Is it safe to use a 220v extension cord for my shop heater?

[dennis thompson]

I have a plug in 220v electric heater for my shop. It is on one side the shop which happens to not be where I spend most of my time. Would it be safe to use a 220v extension cord ( about 15-20’) to place it closer to where I work?
Just realized I should have posted this in workshops but I don’t know how to move it.
Thanks

[Steve Demuth]

As long as it's properly rated for the current draw of heater, and you route and secure the cord appropriately, yes. Resistance heaters often draw close to their full rated amps for extended periods, so you don't want to skimp on the cord's ampacity. As always with an extension cord, you'll get some voltage drop, but that matters less for resistance heaters than for motors, so won't be a problem.

[roger wiegand]

It can be done, but I wouldn't. Instead I'd drop a new outlet where you actually want it; for that kind of load a dedicated circuit wired so that the load doesn't exceed 80% of the breaker/wire rated capacity. Some 10 ga NM cable and an appropriate outlet and breaker will probably be a bunch cheaper than an extension cord rated for that kind of load.

[Mike Cutler]

Yes, it can be safe. If it's just you, at home, in the shop by yourself. In a workplace environment, with employee's, your insurance provider would have a complete conniption fit.
How many watts is the heater, and what is the amp draw? 10awg, SO cord should do it.
With a 15'-20' foot extension cord you will see zero drop in voltage, unless this is a very large heater. Roger does have a point though about the cost. Done correctly, this cord will probably cost you about $40-$50 dollars to make. Don't go cheap on this one, as you're already "coloring outside the lines". Do it safe.

The downside, you will probably void the warranty on the heater. I'd be stunned if it allowed for the heater to be put on an extension cord.

[Jim Koepke]

Yes, it can be safe. If it's just you, at home, in the shop by yourself. In a workplace environment, with employee's, your insurance provider would have a complete conniption fit.

In a home shop your insurance provider may have fits.

This made me consult Dr. Google:

Screen Shot 2023-12-09 at 4.25.22 PM.png

I laughed on the second line.

The one thing most of them have in common is this statement:

most space heaters come with a warning NOT to use them with an extension cord.

Those little 800 watt jobs people have under their desk at work are considered "space heaters."

If the plug at the outlet is warm, you likely have a problem.

jtk

[Mark Wedel]

Back when I worked in computer labs, we sometimes had 220v extension cords for racks - we would usually try get the electrician in and do more outlets, but sometimes, extension cords as the way to go. The fact that facilities provided the extension cords to us makes me think they were safe. These were L6-30 outlets, so I guess from that aspect (twist lock), no worry about something be partially plugged in. And these were typically fairly short (15' or so).
Standard US cords are a bit of a mess, since the cord (extension or otherwise) may not be rated for 15 amps, which is the standard US breaker. One time at work, someone used a monitor cord (rated for 3 amps I think) to plug in a server, which normally had thicker cords rated for 15 or 20 amps. When the server was powered on, that fried the cord, but the breaker did the right thing so nothing too terrible happend.
Most standard US extension cords are meant for things like lights so are rated for less than 15 amps. So I can see why the heater say not to use extension cords - not that it can't be done safely, but rather most people will grab that light extension cord, use it on that space heater, and run into problems.
As my dorm proctor used to say many years ago (he was a firefighter), 'extension cords are the #2 cause of fires' - this was to explain why extension cords were no allowed in the dorms.

[Doug Garson]

Buy a cord with the correct amp rating, monitor the temperature of the cord and plugs after 15 to 20 min of use and if it's not hot to the touch you should be good to go. As others have said a heater is just a resistance load, even is there is some voltage drop in the extension cord, I don't think there is any way the heater could be damaged. I think the manufacturers are concerned someone will use an undersized extension cord and it will overheat and cause a fire. Just don't run it unmonitored until you have run it monitored a few hours to confirm it won't overheat.

[Tom M King]

I've been using heavy cords for 240V for probably 50 years. As long as you use large enough conductors and properly sized ends for the cord it's no more of a chance for problems than wires in a wall. Ever been to a large fair and seen all the black cords on the ground? One person, as they were walking into one of my jobsite houses, said they thought they were going to a fair with all the big black cords on the ground to walk on.

[Bill Howatt]

Other things being equal, it is better than the wires in the wall since it is in free air unlike the possibility of it being surrounded by insulation in a wall. Wire sizing for current is based on temperature rise to a large extent as well as some concern for resistance which is related. I agree with Doug, a resistive load is not going to suffer from a bit of voltage drop like a motor load might.

[Michael Burnside]

I agree with Tom. Extension cords get a bad wrap because it’s all too easy to be a cheapskate and use a less expensive, underrated wire.

[Jim Becker]

I would only do this if I made up the extension cord myself to the exact length required with "upsized" conductors, the same way I do cords and extensions for my 240v machinery if required. I agree with Michael that a lot of folks just use something called an "extension cord" that designed for a lamp rather than a heavy resistance load that that's where the trouble and danger comes into play.

[Bill Howatt]

I think a house fire caused by extension cords is people running them under rugs where they get physically damaged over time (broken wires which means less current capacity and hot spots). They are also likely to be lighter gauge ones to start with.

[dennis thompson]

Thanks for the responses.
I ordered a 25’ industrial welder extension cord ($65).
I will follow the advice given that when I use it for first time I will be in the shop to make sure it doesn’t get too hot.

[Curt Harms]

I think a house fire caused by extension cords is people running them under rugs where they get physically damaged over time (broken wires which means less current capacity and hot spots). They are also likely to be lighter gauge ones to start with.

Being damaged is certainly a possibility. Another possibility is that unless the user is somewhat savvy, they'll probably just buy an extension cord at Walmart or Target or wherever. Many extension cords found in general merchandise stores like those are 16 ga., extension cords intended for clocks and lamps and such may be 18 gauge. Often those cords have female ends with multiple outlets. Uh oh.

[Mark Wedel]

And in the dorms, college kids would go off and buy the cheapest cords possible (actually, most people of any age might) and not understand the implications when using it on a high current load.
Power strips were OK - presumably because those are made with thicker conductors, but are also fused (though the fuse is beyond the cord, so would not help out in the case of a damaged cord, but would at least insure that if the cord is in good shape, too much current is not being drawn through it)