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Old 04-08-2012, 05:17   #1
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amperage question on relay contacts for PM-17AY-120A

some list it at 35 amps, some list it at 25 amps

who is correct, what is the contact amperage at 120v AC?

any ideas? confused

https://www.alliedelec.com/images/pr...N/70213398.pdf

Quote:
The PM Series relays offer 4 double throw poles (4PDT) for up to 35 amp at 277 VAC
28Vdc.
Does lower voltage mean higher amps, as in wattage = amps times voltage
yet amp rating of contact I would think could not exceed 35 even with less volts.

Relay, 4PDT, 120VAC - Relays - Relays - 14H243 : Grainger Industrial Supply

Same relay listed here at 25 amps.
PM-17AY-120 | Datasheet Archive
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Old 04-08-2012, 05:55   #2
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Re: amperage question on relay contacts for PM-17AY-120A

Relay/Switch contact specís (current and voltage) should be looked at as separate specifications, and not as a composite power (wattage) specification.

The contact spacing is the main factor limiting your voltage rating to 240VAC, whilst still expecting it to reliably extinguish the arc produced on opening of the contact.

The contact area & thickness will limit the current rating to 35A (Resistive).
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Old 04-08-2012, 06:09   #3
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Re: amperage question on relay contacts for PM-17AY-120A

Captain May....please allow me an off-topic question. Why is it that you are not a C.L.O.W.? You seem to be rather cluey in the electrics department...
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Old 04-08-2012, 07:16   #4
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Re: amperage question on relay contacts for PM-17AY-120A

Iím not living on water for a number of family/health/financial reasons.
I spent most of my working life in the electrical (construction & engineering) industry.
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Old 04-08-2012, 08:08   #5
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Re: amperage question on relay contacts for PM-17AY-120A

Thank you sir. Hope the problems are fixable and become but mere distant memories...if not, then the strength to get through them.
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Old 04-08-2012, 09:21   #6

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Re: amperage question on relay contacts for PM-17AY-120A

sd, one of those listings you refer to is for a part #...120 while the other is for a "...120A" and I suspect the different part number has a different rating.

The contact amperage at 120VAC is typically the same as shown for 220/240VAC.

A change from AC to DC service changes the game more than the change from 120/240 does.
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Old 04-08-2012, 09:24   #7
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Re: amperage question on relay contacts for PM-17AY-120A

I think this is what I bought, 2 of these here from ebay.

Item # PM-17AY-120, PM Series - Open Style Power Relays on Struthers-Dunn

They were listed as LOT OF 2 STRUTHERS-DUNN PM-17AY-120 *USED*
Got them for $40 includes shipping.
Item number: 330764851475
http://www.ebay.com/itm/330764851475...475%26_rdc%3D1

Does it look like these are 35amp rated?
How does resistive versus inductive affect amp rating?
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Old 04-08-2012, 10:21   #8
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Re: amperage question on relay contacts for PM-17AY-120A

The relay is rated 35A resistive, and 1.5 HP Motor Load.
Inductive ratings are considerably lower than resistive.
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Old 06-08-2012, 07:19   #9
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Re: amperage question on relay contacts for PM-17AY-120A

I discovered what is up with these relays some listing 25 some 35 amps.
I called and talked to SD and he talked to an SD engineer.
Potter Brumfield, TYCO etc... are older relays which were originally rated at 25 amps. This relay series are no longer made by those companies.

The PM-17AY series is now owned by Struthers-Dunn, no one else can make them.
This buyout was done 10 or 15 years ago. Struthers-Dunn recertified the design for 35 AMPS and that is what they are rated for. There were no changes made to the relays they are still the same part, just have a different number printed on them.

He said he cant speak for what TYCO etc... did or if the older ones would work at 35 amps, only what they say about them now that theirs work at 35 amps.
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Old 06-08-2012, 07:42   #10

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Re: amperage question on relay contacts for PM-17AY-120A

So the old relays were simply rated more conservatively than the new ones. Which perhaps just means perhaps they can do 25A fifty thousand times, or 35A 25,000 times, with a reduction in the number of cycles at the higher amperage. (Since the typical failure mode is the contact points arcing or welding as they age and degrade. And just pulling some imaginary duty cycle numbers out of the air, for illustration only.)
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Old 14-09-2016, 09:26   #11
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Re: amperage question on relay contacts for PM-17AY-120A

Hi,

I saw this thread and while it is rather old, it showed up on Google search high on the list so I wanted to clarify some things for future readers.


The contact ratings for the Struthers-Dunn PM Series relay has are what is shown on our UL sheet that has been tested and approved by UL Standards. The UL ratings are generally on the conservative side to leave a little fudge factor room for slight variations that can occur in production of the relays. There have been some wrong information out there because of misinterpretation and "spec-man-ship" that some have tried to play with in the past. We have been trying to correct or perform tests to validate or correct them as we come across them.

Unfortunately the ratings are only provided as maximum Amps at maximum Voltage. The relay contacts can switch at lower current but at a much higher voltage and vice-versa so it is difficult to list all the variables. IF you need help with that we can try to answer your specific questions, just send us an email (info@struthers-dunn.com) with information of what you are needing and we will provide a reply.


Arcing of the switching contacts on AC loads should not be much of a problem. It is the DC loads especially above 40VDC that are difficult to brake the arc without the help of blowout magnets and this design never allowed for that accessory.

Generally contacts can carry a higher load than they can switch and that difference causes some of the problems seen in the field with relays in general. UL Ratings are generally switching at 1 second on and 9 seconds off.

While contacts gaps are important, the following attributes are even more important to ANY relay used:


- Contact and blade material,

- Thickness of the blade and size and shape of the contacts,
- Springs & adjustments to the relay that that apply pressure to the contacts
- Wiping action of the moving contacts when switching between stationary contacts.
- The frequency (more so than the quantity) of switching the loads has a direct impact on the life (lower) of the contacts.
- Environment the relay is situated in Ė damp or dusty conditions cause numerous issues or protectively covered or better yet hermetically sealed.

All of the above comes into play when selecting the best relay for the application.

The PM Series have a very good selection of attributes from the above list and are used in a number of different applications including a more recent one
with a ruggedized version that is used on US Navy Destroyer ships!

The correct UL Ratings for the PM Series relay are as follows:

PM
No. Operations


25 A, 240 V ac/pole
100,000
25 A, 277 V ac/pole
6,000
35 A, 277 V ac/pole resistive
100,000
15 A, 240 V ac (277 V/pole)
100,000
1-1/2 hp, 240 V ac (240 V/pole)
1,000
2 hp, 480 V ac (277 V ac/pole)
1,000
10 A, 240 V ac/pole Tungsten load
6,000
10 A, 480 V ac (277 V/pole)
6,000
20 A, 30 V dc/pole
100,000

I hope this helps to clarify some things. Let us know if you have any further questions. We are sorry for any confusing or misinformation that may be out there on the Web. We working to straighten them out.

Dave Mioduski
Struthers-Dunn, Product Marketing Manager
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