# Joslynn 3 phase vacuum switch



## Industrialsparky (Jul 10, 2012)

In a vacuum switch is there or isn't there a arc prior to contact inside the switch I think not do to the vacuum no air no spark right ????


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## 360max (Jun 10, 2011)




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## Industrialsparky (Jul 10, 2012)

So I'm right no air no flame so there for no pre spark before contact sorry had someone tell me that there was a pre spark in a vacuume I was like huh ? How


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## Zog (Apr 15, 2009)

There is no such thing as a perfect vacuum, so there is some air and yes there is some arcing that occurs. The arcing actually vaporizes some of the metal on the contact surface which is why you have to check contact erosion on VI's as part of your PM program. There is a metal-vapor shield in the VI that is designed to collect the highly ionized metal vapor and solidify it helping to maintain vacuum in the VI.


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## retiredsparktech (Mar 8, 2011)

Industrialsparky said:


> In a vacuum switch is there or isn't there a arc prior to contact inside the switch I think not do to the vacuum no air no spark right ????


I always marvelled at how well they worked and stood up.
We had a Joslyn-Clark that was used several times a day on the electrical test floor. We only had one vacuum bottle fail.
I heard, they only had .400 gap to break 13.2 KV. :001_huh:


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## Industrialsparky (Jul 10, 2012)

Ours is used everyday many times a day to turn our electric arc furnaces on and off they hold up very well


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## Big John (May 23, 2010)

retiredsparktech said:


> ...I heard, they only had .400 gap to break 13.2 KV. :001_huh:


 It is nuts. We've got one of the bottles cut open for display purposes and it's amazing how small the contact gap is. I'll see if I can remember to grab a photo.

-John


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## Industrialsparky (Jul 10, 2012)

Big John said:


> It is nuts. We've got one of the bottles cut open for display purposes and it's amazing how small the contact gap is. I'll see if I can remember to grab a photo.
> 
> -John


I'd love to see it !


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## Big John (May 23, 2010)

Finally remembered to grab a picture of this thing.

It's the vacuum bottle from a 15kV Siemens yard breaker, if memory serves right. I don't recall the amperage. 

You can see in the open picture the gap is very small. I wouldn't be able to get a pinky in there, it's probably about 3/8" or less.


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## Meadow (Jan 14, 2011)

Big John said:


> Finally remembered to grab a picture of this thing.
> 
> It's the vacuum bottle from a 15kV Siemens yard breaker, if memory serves right. I don't recall the amperage.
> 
> You can see in the open picture the gap is very small. I wouldn't be able to get a pinky in there, it's probably about 3/8" or less.


Did you drill that open?


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## butcher733 (Aug 4, 2012)

so are the contacts in a vacuum specifically for the purpose of greatly reducing arcing in high voltage applications? Are there low voltage (480/277) applications such as hazardous locations with combustible vapor?


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## Big John (May 23, 2010)

butcher733 said:


> so are the contacts in a vacuum specifically for the purpose of greatly reducing arcing in high voltage applications...?


 Exactly. If the contacts are in good condition, the vacuum creates a very high open-contact resistance very rapidly, to the point where this can actually cause damage to winding insulation: The magnetic energy in the windings causes a massive voltage rise and normally this would create a brief arc across an air circuit breaker and dissipate that voltage. There is no media in the vacuum bottle to ionize and sustain the arc, so the voltage stays present on the windings until the windings themselves ionize and break down. This is the reason why surge capacitors and arrestors are often installed on large rotating equipment that has vacuum interrupters.


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