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:

511813

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)

[Bill Howatt]

FWIW, here is how much heat is generated by running 20A down the various common sizes of 2 conductor cord (half of shown value for each single conductor):
#12 1.3W Per foot for 2 conductor cable
#14 2.0W
#16 3.2W
#18 5.1W
Only the #12 cable is the legal size for a 20A load so the others are effectively overloaded.
If the load is dropped to a more typical 15A, then the #16 wire value drops to 1.8W per foot for 2 conductor cable
I'm not going to make much of a call on fire risk but I doubt 15A through a #16 cord would heat it up that much such that it would cause ignition. It's not much more than the dissipation of the legal #12 at 20A. However, insulating it such as covering it with carpet would make the heating from the power dissipation worse but I'm going more for the damaged (broken) conductors when under a rug. Also, how well the wire is bonded to the plug and receptacle pins, strain relief and pin construction for a good connection is something I'd be more concerned about on cheapie cords.

[Cameron Wood]

AFAS heat generated in an extension cord, 240 volt makes less. A 1500 watt heater at 120 volts has 12.5 amps current, while at 240 volts, only 6.3 amps in each wire.

240V a higher fear factor because it is less familiar.

[mike stenson]

AFAS heat generated in an extension cord, 240 volt makes less. A 1500 watt heater at 120 volts has 12.5 amps current, while at 240 volts, only 6.3 amps in each wire.

240V a higher fear factor because it is less familiar.

Yet it's usage is way more common than 100-120, and for good reason.

[Bill Howatt]

True about the current at 240 being half of that required for same wattage at 120V. However, he said he has a 240V heater and nothing more so we don't know what the current is.
A common portable construction heater runs about 4800W so is a 20A @240V device.

[Wes Grass]

Physically damaged is one thing... under a rug ... no airflow ...

Otherwise, its just another resistive load helping to warm the shop ;-)

[Carl Beckett]

I would be more worried about running an electric heater in a shop. Definitely I would not leave it unattended.

(I do have an electric garage heater in my shop and do have it running off a short properly rated 220V cord/connector - but I worry more about the heating elements causing a fire than I do the cord over heating) Maybe just fear of the unknown for me.

My sons friend just had his shed burn down last weekend that he was using as a shop. Still under investigation, but the first thought is he forgot to turn off the space heater when he left. Nobody was hurt but considerable damage to the house that the shed sat beside.

[Bill Howatt]

...Still under investigation, but the first thought is he forgot to turn off the space heater when he left. ....

If your wiring is configured suitably it's nice to be able to kill all the power with a single switch or sub-panel breaker when you leave.

At the lab I worked at years ago, I would say the night security staff's largest number of notes pertained to soldering irons left plugged in.

[Greg Quenneville]

Different customs create different standards. I live in the 240v part of the world. Our wall outlets are rated for 10 amps and are just mounted with a drywall clip with no electrical box. Extension cords and cheap power boards are common.

When I moved here I was alarmed at how chintzy the local wiring seemed yet it doesn’t seem to be a problem.

My Dad lost his shop in Canada because of a space heater. He was never the same afterwards.

[Steve Demuth]

My last place of work, banned personal tea/coffee pots in our office because of their being frequently left on, cooking dry, and thus creating a potential fire hazard.

[Charlie Velasquez]

My last place of work, banned personal tea/coffee pots in our office because of their being frequently left on, cooking dry, and thus creating a potential fire hazard.

After retiring from the classroom our district hired me to head an energy management program. Part of the job was a weekly inspection of the buildings to see how well staff was adhering to our energy usage policies. Then I would generate reports describing each building's compliance percentage. Principals hated to be low building in the district. If a staff member was the cause for the low rating more than once or twice, the principal was usually quick to "address" that employee.

[Doug Garson]

After retiring from the classroom our district hired me to head an energy management program. Part of the job was a weekly inspection of the buildings to see how well staff was adhering to our energy usage policies. Then I would generate reports describing each building's compliance percentage. Principals hated to be low building in the district. If a staff member was the cause for the low rating more than once or twice, the principal was usually quick to "address" that employee.
Just curious, what were the most common policies that were not complied with?

[Charlie Velasquez]

Just curious, what were the most common policies that were not complied with?


Most common were:
computer usage.


Computers were to be shut down as soon as the students were dismissed. When we first started the program 87% we’re left on 24/7. After one year a staff member might occasionally forget to shut down their equipment at the end of the day, but no computers were left on 24/7.
Computers were to go to sleep mode after 10 minutes of inactivity. Most staff had had exotic, or cutesy screensavers running that prohibited the computers from going to sleep.



We started the program when all the computers were big clunky boxes and monitors were those big crt things. Cost of electrical usage for computers dropped as they became more efficient and monitors were lcd, or better yet, laptops that could be charged at night. However we kept the policy as a philosophical “buy-in” for the staff.


Lights


off anytime the students left the room
majority of hallway and classroom lights off when students left the building



These were the most common, only because of the number of opportunities. A high school with 600 computers might see 5-10 or so left on after school hours. Later, when the district went to individual laptops and students took them home to charge, we only had computer labs if the curriculum required specific software that we could not license for individual machines.


The more expensive issues usually involved hvac, although at least once an expensive hvac issue was computer lab related.

[Doug Garson]

Most common were:
computer usage.


Computers were to be shut down as soon as the students were dismissed. When we first started the program 87% we’re left on 24/7. After one year a staff member might occasionally forget to shut down their equipment at the end of the day, but no computers were left on 24/7.
Computers were to go to sleep mode after 10 minutes of inactivity. Most staff had had exotic, or cutesy screensavers running that prohibited the computers from going to sleep.



We started the program when all the computers were big clunky boxes and monitors were those big crt things. Cost of electrical usage for computers dropped as they became more efficient and monitors were lcd, or better yet, laptops that could be charged at night. However we kept the policy as a philosophical “buy-in” for the staff.


Lights


off anytime the students left the room
majority of hallway and classroom lights off when students left the building



These were the most common, only because of the number of opportunities. A high school with 600 computers might see 5-10 or so left on after school hours. Later, when the district went to individual laptops and students took them home to charge, we only had computer labs if the curriculum required specific software that we could not license for individual machines.


The more expensive issues usually involved hvac, although at least once an expensive hvac issue was computer lab related.

Interesting, I would not have thought of the computers as the main issue, I would have guessed the lights especially pre LEDs, and thermostat settings.

[Charlie Velasquez]

Interesting, I would not have thought of the computers as the main issue, I would have guessed the lights especially pre LEDs, and thermostat settings.
In most rooms in our district the teacher/employee cannot control the temperature settings with the thermostat. The stat serves only to relay information to our hvac software.
The staff have learned a “forbidden” workaround of our district’s set points of 68° heating and 74° cooling. In the winter they would put a paper towel in ice water and place it on the thermostat, in the cooling season they would put a coffee pot under the thermostat.

It was kinda funny… we would be sitting in our maintenance building and our lead hvac guy, Jeff, would chime in,”Mrs. McDonald in Room 217 at Grant School just put a cold paper towel on her thermostat.” Our hvac software sends a flashing alarm on our computers whenever there is an anomaly or the temp in a room is outside certain parameters. Going from 68° to 45° in 15 seconds will do it .
So Jeff would call Grant School, have the secretary patch him to Mrs. McDonald’s room and say, “Good morning, Mrs. D. The thermostat will work much better without anything restricting the normal air flow. Please remove anything you have on the thermostat. Thank you.”

The teachers were mesmerized when he did that. One teacher spent an hour after school looking for hidden cameras.

[Doug Garson]

In most rooms in our district the teacher/employee cannot control the temperature settings with the thermostat. The stat serves only to relay information to our hvac software.
The staff have learned a “forbidden” workaround of our district’s set points of 68° heating and 74° cooling. In the winter they would put a paper towel in ice water and place it on the thermostat, in the cooling season they would put a coffee pot under the thermostat.

It was kinda funny… we would be sitting in our maintenance building and our lead hvac guy, Jeff, would chime in,”Mrs. McDonald in Room 217 at Grant School just put a cold paper towel on her thermostat.” Our hvac software sends a flashing alarm on our computers whenever there is an anomaly or the temp in a room is outside certain parameters. Going from 68° to 45° in 15 seconds will do it .
So Jeff would call Grant School, have the secretary patch him to Mrs. McDonald’s room and say, “Good morning, Mrs. D. The thermostat will work much better without anything restricting the normal air flow. Please remove anything you have on the thermostat. Thank you.”

The teachers were mesmerized when he did that. One teacher spent an hour after school looking for hidden cameras.
Brings back memories of primary school (60+ years ago). In the winter, one of my teachers would open all the windows during class changes and put a wet paper towel over the thermostat to speed up reheating the room. Funny that I still remember that and his name, Mr Bachelor, don't remember many other teacher names and of course at the time don't think I knew why it worked. Pretty sure he didn't get any calls from the HVAC guy back then. :cool:

[Tom M King]

My Elementary school was heated by a guy that shoveled coal into a boiler. There was no air conditioning.