 240 in the future.

Thanks again!

 

[Innovate1]

The limitation of 4 outlets per GFCI is bizarre. I would be challenging the inspector on that. Maybe some local additional requirement but may also just be his own concoction of a rule. There is no limit on the number of outlets ("receptacles" in the code) and one as the first on a string of 10 is fine AFAIK. The only issue I can think of is if you have multiple devices close to the leakage current limit and have them both connected at the same time the total leakage will trip the GFCI. That might be a reason to have fewer outlets on a GFCI but not a code requirement. Locally there is a rule about how many kitchen receptacles on a circuit (two duplex for total of 4) but it is a total circuit rule not how many on a GFCI as you describe.

As to running 240 from 2 120 GFCI circuits - no, it can't be done. The neutral for each 120V circuit runs through the GFCI current sensing and you can't tie them together after the GFCI. They do make GFCI breakers that have both hots for 240 AND the neutral. You can run any combination of 120 and 240V loads from them.

But putting both 120 and 240V receptacles on the same circuit may not be to code. Not sure on that one.

 

[ycgoat]

If you install (2) 120v 20 amp circuits at each box and want to convert it to 240v later, you would need to eliminate the 120v outlets from those circuits. The advantage of doing that is you may not need to run new wire to make the change. Chances are you will never need to make the change over, or the wire size or locations will still require additional wire.

I try to leave access to make changes like conduit


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[sberry]

If you have dedicated circuits for 240v you don't need to mess with the 120. Wayyyyyyy too much research. Contrary to some belief every scheme found on the internet isn't always a good idea or practical.
I am not even a real fan of multi wire circuits in the common diy/small garage. Prefer a single circuit in a box. Second, once the big pieces are covered at 240 additional equipment in this class is rather rare. I keep table saw 120v. Anything you might want to move is so much easier.

 

[Jagmandave]

I don't know what you're planning to do in your shop that you need an outlet every 4ft (every third stud at 16 OC I assume) ....I found that when I redid my garage a few years ago I eliminated about half of the receptacles (mine were in conduit, I took them down to paint and repair drywall under them) and I haven't missed them.

I think sberry is right, you really don't need a bunch of circuits in a one man shop (which is what most of us have) as no matter how many things you have plugged in you can only use one machine at a time, so you're not overloading a circuit.

Every one's needs are different and we can't say what will work best for you but as I'm planning my build I'm going more for simplicity.

 

[mike93lx]

That is an insane amount of wire and effort for a 2 car garage. 2 pairs of receptacles per wall and a cord reel in the middle would have been plenty

 

[rsanter]

I am a fan of lots of outlets in the garage if you are going to have shop equipment around the perimeter, it is then easy to plug them in and leave them plugged in.

As for things you will plug in for a short time, the best thing you can do is install a drop cord reel on the ceiling. Most convenient thing ever.

If it was me I would install conduit and a blank box on each side of the garage near the door. In case you ever want to add something it makes it much easier

 

[sberry]

I could make it on 2 or 3 circuits and maybe 1 for all the parasitic that accumulate on the bench. I might be inclined to run 1 down each wall, one across the front for tools. A bud of mine makes it on 2 and one with a reel tied to it. He has a dozen tools, 1 use at a time, if I ever needed 2 could run a short cord to the front or wall. Even in my shop rarely use more than 1 tool at a time.
Even with more than one guy it's rather rare, it was notable the other day to use 2 air tools at once,, it was a few seconds really. Didn't notice it from a performance perspective, only from these threads.

 

[ycgoat]

I agree with the above I have 1 outlet on each wall which includes a laundry circuit. I am in the market for a retractable cord to put by the door opener mainly for a drop light


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[u2slow]

If you install (2) 120v 20 amp circuits at each box and want to convert it to 240v later, you would need to eliminate the 120v outlets from those circuits.

Not true. I run 120V and 240V receptacles off the same 2-pole 20A breaker. Works fine.

 

[ycgoat]

Not true. I run 120V and 240V receptacles off the same 2-pole 20A breaker. Works fine.

I know it will work, but is it legal and to my surprise it is at least from what I read in the 2014 NEC, I stand corrected.


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[u2slow]

I know it will work...

Sorry, I was commenting on the viability. NEC isn't my jurisdiction.

 

[ycgoat]

So Article 210.4 says All multi wire branch circuits have to be 120v line to neutral but there is an exception that says unless all current carying conductors are switched at the same time. Such as with a 2 pole breaker

Once upon a time they ran a hot to the device from the panel and ground / neutral came from the nearest source such as building steel. It worked but there were a lot of fires, hence the NEC


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[wyliesdiesels]

So Article 210.4 says All multi wire branch circuits have to be 120v line to neutral but there is an exception that says unless all current carying conductors are switched at the same time. Such as with a 2 pole breaker

Once upon a time they ran a hot to the device from the panel and ground / neutral came from the nearest source such as building steel. It worked but there were a lot of fires, hence the NEC


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umm a grounding conductor and a grounded conductor are not one in the same.

Running a grounding conductor to building steel, metal conduit, or metal water line would NOT cause a fire.

I have never heard of someone running neutral to building steel. that makes no sense.

 

[ycgoat]

This was early in electrical industry before codes (before 1897) The idea of grounded vs grounding did not exist.


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[ycgoat]

umm a grounding conductor and a grounded conductor are not one in the same.

Running a grounding conductor to building steel, metal conduit, or metal water line would NOT cause a fire.

I have never heard of someone running neutral to building steel. that makes no sense.

I was talking smak once about a wire splice I found where the 2 wires were twisted, folded down, and taped with mo box. Then I was shown a 1952 NEC code book that spelled that out as the proper way to make a splice.


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[sberry]

umm a grounding conductor and a grounded conductor are not one in the same.

Running a grounding conductor to building steel, metal conduit, or metal water line would NOT cause a fire.

I have never heard of someone running neutral to building steel. that makes no sense.

Sure, my neutral at service main at service main is bonded to the building steel. (where do we return a fault)
Actually specs it, one place it does is modular home frame if the service is mounted to the building.

 

[wyliesdiesels]

Sure, my neutral at service main at service main is bonded to the building steel. (where do we return a fault)
Actually specs it, one place it does is modular home frame if the service is mounted to the building.

were referring to the neutral from a circuit. not the bond in the main service panel.

 

[sberry]

Ok, gotcha.

 

[sberry]

I was at a place where the old farts had used an abandoned steel water line for electric. The nephew called as he was getting sparks between the box and pipe, was trying to insulate this, fuggin around. Turns out the guy had ran 2 power and used the pipe for n. There was a switch loop of 12 for a light, don't tell but I parallel them and make a white out of it, so fuggin up and they ain't gonna fix it right but I insulated the current at any rate.

 

[sberry]

Not true. I run 120V and 240V receptacles off the same 2-pole 20A breaker. Works fine.

Not that it won't work but why would a diy design something like this right from the start?

 

[u2slow]

why would a diy design something like this right from the start?

Keeps things easy for me. No machines that need more than 20A. And no GFCI requirement here.

 

[7635tools]

If you put it all in conduit, then you usually have options later. I wouldn’t use that glorified extension cord **** (romex) in my shop. I piped my 30x50 shop and have rearranged equipment several times over the last 15 years and with the conduit it just a mater pulling wire out or pulling new wires in.


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