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

Factual Questions
21

Here’s what I found out, and why:

The guy at the home improvement store said that you can you an extension cord with a space heater, but it can only be a maximum of 6 feet . . . use the grey one, for appliances (14 AWG, 1875W).

I saw in the FAQ for another space heater, that this is what you’d want to do, also, if you have to use an extension cord.

But, from talking to customer support of my space heater, I will not be using an extension cord. Why?

Do not use an extension cord with the space heater, because:
1.) They can’t handle the amperage and wattage
2.) The circuit breaker might not pop, because there’s a longer travel distance, and the feedback would be less direct to the thermal and magnetic mechanisms in the circuit breaker . . . An extension cord lowers the chance that the circuit breaker will be able to sense increasing heat from the wire . . . When you introduce an extension cord into the circuit, experience has shown that things can go on that you’re not going to know about [it would be good to have more specific info here]

Q: The 6’, 14 AWG, 1875W grey appliance extension cord says that it’s for use with appliances like air conditioners. So, why not with a space heater?
A: Space heaters are constantly drawing the amps, and do not peak down, as you see with air conditioners or refrigerators . . . It seems like there should be a spec for the cord as to how long it can handle high amps: sporadically vs. infrequently . . . I don’t think that this is common knowledge

How long can a 14 AWG wire handle 12.5 amps / 1500 W? Some have found that the extension cord will get warm. That’s not good.

Do not use the space heater in a bathroom, because:
1.) There is dust in the air, it gets damp, and the dust particles will accumulate on parts inside of the space heater
2.) Moisture is in the air. Moisture will stay in the space heater - it is not evaporated. Moisture and electronics do not mix well.
3.) The space heater will become a fire hazard

http://www.nashobapublishing.com/ci_27281615/fire-marshal-issues-cold-weather-fire-safety-warning

Space heaters need space, so use them in a 3-foot circle of safety, free of anything that can catch fire.
He added, “Space heaters are not designed to replace your central heating system, they are only designed to provide a little extra heat on a temporary basis.
So be sure to turn them off when you leave room or go to bed at night.” [that’s when I want to use it at 66F, from 10 pm to 6 am, when my gas furnace is set to 61F (68F in the daytime)]
It is best to plug space heaters and other heat-generating appliances directly into the outlet.
Overloaded extension cords cause many space heater fires. If you must use an extension cord, make sure it is rated for the same wattage as the appliance and use only one. [this is bad information]

goodsonengineering.com/wp-content/uploads/2011/08/CircuitBreakerMyths_web.pdf

basic breaker operation and design
In order to debunk the myths it is important to understand the basic operation and design of the trip mechanisms in a circuit breaker.
The thermal portion of the circuit breaker works by use of a bi-metallic strip which causes a spring-loaded latch to release and trip the breaker.
The deflection of the bi-metallic strip depends on the temperature, thus the breaker has a trip temperature and it is the heat generated within the breaker that causes the temperature to rise, the faster
the heat rise, the faster the breaker reaches temperature and trips.
Heat is directly proportional to the power (watts), which is proportional to the square of the current (P=I2 x R)

For example, if we assume that an extension cord is rated at 10 amperes (#18 AWG) and is carrying a load of 25 amperes while connected to a branch circuit wire that is protected by a 20 ampere T-M breaker, the 20 ampere breaker may never trip.

Relocatable power taps, more often called power strips, all have circuit breakers present.
In general, these breakers are thermal breakers, and have no magnetic trip level.
They are intended to prevent damage to wiring caused by having too many appliances plugged in (i.e., too great a load), and are usually rated at 15 amperes.
We mention these breakers because they are common, and yet they are very different from the T-M breaker used as a part of branch circuit wiring.

[Do they have a power strip with magnetic trip, or a portable plug-in circuit breaker? Looks like they do for contractors, but maybe it wouldn’t play well with the circuit breaker, like how if you put a GFCI downline from another GFCI, which are both downline from the circuit breaker, which is something you might do, if you don’t understand how these things are designed to work, ie. you shouldn’t put a GFCI downline from another GFCI.]

01/09/15 … Instead of putting the space heater on an extension cord, I’m going to go the other way, and get the computer equipment on a different branch circuit, with two 25 foot, 14 AWG extension cords (14 AWG is good for 15 amps, up to 25 feet) . . . Current thinking: Use some wire ties to hold them together, and duct tape to hold them down on the carpet, especially under the door. Make sure that the door doesn’t abrade the insulation of the extension cords. Be extra aware to not trip over them.

. . . . . could I have done this with just one extension cord, and a built-in splitter on the end? . . . because one extension cord can handle 15 amps . . . maybe, but it can’t hurt to split them for an extra $20 (the extension cords were $19.97 each) . . . maybe things will run cooler

keywords for further research: extension cord for space heater, fire marshal

22

So let me understand this. If I extend, let’s say, 14 gauge wires inside my walls 10 feet to get closer to the space heater, the circuit breaker can detect an overload on the wires. But if I use a 10-foot 14-gauge extension cord to extend the circuit outside my walls, the circuit breaker loses its capability to detect an overload. Is this correct?

23

That’s a great question.

In my house, it’s all 12 gauge . . . so that’s what I’m plugging in to.

I had the building inspector here to check some work I did. He said that it was good that I had everything in 12 gauge. Apparently, some people do wire their houses with 14 gauge.

The wire coming out the back of my ceramic space heater is 16 gauge. It must be stranded wire, as opposed to solid core, which is less flexible.

. . . But, a while back, I looked to see if they had 16 gauge solid core, and no one had it. I have only ever seen 16 gauge stranded wire, which is used for table lamps.

. . . I’ve seen that they have 14 gauge in both solid core and stranded. I observed that the coating on the 14 gauge stranded is pretty cheap, and gets dinged up just from the machine they use to cut.

. . . 18 gauge is pretty thin. I think it only comes in solid core. It’s used in fluorescent lights. I used it to wire this one light in a bathroom, by a fan. The stranded wire previously used had singed (I think it was 16 gauge). I thought that 18 gauge solid core could improve on that (it was only for a 60W bulb, and the insulation on the 18 gauge wire seemed better). I think this fixture gets a lot of vibration, also, so I switched to a 40W or 60W bulb on it, heavy duty.

If you did 10 feet of 14 gauge inside your walls, it would probably be solid core. Is your whole house in 14 gauge? I wonder what the code is. [THEORETICAL / I’M NOT SURE] It seems like 14 gauge solid core would carry the amps better than 14 gauge stranded, and provide a more solid connection all around - so yes, in this case, it seems to me that 14 gauge solid core would work for reliable circuit breaker heat and fault detection.

If you did 10 feet of 14 gauge outside your walls, as an extension cord, it would probably be stranded wire. [THEORETICAL / I’M NOT SURE] Maybe the fact that it’s “stranded wire” has something to do with it becoming a hazard. The path for electrons isn’t as robust. Maybe something in the plug head itself contributes to resistance, and that lowers the ability of the circuit breaker to sense a problem. If you took a plug head apart, I wonder if you’d find anything to support this theory.

[FROM RANDOM DISCUSSION] Volts push the amps down the wire, so you don’t want it to be high amps, over a long distance, for an extended period of time. I think this is what heats up the wire. Resistance is occurring along here somehow.

I’m not an authority on this, so some of the above could be wrong, but I think I’m in the ballpark.

The resistance of a given object depends primarily on two factors: What material it is made of, and its shape. For a given material, the resistance is inversely proportional to the cross-sectional area; for example, a thick copper wire has lower resistance than an otherwise-identical thin copper wire. Also, for a given material, the resistance is proportional to the length; for example, a long copper wire has higher resistance than an otherwise-identical short copper wire. The resistance R and conductance G of a conductor of uniform cross section, therefore, can be computed as . . .

24

Stranded wire will carry more current than solid wire, it is a thing called skin effect. Stranded wire has more surface area on the strands.

When I do any wiring on my house I only use 12 gage wire. 12 gage wire can be connected to a 15 or 20 amp breaker. 14 gage wire can be connected only to a 15 amp breaker.

Many tract homes are built with the lighting circuits on 15 amp breakers, and the outlet circuits on 20 amp breakers.

Using an extension cord on a major load will not have on the operation of the breaker. It is going to trip at 15 or 20 amps. The only way it could effect the breaker would be if the heater is close enough to heat the panel directly.

In an office the fire code prohibits using any extension cords. Only power strips are permitted. And most electric heaters are also against the code. They have thermostatic safeties and tip over safeties.

25

That seems like an odd hypothetical. Surely an extension cord with 20A connectors and 10A wire would be a flagrant code violation.

26

Originally Posted by sludge7051-x View Post

goodsonengineering.com/wp-content/uploads/2011/08/CircuitBreakerMyths_web.pdf
For example, if we assume that an extension cord is rated at 10 amperes (#18 AWG) and is carrying a load of 25 amperes while connected to a branch circuit wire that is protected by a 20 ampere T-M breaker, the 20 ampere breaker may never trip.

[/QUOTE]

Missed this one.
If you have a 18 gage extension cord that is carrying 25 amps and the cord is plugged into a 20 breaker. The only reason the breaker would not trip if the breaker is faulty.

And if the breaker is faulty in a very short period of time the extension cord is going to heat up and begin to melt.

27

Your reasoning is all wrong. Load current measured through the circuit breaker does not become inaccurate due to distance of the load. All the power used by the load (or by the resistance of the wiring) must flow through the circuit breaker, where it will be measured.

What does bear mentioning is that circuit breakers (and fuses, for that matter) do not trip/open the instant the rated load amount is exceeded. In general, the trip time is inversely proportional to the overage (110% load might take an hour to trip, 500% could take a fraction of a second).

The danger with an extension cord is that with an undersized one used for an extended period of time, you may be able to slightly overload it to the point of overheating (potentially causing a fire) without tripping the circuit breaker.

28

The following is a good read on the topic:

http://goodsonengineering.com/wp-content/uploads/2011/08/CircuitBreakerMyths_web.pdf

A 20% overload is not expected to trip a typical home circuit breaker instantly. The PDF linked above says NEMA Standard AB-1 requires “a 20 amp breaker must trip at a sustained current of 27 amperes (135 percent) at less than one hour” and “at 40 amperes (200 percent of wire rating) in less than 120 seconds”. By extrapolation, the 5A overload, being less than a 7A overload, could take even longer than an hour to trip.

Again, this is for an in-spec circuit breaker - not faulty.

29

But at 25 amps it should trip, but in this case the house might burn down before the breaker trips.

30

NVM.

31

I did some informational research on this a few months ago, and I recall the “skin depth” for stranded and solid wire is pretty much the same (all else being equal). But it doesn’t matter… at 60 Hz, skin depth doesn’t come into play for home wiring (12 and 14 AWG).

For a given AWG, though, stranded wire does have slightly more resistance per unit length than a solid wire.

32

yeah for home use the difference between stranded and solid wire is the physical characteristics needed (flexibility, connection type).

33

Related: Here’s why I thought it was ok to go from 16 gauge stranded, to 18 gauge solid core, to wire one 60 Watt bulb:

Volts x Amps = Watts . . . 120V x Amps = 60W . . . Amps for the 60W bulb = .5 . . . and 18 gauge wire can handle 6 amps

Below are what the other sizes of wire can handle, other useful links:

What is the amp rating of 10 gauge wire? 24 amps … A #10 copper wire with an insulation factor of 90 degrees C is rated at 30 amps. Code states that conductors can only be continuously loaded to 80%. 30 x .8 = 24 amps . . . What is the amp rating of 10 gauge wire? - Answers

What is the amp rating of 12 gauge wire? 20 amps … In normal residential use it is 20 amps . . . What is the amp rating for 12 gauge wire? - Answers

What is the amp rating of 14 gauge wire? 12 amps … A #14 copper wire with an insulation factor of 90 degrees C is rated at 15 amps. Code states that conductors can only be continuously loaded to 80%. 15 x .8 = 12 amps . . . What is the amp rating for 14 gauge wire? - Answers

What is the Amp rating of 16 gauge wire? 10 amps … What is the Amp rating for 16 gauge wire? - Answers

What is the Amp rating of 18 gauge wire? 6 amps … A #18 copper conductor with an insulation factor of 90 degrees C is rated at 6 amps . . . What is the amp rating of 18 gauge wire? - Answers

What is the Amp rating of 20 gauge wire? 1.46 amps … 20 gauge copper wire can carry 1.46 amps. Insulated copper wire can carry 6.5 amps. This is assuming a short run of 25’ or less . . . What is the amp rating of 20 gauge wire? - Answers

What Size Electrical Wire Do I Need? (Table) . . . Amperage and Wire Gauge Chart: What Size You Need

Wire Resistance Increases With Cable Length . . . Sizing Electrical Wire for Underground Circuit Cable

Along with wire size, you’ll need to consider the wire cable length. In long runs of wire, the resistance of the wire acts like a load, using some of the capacity of the wire load . . . 6 Different Types of Electrical Wire and How to Choose One

The emphasis really seems to be - Don’t use an extension cord - power strips would be included:

Portable Heater 101 - Buying tips and more - Do not use an extension cord with a heater / How to Measure Savings . . . http://housewares.about.com/od/heatingproducts/fl/Portable-Heater-101-From-Buying-to-Care-and-More.htm

Space Heater Safety - Tips from Experts on Space Heater Safety - Do not use extension cords with space heaters. Plug the cords directly into outlets . . . http://garages.about.com/od/toolsmaterials/a/Tips-From-Experts-On-Space-Heater-Safety.htm

You should never use an extension cord to plug one of these heaters into a power source . . . Correct Extension Cord Sizes Are Critical to Safety

Making Appliance and Product Safety a Priority - I do know how frustrating those short appliance cords can be, but safety is an important product design element. That cord is short - for your safety . . . How to Prevent Electrical Shock

They don’t specify how many accidents were due to the extension cord:

Space heaters involved in 79 percent of fatal home heating fires . . . http://www.nfpa.org/press-room/news-releases/2010/space-heaters-involved-in-79-percent-of-fatal-home-heating-fires

Home fires involving heating equipment . . . http://www.nfpa.org/research/reports-and-statistics/fire-causes/appliances-and-equipment/heating-equipment

I have a gas furnace. I put my thermostat at 68, and let it go to 61 from 10 pm to 6 am.

Unfortunately, I want to use my space heater at night to take a bite out of the cold, while I sleep.

I set the ceramic space heater at 66. When the temp drops to 65, it kicks on, heats to 68, shuts off, and repeats.

I plug it in to the wall. I have put it on a flagstone, as opposed to just leaving it on the carpet.

I had some In-the-Wall 240V space heaters a while back. I never had any problem using them. Maybe there’s more of a chance of something going wrong with these portables. All I can think of it:

1.) it gets tipped over
2.) something flammable get in front of it, like a comforter (I have it a little more than 3’ away from the bottom of the bed)
3.) the circuit breaker fails, when there’s a problem
4.) the thermostat breaks, and the unit doesn’t shut off

This had not occurred to me, you can get 4-in-1 . . . heat, AC, fan, dehumidifier . . . do spot heating, and spot cooling, with one unit:

Many portable air conditioning units have secondary functions and some are 4 in 1 models. Not only can these units cool your home, but some have features to dehumidify, fan-cool and heat your environment as well . . . The 9 Best Air Conditioners of 2023 | by The Spruce

Combination Heating & Cooling Comfort Appliances, Avoid comfort appliance congestions with dual or multifunction appliances (NewAir Appliances Portable Air Conditioner / Heater, MPN: AC14100H, $548.99 - $647.52) . . . The 9 Best Combination Fan and Heaters of 2023 | by The Spruce

Portable Air Conditioner with Heater . . . http://www.homedepot.com/b/Heating-Venting-Cooling-Air-Conditioners-Coolers-Air-Conditioners-Portable-Air-Conditioners/N-5yc1vZc4m4Z1z10dqc?Ns=P_REP_PRC_MODE|0

Portable Air Conditioner with Heater . . . http://www.lowes.com/pd_530393-37374-530393_4294749561%2B4294835907__?productId=50139756&Ns=p_product_qty_sales_dollar|1&pl=1&currentURL=%3FNs%3Dp_product_qty_sales_dollar|1&facetInfo=Portable

34

Are you talking about permanent wiring between a junction box and the light fixture? Because I don’t think you’re allowed to use 16 AWG for that. If it’s a 15 A circuit you must use 12 AWG or 14 AWG NM sheathed cable (“Romex”), or 12 AWG if it’s a 20 A circuit.

For each circuit, the primary purpose of the circuit breaker is to protect all the wiring in the circuit up to each permanently-mounted fixture and receptacle. If the circuit breaker is rated for 20 A, then all the wiring in the circuit must be 12 AWG. If the circuit breaker is rated for 15 A, then all the wiring in the circuit must be 12 AWG and/or 14 AWG.

35

. . . Are you talking about permanent wiring between a junction box and the light fixture?

Yes. It’s a 60W bulb in the ceiling of a bathroom that has a globe around it. 12 gauge wire is in the box, so I wire from the socket to that.

What was in there before? . . . I think it was a hard wired plastic socket, with stranded 16 gauge. The wire was singed around the socket. That didn’t seem good.

So, I got a porcelain socket, which had no leads attached to it. I could have used some 16 gauge I have lying around here from lamps I’ve taken apart, but 18 gauge solid core seemed like it would work. The solid core wire does go more neatly under the screws, so that seemed better, also.

. . . Because I don’t think you’re allowed to use 16 AWG for that.

I believe that’s what they did. They connected the 16 gauge, hard wired leads, to the 12 gauge wire in the box.

. . . If it’s a 15 A circuit

It is

. . . you must use 12 AWG or 14 AWG NM sheathed cable (“Romex”) . . . or 12 AWG if it’s a 20 A circuit.

I haven’t noticed any problems with 12 gauge attached to the 18 gauge, which is attached to the socket. What could happen? There’s a resistor in the bulb, so it would never exceed .5 amps, right?

. . . For each circuit, the primary purpose of the circuit breaker is to protect all the wiring in the circuit up to each permanently-mounted fixture and receptacle. If the circuit breaker is rated for 20 A, then all the wiring in the circuit must be 12 AWG. If the circuit breaker is rated for 15 A, then all the wiring in the circuit must be 12 AWG and/or 14 AWG.

I don’t think this is right. Say you want to replace a ceiling fixture. You take down what’s there, and go to put up the new one. What kind of wire is hard-wired to the new one, that you’re going to attach to the 12 gauge? Probably some kind of stranded wire, probably 16 gauge.

36

Possible issues:

Someone could install a 150W bulb. 2.5 times the load of a 60W bulb.

Someone could use an Edison-base to wall-socket adapter (ex: http://www.lowes.com/pd_17576-43469-6502_4294722558__?productId=3774299) and try to draw a whole lot more.

Maybe unlikely, but doing things to code the first time is usually preferable to having a house burn down.

37

Having 18 gage wire on a circuit protected by a 20 amp breaker means the wire is not protected. If you develop a shore in the fixture that draws 20 amps the wire is going to let the smoke and heat out.

38

. . . Someone could install a 150W bulb, 2.5 times the load of a 60W bulb.

120V x amps = 150W . . . amps = 1.25 . . . 18 gauge could easily handle that (6 amps max)

. . . Someone could use an Edison-base to wall-socket adapter [Project Source 660-Watt Ivory Medium Light Socket Adapter] and try to draw a whole lot more.

120V x amps = 660W . . . amps = 5.5 . . . the wire would almost be maxed out, but should be able to handle this

I don’t think the globe would fit over it, though . . . plus, if they installed one, you’d think that they’d look at the wiring

. . . Maybe unlikely, but doing things to code the first time is usually preferable to having a house burn down.

Yes, but I think 18 gauge is the standard, please see below

. . . Having 18 gage wire on a circuit protected by a 20 amp breaker means the wire is not protected. If you develop a short in the fixture that draws 20 amps the wire is going to let the smoke and heat out.

It’s on a 15 amp circuit breaker

I remembered . . . I asked about this before on Yahoo, here’s the info:

Wiring a light fixture - 18 gauge solid core vs. 18 gauge stranded? . . . Yahoo | Mail, Weather, Search, Politics, News, Finance, Sports & Videos

It looks like I replaced 18 gauge stranded, with 18 gauge solid core, which had a slightly lower temp rating. Responses said that they thought it would be ok.

Any fixture you get at the store is not going to have 12 or 14 gauge leads. I don’t think it will even have 16 gauge stranded leads, either.

If you get a fluorescent, those use 18 gauge solid core inside. I’ve wired a couple. I’ve used some extra 16 gauge stranded, from lights I took apart, that has a plug. I install an AC receptacle on the wall, and then plug the fluorescent into that. So with fluorescents, I have personally never directly connected 18 gauge to the 12 gauge house wire. You want fluorescents to hang down an inch, to prevent the ballast from overheating what it’s hanging from (wood or drywall). I run the 16 gauge wire out the side, or top, and have it go to the plug. I guess you can put fluorescents right up to the ceiling, but I don’t like to.

39

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

40

This. at 60Hz, skin depth is about a 1/4-inch; the average home doesn’t have any wires greater than 1/2-inch indiameter.

Skin depth does matter in bus bars, which carry a lot of current and therefore have a large cross section; they are often made as hollow tubes about 1/4 inch thick (or wide ribbons about 1/4 inch thick), because making them as solid bars would be a waste of copper.

Skin depth is more of a concern at radio frequencies (kHz, MHz).