[TowerTalk] Fwd: X99KP 12VDC RELAY FOR AMERITRON REMOTE ANTENNASWITCHES

[jimlux]

hanslg at aol.com wrote:
>  LM Ericsson, Sweden (the old telephone manufacturer) had a patent many years ago regarding double contacts in relays. They showed that the reliability of a relay was major increased when you had two relay contacts in parallel. I believe you still find a term for this, just can't remember what.
> 
> Hans - N2JFS
> 
> 

It kind of depends on what you're trying to achieve.
Paralleling contacts to improve "reliability" is one thing.
paralleling contacts to improve current carrying is another
Paralleling contacts to improve current breaking capability is yet another.

There's a fairly common scheme using 4 SPST relays to implement a "any 
single relay can fail, and you can still make or break the circuit with 
the remaining 3" using a "all switch together" scheme.

Likewise, there's a scheme using 2 SPDT relays that will tolerate a 
single failure (think of 3-way light switches at home), but it requires 
recognizing that the failure has occurred.