Thanks :mrgreen:
Snitty, to my knowledge most automotive style relays are rated for continuous use. It is more a concern when dealing with Solenoids, as some Solenoids are NOT rated for continuous use. For those who don't know, a Solenoid (and like-wise a contactor) is basically the same as a relay, except on a larger scale.
Main things that would affect the duration of time that a solenoid/relay/contactor could be used for would be how the contacts are configured (if they are large enough to support the load for an extended period of time), the type and gauge wire used for the solenoid/relay/contactor coil (small wire may heat up and either melt completely or melt the varnish coating and short circuit).
I'd imagine in a continuous use solenoid/relay/contactor they make sure the coil is made in such a way that it will not overheat and they use larger contact surfaces which will handle the load better (smaller contacts may handle the load fine for a short period of time, but could be derated by heat which would be an issue when current is flowing across them for long periods of time).
As you'd imagine these things aren't really a concern in situations such as starter motor circuits where on average the solenoid/relay are only powered for 10 seconds or less. That's why I'd recommend against using any "starting" solenoid.
If you can't find a relay large enough, try to buy a DC "contactor" as usually these are rated for continuous use, where as solenoids aren't
Oh and always use protection.... you need to use a circuit breaker or fuse to protect any circuit, especially high current circuits :mrgreen:
-Nick :!: