Hi Dave,

I believe he is going to use a 1000 watt heater, 8.3 amps. How do we stand there?

 

1000 watts is 8.69 amps at 115 volts
That would require 10 AWG wire in a 100 foot cord.

At 100 feet 6.8 amps or 782 watts is the max load at 115 volts on 12 AWG wire.

Something else that is not in this equation is the distance the receptical is from the circuit panel and any other load that may be on it.

If for instance the receptical is 50 feet from the breaker panel, the actual circuit length would be 300 feet. 150 feet from the breaker panel to the block heater and 150 feet back to the breaker panel.
Given that most houses are wired with 12 AWG wire and you plug a 100 foot 12 AWG extension cord into that circuit, at the end of the cord your max load is 4.5 amps at 115 volts. 517.5 watts would be the biggest heater it could run properly.

For a circuit that long to properly supply a 1000 watt heater you should have #8 AWG wire which would deliver 8.69 amps at 116.2 volts.

11.3 amps would be the max load an 8 AWG wire could supply 115 volts to 150 feet from the breaker panel when you take the voltage drop into consideration.

 

Right you are Dave!
Also being a Master Electrician I will tell you, IF you use the #12 cord, only need 50 feet of it, and leave the other 50 feet coiled up, you are asking for melt down.

 

Hehe, I know not to coil the cord! I'm an audio geek and pretty familiar with coils. I also setup sound, lighting and video for concerts and saw what a 220v cord coiled up will do when it goes live. Good times...

Dave, thanks for doing the math for me, I was feeling lazy and didn't want to do it. Due to having a newborn(very thin budget right now) and living in an apartment I'm just trying to work with what I have available. 80' is the closest I can park my truck to the building. Worst case scenario I'll have something else figured out for next winter.

I just ordered up a weatherproof male U-GND receptacle from work so I can eliminate the cord dangling from the front of the truck. I'll be sure to take lots of pics of the install.

I work for http://www.sasco.com/ right now I am just in their warehouse but this summer I will be going into their apprenticeship program.

 

So what is this??? Electrician's Forum???
I am also an electrician here in WA. But I went to the dark side and am now working for WSDOT as an inspector.

 

Take your pick,
Electricians 101
or
How to use your block heater without burning down the house

Why do you think the Electrical code is written by the National Fire Prevention Association?

I know someone was wanting "Burning Down the House" by Talking Heads in the "What are you listening to poll"

 

Hey all, just to stir up trouble, if everything is properly wired, you could run a #12 cord down the block and back and plug in a 1000 watt resistive heater at the end and not create a fire hazard. The heater just wouldn't get very hot...

For personal safeties sake, are you plugging into a GFCI outlet?

 

Ummm, actually I'm pretty sure the Electrical Code is written by NEMA - which stands for the National Electrical Manufacturer's Assn, IIRC.

 

Nope, it is an NFPA pub.

 

National Electrical Code IS a NFPA Document. It is NFPA 70.

 

A 12 ga extension cord of good construction will handle an 8.6a load with no problem. 12ga copper is rated 16a for continuous duty use(>3hr). You only get a 3.4 volt drop at 100' Design drop of 3% is 3.6v. Even if you add another 50' to the panel, the drop will then be 5.1v. So you are seeing 114.9 at the heater.

The cord is run outside with a huge cooler (the winter air) keeping the cord cool. No meltdown here. Probably the worst thing happening here is the heater being a little less efficient.

BTW, standard voltage for electrical calculations is 120v, not 110 or 115. If all you have in your circuit is 110v, either something in the circuit is undersized or the utility company does not have the transformer taps properly adjusted.

 

OK guys I thought this was for block heaters . Not how to wire the house or extension cords. New cords should have the amperage rating tag on them.

 

Every guy I asked in the shop said they would have used 10-3 but I should be fine with the 12-3. They all know their poo so I'm not too concerned.

I'll tae a look at the tag when the kid goes to sleep.

 

Sorry Cheeper it really is the NFPA
Originally written because in early days poorly connected electricity was the cause of many structure fires.

The point about using larger cords is safety and efficiency. If you use an undersized cord it will get warmer than a properly sized cord. heat is the enemy of wire insulation.

Your Block heater will use 1000 watts whether it gets 110 volts or 130 volts at it's cord connection. (1000/110=9.09 Amps) (1000/130=7.69 Amps)

The amperage will change depending on the voltage and more amps on smaller wires create heat which may or may not be dissipated enough to protect the insulation.

When the insulation gets too hot it degrades and will eventually fail.

Remember that these amperages are the same in your heater cord as in the extension cord.

Protect your equipment or replace it more often.

 

Actually the point is this.
An under sized cord gets hot due to resistance.
It takes power to make the heat in the cord.

I prefer the heat be in the engine with a properly sized cord instead of out in the yard where it is only costing me money and doing nothing useful.

Over 50% of the structure fires last year were from electrical issues.