Double throw contactor

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electrofelon

electrofelon

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Cherry Valley NY, Seattle, WA
Looking for a little help here. I am looking for a definite purpose contactor, 20 amp contacts that is double throw. Does such a thing exist? I have been looking around and strangely I cannot find one. They have options to add "auxillary contacts" that I think will do this but the current ratings seem to be quite lower which leads me to believe these are intended for control circuits and not the full current of the main contactor. Of course I could get a two pole with one normally open and the other normally closed, but that seems like a not so efficient way to do it if it could be done with one double throw unit. Is this just the way it is normally done?
 
electrofelon

electrofelon

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Location
Cherry Valley NY, Seattle, WA
Just to give the big picture of what I am trying to do: I need to control 2 groups of several dozen lighting circuits and have one group come on when the other goes off. Just trying to figure out the most economical way.
 
Barbqranch

Barbqranch

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Arcata, CA
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Plant maintenance electrician Semi-retired
There are numerous power relays that will handle 20 or 30 amps available in DPDT. McMaster has one for $34.32. It is bare, so it needs an enclosure.
 
J

jim dungar

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electrofelon said:
Just to give the big picture of what I am trying to do: I need to control 2 groups of several dozen lighting circuits ...
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If you are controlling lights you probably should be using a lighting contactor not a definite purpose one. Check your contact ratings for inrush and such.
 
electrofelon

electrofelon

Senior Member
Location
Cherry Valley NY, Seattle, WA
Besoeker said:
Couldn't you just use two contactors electrically and mechanically interlocked?
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Okay, time to name drop.
Look at a Square D 8903 type L, the 30A contacts are field convertible.
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Many lighting contactors have convertible contacts.
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So that would be two poles, one NO and one NC set up to operate like a single SPDT?

Looking for DP is like looking for trouble. DP is short for "Don't Purchase".
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What do you mean?
 
Jraef

Jraef

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electrofelon said:
So that would be two poles, one NO and one NC set up to operate like a single SPDT?
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Yes, although generally you will end up getting at least a 3 pole contactor, not many people will stock a 2 pole.

What do you mean?
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DP contactors have one singular purpose in life: perform a basic task as specifically engineered by an equipment manufacturer for as long as the warranty on the equipment will last, and do so as cheaply as possible. If you are not an original equipment manufacturer with an engineering team to make all the proper decisions and share those design criteria with the contactor mfr as part of the tender process, you have no business buying and applying DP contactors. Because of this, and most people fail to realize it, DP devices are not UL listed, they are UL Recognized Components (UR), because they CANNOT be used in any manner other than as component part of an assembly that will ultimately be tested and listed as a whole.

So although many people sell them as loose parts, it is allowed only because ostensibly, they are for REPLACEMENT of exact part numbers used in OEM equipment. The fact that many people ignore that is not germane to the manufacturers, how you use them is your business. But if something should go horribly wrong and someone gets hurt of killed, and it turns out to have been an issue with a DP contactor, the mfr will immediately want to know who you worked with to apply the contactors and if you bought them on the open market, they will state that you had no business buying and using it in whatever manner you did.
 
electrofelon

electrofelon

Senior Member
Location
Cherry Valley NY, Seattle, WA
Jraef said:
Yes, although generally you will end up getting at least a 3 pole contactor, not many people will stock a 2 pole.


DP contactors have one singular purpose in life: perform a basic task as specifically engineered by an equipment manufacturer for as long as the warranty on the equipment will last, and do so as cheaply as possible. If you are not an original equipment manufacturer with an engineering team to make all the proper decisions and share those design criteria with the contactor mfr as part of the tender process, you have no business buying and applying DP contactors. Because of this, and most people fail to realize it, DP devices are not UL listed, they are UL Recognized Components (UR), because they CANNOT be used in any manner other than as component part of an assembly that will ultimately be tested and listed as a whole.

So although many people sell them as loose parts, it is allowed only because ostensibly, they are for REPLACEMENT of exact part numbers used in OEM equipment. The fact that many people ignore that is not germane to the manufacturers, how you use them is your business. But if something should go horribly wrong and someone gets hurt of killed, and it turns out to have been an issue with a DP contactor, the mfr will immediately want to know who you worked with to apply the contactors and if you bought them on the open market, they will state that you had no business buying and using it in whatever manner you did.
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you really lost me here. What does the number of poles have to do with it? We must be talking about two different things. The lighting contactors Jim mentioned are available in 2 thru 12 poles...?
 
Jraef

Jraef

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n1ist said:
Sounds like they are talking about "DP" as definite purpose, not dual pole...
/mike
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We were...
electrofelon said:
Looking for a little help here. I am looking for a definite purpose contactor...
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And then:
electrofelon said:
you really lost me here. What does the number of poles have to do with it? We must be talking about two different things.
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This was in response to your comment on my previous post:

jraef said:
Looking for DP is like looking for trouble. DP is short for "Don't Purchase".
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electrofelon said:
What do you mean?
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Keep up... :p
 
StarCat

StarCat

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Moab, UT USA
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Alternating Contactor

Alternating Contactor

The description of duty sounds like Mechanically Alternating contactors I have used in the past.
They are common on some types of 2 speed HVAC compressors, and I have used them on a surface water pump array as well.
They are set up to be electrically interlocked on the control side along with the mechanical interlock feature that is inherent.
Web search is " Alternating Contactor." The last ones I used were 3 or 4 pole.
 
Jraef

Jraef

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electrofelon said:
AHHHHHhhh, gotcha. Yeah I shouldnt have said definite purpose
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By the way if you are only looking for two poles, AB makes an IEC 4 pole contactor that is 2NO, 2NC power contacts, from 9A to 85A. They are commonly used inside of older DC drives but because of that, they are still available. Might be tough to find in stock though.
http://www.ab.com/en/epub/catalogs/12768/229240/229254/229461/229481/Product-Selection.html
2nd group down from the top.

A lighting contactor with convertible poles is probably going to be easier to get off the shelf.
 
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