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Old 10-23-2009, 09:55 AM   #1
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What's the difference between a lighting contactor and a definite purpose contactor?
I notice that lighting contactors are very expensive. I've used a regular old contactor for controling lights before and have never had a problem.

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Old 10-23-2009, 10:52 AM   #2
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Quote:
Originally Posted by Ima Hack View Post
What's the difference between a lighting contactor and a definite purpose contactor?
I notice that lighting contactors are very expensive. I've used a regular old contactor for controling lights before and have never had a problem.
Its a design thing DP contactors are for heat and A/C compressor type applications

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Old 10-24-2009, 10:03 AM   #3
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Originally Posted by rewire View Post
Its a design thing DP contactors are for heat and A/C compressor type applications

So is there any danger or problem in using a definite purpose contactor for a non-linear lighting load ?
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Old 10-24-2009, 10:06 AM   #4
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So is there any danger or problem in using a definite purpose contactor for a non-linear lighting load ?
it would just be a cost issue DP contactors are a little better built than just gp contactors
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Old 10-24-2009, 11:18 AM   #5
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Definite purpose contactors are the 'Kias' of the contator world.


Made cheap, sold cheap, made to be thrown away when they act up.

Lighting contators are made to be repairable and are much more durable then DP contactors.

Compare the physical size of the same rating DP and lighting contactors. There is a reason DPs are much smaller.
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Old 10-24-2009, 11:24 AM   #6
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The following post are from an engineer that posts at Holt's

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First off, I have to admit a specific bias against Definite Purpose contactors, and I used to work for one of the largest manufacturers of them, Siemens (ex Furnas). In my opinion, DP does not stand for 'Definite Purpose", it stands for "Don't Purchase!"

A DP contactor is to the electrical control device world what a Yugo is the the Automotive world; a piece of junk that meets the absolute bare minimum requirements to be called functional. I should also point out that if you are in a State that requires NRTL listing of devices, you have violated the requirements by using them, unless you are a UL panel shop and have paid the copious fees for adding them to your procedure. DP contactors are NOT UL listed, they are UR, meaning UL Recognized. The difference is, you cannot install UR devices unless they are a sub component of a larger listed system, and even then, only after UL has thoroughly investigated exactly how your plan to use them.

Secondly, DP contactors, being the CHEAPEST junk that will do the job, are all notoriously noisy, even if clean and brand new. There is virtually no attention to detail in their design, in fact the only design criteria used is manufacturing cost (#1) and as I said, bare minimum functionality.

Thirdly, ALL DP contactors are now made in third world countries such as China and India. The better one's are made in India by the way, but when I worked for Siemens, who's products are made in India, they made a conscious decision to abandon that industry as far as future product development and promotion goes because they can no longer compete with the likes of C-H, Sq. D and Tyco, who have gone to China. But when Siemens went to China to reduce their costs over India, they found that QC was virtually impossible to manage. The samples they got back from the same factories being used by the other competitors were absolute worthless junk.

So if you want a REAL contactor, and one that will not likely make noise like that, I would opt for an IEC contactor. Some of them even specifically offer special coil options that are exceptionally quiet. they cost more than DP, but they will not embarrass you.

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"Definite Purpose" means that it is used for a specifically engineered application, where you know every detail about the load; FLA, LRA, duty cycle, mounting, connection method, operating temperature, wire temperature rating AND the expected life span.

For xample, you are an OEM of HVAC equipment and you know that know your chiller compressor is going to come on once every 15 minutes, 12 hours per day 7 days a week and you want the contactor to last beyond the 1 year warranty, but not much more because you want to get the service call to replace it when it wears out. So you look at the fact that you want 17,520 operations, you are switching lets say a 10HP 240V 3 phase motor, so 28A FLC and 154A LRC. Then you look at a chart from the DP contactor mfr. that says that a 30A DP contactor will only last 10,000 operations switching 150A LRC, but a 40A DP contactor will provide 20,000 operations switching an LRC of 180A, so you pick that one. This is why UL will not "List" a DP contactor, they will require that you show them all this information (and more) when you go through the process of adding it you your procedure.

PS, especially for you Besoeker (because I think you are n the UK?). You may notice this is not much different from what you would do to select an IEC contactor. The difference is, the IEC contactor will typically have a minimum mechanical life of 10 million operations and an electrical life of 1 million operations. A DP contactor is not that robust but sells for probably 1/2 the cost or less in volume to OEMs.
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Old 10-24-2009, 11:29 AM   #7
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Originally Posted by Bob Badger View Post
The following post are from an engineer that posts at Holt's

Thanks Bob, very helpful.
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Old 10-24-2009, 11:34 AM   #8
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Your welcome, I remembered it because I thought it was good info when I originally read it.

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