Whats the contact rating of a relay for?

[ericmar]

Questions about relay

Hi, may I know what's the contact rating of a relay for?
I understand SPST, SPDT, DPST, DPDT, etc. but I'm not sure about the contact rating. For contact rating - 1 Amp, what does it mean?

Thanks.

 

[Kevin Weddle]

Re: Questions about relay

It's most likely average current. A fuse is rated at peak current, everything else is rated for average current with the peak current obtaining higher values.

 

[echo47]

Questions about relay

A relay has many ratings. That one probably means the maximum current that the contacts can reliably carry while they are closed.

If you know the relay part number, search the manufacturer web site for a data sheet. Also download the manufacturer's "relay user's guide" or whatever they call it. It will explain many important details. For example, here are Aromat's and Omron's guides:
https://www.aromat.com/pcsd/rti.pdf
http://oeiwcsnts1.omron.com/pdfcatal.nsf/PDFLookupByUniqueID/7DB74C1B643A57C286256AF80060A947/$File/M20Z54E11.pdf

 

[Ante]

Re: Questions about relay

The 1A rating must be valid at a specified maximum voltage and also if it is AC or DC, this very important!

Ante :roll:

 

[FoxyRick]

Re: Questions about relay

Another thing to be aware of is that a high power relay might not work well for low power (eg. signal) switching. This is due to the high power cleaning the contacts when they switch - it burns off the oxide layer that gradually forms on them.

Without this the oxide layer thickens and increases the contact resistance, a problem in low power switching.

Relays for lower power have the contacts made from different metals that are less prone to oxidation.

FoxyRick.