Measuring or Guessing, Appliance Extension Cords, and Heaters!

When you have measuring devices, you measure, when you don’t, you guess.

Tester Fluke 12
5 Meg Ohm Impedance on AC

You’re not supposed to use Heaters or High Current Devices on Extension Cords. The large amount of current drawn will overheat the cord and can result in a fire, damaged plugs, or damaged outlets. I use a heater, on the lowest setting, cycling on and off on thermostat, and plugged into an “Appliance Extension Cord”.

Duty Cycle is the amount of time a device is supposed to be on vs the time that it is off. 50% Duty Cycle means in a designated time, it’s off 50% of the time. This is one way of reducing overheating, and why my Heater is always set to cycle, Thermostat not turned up all the way.

The Appliance Extension Cord is AWG (American Wire Gauge) 14/3, or 3 conductors (Hot, Neutral, Ground) of 14 Gauge Wiring. House wiring uses (in the U.S.) 14 gauge for 15 amp circuits, and 12 gauge for 20 amp circuits.

The Heater is 1300 and 1500 Watts. I don’t use the 1500 Setting. But Current equals Power divided by Voltage. I = P/E

1300/120 = 10.8 Amps   and   1500/120 = 12.5 Amps

Extension cords usually found in homes are often 16 or 18 gauge wiring.

A useful link and info on the topic of Extension Cords:

Extension Cord Buying Guide
And, from another source:
“Matching Extension Cord to Load Extension Cord Wire Gauges, Amperage Rating, and Wattage Wire Gauge Amperage Rating Wattage Rating

#18 for 5 Amps (600 Watts)
#16 for 7 Amps (840 Watts)
#14 for 12 Amps (1,440 Watts)”

Both are adequately covered by #14 gauge house wiring, but for an extension cord, 1500 Slightly Exceeded the Max Recommended in the above paragraph, but consulting the U.L. Sticker on the Appliance Extension Cord, it’s rated for 15 Amps (1875 Watts). Old Outlets, plugs that fit loosely in Outlets, loose wire screws on Outlets (Electrician Stuff) can cause overheating at higher current levels. But my house was rewired, the Outlets are new, and are commercial grade.

So, I had 2 Appliance Extension Cords, a 15′ AWG #14/3 and a 12′ AWG #14/2 (with a 3rd Grounding Conductor, the same configuration as the 15′ Cord, but the grounding conductor is often permitted to be a smaller wire) and I figured the 12′ Appliance Extension Cord would supply slightly more voltage.

Measuring voltage at the Appliance Plug, both the cords supplied 121 volts with the heater off. The 15′ cord supplied 118.x volts on the 1300 and 1500 Watt Settings, the 12′ supplied 117.x on the 1300 and 1500 Watt Settings. In this case, the longer cord was supplying slightly more voltage, in use, and I decided to keep it in place. Typically the longer cord will lose more voltage while in use due to a voltage drop across the resistance of the wires. There must be a looser fit on the plug, or slightly corroded connections somewhere, or they cheated on the wire size to account for the slightly decreased voltage in the shorter cord.

I’m going to buy a 6′ #12/3 or #12/2 (with a ground) to better assure no problems with the heater. I may settle for a 6′ #14 (otherwise the same).

#1. You are not supposed to use high current devices with extension cords.

#2. The lower the gauge, the thicker the wire. Use #12 or #14 gauge Appliance Extension Cords if one must be used.

Do not use an Extension Cord with a Receptacle End that accepts the Appliance Plug loosely.

Do not use an Appliance Extension Cord who’s plug or receptacle end is melted or deformed, cords with torn or cut insulation, and similar applies to the Appliance Cord plug end and cord condition.

#3. Do not use Home Outlets if the Plug fits loosely into it, it will overheat. If you have an area where the heater must be used, if needed, have an electrician replace the Outlet and check the wiring to it. When we had the house rewired, the Bedrooms each had a dedicated Outlet installed by the windows for AC. We plug the heater into one in the room we use.
From the Attached Graphic, they add these Good Points: 
  • Do not plug anything else into the same circuit as the one you are using for your space heater. This can cause overheating.
  • Plug portable heaters directly into outlets. Never use an extension cord or power strip. 
I’ve attempted to address the 2nd of these 2 items. Despite telling people not to, some people will use Extension Cords anyway. If you use them as I described, and if you Don’t Run the Heater Continuously, and If You Periodically Check the cord to see if it’s too warm. And if you don’t run the cord Under Furniture, Under Carpets, and DO NOT Tightly Wrap the Cord (if it’s too long, like mine is, it’s loosely laid on the floor out of the way, not folded and tied to organize it, it will build heat if you do), you’ll be safer than trying to use one and ignoring these warnings. 

#4. Try to avoid running a heater on the highest setting, and be sure it cycles on it’s thermostat to be sure to allow its plug and cord, the Appliance Extension, its plug end, receptacle end, and home Outlet a chance to cool.

#5. Heaters should have a Tilt Switch that shuts them off if they fall over. Periodically, briefly tilt over your heater to observe if it shuts off, then stand it up again. It should start again on its own, or consult the instructions for how to reset the Tilt Switch if it doesn’t. 
Be Safe, Be Alert, Make Sure you have Smoke and Carbon Monoxide Detectors in your Home (and that the Batteries are Good and that the Devices Work). They should be, at least, in the Basement, 1 St Floor (In the U.S., Ground Floor in the U.K.) and Bedroom Areas, DO NOT USE A HEATER IN THE BEDROOM anywhere near the bed, or where covers, or fabric, could fall over the heater while it is in use. We use one Safely, Far from the bed, on LOW only, and CYCLING on its Thermostat (We had a heater who’s Thermostat Stuck-on, be vigilant for this condition, turn it off if it does, and have it serviced). 

Author: Dr-Artaud

A Doctor that is not a Doctor, but named after a character in the movie "No Such Thing", as is the Avatar.

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