Re: Safety Questions (fwd)
---------- Forwarded message ----------
Date: Wed, 22 Jul 1998 11:42:52 -0700
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Safety Questions (fwd)
Jim Monte wrote:
> Suppose you want to discharge a capacitor and use a long insulator, say
> a piece of PVC tubing, to insulate yourself from the cap. You don't
> really know until after it's too late whether the insulator will be
> adequate. There may be conductive "junk" on the surface. It occurred
> to me that it would be much safer to ground the end of the tubing that
> you are holding. That way, the short is directly to ground rather
> than through you if the insulator fails. Is there a flaw with this
> reasoning? Is this typically done?
A grounding hook, as typically used in HV pwr supplies, consists
of a large metal hook on the end of a insulated handle. The
hook has a thick gnd strap, of a gauge that can safely carry any
conceivable fault current, and is connected directly to power gnd.
The insulating properties of the handle is then not a factor.
Before maintenence, the operator touches this hook to all ckt points
that may carry stored energy, then it is hung on a suitable busbar or
terminal that will prevent operation of the HV while work is performed.
During normal operation, the gnd hook is stored in the 'home' position,
which is usually a swingarm connected to a interlock microswitch. In
this way the machine cannot be energized with the hook on the busbars.
A picture of a typical gnd hook hanging in the home position is at: