Re: Contactor Question - Order In Circuit

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Ed Phillips <evp@xxxxxxxxxxx>

"Hey guys,

Do you suggest the contactor to be before the variac on the line side or
after it on the output side? One of the primary reasons David is using
one
is to get the surge required to break the multiple spark gaps. From what
I
understand, some of the time when he's just running up the variac, it's
not
firing them. So if he started at 0V to protect the contacts, it would
defeat
the purpose of the contactor anyway."

	I haven't been paying much attention to this discussion but this note
brings something to mind.  Remember that when you connect any iron-cored
device to the AC line the effective voltage across it consists of a DC
voltage equal to the line voltage at the moment of contact plus the
regular AC voltage.  For gadgets like variacs and the like this DC
current flows until damped out by the exponential decay time constant of
the circuit and can cause temporary saturation of the iron and very
large transient currents.  Closing the circuit at "0 voltage" eliminates
the effect.

Ed