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

[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.