Almost burned my shop down and didn't even know it

[SailplaneDriver]

Yea scary...Looks like the neutral contacts inside the outlet were arcing? Were you plugged into the top or bottom? What did the plug look like? Maybe the plug or outlet contacts were a bit old and tarnished?

I believe, 15A outlets on a 20A circuit are allowed (in USA anyway) but not 20A outlets on a 15A circuit.

USA electrical code allows multiple 15A outlets (one duplex outlet is a multiple outlet) on a 20A circuit. One simplex 15A outlet must go on a 15A circuit.

 

[Bentwings]

I follow a number of aircraft sites . They always have redundancy on electrical circuits some time multiple redundancy breakers are usually close to the first items on check lists
I' m just happy to have read all this stuff about electrical wiring, as I am about to wire a 2HP motor in my garage. I tsry to keep to the sensible methods but there are some items here I never knew about. Thanx to all!

I remember the penny thing . At our old house there were the old glass fuses . I remember there bring several punts right in the fuse box. How did we ever survive?
The 80% loading is for continuous loads, but it is a good idea to adhere to this rule for all loads (I use it for all loads).

It is seldom a good idea to use an electrical device at 100% of its rating, since we know the capacity and electrical integrity of devices usually degrade over time.
There are special cases where 100% breakers are used (in industry), but you have to be careful that the entire circuit and every device/contact is also rated at 100% if you use such a device.

Kitchens in the US have had a dual circuit requirement for as long as I can remember (dating back to the late 1950's at least).
Kitchens are suppose to have "split-wired" 120 volt receptacles, ie: the tab that connects the upper and lower outlet on a duplex receptacle is removed, and separate 120 volt circuits are brought to each screw terminal on the "hot" side of the receptacle.
This does put 240 volts in these receptacle boxes, which is not a problem, since you still have only 120 volts to ground during a fault, which is no different than a 120 volt circuit.

There is much confusion about the term "hot", and I don't like to use it since it is a slang term that refers to the conductor in a 120 volt circuit that is not the neutral. The "hot" conductor must be connected to the short prong of a 120 volt receptacle, and the neutral conductor (which normally has white insulation, per Code) is connected to the longer prong/opening in a 120 volt receptacle.

Also there is much confusion between the neutral conductor and the green ground conductor.
The neutral conductor is generally near ground potential, but it does carry full current in a 120 volt circuit.
The neutral should always be insulated on its entire length, and treated just as if it where the "hot" conductor.
Current flows in a continuous loop, which is out the "hot" conductor and back to the source (typically the utility company pole-mounted or pad-mounted transformer outside your house, in the US) via the white neutral conductor.

The green ground conductor (it must be green in color per Code) is used for safety purposes, and what it does is establish a ground plane of equal (grounded) potential across all metallic items such as electrical conduits, metallic junction boxes, and the metallic frames of equipment and appiances.
The ground conductor does not have any current flow in it during normal conditions.
If the "hot" conductor happens to make contact with anything that conducts current in the system, the frame of that piece of equipment should be solidly grounded, such that the stray fault current from the "hot" conductor will immediately flow back to the upstream circuit breaker and trip it.
During a fault, there is no load impedance in the circuit, and so the fault current is high until the breaker trips on instantaneous (via a magnetic coil in the breaker).

Without a ground wire, under a fault condition, the metallic frame of a piece of equipment becomes energized, and there is no low impedance path back to the panelboard, so if a person makes contact with the metallic frame, current flows in the "hot" conductor, through the person, through the ground, and back to the panel, thus generally electrocuting the person (actually starts heart muscle fibrilation ususally).

I have seen many electrical cords with the ground prong cut off, for convenience.
This again is a "Corvair" moment, and is always extremely unsafe.
I don't use any extension cords that do not have the ground prong, and I don't use any electrical device that does not have a ground prong on the cord/plug, unless it is a device specifically designed to be "intrinsically safe" without a ground prong on its cord, due to double insulation or other means.
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[GreenTwin]

Thanks Lloyd for posting that photo.

That is an eye opener on shop electrical safety for sure.

It makes me wonder if all GFCI protected circuits were used to feed a shop, whether that would have stopped your fault before it got so dangerous.
They do make GFCI protection for breakers other than the common 20 ampere single pole, such as two and three pole breakers of all sizes, but it is more of a commercial/industrial thing.

I know arc-flash breakers would have stopped that.

I think you may have saved some folks from fires, or at least made us all think a lot more about electrical safety.

I know electrical systems pretty well, but your photos have really made me think again about how I can avoid this in my shop.

Thanks very much for sharing this information.
Much appreciated.

Pat J

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[GreenTwin]

USA electrical code allows multiple 15A outlets (one duplex outlet is a multiple outlet) on a 20A circuit. One simplex 15A outlet must go on a 15A circuit.

I have seen that, and I disagree with the Code folks on the multiple 15 ampere receptacles protected by a 20 ampere breaker, since people plug in high-wattage devices into 15 ampere receptacles, and the receptacle and cord overheat since the upstream breaker is providing 20 amperes.

For the commercial/industrial work I do, I use #12 AWG minimum for lighting and power, and 20 ampere minimum branch receptacles and light switches.

The weakest link in the chain is the one that will fail.

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[william_b_noble]

If you have degraded wiring insulation in your home, you really need to rewire your house with modern Romex-style wiring.

it's perhaps a matter of opinion but I am strongly opposed to romex, for any permanent wiring I always ensure the wiring is enclosed in a full metal jacket - EMT or for very short runs, flex, for burried or outdoors unsheltered rigid conduit. it's pretty easy to drive a nail through Romex, or to nick it, and I would not trust that in the presence of heat the plastic wouldn't soften and allow a short. Inside a metal conduit, a short is contained, with romex it isn't.

but whatever you do, don't use zip cord. and don't have 40 or 50 gallons of solvents and paint. and don't have urethane insulation. superheated steam does a great job of rusting steel. (not my fire, but a close friend's fire - he's now deceased)

 

[GreenTwin]

I have not permanentely wired my shop, but use various heavy-gauge rubber cords suspended from hooks on the ceiling instead.
Probably not the safest thing to do, and I have to agree with William, use wire in EMT, or flexible metal conduit, etc. for much better safety.

A fire really makes a huge mess of a shop very quickly.

I tend to have several fire extinguishers around the shop in readily accessible locations.

One fire I saw in someone's shop resulted when he cleaned up, and tossed some old powered-tool batteries in a garbage can.
The batteries were not quite discharged, and they shorted against some metal.
He burned up half of his shop, but got the fire put out before it burned his entire house/shop down.
His shop was in his 2-car garage, as is mine.

Some folks disconnect all power to their shop before the leave it, and I am beginning to think that may not be a bad idea.

Another fellow I know narrowly avoided a fire in his garage when his air compressor pressure switch went out, causing his air compressor to run continuously until it burned up.
I make sure my air compressor power is switched off when I leave the shop.
I actually had my air compressor pressure switch stick one one, and luckily I was in the shop when it happened.

The scariest thing I had happen, and probably the closest I have come to meeting the maker in a spectacular and sudden fashion, is when the pressure regulator on my oxygen tank of my oxy-acetelene cutting rig failed while I was cutting something outside.
I heard a pop sound, and then loud hissing.
I ran into the shop, and turned off both tanks, not knowing which tank it was.
Needless to say, never store your oxygen and acetelene tanks inside a house or shop.

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[Saddo]

The most important thing with electricity is if you can't see it treat it with great respect respect. Same as gases etc.

 

[ignator]

Kitchens in the US have had a dual circuit requirement for as long as I can remember (dating back to the late 1950's at least).
Kitchens are suppose to have "split-wired" 120 volt receptacles, ie: the tab that connects the upper and lower outlet on a duplex receptacle is removed, and separate 120 volt circuits are brought to each screw terminal on the "hot" side of the receptacle.

There is no NEC requirement (kitchen) for this that I've ever been aware of or can find. The reference in the NEC 210.4(B) requires that the two ungrounded wires which are sourced from circuit breakers will simultaneously trip if a fault should trip one.
I just wanted to comment so this is not assumed to be a correct wiring method.

 

[ignator]

For reference in the USA and Canada that use the 120V split phase standard, arc fault fires have statistics indicating 50% of fires would be prevented by AFCI (arc fault circuit interrupt) circuit breakers (CB).
In a WIKI article, this does not appear to be an issue in countries using the higher voltage system, so is not as prevalent a requirement in their codes.
https://en.wikipedia.org/wiki/Arc-fault_circuit_interrupterArc Flash is not the same as arc fault, the term being used in previous posts.
In the US the NEC 2020 pretty much requires AFCI CBs for all receptacles in a Dwelling unit, no requirements for attics, crawl spaces, or garages.
Garages only require GFCI per the NEC.
I've seen articles that suggest adding AFCI to garage outlets, especially for tools.

I'm convinced that the OP's initial post has a root cause of a loose contact in the receptacle that got hot enough to char the plastic electrical insulation between the ungrounded wire and neutral which turned into conductive carbon, that continued to arc using the charred carbon of the plastic duplex receptacle. It looks like the fiberglass insulation in the wall prevented oxygen flow, to enable the wood stud from igniting in the wall cavity.

 

[Lloyd-ss]

A few questions.

Arc faults/flash. If you plug or un- plug anything (like a fan) that is under load, can the arc faults handle that and avoid nuisance tripping?

I like having a gfi recept at the beginning of each electrical run, on every circuit in the house and shop.
Are there any recepts sold in the US that incorporate gfi, afi, and-over current, in the same recpt? Or at least 2 of the 3? Sure seems like it would be handy, but I am waiting for the buzz-kill reply, LOL, as the grandkids call it.

No problem, I can handle it. (Grandpa, you know why you tripped on that board? Cause your shop is a mess! (sigh))

 

[GreenTwin]

There is no NEC requirement (kitchen) for this that I've ever been aware of or can find. The reference in the NEC 210.4(B) requires that the two ungrounded wires which are sourced from circuit breakers will simultaneously trip if a fault should trip one.
I just wanted to comment so this is not assumed to be a correct wiring method.

The NEC changes every four ? years, and the adoption of the latest Code can vary by cities and municipalities.
Things also move and change in the Code often, making it difficult to quote a Code requirement without knowing which Code edition applies.

In my opinion, the NEC is very poorly formatted, and it can be very difficult to find anything since the layout is so convoluted.
Luckily the newer NEC code books highlight the changes from the last Code version, which is a very useful feature, but this does not give you a backwards paper trail beyond four years unfortunatly.
The fact that the NEC constantly changes makes it a challenge to keep up, and I often attend seminars just to keep up with the changes.
And often different Code inspectors interpret the Code differently (sometimes), which really makes it difficult.

I have appealed NEC Code rulings to the local Code folks, and been granted variances, since the bottom line of the Code is to not create any unsafe situations.
For industrial electrical work, some processes can become unstable if you trip off a curcuit breaker feeding the process, such as in oil refineries, and so there are sections of the Code that allow deviances, to prevent creating hazardous situations (such as high-resistance grounding to prevent nusiance tripping).

Hyrdrogenating cooking oil with hydrogen is a process that is exothermic, and you don't want to nusiance trip that process either.

Luckily I do industrial/municipal design work only, and so there are not as many Code changes for those applications, compared to resdential work.
I once had the chief electrical Code guy ask me which version of the Code I was using.
I answered "I use my own Code".
He said "What Code would that be?".
I said "My Code is simple, design things so that nothing burns up or blows up......ever......for any reason".
If you burn something down, it does not matter if that design met Code or not, it only matters that the design failed in that application.
There are often unique situations in municipal/industrial work, and the Code cannot address every unique situation, other than to say the electrical system must be safe, and must operate in a safe fashion in all circumstances (expected and unexpected circumstances).

For industrial electrical design, I often exceed the requirements of the Code, since the Code is a minimum standard, and you almost never want to use minimum standards in industrial/municipal.

I run into high temperature situations, and also classified hazardous areas all the time, and this has to be carefully handled.
Classified areas can have explosive gasses or dust.

Much of what I design is medium voltage, which gets into a lot of IEEE/ANSI standards, and not so much the NEC.
There is a lot more to electrical design than what is in the NEC.

In the NEC 2014 version (NFPA 70), the dual circuit requirement for kitchens is Chapter 2 "Wiring and Protection", Section 210 "Branch Circuits", Part III "Required Outlet", 210.52 (B)(3), "Kitchen Receptacle Requirements".

As I mentioned, I dispise the way the NEC is laid out and formated/numbered, but it is what it is.
I think some of the digital versions of the NEC allow searches? and that would be helpful, but I don't use digital versions (yet).

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[Lloyd-ss]

Greentwin, and all. The farther along that this discussion progresses, the more I think:

Complex
Confusing
Controversial
Dangerous

With that said, I think the success rate is phenomenal.

 

[GreenTwin]

This is what happens when you let your 5KV switchgear get worn and too old.

I get calls in the middle of the night, when some very critical process gets shut down, and they say "do something fast".

Those are white-knuckle calls for sure.

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[GreenTwin]

Greentwin, and all. The farther along that this discussion progresses, the more I think:

Complex
Confusing
Controversial
Dangerous

With that said, I think the success rate is phenomenal.

Sorry about highjack.

Maybe we need to split this out, so we can keep it focused.

Life can be confusing, complex, controversial, and dangerous some times, and I think that is why folks gather on forums like this to share experiences, concerns and knowledge.

PJ

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[Lloyd-ss]

Its OK. The discussion has taken on a life of its own.

As the OP, the important points have been made, many folks are looking at this thread, and hopefully, someone's personal electrical disaster will never happen, because of a wake-up call they got here.

 

[skyline1]

Are there any recepts sold

SOLD !

It was embarrassing enough trying to explain to my supplier how I managed to drag over 250 amps off a U.K. domestic supply for about 2 minutes


I could well do without the whole world knowing about it


but seriously GFIs,

or RCCBs as we call them, As usual us Brits have a posh name for 'em Residual Current Circuit Breakers,
These are livesaving devices standard in U.K. Electrical Installations (by law).

For anyone who doesn't know (I suspect I am preaching to the choir here, but i will explain)

they work by checking the current going into one wire against the current coming out of another, It's called Kirchoff's law (IIRC maybe wrong spelling)

So (I'm using U.K. terminology here )

if the current going into the Live wire is the same as the current coming from the Neutral wire then all is O.K.

But if the two differ by a small amount (30mA is is standard in the U.K.) then something is amiss and some part of the electricity is going where it shouldn't be, possibly through you !
If this happens it disconnects the power (all poles of it)
by design (and by law in Europe) they must do so within 2 mains cycles (A few milliseconds)

This is what happens when you let your 5KV switchgear get worn and too old.

Ouch, Big one ! I hope no one was hurt.

I once got blown across the switchroom when a 415v 1000 Amp fuse blew, I wasn't hurt apart from a minor dose of tinnitus for an hour or so.

The Ironic bit was " why was I in the switchroom in the first place" , I was doing a routine check of the switchgear for hotspots with a pyrometer.

Its OK. The discussion has taken on a life of its own.

As the OP, the important points have been made, many folks are looking at this thread, and hopefully, someone's personal electrical disaster will never happen, because of a wake-up call they got here.

Quite so Sir

Being aware of POTENTIAL hazards is the best form of PPE we have and an open forum like this among peers promotes this awareness

As you said "It has taken on a life of it's own" different views, experiences, and knowledge are being expressed and discussed in a spirit of friendship, this can never be a bad thing.

I thank you for opening the thread and your open minded attitude to it's sort of "evolution"

Best Regards Mark

 

[skyline1]

Quick question chaps

What is Romex wiring it's a term I have not come across in the U.K.. Is it similar to what we call T&E (Twin and Earth) which consists of two Insulated conductors and an uninsulated earth (ECC) conductor in a secondary insulated sheath. it is the standard for domestic fixed wiring here.

Best Regards Mark

 

[GreenTwin]

Arc faults/flash. If you plug or un- plug anything (like a fan) that is under load, can the arc faults handle that and avoid nuisance tripping?

I have not used arc protection circuit breakers yet, so I am not sure how sensitive they are.

I have had problems with circuit breakers that have built-in GFCI (ground fault protection), and I have found more than one brand to be very unreliable.
I have resorted to using either a GFCI receptacle at the head of the circuit, with feed through to protect downstream receptacles, or often I use a modular GFCI device, which is like a very short extension cord with a GFCI module.
The receptacle-type GFCI devices seem to be very reliable, and I have never had one fail.

Sometimes I get nuisance trips on GFCI receptacles, but not very often.
Much better to have an occasional nuisance trip than to get electrocuted via some sort of faulted device.

As far as the arc-type breakers, I suspect they may nuisance trip with anything that feeds harmonics back into the power supply, like some VFD's, etc.
Electronic devices in general have gotten much better about not feeding noise back into the power system.
I suspect that if the arc protected circuit breakers work well, they may become standard for most home circuits.

As it is, I really thing every residential lighing and power circuit should have ground fault protection.
I have been very impressed with ground fault protective devices, and have really become a believer in that concept.
There is no doubt that many lives have been saved with GFCI receptacles and breakers.

When I was growing up, all cords had the same prong for the energized and neutral conductors, and no cords had ground prongs on them.
This was extraordinarily dangerous, since many power tools and appliances grounded the neutral conductor to the metallic case of the device.
If you plugged something in with the poles reversed, ie: the engergized prong went into the neutral slot, and the neutral prong went into the engerized slot of the receptacle, the device would shock you badly.
Many people were electrocuted before they started using polarized 120 volt plugs, where there is a large prong and a smaller prong, and you cannot plug it in backwards.

And as I mentioned, I don't use any extension cord that does not have the ground prong, and I don't use any receptacles that don't have the ground prong.
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[ignator]

Quick question chaps

What is Romex wiring it's a term I have not come across in the U.K.. Is it similar to what we call T&E (Twin and Earth) which consists of two Insulated conductors and an uninsulated earth (ECC) conductor in a secondary insulated sheath. it is the standard for domestic fixed wiring here.

Best Regards Mark

Yes that's exactly what it is, Romex is a trademark name of the early company making it.
NEC code refers to it as non metallic sheathed wiring (NM).

 

[Lloyd-ss]

Quick question chaps

What is Romex wiring it's a term I have not come across in the U.K.. Is it similar to what we call T&E (Twin and Earth) which consists of two Insulated conductors and an uninsulated earth (ECC) conductor in a secondary insulated sheath. it is the standard for domestic fixed wiring here.

Best Regards Mark

Mark, here is the usual Romex as used in the US. I think Romex was the original manufacturer back when I was a kid. White sheath is 14 gauge, yellow is 12, and orange is 10 gauge, all so that the gauges don't get mixed up and the inspectors can easily verify.

The 3 cables in the picture are all "with ground." The white and yellow are type NM-B for interior use. The gray one is type UF, 12 gauge, which is rated for direct burial in the ground at a specific depth, and/or in conduit. The insulation on the type UF is much much tougher than the NM, and a little difficult to strip, but it is water tight, and old buried UF cables that I have dug up have shown no corrosion.

This info is supplied as a home DIY'er, and as such comes with no guarantee. Like a home mechanic I used to know who did darn good work. He took your cash, and his guarantee was 60 seconds, or 60 feet, whichever came first. He had people begging for him to fix their cars.

Lloyd