240v wiring question

[Ovidiu]

So my house was built in 1977. It has only one neutral/ground bus bar in the breaker box, and all my 240v stuff inside the house is wired with x-2 cable (6-2 for AC, 10-2 for the range and dryer).

I am going to add 3 240V outlets to the garage. I figured I should use 6-2 wire for the 2 50A outlets I plan to put and 10-2 for the 2 20/30A outlets that I plan to use.

Is this OK or should I run 6-3 and 10-3 respectively? I don't see a point for that since the 2 cables would be tied to the same ground at the breaker panel instead of at the appliance...

I've already bought and run the 6-2 and 10-2 cable and ran it, but I want to make sure 100% that I am doing the right thing before I insulate/drywall...

Thanks in advance guys! :bowdown:

[toolfreak450]

the only reason for 3 insulated wire in your romex is for appliances that are in parrell inside the appliance like dryers and ranges that carry neutrals for instince if your dryer has a light bulb it is probably 110 even though the dryer is a 220 so you need the neutral just like a regular 110 bulb unless your range and dryer are very old NEC electrical code now requires ranges and dryers to be in 3 romex not 2 so you need to find out if your garage plugs will be used for any thing that is parrell inside of the appliance or tool
but you are right about the wire size to amp ratio in your post

[toolfreak450]

one more thing about the common bar in the panel this is very common, but if your appliance is returning voltage to the ground you want it to go back on a insulated wire

[Ovidiu]

For the garage, I will run a welder, AC and an air compressor. I assume those run on 220v exclusively...

[toolfreak450]

the air compressor and the A/C will be ok how many prungs does the welder have on the plug this should give you all the info you need on how many wires it requires just run wires for every prong if the plug has four prongs run xx-3w/ground if they have three prongs run xx-2w/ground

[rinny_tin_tin]

Its hard for me to completely understand the question - but I think you are asking if you can run 2 conductors per circuit, with the neutral also serving as the grounding conductor - since your house was originally wired with an integral neutral/gnd bus, instead of separate ground and neutral busses link with a ground link wire. Its difficult to defend a 3-wire system and the safety benefits in such a circumstance, and if you talk to many master electricians, they would be correct if they told you that nodally, there is no difference between the two architectures. However, you have to recognize that the neutral is a current-carrying conductor in a conventional 120 VAC circuit, and if the ground is directly joined to the neutral, then also any "grounded" metal parts also become current carrying conductors. The "separate" grounding conductor 3-wire scheme invoked in the NEC since at least the last eighty's came about to make a certain distinction and redundancy in electrical safety by insuring a definite "ground" for appliances with metal parts. For instance, if a hot wire should come loose inside an appliance and come into contact with a "bonded" metal part, it would serve to trip the feeding breaker - while at the same time, the grounded part does not serve as the current-carrying return --since that path is provided by the neutral conductor. Your building code folks is the AHJ (authority having jurisdiction) and they can tell you if its OK to run two in lieu of three conductors per circuit because, for instance, you may be grandfathered. However, since you are running a ckt to the garage, which in many, if not all, jurisdictions is classed as a wet/damp space (and perhaps as a classified location if commercial) you need to run GFCI circuits. A 2-wire scenario with an integral neutral/ground would likely cause havoc with the GFCI system - since GFCIs work by detecting and determining an inadvertent ground fault path. I'd run a 3-wire arrangement for all new circuits wherever I can with the eye of ultimately upgrading my two wire panel.

[Charles (in GA)]

I'd run a 3-wire arrangement for all new circuits wherever I can with the eye of ultimately upgrading my two wire panel.

I was going to suggest the same thing. Eventually you may wish to replace the panel, Its difficult to do, because wires are never long enough to reach when you rework stuff, but if you run three wires plus the ground and leave lots of extra wire, then panel replacement in the future is easier.

I have a panel with all the neutral and grounds intermixed on the bars. If and when I replace the panel, I will have to lower it in the wall somewhat (its high right now and all wires exit the bottom except the serv. entrance cable, it comes up beside the panel and loops over into the top)

This was an owner finished log house built in '85 just before the county began building inspections, so everything was done wrong, by amateurs with no one looking over their shoulder.

Charles

[Ovidiu]

Thanks for the replies everyone!

rinny_tin_tin, I am talking about a 240V outlet. First of all, I don't think I've seen a GFCI outlet for 240V, so I will have to do without I believe. Second, if I use a 3-prong cord with my appliance, be it an air compressor or a welder, the appliance should only use the voltage between the two hots that is supplying the 240v; thus the third prong (ground) is not used as a neutral to carry any current back to the panel, right?

If I get a 3 prong outlet with a 6-3 wire, I will have the ground basically dangling inside the outlet box, what good would that do?

Thanks,
Ovidiu

[BigChevy80]

Thanks for the replies everyone!

rinny_tin_tin, I am talking about a 240V outlet. First of all, I don't think I've seen a GFCI outlet for 240V, so I will have to do without I believe. Second, if I use a 3-prong cord with my appliance, be it an air compressor or a welder, the appliance should only use the voltage between the two hots that is supplying the 240v; thus the third prong (ground) is not used as a neutral to carry any current back to the panel, right?

If I get a 3 prong outlet with a 6-3 wire, I will have the ground basically dangling inside the outlet box, what good would that do?

Thanks,
Ovidiu

3 prong dryer and range outlets use 2 hots and a neutral. The newer codes require a 4 prong outlet with a ground for ranges and dryers.

The type of outlet that is used dictates how it is wired. Any outlet prong that is D-shaped like the ground prong on a normal 110v outlet is supposed to be a ground and not a neutral.

If you are using a metal junction box for your outlet, you will need to have a ground wire to ground the box. Plastic boxes obviously don't require a ground.

[rinny_tin_tin]

Hey Ovid - you are correct - no GFCIs for 240 and for single phase 240, you don't (usually) use the neutral. However, some 240 equipment do use the neutral where 120 is needed (and I believe someone here also said such) for instance, a dryer that uses 240 for the heating elements, but 120 for a light bulb, etc. However, a grounding wire is frequently used in many equipment with metal exposed parts to ground the case, for instance from a ground fault (say one of the two hots break loose and come into contact with the case..etc.
Now - equipment identified as "double insulated" do not have metal exposed parts - like my large plastic cased Rigid Shop Vac for example - in which case, the vac is equipped with a two prong plug - as it need not have a ground. Whether or not a equipment needs a ground or not can be determined from the manufacturer's instuctions/manual - or - if it comes equipped with a two prong, versus a three prong plug. As a rule of thumb - if an electrical appliance has any exposed metal parts, than a grounding conductor is generally needed.
However, even for 220 equipment that does not require a neutral (as you say - neutral is simply just dangling loose in the box) a grounding conductor is likely needed anyway as such equipment most always has some exposed metal parts (especially compressors or welders). Consult the manufacturer's guidance to know for sure.

[rinny_tin_tin]

One thing I maybe didn't emphasize as much as I should have --

The grounding conductor (green or bare) and the neutral conductor (white) are two separate conductors -- even though in older installations they are connected together at a buss at the panel anyways.

[rinny_tin_tin]

Here is a graphic that may help delineate the differences between a grounded conductor (neutral) and grounding conductor. It is based on the 1999 NEC and references various NEC articles

[Ovidiu]

Okay, it makes sense now. The bare uninsulated copper wire is not supposed to conduct any current, just be there for the ground, so there needs to be an extra wire. I'll just eat the $60 worth of 6-2 wire that I bought and replace it with 6-3, and put 10-3 for the 30A compressor outlet.

Thanks for the help, definitely makes sense to replace it now than have to take down drywall and replace it afterwards.

[sberry]

So my house was built in 1977. It has only one neutral/ground bus bar in the breaker box, and all my 240v stuff inside the house is wired with x-2 cable (6-2 for AC, 10-2 for the range and dryer). We are getting over our heads here. Likely if these appliances, range and dryer are using 2+ground the wrong wire was used, these need insulated neutral/ground wire. As for the new tools, welder, comp you can use 2+G for those and the issue of neutral ground bar in the main panel is moot anyway, you can use the same bar at this point.

[rinny_tin_tin]

Okay, it makes sense now. The bare uninsulated copper wire is not supposed to conduct any current, just be there for the ground, so there needs to be an extra wire. I'll just eat the $60 worth of 6-2 wire that I bought and replace it with 6-3, and put 10-3 for the 30A compressor outlet.

Thanks for the help, definitely makes sense to replace it now than have to take down drywall and replace it afterwards.


Wait -- before you rip anything out - are sure you do not have a ground wire with your 6 -2 and 10-2? Sometimes the cable markings belie what is exactly there - for instance, I have seen a cable labeled 12-2 and it is actually 2 current carrying conductors (e.g., one white one black) with a ground. sometimes labeled "12-2 w/gnd" Please check what you have and what you need before you rip out anything - as I can't see from here exactly what you have.

Best

[Ovidiu]

There's 3 cables in there, 2 conductors and 1 uninsulated thinner ground, but that can't be used as a neutral.
I believe the standard notation is gage-conductors (like 6-2), and an extra uninsulated ground which is never counted as a conductor. That's exactly what I have (3 wires, 2 conductors 1 ground), but for 240, new standards are indeed 4 wires (3 conductors - 2 phases and 1 neutral - plus one ground).

In the grand scheme of things, $60 isn't quite fatal, so I'll just do it right now, especially since I have bare studs right now and it's easy to do.

[rinny_tin_tin]

There's 3 cables in there, 2 conductors and 1 uninsulated thinner ground, but that can't be used as a neutral.
I believe the standard notation is gage-conductors (like 6-2), and an extra uninsulated ground which is never counted as a conductor. That's exactly what I have (3 wires, 2 conductors 1 ground), but for 240, new standards are indeed 4 wires (3 conductors - 2 phases and 1 neutral - plus one ground).

In the grand scheme of things, $60 isn't quite fatal, so I'll just do it right now, especially since I have bare studs right now and it's easy to do.

OK - what I thought may be the case - you have two current-carrying conductors and a bare gnd wire. If the equipment does not use/need a neutral then what you have is OK and your neutral will "dangle" as you stated earlier and will provide no safety or fire-protection benefit, especially if these two circuits are [dedicated] for the equipment you identified. But..if you want the option for later reassigning these two ckts in a case where the neutral may be needed .....

Also - I erred and there are two-pole GFCIs that are used for 240/220 service, and I'm uncertain why I stated otherwise - especially since I have installed several in my home! :)

[sberry]

but for 240, new standards are indeed 4 wires (3 conductors - 2 phases and 1 neutral - plus one ground). This was stated but to make it clear, the only "new standard" is for appliances with dual voltage, with devices like air comp and welders the x2/w ground is fine. No use running 3 conductor for those.

[sberry]

Another thing, welder circuit requirements are slightly different than other circuits, you can use 8 wire for most units found in home shops.