Re:re: Contactor question

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "David Rieben" <drieben@xxxxxxxxxxxxxxx>

Bart, all,

Thank you Bart and all others that quickly repsonded to
my question regarding contactors. The general consen-
sus seems to be just what I was thinking - no multi-pole
contactor's poles are perfectly synchronized and therefore
one set of the contact points may consistantly take the
brunt of the breaking of the inductive load. I started out
simply paralleling 2 of the 4 poles since I have a 60 amp
main breaker for my control panel cabinet. I noticed that
one set of the contact "poles" sparked a whole lot wores than
the other though and that's what got me to thinking that
they were indeed NOT synchronized. I ended up using all
4 poles in a series-parallel configuration thinking that this
may further distribute the inductive spark energy and it did
seem to help a little bit. I think that I would still prefer to just get
a contactor whose each individual contacts are at least
rated at the 60 amps though. And I mean 60 amps FLA
(full load amps, I assume) not 60 amps resitive load. The
30 FLA (40 amp resistive) contactor that I am currently using
was just given to me anyway so there'll be no big loss by up-
grading, only the cost of the bigger contactor itself.

David Rieben



----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Monday, August 15, 2005 12:41 AM
Subject: Re: Contactor question


> Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>
>
> Hi David,
>
> Yes, I know well what your are thinking here. But, the contactors do 
> not all make or break at the same time. Thus, the last in line to 
> open will see the "full" load for that brief moment. (Inductive 
> loads are nasty on contacts of any size). Likely, this particular 
> contact will always be the "slow one" and it will eventually weld 
> closed if opened and closed during a load, which is the key to it's use.
>
> I use a 50A contactor. It is controlled by the PLC and will open if 
> the VFD has an error or for a few other reasons (dead man switch 
> open, key off, PLC glitch, etc.). This is "error" mode and is the 
> only time the contactor would actually open during a load. During 
> normal operation, I always have the contactor on before putting V 
> and I into the tranny. The contactor I use has had no problems so 
> far. IMO, 30A is a bit small for these swinging pig loads. Even 50A 
> ratings I would consider risky.
>
> Take care,
> Bart
>
> Tesla list wrote:
>
> > Original poster: "David Rieben" <drieben@xxxxxxxxxxxxxxx>
> >
> > Hi all,
> >
> > Just a quick question about relay contactors. Let's say that I have
> > a 4-pole, 30 FLA inductive per pole rated contactor. Does this mean
> > that I will have up 120 amp inductive rating of the contact points if I
> > use all 4 of the poles in a parallel or series parallel fashion in a single
> > circuit to switch my pole pig transformer under a load?
> >
> > Thanks,
> > David Rieben