Grounding the press/cassettes

[falls]

Hi Everyone.
I am planning on using a single heat blanket in my press to begin with. I think I will use it on the bottom mold beneath the layup.
The main risk with electricty I see is that if the blanket is pierced by the aluminium casette then the cassette will become "live" with electricty. I would like to ground the casette and was wondering what is the most practical way to do this.
The controls for the heater will be housed in a steel box that will be connected to ground.
I am planning on mounting this box to the steel of the press which should provide continuity of the ground to the press. However, the aluminium cassettes are isolated from the steel of the press.
I have wired a plug onto the live and neutral wires of my heat blankets that will be connected to a powerpoint in my control system. I am thinking of running a 3rd, earth wire from this plug that will connect to a bolt through the edge of the cassette. The poweroutlet's earth terminal will be connected to earth thus connecting the cassette to earth.
Is this sound thinking?
How have others achieved press and cassette grounding?

[doughboyshredder]

I grounded the press, but not the heat blanket sheets, or cassette.

[krp8128]

Falls,

That is how my setup is grounded. I use a 3 prong 220v plug/reception to plug my blanket into the controller. Since the blanket has no ground, I wired an extra length of cable from the ground prong to the casset.

Doughboy,

Unless your aluminum sheet is bonded electrically to the steel press you might want to ground it. If you poke a hole in the blanket it will leak current into the aluminum and give you a hell of a shock when you touch it.

[doughboyshredder]

220v blanket and with no damage there is a current on the aluminum sheets. Enough to zap you, but not do any damage.

[chrismp]

@doughboy: how's your blanket insulated? is it the standard silicone? if so i guess our insulation isn't that bad, cause we only get small zaps when we don't ground the aluminum sheets.

[doughboyshredder]

yep just a standard mei blanket. Got zapped the first time I used it. I actually am worried about grounding the aluminum sheets with the trace voltage that they pick up off of the blanket.

[krp8128]

wtf.

How are you guys getting "trace voltages"? You sure it isn't just static? Or are you claiming that the insulation is leaking current?

I'm no EE, but 220v through you into the ground is going to hurt like a bitch at the very least. I know on my setup I can touch it all day with the blanket on and not feel a thing.

Can you read anything on a meter if you check between the Al and the ground that you PID is wired to?

[Alex13]

You can send a million volts through yourself with no injury as long as the amps are low enough.

[krp8128]

You can send a million volts through yourself with no injury as long as the amps are low enough.

And it is going to hurt like a bitch, ala static electricity. And anyways, how the heck are you inducing a million volts on the Al casset?

Amps kill, volts hurt

[Jekul]

To try to answer your question: Run a ground wire from your AL cat track back to the earth-ground inside your PID controller. You may want to make sure all of your cat track sections are always touching, or you may end up with an isolated section full of hyper electrons. (You could do this by running a ground wire in between them all, or use a conductive cable to hold them all up...or any other way you would like).

[falls]

Thanks all

@krp: what is your physical connection like to the cassette? I am thinking a bolt through both sheets. Another thought is an alligator clip that would be easier to clip on and unclip.

[krp8128]

Thanks all

@krp: what is your physical connection like to the cassette? I am thinking a bolt through both sheets. Another thought is an alligator clip that would be easier to clip on and unclip.

I only have a bottom cassette, since I bag my skis. I just use a ring terminal that is held to the Al when i screw down the sheet for whatever size I am pressing.

For a top and bottom cassette I would make up A Y ground cable that goes from the PID to the cassettes. At the cassettes you could use a couple 10-32 or such screws and ring terminals or if you change the setup around often use an alligator clip.

The advantage I see to the bolt is that you know you aren't going to walk by and pull the clamp off without realizing.






And as Jekul says, GROUND EVERYTHING TO THE SAME POINT. Controller, press, cassette etc. all need to be at the same ground potential as they are the same circuit (if there is ever a short).

[Alex13]

And it is going to hurt like a bitch, ala static electricity. And anyways, how the heck are you inducing a million volts on the Al casset?

Amps kill, volts hurt

I'm not trying to attack you mate, just attempting to clear it up. Your assertion is mostly true, high voltage with low (ish) amps can give a massively painful but non life-threatening shock. Low voltage with high amps can kill you without the shock.

Static electricity is far higher than 220v, can exceed 20,000V depending on your clothing.

You can send massive amounts of volts through your body with little physical discomfort though, the amps just need to be low enough. There's vids around of people sending visible blue flashes jumping large distances between themselves and other sources (i.e. fingertips to something) through high voltage.

I could be wrong but I don't think 220v is enough to give you a massive shock, which makes it all the more dangerous.

[Alex13]

I stand corrected, 100V+ will give you a noticeable shock through dry skin.

[doughboyshredder]

I just assume it's natural bleed through of voltage. I run a lot of wire and you can't run high voltage line in the same pipe as phone line, because the phone line will actually pick up trace voltage from the 115 line and will cause a hum on the line (which is actually the sine wave).

I have been shocked bad a few times. I have been grabbed by 115 and held for over 5 seconds with the current going through my ass cheek in to wet soil. That sucked.