Newbie here regarding contactors and relays, i had this contactor datasheet https://www.gavazzionline.com/pdf/CC50-CC65.pdf. I'm trying to identify how long the contactor would last and I find the durability category, what's the difference between mechanical and electrical? does the mechanical durability means how many cycles the contactor would work w/o load and electrical means has load?

Also, this durability is for the poles of the contactor? not its coil for activating the contactor?

Does coil for activating the contactor has durability also??

I find it hard to read datasheet that are not detailed at all since i have no one here to ask to that has a lot of experience when it comes to these datasheets. I hope you could help me :)

As for the follow up question also I have this datasheet http://www.te.com/commerce/DocumentDelivery/DDEController?Action=srchrtrv&DocNm=1308242_PRD&DocType=DS&DocLang=English where i'm looking for the numbers of durability for the contacts and as I go along comparing this to other datasheets, i find most of relay and contactor datasheets don't have durability data in common or i mean standard.

I would like the image below, the contactor I saw is on Code Y, Ag, 1 pole and it is capable of 50Amp Load Current. I understand that 50A, 277VAC will have a lifepan of 100k (Hz is not rated if 50/60hz, means it doesn't matter because theres a little difference for affecting the number of cycles it could work?). and here i compared that to a 3HP, 240VAC w/c is also 100k cycles. upon getting the ampere equivalent to 3HP, its around 9.3A only so it'll be 9A, 240VAC = 100k right? why is has lower lifespan compared to 50A, 277VAC w/c has more power rate??)

Is there a way to compute if i wanted to know the cycles it could do having 40A, 277VAC or 40A 230VAC (either capacitive/resistive) using the values given on datasheet?? And if 50A 277VAC = 100k cycles, how can i know the approx. cycle if w/ these parameters only 25A 277VAC?? i know it'll be more than 100k cycle but will it double like 25A 277VAC = 200k cycles?

Also, on the same datasheet, it has this section.

so coil for activating the relay does have durability also??

And lastly, if i have a contactor that has 3 poles, does the durability for the contacts applied separately for the 3 poles?? like 100k cycles for each poles? i mean, i had this idea of using the contactor that has 3 poles to use only 1 pole at a time and if it wears-off, i'll just use the other pole instead of buying another contactor. Is that feasible?

• BTW: From that spec I do not think the Code Y, Ag, 1 pole is capable of 50Amp Load Current. You need a code P. Commented Jan 30, 2018 at 3:26
• Oh yeah, your right, I'll update it to avoid confusion. I even chose the PRD-3DR4-24 w/c is actually Code R w/c is different from other codes, is this for DC application only? Commented Jan 30, 2018 at 3:37
• Yes Code R is for DC and has a magnetic blowout to extinguish the arc. You don't need that feature for AC. Commented Jan 30, 2018 at 3:46
• There also exist Vacuum Contactors and SF6 filled Contactors which have higher extinguishing current and breakdown voltage. Commented Jan 30, 2018 at 3:48
• And as Tony shows in his answer the life relationship is not linear with current. Commented Jan 30, 2018 at 3:50

MIL-HDBK-217 provides a calculation to help “fine tune” a reliability prediction as it applies to a specific application.

It consists of the following formula:

$λ_p = λ_b · π_L ·π_C ·π_{CYC} ·π_F ·π_Q ·π_E$ = Failures/$10^6$ hours.

MTBF = $10^6/λ_p$ hrs

Whereas:

$λ_b$ = Base Failure Rate (temperature factor)
$π_L$ = Load stress factor (load level and type)
$π_C$ = Contact form factor (DPST, DPDT etc)
$π_{CYC}$ = Cycling factor (cycle rate)
$π_F$ = Application and construction factor (general relay load rating and armature type)
$π_Q$ = Quality factor (mil-spec qualification level vs. non mil)
$π_E$ = Environment factor (environment in which the relay is being used)

Below is an OMRON life expectancy on relay contacts that shows the effects of inductive loads. Mechanical Ratings in million operations are no load ratings. Ref MTBF Telednye
Crydon

When inductive Arcs cause contact temp rise, MTBF drops quickly. This is why Tungsten start surge , inductive stop surge and DC inductive has the lowest rating life. Resistive loads have no stored energy to dump unless tungsten lamps , which have 10x peak cold surge curernts.

• never been called Sir Tony... but my wife calls me BabyJan Commented Jan 30, 2018 at 3:56
• hahaha! xD ok, thanks BabyJan :D more power to you and take care. Commented Jan 30, 2018 at 5:43

As you suspect the mechanical durability is how many cycles the thing will mechanically move before something internal will wear out, be that the spring or the hinge points.

The electrical durability is how many cycles the relay can operate at the rated voltage and switching current before the contacts will wear out.

The reason for the difference is that contactors and relays can be operated with additional switch gear such that the relay is switched with no current flowing. If you are using it that way, the mechanical durability is the relevant number.

If you are using the relay at a lower than rated voltage and or current the life expectancy will be somewhere between those numbers.

The coil side is not usually rated for durability. If operated within the rated values, the coil, having no moving parts or switching contacts, has a life that normally far exceeds the other two numbers.

Note the values quoted are usually mean time to failure. Some units will fail earlier and some will last longer.

EDIT re question extension. The HP rating is for the motor it is switching, however, the current that will be switched is significantly higher than the steady state HP value in order for the motor to start.

The coil numbers indicate that the AC coil version will mechanically wear faster than the DC coil. This is due to the increased vibrations in the mechanical parts due to the AC magnetic field. It still is not the coil that is wearing out though.

Your latter idea MAY work to extend the life of the relay if you routinely cycle the contacts as part of preventative maintenance, but once one set burns out there will likely be debris left inside the relay that can cause additional failures.

• Hi Si Trevor, :D thanks a lot. That did clarify my confusions. Also i would like to ask another in related to this one also but i guess you'll get the gist of it much better if I added that question w/ this one. Going to edit my question :) Commented Jan 30, 2018 at 2:51
• @Mheruian see updated answer. Commented Jan 30, 2018 at 3:16
• Putting the contacts in parallel will reduce the steady state current each is subjected to and should improve the life as per the chart below. Commented Sep 21, 2018 at 23:45