Need to ground implosion screen?

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johnp
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Need to ground implosion screen?

Post by johnp »

The vacuum system we're using at NEIU has a glass chamber surrounded by a steel implosion screen. The chamber and screen rest on a rubber seal, so the screen is not necessarily grounded. One of our fusor team wondered if electrons passing by our outer grid would build up a charge in the glass and cause arcing. Would tying the steel screen to ground be the safe thing to do, or does it matter?
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Wilfried Heil
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Re: Need to ground implosion screen?

Post by Wilfried Heil »

I'd definitely ground the implosion shield, especially since that is easy to do.

If left unconnected, the screen will pick up charge, until someone accidentally touches it.
Looks like it could serve as a HV, several 100 pF Leyden jar.
MarkS
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Re: Need to ground implosion screen?

Post by MarkS »

Wilfried has got good advice. It's better to ground and err on the side of safety, unless of course you're intentionally floating something.
Starfire
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Re: Need to ground implosion screen?

Post by Starfire »

It is necessary to ground all exposed electrical conducting surfaces otherwise you can have a P.D. across parts of the circuit [ earth can be part of a circuit ] Grounding establishes equipotential voltage, otherwise lethal charge can build or lightning strike.

Electrical Installation Regulations require all exposed conducting surfaces to be ' Bonded ' and grounded. This is standard practice.
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Chris Bradley
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Re: Need to ground implosion screen?

Post by Chris Bradley »

I would guess its capacitance to ground at no more than a few 10s of pF, so EVEN IF it charged to 100kV and it was truly isolated from any other charged structure it'd still only have a little tickle of a few tenths of joules.

But why the heck would you want to believe my maths! Ground it!
Starfire
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Re: Need to ground implosion screen?

Post by Starfire »

It is not simple about capacity - all apparatus should be earth for protection. If an insulator breaks down and a high voltage path is established then the potential lethal current may have a easy route to ground - via you!

Protection is about prevention.
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