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Thread: 240V receptacle preferences? And a boo-boo confession...

  1. #1

    240V receptacle preferences? And a boo-boo confession...

    Hello, Crickers:

    I'm getting a little bit wrapped around the axle with my wiring.

    First the good news: shop is erected, sheathed, roofed, sided, and mostly caulked. Walk-in door is installed, but needs latch set mounted. Garage door due a week before Christmas. Walls are still open, as it just passed its electrical rough-in inspection. Electrical trim just hit the top of the list.

    So today, I cheerfully opened my wiring device order, looked around the new space for a final as-built count, and realized I roughed the 240V stations (all 19 of 'em, on two circuits) into single-gang boxes.

    D'oh!

    This leaves me with two questions, one important and the second likely futile:

    1. Is there a consensus choice of 240 receptacle types among woodworkers? I've typically used 20A single outlets on 12 AWG romex in a 4s box, but I've got a boxful of 30A breakers mounted so I won't (also _can't_, per NEC, AFAIK) connect 20A outlets to those circuits. So what works well for folks? I've also run NEMA L630Rs in the past, albeit at con$iderable co$t.

    I'll have about four outlets (table saw, dust collector, planer, future upgraded lathe) semi-permanently connected. The balance are for layout flexibility, future changes, etc., and may indefinitely stay wired straight through with blank faceplates. I'm hoping not to open my walls for quite some time after they're paneled up.

    2. Is there, in fact, a 240V 30A outlet generally available that would fit neatly into a 1G box? I mean, I don't THINK so... but the one thing I'm certain of is that I don't know everything.

    Thanks for your indulgence of a non-electrician.

    Cheers,

    Jack
    --Jack S. Llewyllson

    Gratitude is a gift to yourself.

    Purity tests are the bane of human existence.

    Codeine takes the pain from every muscle but the heart.

  2. #2
    250 volt 30 amp power outlet 6-30R will fit a single gang box. Or a 30 amp 250v twistlock rec

  3. #3
    If you put in 30 amp breakers I think you should use 10 gauge wire. 12 gauge wire is only good to 20 amps (if I recall correctly).

    Mike

    [Also, I think they make a four pin receptacle for 30 amps, in case you need to bring out the neutral. It's used for electric clothes dryers.]
    Last edited by Mike Henderson; 12-04-2020 at 9:19 PM.
    Go into the world and do well. But more importantly, go into the world and do good.

  4. #4
    Quote Originally Posted by Mike Henderson View Post
    If you put in 30 amp breakers I think you should use 10 gauge wire. 12 gauge wire is only good to 20 amps (if I recall correctly).
    Thanks, Mike. Happily, that part I got right -- my 120V are wired with 12 gauge for 20 amps, and the 240s with 10-gauge.

    [Also, I think they make a four pin receptacle for 30 amps, in case you need to bring out the neutral. It's used for electric clothes dryers.]
    Four-wire is probably also great for grand, world-conquering Felders, but those aren't in my budget if I ever want to pay off this shop.
    --Jack S. Llewyllson

    Gratitude is a gift to yourself.

    Purity tests are the bane of human existence.

    Codeine takes the pain from every muscle but the heart.

  5. #5
    Join Date
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    With 30 amp breakers you need to run 10 ga. You may find a 30 amp receptacle that can mount in a single gang box, but you likely will exceed the allowable box fill, especially if you run neutrals and especially if you daisy chain the circuit, meaning you have 3 wires entering the box and 3 wires exiting the box to go to the next receptacle.

    Here's a decent box fill calculator that will tell you how many cubic inches you need for different scenarios: https://www.constructionmonkey.com/c...trical/boxfill

    But even if you can meet the box fill requirements, it's going to be a *^*&( to wire. As painful as it might be, I'd rip them out and put in 4" deep boxes.
    --Certainty is the refuge of a small mind--

  6. #6
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    All of my 240v receptacle in my shop are twist locks and amperage specific. The 30 amp versions do benefit from a "more generous" box, IMHO. The 10 gage wire is quite stiff and harder to bundle up neatly in a really tight space. I honestly like at least deep boxes for almost any application, not just 240v terminations.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  7. #7
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    I'm with Jim. All of my 240V outlets are twist lock 250V 20A. I like have the super obvious differentiation between the 120V outlets and the 240V.

  8. #8
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    Quote Originally Posted by Paul F Franklin View Post
    With 30 amp breakers you need to run 10 ga. You may find a 30 amp receptacle that can mount in a single gang box, but you likely will exceed the allowable box fill, especially if you run neutrals and especially if you daisy chain the circuit, meaning you have 3 wires entering the box and 3 wires exiting the box to go to the next receptacle.

    Here's a decent box fill calculator that will tell you how many cubic inches you need for different scenarios: https://www.constructionmonkey.com/c...trical/boxfill

    But even if you can meet the box fill requirements, it's going to be a *^*&( to wire. As painful as it might be, I'd rip them out and put in 4" deep boxes.
    This....

    Leviton has the specs for that 6-30R having a volume of about 8 cu. inches, then the wires, pigtail for the ground, not sure if that receptacle is rated for two wires at the terminals, else you have a red and a black pigtail. My calculations have the fill at about 23+ cu inches with only the ground pigtailed.
    But that may be moot Leviton has the width as 52mm wide. That exceeds the NEC limit of 50mm for a single gang device, by just a tad. It will physically fit in the box, ....but....
    Comments made here are my own and, according to my children, do not reflect the opinions of any other person... anywhere, anytime.

  9. #9
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    Here is an out of the box idea ... what about surface mounting a 4” square box in front of the single gangs to give you extra room for the wiring? I don’t think that violates code but I’m not an expert on those particulars.
    There is a very fine line between “hobby” and “mental illness.” - Dave Barry

  10. #10
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    You said the walls are still open, just bite the bullet and replace the boxes.

  11. #11
    I'd also vote for switching everything out to 4" square boxes. The guys who wired my shop did everything with "4 squares" (as they called them) and it has made it a lot easier to modify after the fact. Even the light switches are 4" boxes - no stuffing & twisting, just simplicity.

  12. #12
    Quote Originally Posted by ray grundhoefer View Post
    250 volt 30 amp power outlet 6-30R will fit a single gang box. Or a 30 amp 250v twistlock rec
    Cool; thanks. I'll give one a try, but I don't value my chances of stuffing it in there with daisy chain pigtails.
    --Jack S. Llewyllson

    Gratitude is a gift to yourself.

    Purity tests are the bane of human existence.

    Codeine takes the pain from every muscle but the heart.

  13. #13
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    Quote Originally Posted by John Lanciani View Post
    You said the walls are still open, just bite the bullet and replace the boxes.

    In my opinion, this. Easy to do now while the walls are open, I can't imaging it's hundreds of boxes to change out... you'll be done box swappin' in 20 mins.
    - Bob R.
    Collegeville PA (30 minutes west of Philly)

  14. #14
    Okay, I'm pretty well settled on this one: 1G boxes are coming out. I knew better in the first place, but wasn't thinking fast. I'll plan to replace with the same type boxes used for my 120V double duplexes with 2 circuits, which are the extra-capacity blue Carlons with 48.2 cu. in. capacity. That gives me room for stiff fingers to wrassle the stiff romex.

    Re outlet types: is the consensus choice to use twist locks? I have done that once before, and thought it worked well in practice.

    One thing I'd rather NOT do is replace the pricey breakers, which are at 30A. I believe that NEC requires 30A-rated outlets due to breaker sizing, which may herd me into using L6-30R twisties. The straight blade 250V 30A outlets don't seem to be as commonly available near me.
    --Jack S. Llewyllson

    Gratitude is a gift to yourself.

    Purity tests are the bane of human existence.

    Codeine takes the pain from every muscle but the heart.

  15. #15
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    If you happen to find some matched twist lock cord ends snap them up. Do not worry about amps or 3 or 4 wire. When I work on a big machine I cut the motor cord and install a twistlock set. Cut cord as close to the motor as possible then install new short cord into the motor on the bench. Makes any trouble shooting much easier as well as motor work like bearings etc.
    Bil lD

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