240V Only Sub Panel

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Old 05-22-16, 11:06 AM
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240V Only Sub Panel

Thinking of putting a 60A sub panel in my attached garage. I'll be pulling a line off a 4 AWG AL 3 wire (2 hots and a ground) and was thinking I would use #6 Cu to feed the sub. Since I don't have a neutral wire this would be a 240V only panel, can I go ahead and buy a sub panel with only 1 neutral/ground bar since I'll just be using it for the ground? Yes, I already know not to combine neutral and ground in a sub, since I only have a ground wire this isn't even possible.

Is there anything else I would need to do to for code/safety? I read I should maybe label the sub something like "240V ONLY NO NEUTRAL". Am I missing anything?
 
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Old 05-22-16, 11:28 AM
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Yeah, the entire code thing, really. Where are you pulling your #6 from? Is in your existing house panel. You say you are pulling it from a #4, so we don't know where that junction will be made. Subpanels will need to be 4 wire with neutral, ground and hots. The reason is that someone else may buy your house, decide to run 120 volt circuits in the garage and it won't be adequate. They will try to use the ground as a neutral, and..............you see why?
 
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Old 05-22-16, 11:48 AM
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The #4 comes from my main panel to a junction box in the garage, currently on a 30A breaker but I'll be replacing that with a 60A. From the junction box I plan to run the #6 to the sub, nothing else will be using the #4 line. It was my understanding that a 240V sub panel was ok. Someone else incorrectly using a ground as a neutral being the reason for me not being able to make a 240V only panel is unacceptable, you can do that today with any wires in your house...
 
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Old 05-22-16, 12:11 PM
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Is your garage attached or detached? Is there a lighting, general receptacle circuit in the garage, now? If it is detached, you can only have one circuit, so that is why I was questioning its use now and in the future.
 
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Old 05-22-16, 12:18 PM
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Attached. The rest of the outlets and lighting are on separate circuits from the main panel. The #4 currently only has my heat pump compressor on it and I'm looking to move that to a sub panel on a 30A. Basically I want to get the capacity of that #4 (60A) so I can install a plug for an electric vehicle. We already worked out the power requirements on another thread and I should be good at 60A.
 
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Old 05-22-16, 03:26 PM
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I am not aware of any code requirements to run a neutral to a panel that will only have line-to-line loads. That stated, a neutral is almost always run to any panel just because the cost is (usually) minimal and no one knows what might happen in the future. I would prominently mark the panel as being 240 volts only with no neutral present. This is not unprecedented in commercial and industrial work but I have never seen it in residential work.

Am I correct in assuming that you will cut the #4 and run it to the new panel and then run #10 or #8 from a 30 ampere CB back to the heat pump?
 
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Old 05-22-16, 04:18 PM
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Here's a diagram of what I'm proposing. The #4 Al wire is already there and I'd rather not have to run a new line with a neutral if I don't have to. The #4 also ends in a junction right in my attached garage so I can't really run it all the way to the panel.
 
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Old 05-22-16, 04:33 PM
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The only reason I was mentioning the neutral is to future proof the installation, but since you already have your 120 volt stuff taken care of, there is no need to run a neutral for a pure 240 volt circuit. UNLESS the end product required it as with a timer, clock, or control module requiring 120 volts.
 
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Old 05-22-16, 04:35 PM
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A 240 only sub panel is code compliant then correct?
 
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Old 05-22-16, 05:30 PM
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So long as you never need 120/240 for a different car charger that should be okay and code compliant. If this is aluminum THWN or XXHW all the way you might want to use a 60 amp breaker to give you a bit more cushion.

I'd install a ground bar in the panel, their cheap, rather the use the neutral bar to avoid any confusion by someone else. If you do convert it be sure to install the bonding screw.
 
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Old 05-22-16, 05:43 PM
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What's the point of using a 14-50 outlet? Use a 6-50 and forget the label.
 
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Old 05-22-16, 06:24 PM
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Ray:

Yeah I was thinking I'd have to ensure the the strap was grounded to the enclosure. The #4 is Aluminum XHHW and I'm planning on putting a 60A breaker on it at my main panel, was that what you were referring to?

This is the panel I was going to use: http://www.amazon.com/Siemens-E0816M...ords=sub+panel

Pat:
I thought about 6-50, but the Tesla comes with a 14-50 plug and I'd rather not have to rig up an adapter. Just less stuff to buy.
 
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Old 05-22-16, 07:44 PM
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I'm planning on putting a 60A breaker on it at my main panel, was that what you were referring to?
Yes. Sorry I just read too quickly.
 
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Old 05-22-16, 08:54 PM
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You could up the circuit breaker to a 70 ampere under the "next larger size" rule as aluminum #4 XHHW is rated at 65 amperes. I would be tempted to use more of the #4 XHHW aluminum rather than going with the #6 copper. Be sure to use aluminum compatible splicing materials.
 
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Old 05-23-16, 05:22 PM
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Yeah I'll probably go 70A on the #4 just for the capacity. Unfortunately it ends in a junction box in my garage up near the ceiling, so I'll have to run #6 down to my sub.
 
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Old 05-23-16, 06:12 PM
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Unfortunately it ends in a junction box in my garage up near the ceiling, so I'll have to run #6 down to my sub.
You can't run 70 amps on #6 aluminum and actually #6 THWN and XHHW are 65 amps but can be up-rated to the next available breaker size. It is my understanding NM-b is limited to 55 amps (60a if no 55 amp breaker available.)
 
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Old 05-23-16, 06:26 PM
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Correct, I'll be using #6 Cu as in my diagram, THWN. I've read the same about NM-B so I won't be using that.
 
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Old 05-23-16, 07:58 PM
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If it hasn't already been written, you will need special split bolts to connect copper to aluminum. You need split bolts specified for aluminum/copper connections that keep the copper and aluminum wires from touching.
 
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Old 05-23-16, 08:09 PM
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From post number 14:
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Be sure to use aluminum compatible splicing materials.
 
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Old 05-24-16, 11:09 AM
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Hmm, I'm having a hard time finding connectors that will fit a #4 wire. Any suggestions for #4 Al to #6 Cu?
 
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Old 05-24-16, 12:06 PM
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Old 05-24-16, 12:12 PM
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Polaris connectors. https://www.zoro.com/polaris-insulat...4b/i/G4038483/
(I have no connection with Zoro, never had any dealings with them at all.)
 
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Old 05-24-16, 12:16 PM
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The split bolts are more of a hassle because they have to be taped but as you can see from Furd's link and my link split bolts are cheaper.
 
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Old 05-24-16, 12:47 PM
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Note well that the split bolts that Ray linked to have a moveable "bridge" to prevent the copper conductors from contacting the aluminum conductors. It is the galvanic action of the two dissimilar metals that cause problems and that means that standard split bolts are NOT acceptable.
 
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Old 05-24-16, 12:58 PM
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Ah, good catch. I've seen wire nuts for smaller gauges to combine aluminum and copper (the purple ones), but those have an anti-oxide paste inside so that apparently makes it ok for the conductors to touch. I assume with a split bolt like this I would still need to goop the aluminum side to prevent an oxide layer from forming?

From what I've read it's more about preventing the oxide layer on aluminum than galvanic corrosion between Al and Cu (which would require an electrolyte).
 
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Old 05-24-16, 01:38 PM
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Actually, those purple wire nuts have a fairly high failure rate, especially when heavy currents are involved. The anti-oxidation paste is more for conductivity than corrosion prevention although it does serve as such. The moisture in the air will serve as the electrolyte causing corrosion of dissimilar metals.
 
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Old 05-24-16, 01:52 PM
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In that an oxide layer reduces conductivity, yes. Ambient humidity is not an electrolyte. In any case taping the connections is required so that should mitigate any issues.
 
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Old 05-24-16, 02:59 PM
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No need to tape the Polaris. Splitbolts wrap with rubber self fusing tape.* Wrap the first layer of tape sticky side up then go to sticky side down. That makes it easier to remove the wrap if you ever need to. You can just slit it and peal it off.

*http://www.homedepot.com/p/3M-Scotch...BA-5/202195402
 
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Old 05-24-16, 03:17 PM
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I'd use Scotch 2242 rubber tape, it's cheaper than the 2228 and works just as well.
 
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Old 05-24-16, 03:22 PM
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Pat wrote:
I'd use Scotch 2242 rubber tape
2242 SPLICING TAPE - Walmart.com
 
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Old 05-28-16, 07:45 PM
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Quick question, what size ground would I need to use? Can my conductors be #6 and my ground be #8?
 
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Old 05-29-16, 01:31 PM
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Well I found it per NEC Table 250.122 so I went ahead with the #8 ground.

I've attached pics of the final install. I'm a little disappointed with the routing conduit routing, but I'm not sure how else I could have done that, any suggestions for when I put in the 14-50 outlet?

If I were to get this inspected is there anything here that wouldn't pass? The LnI website has done a pretty good job of convincing me I need to get a permit if I want to avoid hassle when it comes to selling this place (though I don't plan to for the next decade or two).

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Old 05-29-16, 02:24 PM
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I know I said it was okay but on second thought I would have added a ground bar not re-purposed the neutral bar. That would make it less likely an inspector would red flag you for an improper use of a neutral bar. For less than $10 a good way to avoid a possible a hassle from the inspector even though electrically you are correct.
 
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Old 05-29-16, 03:05 PM
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Hrm, don't think I left enough wire to run to the bottom of the panel. I'm assuming I could mount a bar vertically to the right there.
 
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Old 05-29-16, 03:18 PM
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The heat pump requires a dedicated circuit. You should not have tapped that circuit. You have nopw created a violation where none existed.
 
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Old 05-29-16, 03:23 PM
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Nope. The heat pump still has its own dedicated circuit. That's the 30A breaker you see in that sub panel.
 
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Old 05-29-16, 05:44 PM
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Pat wrote:
I'd use Scotch 2242 rubber tape
2242 SPLICING TAPE - Walmart.com
It's less than $5 at Lowes'. Wally World isn't that cheap on stuff like this.
 
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Old 05-30-16, 11:11 AM
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I'm really not thrilled about that conduit routing on the feed line, it looks amateur to me. I might be able to redo it when I put in the 14-50 outlet and not waste materials. I would appreciate any suggestions as to how to come down from the ceiling around those bends and into the panel.
 
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Old 05-30-16, 01:38 PM
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I don't think there is much you can do about the conduit other than adding more clamps to make it straighter.
It would have looked cleaner if you used rigid conduit and 90 pull ell or LB, but it would be bit harder to pull wires because you can not pull wires in one shot.
 
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Old 05-30-16, 04:11 PM
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Yeah I might take the FMC straight to a junction box centered with the panel, then rigid down to bend around those corners and into the panel. There is no stud in line with the center of the panel though, can I put an external jbox into just drywall?
 
 

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