# Dressing contact points



## Southeast Power (Jan 18, 2009)

One word,
Magic Eraser


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## mattsilkwood (Sep 21, 2008)

Fingernail file.


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## JohnR (Apr 12, 2010)

How about Graingers they have almost anything. It is an industrial staple here when you can't find the part you want.


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## John Valdes (May 17, 2007)

jrannis said:


> One word,
> Magic Eraser


Good suggestion. 
OP. It is not a good idea to use files, sandpaper or anything too abrasive on contacts. The contacts have a thin silver plating and dressing them removes the plating. I like regular pencil erasers. They work great and if they are not cleaning the contacts good enough you need to replace the contacts or the device.
Dressing contacts is IMO not a good idea period.


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## den (Mar 28, 2009)

auto supply places sells points files. I have also used the file on torch tip cleaners but was also going to say the same as John Valdes as to the coating so don't file to much


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## Zog (Apr 15, 2009)

subelect said:


> Does anyone know a good source for purchasing a small, flexible file for dressing contact points on electrical starters and pressure switches?
> 
> I used to try and use Scotchbrite or sand-paper, but the majority of the time it is quicker to use a file to get the customer back on line and replace the contactor at a later date.
> 
> ...


Using a file or sandpaper can cause abrasive material to fall into the mechanism, causing shorts (Files) or binding (Sandpaper). 

Scotchbrite is the industry standard for dressing contacts, if necessary. 

However, usually it causes more damage than good. As John mentioned contacts are typically silver plated over the copper. The reason this is done is that the material will oxodize, no matter what it is. While the conductive properties of copper and silver are similar, silver oxide is a great conductor while copper oxide is a very poor conductor. Sivler oxide looks like a brown coating on the contact surface, you do not want to remove that layer, doing so will remove some of the silver and if the copper is exposed the resulting copper oxide will lead to heating and eventual failure. 

Contacts that show pitting or <50% contact area (From impression check) should be re-plated or replaced.


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## MDShunk (Jan 7, 2007)

Hmmmm.... when contacts get to the point that you feel compelled to clean them, you're probably due for a contact kit or a new contactor/relay.


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## drsparky (Nov 13, 2008)

Get a contact burnishing tool. It's only purpose in life is to clean contacts.


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## tkb (Jan 21, 2009)

I would not recomend using a file ever on a set of contacts.

I have used a fiberglass eraser for contacts for years.
You can get the holders and refills here.

http://www.eraser.com/browsecat.cgi?mode=open&id=113


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## oldtimer (Jun 10, 2010)

When I worked in industrial (mining), we often had to repair contacts in starters etc. As was previously mentioned burnishing tools are available.


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## RIVETER (Sep 26, 2009)

jrannis said:


> One word,
> Magic Eraser


That is two words.


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## subelect (Nov 25, 2007)

Thanks, I will take a look at Grainger. 
Yes, I would rather replace every bad contact/contactor that I come across, but that is not practical. 
Just trying to get the customer thru another day until the weekly supply truck shows up. 
Thanks again,
Rick


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## John Valdes (May 17, 2007)

subelect said:


> Thanks, I will take a look at Grainger.
> Yes, I would rather replace every bad contact/contactor that I come across, but that is not practical.
> Just trying to get the customer thru another day until the weekly supply truck shows up.
> Thanks again,
> Rick


How often do you find bad contactors. If a contactor cycles to much you need to be thinking about something else. One place where cleaning contacts is practical is on large NEMA contactors. When a set of replacement contacts runs into the 100's of dollars. 
Small contactors should be tossed or the contacts should be replaced. Some IEC contactors have easy replacement contacts today. The ones we used to toss now can be economically replaced in the field. They are designed to be replaced.


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## Introyble (Jul 10, 2010)

I think what your looking for is called a Needle File set


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## subelect (Nov 25, 2007)

Most of the time that I have the need to dress contacts are on the aeration fans for grain bins. Some of these fans have contactors that are one of a kind, fit in a tiny enclosure, the company went out of business ...etc. 
The majority of these single phase fans have a 10.5-12 Hp motor and came with a 50 amp cord and plug. So, they were wired up with a 50 amp plug-in, even though the nameplate data shows 54 amps for full load.
So, when you try to figure out why they are having intermittant problems (exposed in the elements for 30 plus years), it could be anything.
I would like to have something on the truck to clean up the contacts without having to buy a new contactor everytime until I can figure out what the intermittant problem is. 

Thanks for your advice. 
Rick

PS By far the worst problem that I come across has to be the generic friendly neighbor who tries to help out his farmer-buddy with his electrical skills. They live out in the boonies and will do anything they can to keep the equipment running without calling an electrician. 
I should have taken a pic, but the funniest one was where the single phase fan had problems with the motor thermal shutting down the fan after a few hours. He "cured" this problem by manually engaging the contactor with a piece of corn cob wedged in it. 
Oddly enough, the motor burned up when the bearings finally fell apart.
Turned out to be a pretty expensive corn cob.


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## Introyble (Jul 10, 2010)

Needle files are made in a curved riffler style and come in sets. Riffler needle files I think is what your looking for. I have a set that I use for similar purposes.

You never did say what the intermittent problem was, maybe somebody here can help you. Good luck :thumbsup:


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