Intermatic timer question ??

[Toolfool]

After shooting a pump problem I found that the contacts on the timer were not working.
They work like a set of "points" it a "make/break" contact
Although they were making contact mechanically, the contacts for some reason were electrically insulated. I cleaned the contacts with sandpaper and they worked fine.
It worked fine for a week and now it's failing again.
I know I can replace the timer BUT what's causing this ???
My last pools timer is fine after 20 yrs and I never heard of an issue like this.
Is this more common than I think??

 

[jblizzle]

I have never heard of a problem like this. Maybe try some dielectric grease on the contacts?

 

[Bama Rambler]

That is odd. Usually the only time you have that problem is with low voltage and low current loads. Next time you clean them, use extremely fine emery cloth.

 

[gtemkin]

I would not use silicone based dielectric greases or any silicone sealants near arcing contacts.

I became aware of this concern when the Lance Armstrong silicone rubber bracelets were in vogue and many of the assemblers on our switch production line were wearing them. We started to have early life testing failures and it was determined the bracelets were introducing silicone oils to our contacts. Here's a blurb from a contact lubricant manufacturer about the phenomenon.

"Silicone Contamination
Silicone contamination poses particular problems which can also be overcome by contact lubricants. Silicones are found in lubricants, sealants, polishes and mould release agents. As silicones can "creep" great distances, these products should not be used in switch assembly areas. When silicones are present between moving or vibrating contacts, they react under arcing conditions to form silicon carbide. These crystals abrade the contact surface and cause electrical breakdown. Silicone contamination is very difficult to remove, particularly after the formation of silicon carbide. It cannot be removed by solvents. There are certain contact lubricants that can prevent the damage caused by silicones and can even restore damaged contacts. One such treatment from Electrolube reacts with the silicon carbide to form volatile silicon tetrafluoride gas, thus slowly breaking down the hard particles.

If a contact lubricant is used on the switch prior to the introduction of silicones these problems are avoided."

Was silicone RTV possibly used to seal someplace close to the contacts?

 

[Pool Clown]

I have experienced this as well. Once had ants get in between the contacts at the moment that they closed causing the insulation. Other times, it was the HIGH current draw through the contacts due to a motor beginning to fail. Sanding the contacts i found (as you did) would only remedy the problem temporarily. I'm guessing that, no matter how fine, sanding "roughs up" the contacts then making them more susceptible to the failure.

Interesting article on silicone creep.