Re: 24V (was apartment grounding)

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>

I also use 24v to energize the power source contactor from my deadman 
switch. The deadman switch is there only in the event that the user 
holding the deadman switch closed gets hit by a strike or other 
electrical event. There is always a possibility that "any" 
configuration has a chance at failure. However, the probability that 
the control user takes a jolt and the contactor welds closed "at the 
same time" is very low. In the event of a contactor weld, the user 
can still shut down power via disconnect. In the event the user gets 
hit by a strike, the deadman switch is there to remove power.

All in all, it's a very safe, simple, and low cost safety feature.

Take care,
Bart

Tesla list wrote:

> Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>
>
> At 11:12 AM 3/15/2006, you wrote:
>
> > Original poster: "Rich" <rdjmgmt@xxxxxxxxxx>
> >
> > Jim
> >
> > Well I thought having a 24v control system in my power control unit
> > would provide me a small level of protection.
>
>
>
> It does.. and it gets the line voltage away from your hand, which is 
> a good thing.
>
> Just think about worst case scenarios though, too..  What if your 
> switch shorts?
> What if the relay doesn't open?  What if just one fuse opens?  Run 
> through all those possible "credible single faults" and make sure 
> that something isn't unexpected.
>
> > My 24v deadman switch runs
> > the out put relay. The 120v line runs thru standard 20amp line filter,
> > type in a 3x3 metal box, it then goes thru the Variac, then the relay,
> > last thru 50amp line filters , 2.5 dia x 5" long. The 50 amp filters are
> > to RF ground. Both sides of the line going from the Variac are fused
> > also with neon indicator lights on the control panel that will light if
> > the fuse fails.