Re: Control panels safety questions

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Kidd6488-at-aol-dot-com>

In a message dated 10/12/01 10:19:14 AM Eastern Daylight Time, tesla-at-pupman-dot-com
writes: 


>
> One convenient way to do this is to use a relay/contactor for main power. 
> You set it up as a latching relay with a "momentary push on" circuit, and a 
> "momentary push off" circuit.  The off circuit is a normally closed button 
> in series with the coil and the latching contacts.  The push on circuit is 
> across the latching contacts (Normally open).  Then, your continuous run 
> switch is set up as a double pole switch. One pole (call it normally open) 
> is set up in series with the coil power (after the big contactor).  The 
> other pole, opposite sense (normally closed) is in series with the "turn on" 
> switch. 
>
> With this setup, you can't turn on the main contactor unless the continuous 
> run switch is in the OFF position. 
>
> For what it's worth, this kind of circuit is also nice for interlocks.  The 
> normally closed interlock circuit is also in series with the contactor coil. 
> A break in the interlock (i.e. any switch goes open) causes the main 
> contactor to drop out, requiring another press of the "turn on" push button. 
> Your key switch could be in the interlock loop. 
>
> When working out all those relays, one should give some consideration to 
> failure modes.  Think about what happens if a switch fails, a wire falls 
> off, etc., and make sure it "fails safe", i.e. power off. 
>
> Suitable contactors turn up surplus all the time at reasonable (<$10) 
> prices.  New, they're going to be pretty pricey.  A secondary advantage is 
> you get that nice satisfying "thunk" when you turn on main power. 



Hi, I know this is asking a lot, but could you, or someone else link me, or
create a schematic showing this setup? It's kinda confusing to me :-\  Also is
this for the 120V setup? or is it using a 12 / 24 V setup? 
Thanks.. 

--------------------------------------- 
Jonathon Reinhart 
hot-streamer-dot-com/jonathon