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I’m trying to change the cord on a second-hand dryer that came with a 3 prong cord to a 4 prong to match the outlet I have.

I have a decent sense of what I need to do to match up the hot-neutral-hot wires but my issue is what to do with the ground wire.

For whatever reason the current 3 prong configuration had the green ground screw already in place but with the head on the interior of the dryer (see image). So I cannot simply unscrew and then screw on to attach the ground wire as-is.

Is it imperative that the ground wire on the 4 prong cord be fastened through that screw or is there some easy way around this? I also am unsure if I can even remove the entire back panel because there are a few other inverted screws with heads on the interior of the machine.

enter image description here

EDIT: I also now noticed that internally the current backwards ground screw is connected to a green wire, shown poking out in the pic

enter image description here

EDIT

Here’s my current configuration! I wasn’t able to find an up-to-code green ground screw that could thread itself but I got a similar sized sheet metal screw that seems to work.

Follow up questions:

  1. Is there any safety issue with not technically using a green ground screw?

  2. Is the ground wire making enough contact, as much as can be seen from the picture? I was told that essentially as long as it’s touching the chassis that’s enough. The angle is super awkward with the plate that holds the wires in.

enter image description here

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    Is the other hole to the right of the ground symbol also threaded to take a screw? – brhans May 30 at 3:49
  • It seems threaded but I am not 100% sure since it doesn’t seem to accept the same sized screw as the others, if that makes sense? – Josh P May 30 at 8:36
  • I wouldn't mess with the inverted screw, it may be holding a stake-on on the backside, and if the threads are imperfect you could back the screw out and lose the grounding to some unseen component. – NoSparksPlease May 30 at 13:15
  • Hi all, I added a picture with my current configuration. Appreciate a comment letting me know if this is safe or not! – Josh P May 30 at 16:53
  • Looks spot on and as the factory intended. The sheet metal screw was an error: it needs to be tapped -32 or finer to have reliable grip and make good enough electrical contact. 30A breakers are rated to instant trip at 300A, so it's a bit of current. Next time you're at a REAL hardware store (the kind with a wall of 1000 drawers for screws), just pick up any 10-32 self-tapper. Does not have to be green. Does have to be -32 and the hole is probably punched for #10. – Harper - Reinstate Monica May 30 at 18:23
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Brhans has the answer in a comment. There are two plainly marked ground screw holes: one is occupied from the backside, and the other awaits a #10-32 self-tapping screw you'll need to get from a hardware store*. My local shop sells them by the one for a dime. It doesn't have to be green, but from the look of it, it has to be self-tapping.

Do not use a sheet metal screw. Thread pitch must be -32 or finer. Any competent hardware store* will have 10-32 self tappers. They do not need to be green, that's just a marketing gimmick.

The main thing when converting 3-prong to 4-prong is to make sure neutral is isolated from the dryer chassis. Typically there will be an obvious jumper which does this, I presume you have already removed it. The isolation can be tested with an ohm meter.


* Hardware stores are not lumber yards. Home Depot and Lowes are lumber yards. Ace, TrueValue and HWI are hardware stores, but your best bet is the local family-owned store that's been there for 100 years.

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  • Thank you, although I am a bit confused by the last part. I did not see an obvious jumper connected to the neutral. Also I did edit my post to include new info regarding the current ground screw which seems to be attached to something internally. – Josh P May 30 at 9:04
  • @JoshP 3-prong plugs have to connect the white wire to the case. 4-prong plugs can't, so you need to break the connection. You can verify this was done correctly with an ohm meter (or multimeter set to ohms). Probe the ground screw and the screw holding the white wire from the plug. You should see infinite resistance (the same as if you weren't touching the leads to anything at all). If you see finite resistance, that green wire inside is likely attached to white somewhere and that needs to be addressed before you can even safely plug your dryer in. – Everly Foxton May 30 at 18:16
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    Chances are that green wire is connected straight to a white wire just inside. If that's the case, this is your ground strap. Disconnect the end from the dryer case and attach it to the same screw as the white wire from the plug. Make sure it really is a ground strap before doing this though. Note: Most dryers are made so you can open the lid, which would give you easy access to the inside of that screw. It may be worth looking up how to open yours. – Everly Foxton May 30 at 18:30
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You may be able to use a nut with the correct threading, but then you might have to be careful you don’t back the screw out. If it does get backed out and you end up losing it, maybe you could get a replacement grounding screw and put it in head-out when you hook up the ground. Then again, maybe you could use a replacement screw in the hole to the right of the ground symbol.

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    A nut is unlikely to work with a self-tapping screw like that appears to be. It appears also that the screw is actually holding a grounding wire for something on the inside, in which case it would be bad to accidentally unscrew it. – jpa May 30 at 14:01

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