Electric space heaters run at full 1500 watt rating tend to burn up AC sockets. Common or not?

[rat_avatar]

@beowulff

Right, and 13A is fine for 12.5A load.

The problem is people who use a cheesy 6A rated extension cord to run their 12.5A space heater.

When it is new, and in perfect shape.

Note 4-NFPA 79-2013 table 12.5.1 related to the ampacities and acceptable temperatures.

https://www.nfpa.org/Assets/files/AboutTheCodes/79/79_A2014_EEI-AAA_SD_SRStatements.pdf

Looking at the heater I mentioned above, 18 gauge wire with:

75 C rated insulation at 7 amps below 167 F
90 C rated insulation at 15 amps as long as the temperature stays below 194 F.
Now consider that ASTM C1055 (the Standard Guide for Heated System Surface Conditions that Produce Contact Burn Injuries).

It recommends that surface below 140 F because the average person can touch a 140 F surface for up to five seconds without sustaining irreversible burn damage.

At 72 C or 162 F, which are still acceptable under 4-NFPA 79-2013 for new perfect 18 gauge cable at 7 amps, ASTM C1055 states that 5 seconds of contact exposure will lead to Protein Coagulation.

From that above NFPA Chart, lets look at what they find acceptable for 60C/140F level insulation, that you know will be within safe temperatures for items that pull a lot of power for a long time.

18 gauge - 7A
16 gauge - 10A
14 guage - 20A
12 gauge - 25A

That NFPA link is the change logs and notes but you will also note the correction factor changes etc…

For a portable heater manufacture the ~$3.12 that they save in materials for using 18 gauge vs 14 gauge is significant. For me I would rather pay a bit more for the safety margin.

I should disclose that 18 years ago I was driving down the freeway in a 1960 Pontiac Ventura with the windows down. A small electrical fault from a previous owners stereo install shorted out and some hot insulation ignited the jute filled seats. By the time I managed to pull off into the median and jump out I had 2nd and 3rd degree burns over 33% of my body.

While modern materials are far less likely to have such a fast growing fire it happens faster than you think. If you have small, overloaded extension cords piled up with some dust bunnies it can lead to fire.

I admit that anecdote isn’t data, and my view is biased. I love learning and sharing what I can contribute on here, but I hope that none of you ever have to have a similar experience. By spending a few dollars more it is easy to dramatically increase the safety margins.

[Weisshund]

@Chronos

And what plastic would you suggest for that? People tend to get touchy about making things from asbestos. I suppose there might be some silicones that would work, but I don’t know if they’d have the right mechanical properties.

bakelite?

[BobWNY]

@ZonexandScout

This topic looks like it has had the hell discussed out of it, but I’ll throw in a bit more information:

Yes, you can run 120VAC on both 18 AWG and 16 AWG conductors as power circuits. In fact, fixture wire is often used for this purpose.

Per NEC, if you use 16 AWG conductors, the overcurrent protection (fuse or circuit breaker) may not be larger than 10 amps. If you use 18 AWG conductors, the overcurrent protection may not be larger than 7 amps. (Reference NEC Article 240 if you need to.)

I think you can confidently extrapolate from this that running more than 7 amps on an 18 AWG conductor or 10 amps on a 16 AWG conductor is a bad thing. Don’t do it.

Unfortunately, while the US has standardized plugs and receptacles for 15 amp and 20 amp circuits, we don’t have any common ones for 7 amp or 10 amp circuits. We end up with crappy 18 AWG and 16 AWG extension cords that SHOULD not be permitted to carry more than 7 or 10 amps, but you can plug them right into a 15 amp outlet. Go figure.

(Yes, I am a licensed electrical contractor.)

Hello,
I’m new to this Board. I’m also not an electrical expert by any stretch.
I’ve had a similar problem with a 1500W electrical space heater is causing warming of the wall receptical and heater plug, and over time, scorch/partially melted both the receptical and heater plug. The heater is directly plugged into the wall receptical.The receptical itself is a standard 15A.No extension cord is used. The house wiring to that receptical is #12-2 AWG. The breaker is 20A. I replaced the receptical with a 15A contractor grade unit and the plug with a heavy duty 15A unit.

After about a year or so I started to notice the scorching smell again and unplugged the heater. I tried the heater on other recepticals that are on different circuits and found some warming as well.

I noticed that the heater/appliance cord is 16-3 stranded wire as provided by the manufacturer. I’m concerned that the manufacturer supplied cord is marginal (1500W/120V = 12.5W). ****From the above post it appears that the max current for a 16-3 AWG wire is 10Amps. ****Should I be replacing the heater cord with a minimum of #14 AWG? Also, FYI on the recipitical that I replaced I used screw-in side posts and not the ones that you insert through the bottom of the receptical.

Any insight that you may be able to provide will be greatly appreciated.
Thank you

[Kent_Clark]

@BobWNY

I noticed that the heater/appliance cord is 16-3 stranded wire as provided by the manufacturer. I’m concerned that the manufacturer supplied cord is marginal (1500W/120V = 12.5W). ****From the above post it appears that the max current for a 16-3 AWG wire is 10Amps. ****Should I be replacing the heater cord with a minimum of #14 AWG? Also, FYI on the recipitical that I replaced I used screw-in side posts and not the ones that you insert through the bottom of the receptical.

Frankly, I’d throw out the space heater entirely, get a new one with at least a 14 gauge cord, and probably replace the outlet, as well (just because it was brand new doesn’t mean that it was 100% right.) And try a drop of solder on those screw-in posts to make sure they stay tight.

[Tim_T-Bonham.net]

@BobWNY

The receptical itself is a standard 15A.No extension cord is used. The house wiring to that receptical is #12-2 AWG. The breaker is 20A. I replaced the receptical with a 15A contractor grade unit and the plug with a heavy duty 15A unit.

With 12-2 and 20A breaker and a heavy load*, you should use a 20a receptacle for that one. They are available, but a bit more expensive (around $2-$3 each). Might have to look for “commercial” or “industrial” grade devices. You can recognize 20A receptacles by the T-shaped slot on the front left slot (see here).

*Normally, 15A receptacles are legal on a 20A circuit, because there are multiple of them in the circuit. But in this case, you are pulling almost the entire capacity of the circuit through that one receptacle for the heavy space heater load. And it’s probably full on for a long time. 15A receptacles are over-built, and can handle up to a 20A load temporarily – but this is pushing it. (As the scorching showed.)

[EdelweissPirate]

@sludge7051-x

---

I was thinking, if you need a 10 foot extension cord, but now know that it’s a bad idea to use an extension cord,
and you don’t want to take your walls apart to run a new wire and plug in there,
you could run some 12 or 14 gauge armored cable, from the outlet, to a new, externally mounted outlet,
and plug the space heater into that,
it wouldn’t be pretty, but it should then be safe:

Electrical / Electrical Wire & Cable / Armored Cable
http://www.lowes.com/Electrical/Electrical-Wire-Cable/Armored-Cable/_/N-1z0yt2t/pl?cm_sp=RoughElectrical-_-Electrical|PopularCat-_-Merch|Armored_Cable&cm_cr=Electrical-_-Web+Activity-_-Electrical+Top+Flexible-_-SC_Electrical_TopFlexible_Area-_-10485557_12_Armored_Cable#!&N[]=1z0w65c&N[]=1z0w65d&N[]=1z0yt2t&Ns=p_product_price|0&page=1

@Chronos

And what plastic would you suggest for that? People tend to get touchy about making things from asbestos. I suppose there might be some silicones that would work, but I don’t know if they’d have the right mechanical properties.

PEEK would be an ideal polymer for this, I’d think. It’s very strong (its yield strength is similar to that of some medium-strength aluminum alloys) and it handles high temperatures well. The problem is that it’s VERY expensive—so expensive that it’s unlikely anyone would buy electrical fixtures made from it.

[Melbourne]

An amusing side effect it that safety advisers in Aus often believe that it is a bad idea to plug electric heaters into power boards. Because they’ve read it somewhere, or been told it by someone. Even though (1) Most of our 10A power boards use (American) design standards and are good for 12.5A, and (b) Most of our heaters are 8 Amp/2KW or less

It actually was an issue here 50 years ago, when 10A heaters were plugged into 10A wall sockets. But there’s not that many of us left who know that. And even fewer 10A (2K4W) electric heaters.

[Tim_T-Bonham.net]

@Melbourne

An amusing side effect it that safety advisers in Aus often believe that it is a bad idea to plug electric heaters into power boards. Because they’ve read it somewhere, or been told it by someone. Even though (1) Most of our 10A power boards use (American) design standards and are good for 12.5A, and (b) Most of our heaters are 8 Amp/2KW or less

It actually was an issue here 50 years ago, when 10A heaters were plugged into 10A wall sockets. But there’s not that many of us left who know that. And even fewer 10A (2K4W) electric heaters.

What the hell is a “power board”?

[engineer_comp_geek]

@Tim_T-Bonham.net

What the hell is a “power board”?

An Australian power strip.

[Cleophus]

@Melbourne

An amusing side effect it that safety advisers in Aus often believe that it is a bad idea to plug electric heaters into power boards. Because they’ve read it somewhere, or been told it by someone. Even though (1) Most of our 10A power boards use (American) design standards and are good for 12.5A, and (b) Most of our heaters are 8 Amp/2KW or less

It actually was an issue here 50 years ago, when 10A heaters were plugged into 10A wall sockets. But there’s not that many of us left who know that. And even fewer 10A (2K4W) electric heaters.

Note that in 240 V countries, the current requirements are halved. The OP’s 1500 W space heater needs but only ~6 A at 240 V, which requires much less robust power delivery equipment. The Technology Connections Youtube channel has an interesting (though long) video examining how the 120 V/15 A limits in the US means virtually all space heaters on the market here max out at 1500 W regardless of whether they’re marketed for “small” or “large” rooms.