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pdxmonkeyboy

any electricians in the house ?

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2 hours ago, pdxmonkeyboy said:

 

I have a question about contactor failure.

 

thought i would throw it out there

 

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Ok... what did you do now?  

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well, this happened yesterday...

40 amp two pole, normally open relay. Pushing about 28 amps though it. 8 gauge wire in, 10 gauge wire going out (to two seperate circuits.. each 14 amps).

this is about the third time this has happened in about two years.

I am trying to figure out WHY this is happening. i asked the guys at platt and they said.. your going to love this "it got to hot". Really??

all the relays flip.on and off twice a day. the contacts of the relay look fairly scored and pitted. Do you think that the daily arcing is wearing out the contacts so they are not making a good connection and thus shorting and over heating??

I am just thinking perhaps i should routinely replace them? Its odd though, they should have a much higher duty cycle. I have some 200 amp relays that are going on 4 years without a hiccup.

thought? 7d3b2ef89413325742c83bcd64da97a9.jpg

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Yes, the contacts arcing over time will cause them to get pitted and also cause carbon build up.  This increases the resistance across the contacts causing them to get hot. At some point the damage is too much and they either weld shut or just make enough contact to burn them up.  A larger capacity contact or a 4 pole contact with two poles tied together to effectively make a two pole should solve the issue.  You can also go solid state as long as you get the appropriate heatsink to go along with it.

31A9E505-4572-4695-BF2B-344E9B72D63A.png

Edited by cjmdh

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Yes, the contacts arcing over time will cause them to get pitted and also cause carbon build up.  This increases the resistance across the contacts causing them to get hot. At some point the damage is too much and they either weld shut or just make enough contact to burn them up.  A larger capacity contact or a 4 pole contact with two poles tied together to effectively make a two pole should solve the issue.  You can also go solid state as long as you get the appropriate heatsink to go along with it.
31A9E505-4572-4695-BF2B-344E9B72D63A.thumb.png.4644380c5a32d31a0364a39222983387.png
thanks man. thats what i figured was happening. I have zero experience with solid state relays. i thought they were only for low voltage stuff??


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Nope, use them quite a bit at work for 208v applications. Just need a good heatsink for the higher current stuff.

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