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My mom just bought an old house (1917). The Main Breaker has 3 wires two hot from a 30amp 220 breaker and one ground going from the main into a sub-panel, there is no room to feed a 4th neutral wire. So there is not a neutral wire. Can I add to the sub-panel a grounding rod from the ground to a grounding pole into the dirt? I then want to use the sub panel to only hook up the one 3 wire 220-volt plug. The ground to the ground bus in the sub-panel would be connected to the ground in the main and the grounding rod at the sub-panel. The 2 hots to a 30 amp 220-volt breaker in the sub-panel. The sub-panel would never have 110 volts or anything using a neutral and would not have a neutral bus. As long as only the one 220 volts was connected this way would this be safe?

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    Well, typically older 3-wire connections like this are hot-hot-neutral no ground. Are you saying you want to re-task that neutral(?) wire to be safety ground, and then use it 220V-only, no neutral wire and no 110V loads? – Harper - Reinstate Monica May 1 '20 at 7:16
  • What are you planning to plug into that plug? – ThreePhaseEel May 1 '20 at 11:45
  • Is the wiring between then two panels in metallic conduit - entirely likely given the age? – Ecnerwal May 1 '20 at 12:56
  • Yes, I want to make the Neutral into the ground. The sub panel only has three wires available. So I can do hot-hot-ground or hot-hot-neutral. I was going to go with hot-hot-ground leave in the bonding screw and make sure no other connections were used. The only purpose is to plug in a ceramic Kiln. It has a three-prong 220-volt plug. The garage already has 110 plugs everywhere. I would run hot-hot-ground from the plug to the panel. I was going to add a grounding rod to the ground in the subpanel for added safety. There would be no neutral bus in the sub panel. Thoughts? – Aaron May 2 '20 at 6:19
  • The Conduit between is grey PCV electrical grade. – Aaron May 2 '20 at 6:22

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