Electrical short in control panel!

Ok so I'm gonna try to describe this as best as I can and hopefully someone can shine some light on this mystery.

Systam setup:

I've attached the schematic of the wiring system I am using. Basically the whole unit is wired like so: 4 Prong dryer outlet > 50amp Spa Panel > Control Panel > 5500w heat element.

A few modifications to the wiring diagram include:
- All power coming "IN" to the control panel is fed through a 660v 40a ON/OFF -switch.
- Instead of a PID I decided to go with a PWM.
-The emergency stop is not wired into the circuit.

Now onto the problem. After getting everything wired up I plugged the boil kettle into the control panel. Everything good so far. I then go to plug the control panel into the spa panel and I see a spark where I am plugging it in and the panel trips.

After that I decided to plug only the kettle into the spa panel after resetting it. Everything works fine the element comes on and the water starts heating up.

I then decide to revisit the control panel this time with a different approach. I turn the control panels main power switch to the ON position. I then plug the control panel to the spa panel first. Everything good so far. I then plug the kettle to the control panel. Everything is still good. I then activate the pwm circuit and everything works like it should the element is firing when the ssr light comes on and it all seems to work perfect.

But wait.....After I thought the testing was over I unplug the control panel from the spa panel. I then turn the main control panel switch to the OFF position and i get this huge arc inside the control panel which then smelt like something got burned.

What is going on here. Does anyone have some insight for me.

Thanks!!!

Unplug everything and open up the panel. Check for stray wires, burn bits etc.
Post pictures. Maybe moving around the panel is shifting a stray wire?

It's going to be hard to help without pictures since the wiring diagram you posted is not what you really have going on.

Again (from your other thread) I will ask: DO YOU HAVE A MULTI METER? If not you really need to get one.
You can check continuity to see if you have a short between one of the hot legs to ground or a phase to phase short and narrow down what you're looking for.

Ya I guess i'll have to look into getting a multi meter. And I think I just gonna have to rewire the whole thing in a bigger control panel everything is kinda crammed into the one I currently have and some wires might be touching something they're not suppose to when I close the box.

I just find it weird that on 2 different scenarios it arc'd in 2 different locations. And the second time it wasn't even plugged into the main power source when I turned off the switch and it blew.

My first guess is that your main on/off switch is wired incorrectly such that it is shorting two off the four input wires together in the off position. This would explain why the spa panel tripped when you first plugged it in.

For the second situation there needs to be capacitance somewhere in the system to store a charge when the panel is unplugged. The only place where you have capacitors is the power supply to the PWM. My guess is that you are using an older transformer based wall wart to power the PWM. In this case if the switch shorted the +120v and neutral going to the wall wart, then you could have a rather large amount off current flowing from the capacitor discharging on the other side of the transformer. Take the wall wart out and test it on a normal GFCI outlet and see if it still works. My guess is that the second arc came from there and now it's toast.

Get yourself a multimeter and test for shorts on the 4 input wires when the switch is in the off position.

Crane,

You seem to have a good point here in your first statement. The switch i am using is a cheap one i got off ebay and before I got the change to install it in my panel I took it apart and maybe I just didnt put it back together correctly. Come to think of it every time the circuit tripped the switch has been in the OFF position.

My pwm is powered independently of the 240v circuit. I didn't have enough room in my panel to include the wall wart in it so it gets plugged in to a separate 120v circuit so it shouldn't be a problem.

Do you think it has something to do with this? (See picture below) I have 3 wires (Neutral, Hot, Hot) coming into the switch and only 2 wires (Hot, Hot) coming out.

As you can see the red wire on the left is where it sparked it has a black spot on it where it burnt.

Yeah the neutral shouldn't be connected to the switch. Since you're powering the PWM separately you can just cap it off.
You also probably have the two different sources connected somehow to get the short when the 220V power is not plugged in.