Cerakote / Powdercoat curing oven problem. Solved.

[Ken226]

Just wanted to post this here in case anyone else has a similar issue pop up in the future, they'll be able to find this solution in a search.


So, in 2016 I built a curing oven out of a stainless cabinet smoker. I used rivets, 1” angle and 1/16" shear cut galvanized plates to insulate and double wall the interior. I wired a dryer heating element with a PID, Inkbird Timer and solid state relay to control the temp and auto shutoff with an audible alarm, after a specified bake time.



It's been running perfectly since I finished it in 2016, until a couple days ago.



I walked out to the shop to turn off the lights before bed, and it smelled strongly like smoke. I gave it a minute to clear some smoke, then went in to figure out what was going on.

Everything looked fine, so I walked through and checked on each machine. When I got to the oven, I could feel heat.

The oven was still off, but when I opened the door the heat element was bright red. Naturally, I unplugged the oven.





That's where it started getting weird! I knew SSRs (solid state relay) can fail shorted, which would have explained the heating element running while the PID and electronics were all switched-off. Though it would be really weird for a SSR to spontaneously fail to short, while not in use.... when I opened the enclosure, and plugged the oven back into the wall socket, the element went right back to bright red! the SSR showed to be off, unpowered. So, I swapped in a new SSR anyway.

That didn't work. With the brand new SSR in, and unpowered, I still had full power to the heat element. so I tested both SSRs.
They tested good.



The heat element only has 1 circuit. Two wires! One from the power source direct to the element, and the other broken at and passing through the solid state relay. So, somehow the current was flowing through the SSR, while it was off! But the old one, and the new one tested good, and what are the chances of a new one being dead, and in the same way as the old one?!



So I disconnected the element wires from the SSR, and plugged in the oven. The element immediately went to full power, bright red, with one of it's two wires completely disconnected!


Continued after dinner:

 

[Ken226]

So, I unplugged the wires at the element, plugged in the oven and used my multimeter to check the voltage at the element. 0v. Nada!

I checked the current draw at the SSR leads. 0 amps. Nothing! This, while the heating element was bright red! Kinda a head scratcher!

So, I pulled the interior panels out and hand checked every inch of the element wires, all the way up to the SSR. They were bsolutely perfect. Not a single nick in the insulation..





Then I happened to spot a broken insulator on one of the heating element coils, and noticed that a coil was touching the housing. When I moved the coil out of contact with the housing, all problems went away. It worked perfectly again! I checked the voltage between the housing and the coil, and got 120v. At that point I had an idea of what was happenning.






I pulled the 3 hole dryer plug out of the wall and found 4 wires, 3 connected to the dryer outlet and one capped off. At some point in the past, someone swapped from an 4 wire outlet to a 3 wire, but connected the neutral to the outlets ground hole instead of the ground.
So, when that elements insulator broke and the coil drooped into contact with the chassis, it closed the non-broken leg of the 240v with the neutral, through that miswired plug, and the element was drawing 120v @ 40 amps, through a 30 amp, 240v breaker!


Anyway, I swapped in a fully insulated kitchen range top spiral type element, and put a magnetic contactor into the heating element circuit. Oh, and I fixed the wiring in wall outlet.



All is well now. The range top type element can touch whatever now, with no current flow. It's surfaces are insulated from the actual conductors. Also, if the SSR ever fails shorted the heating element won't self activate because the magnetic contactors prevent both legs of the heating element circuit from closing unless the PID is switched on!

And the element can be replaced for 20$ from Home Depot.

 

[larry4406]

Nice detective work!

Do you have a build thread on your oven anywhere? I would like to do this when I get back to my car restoration.

 

[graham-xrf]

I almost did not spot that it was someone else who made it possible for a current to run to earth without tripping the RCD breaker.
Well done

Just so we know it's good, a safe system has it that all currents going into the house live conductors must match the current returning down neutral to within about 30mA, this balance being detected by the RCD safety breaker (Residual Current Device). Any current finding even a partial alternative path to a properly grounded casing, should instantly trip out.

In my place, any contact from live or neutral to the earthed casing, whether switched on or not, will cause it to trip, and the fault has to be fixed before it can be reset. The neutral is connected to earth, but only at a single point upstream of the earth leakage RCD safety breaker, where the power enters the house at the power distribution box.

 

[Ken226]

Nice detective work!

Do you have a build thread on your oven anywhere? I would like to do this when I get back to my car restoration.

No, I never did a build thread on it but wasn't very difficult. There are lots of guides on the internet that cover wiring up a Mypin ta4 pid and SSR to a heating element.

Riveting in some aluminum tube, fiberglass insulation and galvanized panels to double wall it was super easy.

PID Temperature Controller Meter Indicator, Jaybva Digital Programmable Universal Thermostat Fahrenheit and C Display SSR and Alarm Output 25A Solid State Relay Thermocouple Probe Included

https://www.amazon.com/dp/B07XNQ538P/ref=cm_sw_r_apan_glt_fabc_7X00RZ105JDBN6T5FH0S

I also wired my pid outputs to the SSR and a cheap 240v alarm, through the NO/NC relay on an Inkbird Timer.

The NC side to an Inkbird Timer cuts power to the SSR when the timer reaches zero. The NO side activates a buzzer.

 

[Ken226]

Inkbird Digital Cycle Timer Switch Preset Scale IDT E2RH Relay Tact NPN PNP Input Dual Function Register 100-240V Programmable Time Setting https://www.amazon.com/dp/B008KV65MS/ref=cm_sw_r_apan_glt_fabc_QQF69SNNP7GCB5V3A9VW

(2 PCs) 240V AC (22mm RED) LED Flashing Buzzer Alarm Signal Light AD16-22SM | eBay

AD16 seriesLED Flashing Buzzer Alarm Signal Light as the light source. It is the advanced product of all kinds of the incandescence Flashing Buzzer Alarm of the AD type. The cover of the lamp is made of PC material, and have good shock resistance.

www.ebay.com

 

[graham-xrf]

Double insulated stuff, like is common on electric drills, do not care which way around (live or neutral) they are connected. They have a plastic casing, and no provision for a third wire for earthing.

Normally, on things like stoves, heaters, anything with metal in the casing, the casing is earthed, and any inadvertent contact of the element conductors, or liquid spill, should trip the circuit. If you don't have that in your house, you can get a local leakage breaker for only a few bucks to plug into the socket, and plug the heater into that.

 

[Ken226]

Double insulated stuff, like is common on electric drills, do not care which way around (live or neutral) they are connected. They have a plastic casing, and no provision for a third wire for earthing.

Normally, on things like stoves, heaters, anything with metal in the casing, the casing is earthed, and any inadvertent contact of the element conductors, or liquid spill, should trip the circuit. If you don't have that in your house, you can get a local leakage breaker for only a few bucks to plug into the socket, and plug the heater into that.

I'll go pull the covers of the breaker box and take a look, as soon as the temps get somewhere above freezing.

The house was built in 1984, and a previous owner built the shop and added the sub panel.

Just to clarify, when I check the sub panel, neutral should NOT be connected to earth in the sub panel?

 

[graham-xrf]

By the time this thread is done, you and everybody else will understand, and feel OK about it. It's quite easy.

Neutral should not be connected to earth except at the power station, or, in the case of a system known as "PME", which stands for "protective multiple earth", it might be at the pole outside, or in the house upstream of the meter. It might even be right at your power distribution box, BUT, not at a place you would normally use, and in any case, always BEFORE a RCD safety breaker, which should be in the box. Sometimes, the RCD breaker doubles as also being a main isolator.

Other over-current type magnetic, or magneto-thermal trip switches are separate things for the house sockets, and lighting circuits, and are not to be confused with earth leakage safety. Definitely no neutral connection to earth on the house side of the RCD trip, and definitely not anywhere else in the house.

Depending on how rural is your place, what country it is in, and what local regulations were applied, you might find absolutely any setup, which is why, if you can't find it, and identify it, I suggested a local gadget at the socket.

2P RCD 63A 10mA 30mA 6KA RCCB Electromechanic Residual Current Circuit Breaker | eBay

RCCB designed for household installation and other similar application, is for non-professional operation.

www.ebay.com

GFCI Leakage Protection Safety RCD Socket Home Circuit Breaker Switch 16A EU | eBay

Find many great new & used options and get the best deals for GFCI Leakage Protection Safety RCD Socket Home Circuit Breaker Switch 16A EU at the best online prices at eBay! Free shipping for many products!

www.ebay.com

or similar. You can find them on Amazon, or wherever. Get one of the right rating.

Universally, for decades, earth leakage protection devices have been used as standard on homes just about everywhere, and definitely in USA. You should be able to discover it. At this time, all new installations in UK have to have all circuits protected in this way, but it has been traditional to use RCD breakers only on power to sockets, and higher current stuff, like heaters, showers etc. Lighting circuits were often not taken through a RCD trip, or given a separate one, so that the lights stayed on, even if the kettle went kaput and took out the whole house!

The main difference between USA houses, and UK is that UK uses a ring main, and every plug has a fuse. This does not affect the provision of RCD safety devices. They work in the same way.