On Wed, 12 Oct 2011 14:17:18 -0500, Ignoramus2083
wrote:

I bought a size 2 motor starter on ebay. It is Allen Bradley and looks
like 500 series. (the label does not say what series).

I want to use it for my 10 HP compressor, which is the kind of service
where it would restart the motor many times per day.

Anyhow, I opened up the cover to look at contacts and it appears that
they have some wear. I cannot really tell if it is too much or not,
because I am not qualified to tell.

So, I have a couple of questions.

1) How can I know if the contacts are too worn?

Open up the contactor and look at the fixed and moving contacts,
then use your good judgment to assess them. Duh.

No, seriously. They are going to develop little pits and craters
from the arcing of normal operation, but they tend to self-correct as
they age (a bump on one side forms that fits into the crater of the
mating contact) until they totally run out of metal.

As long as they are overall flat, and the little button has a good
1/16" or so left, and they are all even with each other, you're good.

You can file the old set down to see what the actual contact area
is, but don't make a habit of it - you just kill them a lot faster.

The only time I really get crazy filing them is to get a totally bad
set working JUST long enough to run and get replacements. And they
have to start flat - because you swap the really bad contacts around
so at least one side has a little contact left. Bad moving set to two
halfway decent fixed points, and vice versa. Cross your fingers, and
get on your horse.

The real way to tell is to buy a replacement set of contacts -
that's the "before" that you want to remember how they look, and you
want it to still maintain the same basic profile allowing for a little
pitting.

You don't have to change the contacts now - just wrap the box up and
stash them - I'd put them *inside* the contactor enclosure, and when
it eventually fails on you... You open the box and see the 'present'
you left for yourself. Ten minutes later, you're good to go.

2) If I buy an "aftermarket contact kit", are they really as good as
the originals? Do the original contacts have silver plates?

The factory contacts are usually a Coin Silver alloy welded to a
plated Copper based bar or screw lug base. When the Silver runs out,
it'll start eating into the copper fairly fast - but they usually run
out of spring overtravel by then and the gap grows too large.

The replacements are supposed to be the exact same thing, because
there's often a UL Listing involved. But I would be really wary of
aftermarket ones made overseas, only because they might cheap out on
the contact buttons and they won't last nearly as long.

Heck, the replacements might be from the same factory that makes
them for the OEM, they just decided to sell direct too. But you have
no way to know. Caveat Emptor.

-- Bruce --