I need to make a 220 volt, 20 foot extension cord/ 3 to four prong converter

[CalG]

Receptacle circuits and 15A outlets are predicated on that normal plug in devices are rated closer to 15A rather than 20A and there may be more than 1 device plugged in. Devices that require more than 15A have a 20A plug and you need to have a 20A receptacle to receive them. I always use 20A receptacles in my shop or areas where I may need a 20A plug in.

Ron

Yes, but the OP wants to power his dirt heater. It's a specific application! Wire to the task! Or pay more for internet conservatism. It's the OP's choice.

 

[4570Man]

Yes, but the OP wants to power his dirt heater. It's a specific application! Wire to the task! Or pay more for internet conservatism. It's the OP's choice.

Would you put 5000 pound rope on a 10000 pound winch even though you only planned on pulling 4500 pounds?

 

[CalG]

Googling how long can 14 gauge carry 40 amps didn’t bring up anything. I’m guessing the load in .3 seconds on a dead short is a lot more than 30 amps.

So you are going to let the internet determine when the insulation will burn through and the fire will start?

You know those lines over head, those bare un insulated wires that carry the power to your house and all those around you. The are not so very large, but they carry thousands of volts and hundreds of amps. and they don't burn through. They are well "ventilated".

The electrical code is based on conductors that will burn through to open any short. That's right, the design is that the conductor will burn through in the event that the "protection" fails.

Size the wire to carry the load, Size the protection to protect the wire. Let the device burn if it will.

The OP may be advised to change the amp rating for the beaker that powers his soil heater.

 

[Fuddy1952]

I didn't read all replies but this is what I made years ago for a Lincoln stick welder.
I rarely use it, but it's 10 gauge 25ft. 120v.
I cut the one plug about a foot from end, wired to a 220v female dryer outlet. The longer end wired to male 220v plug.
Now plugging the 120v ones together I have an 220v extension cord. Reversing I have a 120v one plugging dryer 220s together.

 

[Jstpssng]

So you are going to let the internet determine when the insulation will burn through and the fire will start?

You know those lines over head, those bare un insulated wires that carry the power to your house and all those around you. The are not so very large, but they carry thousands of volts and hundreds of amps. and they don't burn through. They are well "ventilated".

The electrical code is based on conductors that will burn through to open any short. That's right, the design is that the conductor will burn through in the event that the "protection" fails.

Size the wire to carry the load, Size the protection to protect the wire. Let the device burn if it will.

The OP may be advised to change the amp rating for the beaker that powers his soil heater.

I've read through the responses, and have decided to have a licensed electrician replace the cord with a properly sized wire. The numbers I gave came directly from the specs in the manual, so I am going with what I have provided.

Thanks to everyone for the input.

 

[chim]

I知 pretty sure it痴 against code to use a wire too small for the breaker. .......................................

With few exceptions, that is true (when referring to permanent installations). For loads that are temporarily connected via plug and cord, things are different. A cord should be sized for the load. One example of this is the 18 gage cord on a table lamp that plugs into a 15 or 20 amp circuit.