Re: Contactor question

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

Original poster: "Crow Leader by way of Terry Fritz <teslalist-at-qwest-dot-net>" <tesla-at-lists.symmetric-dot-net>

If you want lots of safety, you can do what they do in microwave ovens. The
door safety switch shorts out the power supply just after the fuse if there
is a fault where the power supply does not switch off when the door is in an
open position. A normally closed switch is "less" likely to faill than say a
stuck relay or shorted triac. To keep these safety switches cheap and
simple, they are not even always a real microswitch, but just two strips of
metal in a microswitch looking housing. It's basically designed for one use,
and has no snap action since it never switches any current (until there's a
fault and it blows te fuse).

KEN

----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Wednesday, June 25, 2003 11:41 PM
Subject: Re: Contactor question


 > Original poster: "Richard W. by way of Terry Fritz <teslalist-at-qwest-dot-net>"
<potluck-at-xmission-dot-com>
 >
 > The contactor will be the master switch for the system. The deadman switch
 > is in series with the coil. There is also an over-current circuit that
will
 > shutdown the system in case of extreme currents. Before this system is put
 > into actual use I want to make sure the contacts can survive opening with
a
 > minimum amount of burn. I've found variac brushes to be expensive and
 > contacts for a contactor are expensive to replace as well. Aside from that
a
 > welded contact would mean a very unsafe condition allowing power to flow
in
 > a situation where shutdown should have occured.
 >
 > Rick W.
 >
 > ----- Original Message -----
 > From: Tesla list <tesla-at-pupman-dot-com>
 > To: <tesla-at-pupman-dot-com>
 > Sent: Wednesday, June 25, 2003 5:12 PM
 > Subject: Re: Contactor question
 >
 >
 >  > Original poster: "Crow Leader by way of Terry Fritz
<teslalist-at-qwest-dot-net>"
 > <tesla-at-lists.symmetric-dot-net>
 >  >
 >  > The contract opens as in shuts off? Maybe your the coil is dropping out
 >  > because it's not getting whatever it needs to hold the contacts closed.
Is
 >  > it an AC or DC coil?
 >  >
 >  > KEN
 >  >
 >  > ----- Original Message -----
 >  > From: "Tesla list" <tesla-at-pupman-dot-com>
 >  > To: <tesla-at-pupman-dot-com>
 >  > Sent: Wednesday, June 25, 2003 11:46 AM
 >  > Subject: Contactor question
 >  >
 >  >
 >  >  > Original poster: "Richard W. by way of Terry Fritz
 > <teslalist-at-qwest-dot-net>"
 >  > <potluck-at-xmission-dot-com>
 >  >  >
 >  >  > Hey List,
 >  >  >
 >  >  > Scenerio:
 >  >  > Variac stack feeding a 10Kva pig 240vac at 35 amps.
 >  >  > 2 poles on the contactor are being used (red and black wires)
 >  >  >
 >  >  > Contactor
 >  >  > Arrow Hart Size 3
 >  >  > 240v 25hp 1 phase
 >  >  > 120 FLA
 >  >  > 720 LRA
 >  >  >
 >  >  > Under the above conditions the contactor opens....
 >  >  > Do I need some kind of arc protection and if so how?
 >  >  >
 >  >  > Thanks
 >  >  >
 >  >  >
 >  >  >
 >  >
 >  >
 >  >
 >
 >
 >