Relay Contact Ratings

[Wp100]

Hi,

Got my mind stuck on a simple thing, when selecting a 3 pole 10amp relay does that mean a 10 amp load per contact or 10 amps shared across all 3 contacts?

Relay in question https://www.farnell.com/datasheets/1465672.pdf

thanks

 

[crutschow]

It's 10A per contact.

 

[dr pepper]

Unless its marked otherwise.

 

[Reloadron]

As mentioned it means 10 A per contact. Keep in mind though, that does not mean you should be able to parallel 3 contacts and be able to switch 30 amps. When the contacts close and open they do not all act at the same instant in time. Due to the mechanical issues when the relay opens under load (or closes) if two of three open before the last that last sees all the current. I am not saying that parallel contacts won't work, I am merely saying it isn't a good practice to wire a relay that way to handle higher currents than a single contact would handle.

Ron

 

[KeepItSimpleStupid]

Be careful too, sometimes switching current is different than carry current. In some relays I used, they had to be switched with no current thru the contacts,

 

[Wp100]

Hi ,

Thanks guys, had got a bit of a metal block as to which way to read the contact ratings.

Am actually switching 3 separate lines, 2 very small ac currents but the 3rd line is up to 5 amps @ 12vdc so that would have been too much for one contact if the 10amp rating was shared across the 3 contacts.

Good point from ReloadRon about not paralleling a load across multiple contacts.


Just off this particular point, but something that always made me wonder why, on some industrial machines at work, typically for turning on heating elements of around 5 to 12 amps @230vac ; they used a 16a relay and a power triac in parallel.
Heard various views as to why they used 2 devices though nothing convincing; any thoughts ?

 

[KeepItSimpleStupid]

I did a few designs at work where I put a relay in series for 3 reasons:

1) Auto drop out on power fail
2) Over-temp (Shorted triac)
3) Isolation - Heaters were inside a vacuum system and exposed

Parallel - self-test for shorted triac/open load?