Assume for a moment that you have to wire an adapter between two 220v plugs. One plug is a 4 pin plug, with a ground, a neutral and two 110v hots. The other plug is a 3 pin plug, with a neutral and two 110v hots. If the source of our energy is through the 4 pin plug, and the load is on the 3 pin plug, is there anything wrong with wiring a jumper wire between the neutral and ground lugs in the 4 pin plug? (I.e. in the 4 pin plug, you'd then have two 110v hots, and 2 ground/neutral pins tied together).
Does your analysis change at all if the source of the energy is a generator with a 4 pin 220v outlet on it?
I believe the NEC states that the 'ground' and 'neutral' are only supposed to be connected together at the service entrance/main panel. Even at subpanels you are not permitted to connect them together. Typically 220 outlets only have the two hots and the ground and no neutral. There is a good reason for this but I can't remember it off the top of my head. If the 'adapter' is plugged directly into the generator then it won't matter as the generator if wired correctly will have the ground and neutral tied together right near the outlet. I will assume that the generator is properly grounded to the earth.
Last edited by tiredone; 05-05-2006 at 12:30 PM.
Reason: forgot the second part
Don't tie ground and neutral in a plug or receptacle. This is always wrong. It is dangerous because any current flowing through the neutral will tend to elevate the voltage on all the metallic objects in the circuit.
If the supply receptacle has 4 pins with ground and neutral separate, and you are fixing up an adapter, then it is almost always correct to connect the ground, and to not use the neutral at all. Typical examples would be welders and air compressors.
The one possible exception is if you are trying to use an older electric range or electric dryer. The correct way to fix this is to rewire the appliance to take a 4 wire cord, and separate ground and neutral in the appliance, and get rid of the 3 wire cord. But if you insist on using an adapter, then you would connect the neutral and not use the ground. This is a code violation, so do so with caution.
The 4pin stove outlets have the two 110v pins, a return for one of the 110 phases to power clocks and the like on the stove, and a ground. Most three wire 220v stuff I have dealt with had the two hot leads and a ground, no neutral. The voltage was derived by the two hot leads being in opposing phases, making a total potential of 220v between them. At least that's the way my welder works.
What are you hooking up?
My house has a 'generator outlet' on it, that is 3 pin, 220v. One ground/neutral, and 2 110v hots. It is wired into a transfer switch, with the ground/neutral going to a grounding strip, and the 2 110v hots going through fuses to the transfer switch.
I just rebuilt a generator, but it has a NEMA L14-20 4 pin plug on it...neutral, ground, and 2 110v hots. I'd like to make a converter cord to go from the generator to the generator outlet. THe question is what do I do with the 4th pin on the generator? Do I leave the neutral disconnected on the generator? Do I tie from neutral to ground at the generator?
If I installed a new 4 pin outlet as the 'generator outlet', the ground and neutral would be tied together in the transfer switch box the outlet is attached to, so there doesn't seem to be much point in worrying about it, but I wanted to seek some second opinions.
Well, you can call the third (non-hot) prong in the 'generator outlet' whatever you want...ground or neutral. The fact is the transfer switch is next to the main breaker box, and the third prong is wired, through the transfer switch, to the neutral/ground slot on the breaker.
I'll investigate sticking a ground rod in for separate grounding of the generator, and bypass the ground lug in the generator outlet.
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