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

[delalio]

Hey OP

Thanks for posting this. Very relevant and very informative, and it's started a great discussion too.

Very glad you caught this when you did. Where is your workshop? In your house/garage, or in an outbuilding?

Wishing you all the best in your repairs and rewiring.

Del

 

[Technician7286]

Two things I note here. One the smell you noticed was most likely ozone (O3). Ozone is created by the arcing. It’s responsible for the fresh smell after a thunder storm. Our noses are very sensitive to it. Arcing also sounds very much like bacon sizzling. Running the machine unlikely to hear that. They do make tension testers for plugs and plugs do wear out. Also many outlets purchased to are 15 amp use with 20 amp pass through capability.

 

[fwwbronco]

This is why I use metal boxes and true 20 amp plugs for shop 110/120 volts and also only 12 gauge wire. You might want to check the wire, (looks like 14 from the picture). 14 is run in most houses but can only be used with a 15 amp breaker on it, in our area (code). Furthermore, don't know how big your shop is or how long a run it is, or what gauge wire feeds your breaker box all this is fed from. However, it looks like one of the plugs you buy in mass from your local builder's supply, and sometimes the screws don't tighten down properly or as the IGNATOR says above, another cheap mfg process, because of mass production. finally, check and make sure the neutral and ground wires are tight in the breaker box. I am betting on a bad plug. Use to be all good plugs only had metal connectors to the screw lugs and none of it was on a printed card. my two cents worth and I bet a true 20 amp plug is still made that way that is why they cost more.

 

[Lloyd-ss]

Hey OP

Thanks for posting this. Very relevant and very informative, and it's started a great discussion too.

Very glad you caught this when you did. Where is your workshop? In your house/garage, or in an outbuilding?

Wishing you all the best in your repairs and rewiring.

Del

Thanks Del.
Agreed, great discussion. First, your questions. The shop where that happened was a detached garage, then moved my shop temporarily to a basement, and now it is in an attached garage (misnomer- no cars ever go in it, LOL) with a cinder block firewall, fire code sheetrock, and various sound insulation methods.

Take-Aways from the Discussion

Here is a list that I came up with, and I would guess that folks will add some for their own personal situations. Some of the items were not discussed, but are certainly relevant, for shop and home.

1. More smoke alarms.
2. More fire extinguishers.
3. Keep all receptacles that are in use, visible, especially those that see high current loads.
4. Change out all of my machinery receptacles to the 20A variety. I have seen some of these with additional certifications on the package, and also listed as hospital grade. But the certs and amperage are the most important part.
5. Do some sort of "pull test" for all plugs in receptacles.
6.Check condition of all power cords.
7.Instead of using a semi-permanent extension cord for any machinery, buy a nice heavy extension cord of appropriate length and gauge, cut off the female end and wire it permanently into the motor.
8. Check all recpts and plugs and cords, etc, for heat, with your hand and an infrared temperature sensor.
9. Verify that the electrical circuit layout and breakers in your shop are appropriate, and know which breakers control what.
10. GFI's for all circuits.

All of these are easy fixes/inspections that could make a BIG difference.

Got some more?

Lloyd

 

[Lloyd-ss]

This is why I use metal boxes and true 20 amp plugs for shop 110/120 volts and also only 12 gauge wire. You might want to check the wire, (looks like 14 from the picture). 14 is run in most houses but can only be used with a 15 amp breaker on it, in our area (code). Furthermore, don't know how big your shop is or how long a run it is, or what gauge wire feeds your breaker box all this is fed from. However, it looks like one of the plugs you buy in mass from your local builder's supply, and sometimes the screws don't tighten down properly or as the IGNATOR says above, another cheap mfg process, because of mass production. finally, check and make sure the neutral and ground wires are tight in the breaker box. I am betting on a bad plug. Use to be all good plugs only had metal connectors to the screw lugs and none of it was on a printed card. my two cents worth and I bet a true 20 amp plug is still made that way that is why they cost more.

Bronco, I've covered most of this already, but it certainly bears repeating.

First, I built that shop myself as a detached garage (less the cars, LOL) with radiant heat slab (gas hot water heater) AC, well insulated, water, and plenty of power. A 100amp sub panel. All circuits 20 amp, even the lighting. As many have noted, the use of cheap 15 amp recepts was probably the downfall. That, plus not having the cord/recept visible, with stuff in front of it.
It was a nice shop, but I have since moved and have another nice shop again, but smaller. I had to shift a wall and yield some square footage to my wife's need for a much-deserved plant potting and propagating "studio" with sink and grow lights, etc.

I will be implementing items listed in post #24.
Lloyd

 

[GreenTwin]

Another thing I see at the hardware store is #16 or smaller extention cords.

Depending on what you plug into it, you can easily overheat a #16 cord, but there is nothing to stop you from plugging a space heater into one.

All extension cords look about the same, but they have very different ampacities, and if you are looking for lowest cost, you may be creating a fire hazard.

For heavy loads, I use a #12 AWG extension cords.
For lesser loads I use a #14 AWG cord.

I don't use any cord less than a #14 AWG for any reason in my shop.

It is not worth it to save a few dollars on a cord, only to have it fail in use.

.

 

[Mike Ginn]

Metalmangler. In the UK many fires can be attributed to heaters. You don't give their rating but in my experience you should avoid running 3kW heaters for long periods on a 13A circuit with square pin UK sockets. Keep to 2kW. The issues with 3kW is basically one of inline resistance. Socket contact resistance can be caused by long term use of the socket. There are many sockets on the market and they are not all equal. The same applies to the plugs.

I always use metal clad sockets and switches and keep the 2kW heater(s) on separate circuits. I also use a 13A fused switch to control the power to my lathe circuit which has 8 sockets attached. This ensures that I can easily turn off the equipment.

Occasionally check the plug to see if the pins have heated up - that's the first clue to problems.

Mike

 

[metalmangler]

I also use a 13A fused switch to control the power to my lathe circuit which has 8 sockets attached. This ensures that I can easily turn off the equipment.
Mike

I have a several Big Red Buttons which, when pressed, instantly isolate all the sockets in the workshop, leaving only the lights on. So far I've only used it to make sure everything is inert when children are visiting.

 

[metalmangler]

Got some more?

Lloyd

Make sure you have a alternative route out in case of fire. My workshop is split into two rooms, woodwork and metalwork, with a fire-resistant wall and door between them. The usual entrance is via the woodwork end, but I have a external door, secured by bolts inside, in in the metalwork end in case the woodwork end is on fire.

 

[Rocket Man]

The new outlets where you plug the copper wire into a hole instead of putting the copper wire on the screw are dangerous. Every time my shop door slams shut it shakes the wall and 1 outlet keeps burning up. Last time I replaced the outlet I put the copper wires on the screws that stopped the problem. No more outlets have burned up in 20 years.

 

[the artfull-codger]

Looks like a push on type plug.
A fire in making.

Dave

Oh dear bet your bum was nipping after that!!,my Son [a lot of yrs ago] was in our workshop & it was winter & he kept stoking the pot belly stove up,we were in the house & the earth leak trip went off, looking outside there was flames from the roof it's an old cow byre the chimney was glowing, boy did that frighten me we got it out with garden sprays bur very frightening especially for the young lad, Wife wanted to call the fire brigade but I wouldn't as they would have trashed the place with water everywhere. [carefull now]

 

[Lloyd-ss]

Oh dear bet your bum was nipping after that!!,my Son [a lot of yrs ago] was in our workshop & it was winter & he kept stoking the pot belly stove up,we were in the house & the earth leak trip went off, looking outside there was flames from the roof it's an old cow byre the chimney was glowing, boy did that frighten me we got it out with garden sprays bur very frightening especially for the young lad, Wife wanted to call the fire brigade but I wouldn't as they would have trashed the place with water everywhere. [carefull now]

Well, it certainly looks like Smith Door Dave thought that I used the back-wire push-in terminals but I did not. Never have, never will, I don't trust them. I always use the screw terminals. The most likely cause of that incident was a loose plug from the machine where it was plugged into the receptacle.

With that said, chimney fires can be extremely difficult to extinguish. Glad you made it thru that!

 

[packrat]

Thanks for posting about your problem, I am sure you have reminded all of us to check our plugs and receptacles for
damage and proper set up. Regards packrat

 

[Engineeringtech]

I'm speaking as a guy who was educated at an MIT level engineering institution (Rensselaer Polyechnic), and spent 20+ years doing electronic design followed by 24 years doing mechanical design and machining. Circuit breakers are NOT as reliable as fuses. The government mandated circuit breakers because idiots were putting the wrong size fuses for the circuit, or putting pennies in the socket. (Note that they COULD'VE designed the fuse boxes to be idiot proof.) Fuses are much more reliable protection that a circuit breaker because they are a simple piece of metal that melts in response to an overload. Circuit breakers have many moving/ pivoting parts. They are convenient to reset. You don't have to go out and buy a new fuse. But that convenience leads people to keep resetting them instead of identifying the overload that caused the trip. And the more you cycle them on and off, the more wear on the mechanism. MOST of the time the wear eventually results in nuisance tripping. The breaker will trip before the specified current level is reached. But less frequently, the wear will cause the breaker to hang up and not disconnect when you have an overload. Then your house burns down. I don't know what the incidence of the failure to trip is, It may be 1 out of 500 overloads. But I HAVE seen it. So if you have a fuse box in good repair, and know how to size the fuses properly. you have better protection than a circuit breaker panel. And I would also recommend that you stop using breakers daily to turn circuits off. Incidentally, I did medical electronics design for 5 years, and learned the government does not even allow circuit breakers on medical monitors. They are protected by FUSES.

Finally, I will reinforce what others here have said about loose sockets. The increase in resistance can cause burns and fires. It is not a good idea to keep plugging and unplugging cords or heavy wall transformers.

 

[Engineeringtech]

Well, it certainly looks like Smith Door Dave thought that I used the back-wire push-in terminals but I did not. Never have, never will, I don't trust them. I always use the screw terminals. The most likely cause of that incident was a loose plug from the machine where it was plugged into the receptacle.

I think you may be wrong about push in terminals. Push in terminals dig into solid copper wire and apply steady spring tension to maintain good electrical continuity. It is not unlike the "gas tight" connection of a wire wrap terminal. Wire wrapping was a method used for decades to construct electronic assemblies. A solid, silver plated wire was wrapped around a gold or silver plated square pin multiple times. Done properly, it was considered more reliable than a screw connection or even a solder joint. (It is not done anymore because we have miniaturized our electronics.) Screw terminals compress wire against a plate. Unless there's a toothed lock washer present, the contact area is only as big as the deformation of the wire by the screw pressure. (Stranded wires contact in more places.) I think screws are more likely to loosen up due to vibration and corrosion, especially when using solid copper (or especially aluminum) wire.

 

[Lloyd-ss]

I'm speaking as a guy who was educated at an MIT level engineering institution (Rensselaer Polyechnic), and spent 20+ years doing electronic design followed by 24 years doing mechanical design and machining. Circuit breakers are NOT as reliable as fuses. The government mandated circuit breakers because idiots were putting the wrong size fuses for the circuit, or putting pennies in the socket. (Note that they COULD'VE designed the fuse boxes to be idiot proof.) Fuses are much more reliable protection that a circuit breaker because they are a simple piece of metal that melts in response to an overload. Circuit breakers have many moving/ pivoting parts. They are convenient to reset. You don't have to go out and buy a new fuse. But that convenience leads people to keep resetting them instead of identifying the overload that caused the trip. And the more you cycle them on and off, the more wear on the mechanism. MOST of the time the wear eventually results in nuisance tripping. The breaker will trip before the specified current level is reached. But less frequently, the wear will cause the breaker to hang up and not disconnect when you have an overload. Then your house burns down. I don't know what the incidence of the failure to trip is, It may be 1 out of 500 overloads. But I HAVE seen it. So if you have a fuse box in good repair, and know how to size the fuses properly. you have better protection than a circuit breaker panel. And I would also recommend that you stop using breakers daily to turn circuits off. Incidentally, I did medical electronics design for 5 years, and learned the government does not even allow circuit breakers on medical monitors. They are protected by FUSES.

Finally, I will reinforce what others here have said about loose sockets. The increase in resistance can cause burns and fires. It is not a good idea to keep plugging and unplugging cords or heavy wall transformers.

Eng,
Some very good points in both your posts, but I will still use the screw or clamp terminals on the sides of my recpts. Sounds like we have some similarities in our backgrounds. I went to VaTech, another nice engineering school. Worked for a short time in Maryland near Pa, and the name "Rensselaer" was treated with some reverence. I ended up working for my final 25 years at a company that made the inertial nav systems for Navy ships (high end stuff) and remember talking with a connector application engineer who made the statement "soldering is an art, crimping is a science." The broader implication of that simple statement has stuck with me forever, and it has guided me many times. We had a wire-wrap machine that was used for wiring the multi-layer backplane boards that fit into the Nav and I/O racks of the electronics cabinets for the Nav systems. First time I saw the wire-wrap stuff I thought, what kind of antiquated technology is this? But after I got a full "lecture" on the reliability and the customization capability that wire-wrapping offered, I was a believer. (I had no choice, LOL)

In the US we are stuck with a couple of regrettable systems that would be almost impossible to change for the "good of the future." One is the imperial system of measurements, sigh, what a mess. I remember in elementary school talks about how we'd be changing to the metric system. I wish that had happened. Another is our 120v electrical systems and NEMA 5-15 plugs and recepts, with a DIFFERENT plug for the 5-20 outlets. The nice UK 220v system with switched recpts and better and safer prongs/blades, seems safer and more robust, at least the newer installations.

And one last thing about fuses vs CBs. I remember (its so annoying when old farts say, "I remember," LOL) I have had to replace fusible links (elecrical and heat) in more than one small and major appliance. The appliance just stops working and you are forced to take it apart and fix whatever caused the failure. Although, my grown daughter has on more than one occasion accused me of, " Dad, did you just disable ANOTHER safety device." She is just joking, doing that is not smart.
Lloyd

 

[GreenTwin]

A few more comments on electrical things.

The members on the board that writes the National Electrical Code for the US is comprised of people from various backgrounds, such as manufacturers and installers, and each has input into the NEC.

The manufacturers want to sell products that maximize their profit.
The installers want products that are easiest and quickest to install, again to maximize profit.
The other folks mainly want to prevent the electrical systems from burning up.

Its like Ralph Nader said about the Corvair, it is unsafe at any speed.
Likewise, the push-in connectors on receptacles are a Corvair-type affair, and they should never be used for any reason.
The fact that there are push-in options on receptacles just means that they were allowed by Code for various folks to maximize their profits.

The spring on the push-in is very small, and the contact area is also small.
The spring can weaken over time, and with a little oxidation of the copper, the joint will become unsafe, especially at any significant load.

Studies have shown that a screwed copper joint will stay tight indefinitely (unlike a screwed joint with aluminum wiring).
In the process of tightening the screw, the oxides on the copper wire are scrapped off, thus providing a very low impedance joint that operates at a low temperature.
The area of a screwed connection is far more than the area of a push-in connection, and the force on the conductor with a screw remains indefinitely tight.

Aluminum wiring tends to creep, ie: it flows when pressure is applied, and so a screwed joint with an aluminum wire must be re-tightened every so often.
The oxides on an aluminum wire are much worse than on a copper wire, and without cleaning the aluminum wire and immediately applying de-oxidation compound, the oxides in an aluminum wire joint will overheat the wire due to high impedance.

Aluminum wiring for residential use is like the Ralph Nader Corvair; unsafe at any speed.
I have seen the very best modern aluminum conductors installed under the most stringent conditions in industry fail and burn up large distribution panels.
Don't use aluminum wiring for anything, and don't believe the sales pitch about residential aluminum wiring being safe (it is not).

Aluminum wiring is used extensively in medium voltage utility company power distribution, but this is a different animal operated a a much higher voltage, and terminated by a professional lineman.

I don't believe a combination receptacle and switch is more safe than just a receptacle, and in fact I think it is less safe, because you have to worry about worn switch contacts and worn receptacles contacts, and so two points of failure instead of one.

I think the reason that the 240 volt receptacle circuits can be more safe is that the amperage for any given load is 1/2 that of a 120 volt circuit. The heat generated in the joint of a receptacle is (I squared R), where I is the current in the circuit, and R is the resistance of the joint.
If you reduce the current by 1/2, you also reduce the heat produced by the receptacle or connection joint by 1/2.

I would guess that 90% of the receptacle branch circuit failures in the US are caused by poor connections, especially push-in connections, and worn contacts on receptacles and plugs.

If you plug a small cord (say a #16, or even a #14 AWG) into a 15 or 20 ampere receptacle, and draw more current than that that cord can safely dissipate, you will melt the cord and probably the receptacle.

Almost all 120 volt plugs on almost all commercial equipment are the 15 ampere style, and 12 amperes is about the most you can pull through them when conditions are idea; ie: the plug and receptacle are not worn.

I really never seen any 20 ampere 120 volt plugs used, except perhaps in some special industrial setting.

I do recommend using 20 ampere receptacles and switches in a residential setting, to give an additional margin of safety as far as current capacity, but you have to watch the Code requirements on that, since some codes assume a 20 ampere receptacle will have a 20 ampere load on them, which is false.

.

 

[Mike Ginn]

Umm.... I think I would take issue with Engineeringtech re wire wrap. I agree that it was used for many years in electronic assemblies BUT the tools needed to be calibrated and regularly checked. This resulted in many repair shops soldering the joints. In my view push-in connectors are fine for low current but must be questioned for high currents. Although I don't have data, I cannot see how a push-in connector can achieve the same level of performance as a screw connector. Although convenient, I remain to be convinced that have the same performance as screw connectors.

Discuss!

 

[GreenTwin]

As far as fuses vs circuit breakers, I am firmly in the circuit-breaker-only camp.

In industry, where 3-phases are used, you never want to trip off only one phase to motors and such, and so many industries outlaw fuses except in special circumstances.

In residential use, fuses are fine, but are not renewable, and so you have to stock a supply of every size.

You may get slightly better protection with a fuse in some circumstances, but a fuse does not necessarily offer better overcurrent protection than a circuit breaker.

A circuit breaker is comprised of two components, which is an instantaneous-trip magnetic coil, and a thermal element that heats up over time to trip a breaker.
The idea is for a large short circuit, the magnetic portion of the breaker will trip it instantly.

For an overcurrent, which is not a short circuit, but rather a slight excess current above the breaker rating, the breaker is designed to not trip immediately, since it takes time for the bimetalic element to heat up and trip, so that motor staring surges or other temporary surges will not trip a breaker.

.

 

[GreenTwin]

Umm.... I think I would take issue with Engineeringtech re wire wrap. I agree that it was used for many years in electronic assemblies BUT the tools needed to be calibrated and regularly checked. This resulted in many repair shops soldering the joints. In my view push-in connectors are fine for low current but must be questioned for high currents. Although I don't have data, I cannot see how a push-in connector can achieve the same level of performance as a screw connector. Although convenient, I remain to be convinced that have the same performance as screw connectors.

Discuss!

The problem is that the general public has no knowledge of the connection type or its capacity.

A relative of mine plugged a space heater into a receptacle on the end of a house branch 120 volt circuit, and the push-in feed-through connectors in a receptacle in mid-circuit started to burn. They narrowly avoided a disaster, as the original poster of this thread did also.

It should be noted that Code requires multiple receptacles in a branch circuit to be pigtailed, ie: the branch circuit must be tapped, and the circuit not fed through a receptacle.
The exception is GFI receptacles which have two screws to allow feed-through connection to protect downstream loads with GFI protection.

But people do their own home electrical work, and so I see all sorts of dangerous things done, such as loose terminals (screws), feed through on receptacles, ground wires used as neutrals, reverse polarity on 120 volt circuits, joints made without wire nuts, etc. It is a miracle that more houses don't burn down.

It is very easy to plug one or more 120 volt devices such as hair dryers, space heaters, and many other loads into multiple 15 ampere receptacles on the same circuit, with each device drawing 12 amperes.
You have to hope that your branch circuit integrity is excellent, and hope that the upstream breaker in your panelboard trips correctly during an overload.

The US would be better served if it adopted a 240 volt branch circuit receptacle for general use, and limited the current on that circuit to about 8 amps, or perhaps a little less per receptacle.

.