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I fried my SSR........ HELP!!!
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dmills:
 What does that PID controller output on its control terminals? For SSRs it should be dc of a modest number of volts, not mains!

No you should NOT earth ether end of the heating element! That you suggest this says you probably want to find someone who understands US style split phase wiring.

There should be a modestly rated fuse or circuit breaker separating the control power from the heavy current, otherwise a fault in the PID controller could cause many, many amps to flow thru its supply wiring, which would be bad.

SSRs are not usable as isolation, so given you need a separate isolation switch to make touching the elements safe, you may as well just use one 240V rated SSR instead of two, and leave one  end of the load connected to one leg of the supply, this saves you half the heat load in the control box as each SSR will drop around a volt, so at 30A will be burning off 30W as heat.
floobydust:
I drew a circuit and realized you may have wired the heating elements wrong. How many ohms are they each, or as a quad? Originally they have might been wired in pairs, as 120V elements each? This could overcurrent the SSR.

I have a few issues with safety, the galvanized enclosure and kiln must both be grounded.
Why are you using cheapola PVC speaker wire when this enclosure sure looks like it gets very hot. The indicator lamps have high temp wire so I'm worried the whole thing will melt.

Can you touch the heating elements (when the kiln is cold) ? Usually this is the case, when putting stuff in or out of the kiln. Using SSR's (instead of a contactor) there can be an electrocution hazard due to the SSR's leakage current putting stray voltage at the heating elements, despite the SSR's being off. You'll need to measure ACV at the heater when the controller is off, to make sure.
DBecker:

--- Quote from: dmills on January 25, 2020, 07:21:30 pm ---
SSRs are not usable as isolation, so given you need a separate isolation switch to make touching the elements safe, you may as well just use one 240V rated SSR instead of two, and leave one  end of the load connected to one leg of the supply, this saves you half the heat load in the control box as each SSR will drop around a volt, so at 30A will be burning off 30W as heat.

--- End quote ---

Most SSRs are rated for and suitable for line isolation.  Internally they use an opto-triac.  Most types have excellent isolation at very low cost, with the circuit board layout generally being the weak point rather than the component.

A kiln will have incompletely shrouded heating elements, so both sides of the supply will need to be switched, likely including a safety switch on the lid hinge.
james_s:
Almost all of those low cost Chinese SSRs will have a 10A triac in them regardless of what the label says. There is no need to explore other options until this part is taken care of, if you look at the bottom of the SSR and see the end of a screw that is a dead giveaway that internally it contains a standard TO220 triac instead of a proper design with the die bonded to the plate. there is no way that a 10A triac is going to control a 30A heating element without burning up, that is your problem.
floobydust:

--- Quote from: DBecker on January 25, 2020, 07:52:55 pm ---
--- Quote from: dmills on January 25, 2020, 07:21:30 pm ---
SSRs are not usable as isolation, so given you need a separate isolation switch to make touching the elements safe, you may as well just use one 240V rated SSR instead of two, and leave one  end of the load connected to one leg of the supply, this saves you half the heat load in the control box as each SSR will drop around a volt, so at 30A will be burning off 30W as heat.

--- End quote ---

Most SSRs are rated for and suitable for line isolation.  Internally they use an opto-triac.  Most types have excellent isolation at very low cost, with the circuit board layout generally being the weak point rather than the component.

A kiln will have incompletely shrouded heating elements, so both sides of the supply will need to be switched, likely including a safety switch on the lid hinge.

--- End quote ---

It's not the isolation I'm talking about, it's the leakage currents from the triac and snubber that are significant in any SSR. They flow mA's when off and that's enough to keep a floating load hazardous live.

I think OP should have a Neutral wire in there and the heaters may be all be 120V elements. Have to check the kiln's make and model to see how it was originally wired.
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