Electrical adapter

I need to adapt a 4 pole 220v to a 3 pole 220v plug. This is to run my air compressor off my welder/generator. The welder has a 4 pole 220v plug, (2 hots, neutral, ground) the compressor has a 3 pole plug(2 hots and a ground). I'm thinking that all I need to do to make this work is to just use the 2 hots and the ground from the 4 pole(not using the separate neutral) and attach them to the 2 hots and ground on the 3 pole, and it should work.
Any other thoughts on this, maybe from an actual electrician?
The reason for this is that our house is 50 years old and has limited capacity for any more electrical load, or space for new breakers.

Thanks,

John

That will work if there are no 120 volt loads in the air compressor, like a contactor coil.

If there are any 120 volt loads (connected to neutral) its not considered safe these days. Where there are 120 volt and 220 volt loads, I've seen this connection kill.

Gerald J.

But if the compressor comes with a 3 prong plug to start with, then it wouldn't have any 120 volt loads assuming of course that it is a 220/240v compressor with 2 hots and assuming the 3d wire is a grounding connector and not a neutral/grounded connector. But this calls for making too many assumptions which isn't a good idea.

Guess I'd like to hear more about the information on the compressor motor data plate, the age of the compressor, what shape are the prongs on the compressor connector. Bronco needs to provide some more info before someone sticks their neck out here with advice.

I'm thinking that a dryer plug is 4 wires since it uses 110 to run the light, etc. I forget what a 220 electric water heater uses as it can run one element or both.

Yes you can do that no problem assuming that the compressor doesn't draw more than the generator outlet and cord is rated for.
Just tape off the neutral at the compressor.
Be sure to bond the unit with the bare or green wire.

The compressor is a Sears that I've been running on a 3 prong dryer outlet for 20 years or so. Data plate on compressor says 240v, 60hz, 1 phase, 14 amps.

The problem is that I have a 220v plasma cutter that I don't have an outlet for. I can't run both off a 30 amp dryer outlet at the same time. One of them is going to have to run off my Weldanpower G8000.
The plasma cutter has a 3 prong plug just like the one on a Lincoln AC225 buzzbox. So that's the situation as it stands at this point.

Okay, heres the deal:

1) IFFFFFFF the air compressor is straight 240 volts WITH NO 120 VOLT (No need for Neutral) then you can run it with 3 wires, 2 hots L1 and L2 and an Equipment Ground. Thats likely what it is since it has a 2 pole 3 wire grounding plug, i.e. 2 hots and an equipment ground....assuming thats the plug it has ???????

2) Its permissible to run plug n cord connected loads (like say that welder) from a portable generator having its own mounted receptacle with no grounding electrode attached to the generator.

3) BUTTTTTTT the gennys Neutral should be bonded to its iron frame !!!!!!!!!!!!!!!!!!!

SOOOOOOO THE QUESTION IS ???? Is the gennys Neutral bonded to its iron frame???????????? A simple continuity tester or an ohm meter (Neutral to frame ohms continuity test) can answer that question in a few seconds.

BOTTOM LINE if youre gonna use that genny to run a straight 240 volt (NO 120 No Neutral needed) air compressor via a plug connected to a genny mounted receptacle, I suggest you check to insure the gennys Neutral is bonded to its frame.

CAUTION check with your local authority and be cautious of lay "opinions" offered here or from anyone before you proceed, these electrical precautions CAN SAVE YOUR LIFE !!!!!!!!!!

Best wishes n God Bless

John T Longgggggg retired Electrical Engineer and rusty on the latest NEC so CHECK WITH LOCAL AUTHORITY cuz its been toooooooo long since I practiced lol

But for 70 years, a three wire plug WAS used for ranges, dryers, and other things with 220 and 120 volt connections. So the precedent is there, just that if there's a break in the ground or neutral, the person touching the appliance or holding a grounded tool that depends on that ground gets 120 volts. And that can be an unhealthy shock, deadly in fact.

The use of four wires for 240/120 volt loads is relatively recent, maybe the last 20 years, but it can provide a significant improvement in safety by keeping the safety ground separate from normal current carrying conductors.

Its better to not guess at the safety of the three wire connection but to remove and discard that three wire plug and wire a four wire cord and plug making sure of the neutral and ground connections in the appliance and the available outlet. If there aren't enough outlets, hire an electrician to add more. Cobbles often hurt.

Gerald J.

These are the plugs I'm dealing with.
First picture is the welder wiring diagram, second is the welder outlet, and third is the two plugs I'm trying to adapt to the welder outlet, Plasma cutter plug on the Left, and air compressor on the right.

Is there is connection to earth to the welder chassis when all this is running?
Best solution would be to install a new panel with more breakers.
Better yet a generator transfer panel with extra load breakers. There will be four new breakers to supply a new panel or plugs in the shop. And the welder-generator can be used to power the house during outages. Without a hilly-billy cob job backfeed abomination.
This panel installs between the existing meterbase and existing breaker panel



TWB2012DR Panel/Link®

The Panel/Link TWB includes a 200A main circuit breaker interlinked with a 30A - 125A generator breaker feeding a heavy-duty copper bus with feed-through lugs. The interlinked circuit breakers keep the generator isolated from the utility at all times, even with the deadfront removed. The TWB is suitable for service entrance and may be used as a main panel or feed-through to a sub-panel or main panel. The TWB has provision for 4/8 branch circuits and is ideal for applications requiring the entire service panel to be available for generator power.



MODEL TWB2012DR
MODEL DESCRIPTION Panel/Link
MAX. GENERATOR RUNNING WATTS 30000
PHASE Single
MAX. NUMBER 1" CIRCUIT BREAKER OPENINGS 4
MAX. NUMBER OF CIRCUITS USING TANDEM BREAKERS 8
MAX. UTILITY INPUT AMPS 200
MAX. GENERATOR INPUT AMPS 125
POWER INLET, NEMA None
WATTMETERS No
SHIPPING WEIGHT [lbs.] 37
DIMENSIONS H x W x D [inches] 27 x 14.5 x 4.5
CABINET TYPE, NEMA Outdoor, NEMA 3R

A

So you need a male to plug into what you got and a female that you dont have for the male that you got.Box mount,cord, new female and male to match existing female.Bring picture to show counterman at supply house Make up short cord to box with female you need.Go to supply house about ten AM so contractors are done picking up and counterman has patience.[Dont bring the schematic]

Air compressors are power hogs, it may eat your generator.

It seems that my original idea will work. I just need to get a 4 prong pigtail and wire it up to the outlet that I have for the compressor. I think I will add an external ground from the welder to a nearby water pipe or drive a rod into the ground to use, just to be on the safe side.
Thanks for the replies.

John

Isn't wear, tear, fuel, noise and the cost of an adapter eventually cost more than running everything from the utility?