Space Heater + electrical cord question

[Kneedragger]

Oh, sorry you wound up here. Do you post at Electriciantalk? This forum is kind of a waste of time.

No worries man! I wasn't offended.. Just tried to explain it easily to OP.

No I don't post at Electriciantalk.

 

[John Connor]

The heater load is 12.5 amps

So accroding to my shitty math skills...that's 3.3 percent over the 80% tolerance (?) you talked about. I guess it will fare.

 

[pcgeek11]

While it isn't the highest quality cable out there, but cheap? It weighs a good bit more than my roommates 10AWG cable which is the same length. I have a box of cheap extension cords. This might not be an uber professional grade one, but it's far from cheap. I ran a big ass floor buffer with it for half an hour straight and it barely got warm to the touch.

The point is: Too Long, Small gauge wire.

 

[crashtech]

12 gauge is not small for extension cords like that. It's on the heavy end of what can typically be found.

 

[stormkroe]

In any circuit, the load placed on the supply wiring should never exceed 80% of the circuit wiring maximum current capacity.
Therefore you have a 20% headroom.

I hope this clarifies.

Would you mind putting up a NEC code reference? This isn't true of the CEC, though standard breakers are rated for 80% continuous load, wire has no 'headroom' allowance other than derating for temperature, length, etc.
thanks

 

[skyking]

It's a combination of wire size plus length @amps of load.
Voltage drop calculator:
http://buyextensioncord.com/info_voltage_drop.shtml
Ohm's law states that as voltage drops, the load increases. It is a cascading effect.
here's another little gem to take into account.
You measure 120 volts no load at an outlet.
Plug your heater in.
Now measure the voltage at the other plug of the same outlet.
if it has a long run of 14 ga copper already, you will see a significant drop!
Now add in your extension cord. It is easy to see how things get burned down.

 

[NAC4EV]

So accroding to my shitty math skills...that's 3.3 percent over the 80% tolerance (?) you talked about. I guess it will fare.

[FONT=&quot]4 out of 3 struggle with math [/FONT]

 

[natto fire]

It's a combination of wire size plus length @amps of load.
Voltage drop calculator:
http://buyextensioncord.com/info_voltage_drop.shtml
Ohm's law states that as voltage drops, the load increases. It is a cascading effect.
here's another little gem to take into account.
You measure 120 volts no load at an outlet.
Plug your heater in.
Now measure the voltage at the other plug of the same outlet.
if it has a long run of 14 ga copper already, you will see a significant drop!
Now add in your extension cord. It is easy to see how things get burned down.

Also, as a conductor heats up, it's resistance increases, causing more voltage drop and heating of the conductor. I have seen glowing connections inside of wire nuts due to this factor. A poor splice adds extra resistance, shed through heating of the conductor. As it heats up, the resistance increases, and the connection can melt the wire nut in short order, even on a smaller load.

 

[stormkroe]

It's a combination of wire size plus length @amps of load.
Voltage drop calculator:
http://buyextensioncord.com/info_voltage_drop.shtml
Ohm's law states that as voltage drops, the load increases. It is a cascading effect.
here's another little gem to take into account.
You measure 120 volts no load at an outlet.
Plug your heater in.
Now measure the voltage at the other plug of the same outlet.
if it has a long run of 14 ga copper already, you will see a significant drop!
Now add in your extension cord. It is easy to see how things get burned down.

As long as the draw on the long extension cord isn't out of apec for the conductor supplying the branch circuit, you should have virtually no voltage difference at a different outlet on the same circuit. In fact, as long as the end load isn't higher than the conductor can support (say 12 amps on a 14ga wire with a 15a breaker), there is NO length of cord that will cause a heat danger. The real problem with extra long runs of wire is the voltage drop, which can ruin electronics and some inductive loads. A resistive load, like a heater, will be just fine though it will make leas heat.
Think of it like this: if you have an extension cord long enough that the resistance of just the conductor is 10 ohms (this would be VERY long and the voltage measured there would be almost nothing), you can short the hot and negative together and it will lay there making your power bill go through the roof. 120v with 10ohm resistance is 12amps, just fine for continuous use on a 15a breaker and safely under the 15a rating of 14ga wire.
Upsizing wire for distance is solely to prevent voltage drop.

 

[tortillasoup]

As long as the draw on the long extension cord isn't out of apec for the conductor supplying the branch circuit, you should have virtually no voltage difference at a different outlet on the same circuit. In fact, as long as the end load isn't higher than the conductor can support (say 12 amps on a 14ga wire with a 15a breaker), there is NO length of cord that will cause a heat danger. The real problem with extra long runs of wire is the voltage drop, which can ruin electronics and some inductive loads. A resistive load, like a heater, will be just fine though it will make leas heat.
Think of it like this: if you have an extension cord long enough that the resistance of just the conductor is 10 ohms (this would be VERY long and the voltage measured there would be almost nothing), you can short the hot and negative together and it will lay there making your power bill go through the roof. 120v with 10ohm resistance is 12amps, just fine for continuous use on a 15a breaker and safely under the 15a rating of 14ga wire.
Upsizing wire for distance is solely to prevent voltage drop.

I've seen situations where because someone used an undersized extension cord for an electric space heater, it caused a small fire in the junction box of the outlet or an outlet on that branch of the circuit. You don't want more current flowing through a connection than the connection is designed for which is what can happen if you don't use an appropriate gauge extension cord regardless of the load.

 

[stormkroe]

I've seen situations where because someone used an undersized extension cord for an electric space heater, it caused a small fire in the junction box of the outlet or an outlet on that branch of the circuit. You don't want more current flowing through a connection than the connection is designed for which is what can happen if you don't use an appropriate gauge extension cord regardless of the load.

A small gauge extension cord cannot increase the current flowing through a circuit. It's true that having too small of a gauge of cord for the connected load can cause failure of the cord, but if you saw a fire IN THE JUNCTION BOX, it had nothing to do with the cord and everything to do with poor connection or faulty plug. The very purpose of the breaker is to trip before the load exceeds the ratings of the devices. So in your example either
A. The breaker allowed more than 15 amps through without tripping, or
B. The receptacle, or connection at the receptacle, was faulty or in other ways not able to handle the up to 15a allowed by the breaker.

 

[Kneedragger]

A couple of things here..

It doesnt matter how large wire size you go with this situation. The main concern is the connections when using a heater. Even if you had a 1 foot cord with this heater and the connection to the receptacle was loose you can still have a fire.

With wire length we really don't start to worry about voltage drop till around 100 feet.

We do only want to use only 80% load of a breaker and you cant trust a breaker 100% of the time to do what it was designed to do.I have seem 20amp breaker not trip when designed to and weld to the busing..

 

[Imp]

We do only want to use only 80% load of a breaker and you cant trust a breaker 100% of the time to do what it was designed to do.I have seem 20amp breaker not trip when designed to and weld to the busing..

That's my biggest concern. How much do I trust these safety mechanisms that are so cheap and have no real way of being tested without doing something dangerous (i.e. overload the circuit)...

 

[Humpy]

I have seem 20amp breaker not trip when designed to and weld to the busing..

Years ago while remodeling large office spaces, that were still partially occupied, we sometimes needed to shut off circuits without being able to access the panel or risk accidentally shutting down someone who was working.

The boss would bend a scrap of wire into a U and jam it in to a receptacle to trip the breaker. I was amazed at how long it could take to trip, and that some times it wouldn't trip at all.

Good times.

 

[stormkroe]

Years ago while remodeling large office spaces, that were still partially occupied, we sometimes needed to shut off circuits without being able to access the panel or risk accidentally shutting down someone who was working.

The boss would bend a scrap of wire into a U and jam it in to a receptacle to trip the breaker. I was amazed at how long it could take to trip, and that some times it wouldn't trip at all.

Good times.

Yep, federal pioneer/pacific is infamous for that, the panels are no longer manufactured due to their weld-ready 15 and 20 amp breakers. I believe there were independent investigations before they were cancelled that showed 30% to over 100% overspec tolerance.
square d and homeline seem to be quite ready to trip though, QO and QOB are great.

 

[Red Squirrel]

14 or 12 gauge is fine for a 15 amp circuit. The in wall wiring is probably 14. I would overrate a long extension cord though just to reduce overall voltage drop. So that 12 should be ok, and surprisingly it appears to be made in USA, which is rare to see for Amazon stuff, as usually it's only Chinese rip off stuff on there which usually will have zero type of certification or even guarantee that it is what it says it is. But that particular one should be alright assuming it's not a Chinese company that's outright lying. Temperature rating is also something to consider though, ex: can it run for extended time at a certain temp.

If you want to really play things safe, buy 12/3 heavy duty outdoor rated extension cord cable from the hardware store or electrical distributor and the two ends to go with it and make your own cord. You will probably pay a bit more but you know 100% what you're getting. You can make it the exact length you need too.

If this is going to be more or less permanent I would look at running a dedicated 20 amp circuit to avoid needing an extension cord though. When I finish my basement I'm probably going to put dedicated 20 amp outlets at the windows, that way they can accommodate heaters or air conditioners if needed.

 

[stormkroe]

Here's some code info, from the CEC
1500 watt heater @ 120v = 12.5a
Table D3
14ga wire @12.5a = 1% voltage drop per 4.9 meters
12ga wire @12.5a = 1% voltage drop per 7.8 meters
10ga wire @12.5a = 1% voltage drop per 12.4 meters

Total allowable voltage drop from the powco meter is 5%, no more than 3% of that can be across the branch circuit (at an outlet of some type).
The important thing to note is that longer wire DOES NOT cause an increase in current, quite the opposite, the increase in series resistance to the circuit from adding so many ohms/foot of wire actually DECREASES the current traveling through the circuit. This is exactly how a current-limiting resistor works on a circuit board.
So, with that in mind, because a resistive load like an incandescent light or coil heater are VERY tolerable to voltage drop (except if the heater has a fan, the inductive load not like the volt drop and could burn out), though it will perform worse than advertised it should be perfectly safe.

 

[Kneedragger]

That's my biggest concern. How much do I trust these safety mechanisms that are so cheap and have no real way of being tested without doing something dangerous (i.e. overload the circuit)...

Years ago while remodeling large office spaces, that were still partially occupied, we sometimes needed to shut off circuits without being able to access the panel or risk accidentally shutting down someone who was working.

The boss would bend a scrap of wire into a U and jam it in to a receptacle to trip the breaker. I was amazed at how long it could take to trip, and that some times it wouldn't trip at all.

Good times.

Yup! You can't trust them at all. On a residential job I did in the past no lie started to hear sizzling coming from a jobsite spider box. A spider box is a temporary box with multiple receptacles so a job being built has power while permanent power wasn't finished. Anyways... I walked over to the spider box I heard the sizzling and a flame shot up from the end of the adapter and just hovered there about a foot off the adapter. I was in such awe I just stood there looking at it for about a minute lol. Breaker never tripped ..

 

[BUTCH1]

Yep, federal pioneer/pacific is infamous for that, the panels are no longer manufactured due to their weld-ready 15 and 20 amp breakers. I believe there were independent investigations before they were cancelled that showed 30% to over 100% overspec tolerance.
square d and homeline seem to be quite ready to trip though, QO and QOB are great.

I have one of those Federal Pacific boxes, my house was built in the early '70's before anyone knew how bad they really were. Dozens of house fires and lawsuits later they filed bankruptcy. Some insurers won't write a policy on a home with a FP panel in it, I've priced having it swapped out but it's pricey @1500-1700 to have it done. I run everything on high quality power strips with their own breaker. One day a zener diode shorted out in my dishwasher and fried the control board, sparks and smoke but no tripped breaker.