[Read!] Damn Near Burned The House Down - Space Heaters

[JohnDB]

Mine almost did, or at least could have if I hadn't caught it in time. My home was built in the 70's, but all copper wire except for the central heating which is aluminum, a 90 amp circuit. I smelled hot bakelite one day and found the connection of the aluminum wire to the fuse block connection on the unit to be bad and was getting really hot. Things were getting pretty charred in that area before I caught it. The good news is the connection enclosure is all metal. I replaced all of the heavy power handling components in that area and properly treated the wires with NoAlOx goo. I check it at least once a year now with an IR thermometer, along with the connections at the breaker panel.

Aluminum wire moves more than copper. It's not an uncommon problem even in industrial settings. Especially when the equipment has vibration.

A LOT of times you will see a junction box or disconnect next to a piece of equipment....because when the lugs and wire burn its a shorter run of wire to replace. And often some plants require the lugs to be replaced on a scheduled basis.

 

[GeneT45]

Today the standards are much much different.
Lights are always on a circuit of their own (at least one if not two) 9 plugs to one circuit (20 amp or 15 amp depending upon who is doing it)
Bathrooms all share a single dedicated circuit for their plug and so do the outside plugs. Same for the clothes washer...it gets a dedicated plug for the imaginary iron.

Water heater, dishwasher, both get their own too.

Today it's always roughly 100 amps per 1,000 sq feet for a single family dwelling but shrinking amps after 3,000 Sq ft. Not that this is the actual formula for the house service.

The amount of volt/amps per Sq ft is increasing as the years go by.

If you got snakes skin romex....well you got the old stuff. Otherwise it's glass knobs and tubes that the wires were run in. And I've run into it before. Mostly I just see snakeskin romex. (Silvery coated romex cable that has asbestos and rubber wrapped wires)

A word about asbestos and electricity...the big paper fuses have the asbestos that is bad for you...so don't cut open fuses to look inside...you will dull your knife or saw and expose yourself to a case of cancer.

Interesting, and perhaps there's some variability by state? My home was completed in 2019 and lights (at least in the shop / garage) share a circuit with several outlets. My outside plugs are also not on a separate circuit.

Everything else seems to jibe with what you've said.

GsT

 

[pontiac428]

Now, I read NEC for whatever I am doing, but I'm not doing it daily or weekly, so I may have missed it, but it is a convenience feature and not a requirement to run lights and receptacles on separate circuits. Often, people run receptacles and lights on the same circuit if they want switched outlets in their home.

I get peeved when they make local standards that aren't from the NEC. My buddy just had to add an additional outdoor GFCI outlet because he installed a split heater system and there wasn't a receptacle within 10 feet of the new wiring. The "logic" was typical: If the inspector can imagine something being a problem it was a problem. He feared some schmuck would try to plug some crap into the outside of his house, but if there was no outlet near the AC unit, he would (naturally) pry open the panel and start twisting wires together. If that was my inspector, I would tell that guy to get off my property and not come back without bringing his boss. Don't second guess how I'm going to live my life, if I don't need an outlet there, I'm not putting one there. The end!

 

[JohnDB]

Interesting, and perhaps there's some variability by state? My home was completed in 2019 and lights (at least in the shop / garage) share a circuit with several outlets. My outside plugs are also not on a separate circuit.

Everything else seems to jibe with what you've said.

GsT

Nope....current NEC standards.
Switched plugs were a thing because people used to have floor lamps and when the house was new that plug was upside down from the rest....and sometimes only half of it was switched at install.
But "Bubba" tends to want to "fix" things.
The switched plug was so that they didn't have to install a boob light in the ceiling.....you know the glass frosted bowl with threaded brass or black retaining nipple.

NEC standards change every 3 years. The city, county or state you reside may or may not adopt the new standards every time they are issued. Many states skip one new book but pick up the next. Like here they skipped 2014 but picked up 2017. And if the Authority Having Jurisdiction (AHJ) doesn't enforce a standard...it isn't followed. But some AHJs require odd things like an unnecessary neutral being pulled...(Chicago)

Residential wiring is the lowest skill of all electricians. No motor controls, no real coordination between trades, and I've seen instances where not one wall plate was straight. But people don't really look and see those things....they stare at finishes and colors and trim...as if the actual functions of the house were less important. They care more about the color of paint or tile than if the electrical system was sound. The electric is much much more difficult to fix when wrong than a coat of paint.

2011 and 2014 had the most Residential wiring updates I've ever seen...hardly any commercial/industrial changes. Mostly because of electrical fires and injuries caused exclusively by homeowners doing things they should not be doing.

Remote buildings should have both a neutral and a ground from the main as well as their own ground rod. But usually home shops are wired by someone who has a little knowledge but insufficient to do that job.

GFIs are the only code for protection of people...not wire and equipment which is what the NFPA NEC is focused upon....I recommend taking EVERY advantage of that one code.

 

[luap]

Had a bit of excitement this morning, and before I even had my coffee.

My roommate uses a small space heater in the bedroom to supplement the house central heating. Practices good safety with regard to the heater, not close to any combustibles, plugged directly into the wall, etc.. No problem there. It's a standard 1500/750W heater, with tip over safety switch and all UL approved.

About 2 weeks ago the original 15 Amp receptacle was getting a little loose after 40 years and appeared to be overheating. I replaced it with a 20 Amp Leviton commercial grade receptacle, nice and tight, good connection. At the same time I inspected the cord and plug on the heater, and other than some slight discoloration on the prongs I didn't see any problems. Cleaned up the prongs and life is good, everything is working fine.

Fast forward to this morning.... FIRE !!!! OH CRAP! Run to the breaker panel and hit the main, which happens to be about 5 feet from the offending area. This all happened in the space of about 30 seconds. Then a glass of water to douse the flames. It was basically the plug end of the cord burning, and maybe the receptacle, and it pretty much self extinguished once the power was off. OK... No real damage except to the cord and receptacle, just a little black soot on the wall above the plug. The wiring in the box showed no sign of damage.

View attachment 401487

View attachment 401488

Failure analysis: So how did this happen?

Facts:

• About 2 weeks ago the original receptacle was showing signs of overheating
• Receptacle was replaced
• Cord and plug was inspected
• The fire started a few seconds AFTER the heater was turned OFF.

The cord is the standard over molded 2 conductor. Probably due to the loose receptacle connection and subsequent overheating, the plastic in the plug started to carbonize internally thus creating a current path between the terminals, but not visible externally. As long as the heater was on, the current path was through the heater with very little current flowing between the terminals of the plug due to the relatively low resistance of the heater vs. the current path resistance between the plug terminals. (see Ohms Law for parallel resistors). Once the heater was turned off, the only current path was then between the terminals. And this immediately caused the plug to become a heater. Interestingly enough, the current stayed low enough not to trip a 15 Amp breaker.

Conclusion: The cord was damaged due to overheating. Likely due to the loose receptacle connection over time.

Prevention: In the future if a receptacle needs to be replaced due to signs of overheating, the mating over molded plug needs to be replaced also. You can't see the hidden damage inside of the plastic plug. I would recommend a good quality back wired plug. Don't plug space heaters or other high current draw devices into loose receptacles. I would recommend replacing the cheap over molded plugs on high current draw devices with a quality plug right out of the box. I will be doing this from now on.

We lucked out on this one, there were people in the immediate vicinity and were able to catch it before a disaster occurred.

.
UPDATE: I just ordered 10 Leviton 5266-C industrial grade plugs. https://www.amazon.com/Leviton-5266-C-Industrial-Grade-Grounding/dp/B00HCNVR7S/ref=sr_1_10?crid=27RGBHCD822YO&keywords=120v+plug&qid=1648069481&sprefix=,aps,160&sr=8-10

I'll be replacing a few plugs on stuff around here.

Hello,you might want to investigate the option to use the double horizontal prongs,. Nobody talks about it anymore. But if you look at a. New outlet you Can see that the two horizontal inlets have more contact area .more surface area for higher load?
Also the original 15 amp breaker find out if that matches the current rating of the conductor ,it probably does since you put a higher amperage breaker , an that one should be checked to see if it matches the conductor rating .
A time delay breaker could be used if you have a dedicated circuit for the heater.
Long or short delay trip , is the question .
All this because of safety , be careful what you plug in .
It should trip right away.but because there is no short circuit the wires don't know when to quit ,they get hot ,what is the answer??........
Heaters do cause problems ,
Remember Safety .



Thought I would put my two cents in .

 

[epanzella]

Sometimes inspectors can get hung up on pet peeves and abandon common sense. My house has about 20 windows that my wife would be putting candles in for Christmas. I also like to put an array of Christmas lights out side. When I built the house I decided to incorporate a "Christmas circuit" that would energize all the window candles and exterior decorations with one switch rather than run around for 10 minutes plugging things in. The building inspector had a problem with this because two of the windows were in the kitchen and he wanted every kitchen outlet to be a home run. We went round and round and finally called a truce when I suggested putting all the Christmas outlets sideways under the window sills to denote a "special use" circuit.

 

[JimDawson]

Also the original 15 amp breaker find out if that matches the current rating of the conductor ,it probably does since you put a higher amperage breaker , an that one should be checked to see if it matches the conductor rating .

I did not install a new breaker, that circuit is fed with a 15 amp breaker. I did bump up the plug rating, and replaced both the plug and receptacle with industrial rated hardware.

A time delay breaker could be used if you have a dedicated circuit for the heater.

That would be a really bad idea for a normal household circuit. I do use those in some cases in industrial applications where a circuit has a high inrush or start load.

Long or short delay trip , is the question .

Normal delay trip in house plug circuits. C or D curve trip is only used for high start loads.