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I have a 3-wire connection for the clothes dryer, and I would like to make it compliant with current code the simplest way consistent with reasonable safety. I haven't looked at the connection block but it must be that the neutral is bonded to the chassis because the chassis is grounded.

The heavy ground wire that leads to the panel is grounded to the cold water pipe supplying the clothes washer and is exposed right next to the dryer. I could connect a wire from the ground terminal of the dryer to that ground wire and not change to a 4-wire plug and cord. In the connection block of the dryer I would remove the neutral to chassis ground bond.

Code violation? Someone could later disconnect that ground and the chassis would not be grounded. I could change to a 4-wire receptacle and connect a ground wire inside the wall or outside to the nearby heavy ground wire going to the panel.

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    Is this in North America? (BTW, you might want to complete some bits your profile.) – wallyk Nov 23 '16 at 23:52
  • Is the box for the dryer outlet flush with the wall or mounted to the surface of the wall? – ThreePhaseEel Nov 23 '16 at 23:55
  • The box is flush with the wall, i.e. inset into the wall with the cover plate of the receptacle on the room side surface of the drywall. – Jim Stewart Nov 24 '16 at 23:50
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NEMA 10-30 receptacles are grandfathered, illegal for new installation but legal to leave alone if already installed. It is not safe and it has a body count. It is legal because of lobbying by the appliance industry.

By modifying it you lose your grandfathering and make it illegal.

Your proposal solves the safety problem electrically, but mechanically it is not code legal. I am reluctant to say it would be "safe" because generally, code is written in ash and blood, and they wouldn't outlaw a thing unless experience has shown it causes fire or fatality.

Your best bet is to retrofit a NEMA 14-30 4-pin receptacle, and connect hot-hot-neutral to those same wires on the 14-30. Connect ground as follows:

Code (as of NEC 2014) allows you to retrofit just a ground wire, simply by running a solo ground wire. It does not need to use the same route as the conductors. It cannot simply go to the rod/pipe ground source that the panel uses. It must go back to the panel, and the same panel as the conductors.

The ground path must be the required wire size its entire run. As long as that is true, multiple circuits (out of the same panel) can share a ground wire when retrofitting grounds.

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    Actually, it can go to the grounding electrode system as per 250.130(C)(1) considering this is an existing non-grounding-type receptacle for which 250.130(C) applies... – ThreePhaseEel Nov 24 '16 at 0:29
  • @Tester101, that has been part of the NEC for a long time. – Speedy Petey Nov 24 '16 at 0:48
  • @SpeedyPetey not sure why I thought it was a recent addition... deleted. – Tester101 Nov 24 '16 at 0:50
  • Must the 'solo ground wire' go back to the panel as one wire or could I run a ground out of the NEMA 14-30 and connect it to the nearby heavy bonding wire from the panel? This wire is exposed on and clamped to the cold water pipe supplying the clothes washer. – Jim Stewart Nov 24 '16 at 1:06
  • I'd run it back to the service panel, seriously. The panel-ground rod bonding wire cannot have splices, but the retrofit ground can, as long as it's inside a junction box. Your house's grounding system sounds squirreley to me, bonding to the washing machine's pipe is definitely wrong. It should only bond on the city's side of the water meter, other than that, never use water or gas pipe as ground paths. Wire so you don't have to re-wire if someone replaces that grounding system. – Harper Nov 24 '16 at 1:25

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