PID Blows Up

[Alstep]

I made up a PID system from info learned here. I'm electrically challenged, but I can read & follow directions, and have had no problems with it. Have it hooked up to an old Lyman 61 pot, and it has worked flawlessly for years. The other night the thermocouple literally blew up. Sparks and flame came out of the wire end of the thermocouple that was in the pot, and the whole braided wire going back to the controller got red hot. Set some stuff on the bench on fire. Luckily the pot was near empty and I was about to fill it. Had my hands full for a few minutes getting the situation under control. Good thing I had my heavy gloves on when it happened, so no harm done. Had I left it unintended while waiting for the next batch of lead to melt, I'd probably be homeless today.

Anybody else have a similar experience? What would cause something like this to happen???

[OS OK]

Maybe the thermocouple got up against a 115VAC hot component/screw/whatever inside the box and then shorted out on the pot.
A picture of the PID would give a better estimate of what the workmanship looked like inside. The PID circuit is an input circuit rated in millivolts...not hardly the voltage required to fry thermostat wire and set a fire.
Another possibility would be that the pot is the part that shorted out and went to ground through the PID control via the thermostat wire.
Can't successfully do much troubleshooting of this sort over the forum without any evidence...ie. pictures.

[HATCH]

Combination of PID / Thermocouple failure.
The thermocouple has voltage running to it.
If the TC shorted out to ground (stainless braid) it is possible that the PID allowed too much current to flow.
Just wondering who makes the PID that you used??



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[Mal Paso]

If the pot was a 2 wire Lee and the PID had a ground plug the pot may have shorted.

[Alstep]

Got all the components from Auber Instruments, seams like quality stuff, don't know that I can blame them. They've got a lot of trouble free hours of service. The pot is an old Lyman model 61, also trouble free. It is two wire and no ground. I just mounted all the PID components on a board, so no loose wiring that might short out. I've got new components ordered, and when I set it all up again, I'll run a ground to the pot.
Anybody have more thoughts or suggestions?

[HATCH]

Plug the pot into the wall and take a volt meter between ground and the metal on the pot to check for voltage


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[6bg6ga]

The thermocouple has 1.3VDC across it un-terminated. This is hardly enough to cause the problem. Going to short mine to see what happens if anything.

[6bg6ga]

Combination of PID / Thermocouple failure.
The thermocouple has voltage running to it.
If the TC shorted out to ground (stainless braid) it is possible that the PID allowed too much current to flow.
Just wondering who makes the PID that you used??
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Thermocouple has only 1.3VDC across it un-terminated. Thermocouple short to ground won't do anything. I just tried it with my Auber.

I suspect a simple wiring problem that finally reared it ugly head.

[HATCH]

Your right.

What’s amazing is that a circuit breaker didn’t trip


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[6bg6ga]

Your right.

What’s amazing is that a circuit breaker didn’t trip


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Was the PID in question fused? Most often people forget to incorporate an in line fuse when they make one of these jewels.

[HATCH]

I don’t put fuses in my PIDs. Don’t need to.
99% of the pots don’t have fuses.
Heck my master Caster doesn’t have a inline fuse.

120v standard outlets are hooked to a 15 amp breaker.

I suspect that a fuse wouldn’t of made a difference if it didn’t trip the 15 amp breaker.

[6bg6ga]

I don’t put fuses in my PIDs. Don’t need to.
99% of the pots don’t have fuses.
Heck my master Caster doesn’t have a inline fuse.

120v standard outlets are hooked to a 15 amp breaker.

I suspect that a fuse wouldn’t of made a difference if it didn’t trip the 15 amp breaker.

I guess working with electronics for years has me fusing things. I would have put a fuse in line with the 120 AC feeding the PID. I would have fused the Pot. But thats just me and my knowledge of the U.L. standards I deal with. If the PID or the Pot had caused a home fire you would be explaining to the fire marshall why your home made device wasn't fused. You might also have a problem with your home owners insurance with your home built device without any short circuit protection at the device itself.

[Lloyd Smale]

yup I run all my reloading room stuff through ground fault interrupter outlets. But then I'm an overly anal ex lineman.

[HATCH]

Yes UL508 requires some sort of short circuit protection. I worked in a UL listed panel shop for over 15 years.

LOL - if your PID was the cause of a fire that a Fire Marshal has to inspect they wouldn’t be able to pin point it to the fact it was unfused device as the heat of the fire would of melted everything but the metal housing.
As far as homeowners insurance goes you are making this a bigger deal then it is.
Do you think a smoker has to explain to their home owners insurance on why their cig causes a fire that burned down their house??


You points are noted.
In fact I am ordering 15 amp panel mounted breakers for my PIDs right now. I will even put a small 1/2 amp fuse on the PID itself.
But all of that isn’t really needed.

[OS OK]

Ahhh...the ole NFPA's NEC requirements. There never was a more scrutinized book on the planet besides the Holy Bible and most electricians always referred to the NEC as their Bible also. I had to live by it for many decades a couple decades ago...especially machine control & power distribution.
Here's an interesting article on machine control and Class 1,2 & 3 controls.
http://www.ecmweb.com/content/making-sense-necs-rules-industrial-controls
It might be good to review this before deciding off the top of your heads what is and what ain't...required.

It's been way too long since I've cracked that book open to argue with inspectors and such...I hate to see you guys puffing up over it too, define your control circuit, break out the NEC and find your 'minimum' requirements. NFPA's NEC is considered 'minimum requirements' as each inspection authority has the power to 'add-to' the NEC as they see fit.

[JonB_in_Glencoe]

Sparks and flame came out of the wire end of the thermocouple that was in the pot, and the whole braided wire going back to the controller got red hot.
That sure does sound like the line cord (or heater element or heater element connection) for the old Lyman 61 pot had shorted out to the chassis...then making a circuit through the braided shield to earth ground.



Plug the pot into the wall and take a volt meter between ground and the metal on the pot to check for voltage


Your right.
What’s amazing is that a circuit breaker didn’t trip
Maybe the braided shield, acting like a load, didn't draw enough to pop the household fuse/breaker?

I too have spend much time digging through the UL508 rule book, looking for loopholes to allow a component that isn't listed...that wasn't available as a listed component. In three different panel shops that I worked, It seemed I was always to "go to" technician when the UL inspector came to visit.

FYI, the PID box I built for myself has a 10 amp circuit breaker on the incoming line. But if my hunch is correct, that wouldn't have helped with this short circuit fire failure that the OP had.

[OS OK]

I would imagine that the wire in the thermostat connection, called 'chromel/alumel' acted like a heat wire as in heating elements and hot wire cutters. The chromel is also called 'nichrome 60' and it is a heat wire also.
It's small AWG/gage aided in limiting current flow, hence it didn't conduct a huge inrush of amperage and trip the thermal/magnetic circuit breaker. It would have turned red hot, slumped and sat there setting anything combustable on fire within a few seconds or so.

[Handloader109]

OS OK, I agree, that nichrome wire IS used as a heat cutter and that is probably what happened.
Don't walk away from these things.... And I fussed a few years ago about some putting the electonics in cardboard and wood boxes. Wonder why?

[OS OK]

Yeah, I love riddles like this one...prolly one thing we haven't talked about though, if it was the Pb pot that shorted...the current may have run throughout his PID controller as it went to a grounded source and knocked sub circuits out of that unit out too. Current doesn't have to find a dedicated ground to short out, it can do that by a neutral wire within the unit. Neutrals and grounds are at the same potential in a typical 115/230VAC single phase 4 wire system. The ground buss and neutral buss are joined in the main panel with a bonding jumper.

[Alstep]

Just did a little investigation with my volt-ohm meter. Sure enough, the Lyman 61 pot is shorted out. Pulled the control cover off, and there's a wire going to the rheostat that's frayed and shorting out on the sheet metal.

Have to get a short piece of high temp wire to replace it. Only need 3 or 4 inches or so. What should I be looking for, would a hardware store or appliance shop have something like that? Or maybe I could salvage a short piece off of an old electric stove at the junk yard?

Have a new controller & thermocouple on order, I'm sure the controller is fried.

Thanks to all for your input. Appreciate it.

[HATCH]

Does the controller power up?


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[Mal Paso]

Appliance repair or parts store has high temp wire. 14 or 12 gauge is common and plenty for your needs.

You can make the Lyman pot 3 wire with a new cord. Attach the green wire to the pot frame with a #10 screw.

Yea, I would see if the controller works. It was the TC wire outside Shield that burned, not necessarily the wire.

[tomme boy]

Disconnect the heating coil and ohm the coil. It should have some resistance. If it does not then the coil has a open break in it. You may be better off getting a new pot.

[6bg6ga]

One could argue that an in line fuse isn't needed. One could argue that code on this matter is questionable. One could also argue as to what the fire marshall might think about the absense of a fuse. All of this really doesn't matter in my opinion. If one takes the extra step to incorporate an inline fuse to the PID and fuse the pot then one has gone the extra step to protect the item that is being used by the end consumer. If one is selling the item as Hatch is then Hatch can and should incorporate the extra cost of these safety items in the end cost of the item.

If I were a potential customer of the product I would gladly pay the extra $30.00 that these devices would probably cost considering the extra labor involved in implementing them. If I were marketing the item I would have the product ready to pass a UL test and thus have a more marketable item.

[Plate plinker]

LOL I torched my first thermocouple, it was a similar episode. Just chalked it up to chinesium quality controls. Second one seems fine. All my Chinesium was sourced off fleabay.

[lightman]

This incident certainly should make one think about leaving one on and unattended. I leave mine on when I'm casting and take a break for lunch but I cast on a steel work bench with very little flammable material present. Glad you were present when the meltdown happened and nothing worse happened.

Like OC, I spent most of my life around the NEC. I'm not sure what is in the code book that covers PID's, homemade devices and fuses. The code changes every three years so you would need the most recent copy to get current info.

[gwpercle]

All this reminds me....I need to get a new fire extinguisher for the loading bench. When you need one, you need one close by and working.

Even though I don't use a PID , they weren't required in the Dark Ages, beeswax flashing while lube making isn't fun.
Gary

[HATCH]

I have ordered 15 amp resettable breakers and 1 amp pico fuses.

They will be incorporated into future builds starting in March.

Breakers will be on the incoming power and the pico is for the PID power.

None of that would of helped in this situation.

[OS OK]

I'd say that you have 'covered your butt' as a manufacturer on this deal HATCH . . . and whether it makes sense or not at the moment, I think you did the right thing.
You know how 'Sue-Happy' the world is now!
With electricity you can't always out engineer all the variables but you have tried to fuse it correctly. In a court of Law that oughta make some difference.

Many decades ago, when I first got into controls, hardwired magnetics...believe it or not but...they used to fuse the control source neutrals too! Go figure!

[tomme boy]

Did you have a ground fault breaker? This should have kicked out.

[6bg6ga]

Did you have a ground fault breaker? This should have kicked out.

Not a bad idea either. Some of us have made positive suggestions to a person who puts together systems to sell with the expressed purpose to help that person cover his butt in the event that God forbid something was to happen to one of the systems he put together and sold. I sincerly hope that dispite the apparent experience that person has had in control systems that what was suggested hasn't been taken wrong. In this sue crazy world we live in the fact that a product doesn't have a U.L. sticker automatically makes it fair game for someone wanting to sue.

[Mal Paso]

Get certified as a Firefighter. If you burn down a home no one can touch you.