I get passed on highways by cars running on emergency spare tires at 80 mph. Just because I don't see them do somersaults off into the canyon does not mean the practice is the most intelligent. Hell my uncle in Montana controlled a pedestal grinder with a foot dimmer switch, and down here an English National Geographic magazine stands a good chance of being dismembered in an outhouse. A friend loaded his '50 Chevy pickup with three and a quarter tons of asphalt and limped six miles to his house to pave his driveway. IT WORKED! Is this abuse "recommended"?
Relays have ratings. The ratings including duty cycle should be obeyed. The only constant duty 12-volt relay I know of rated for 400 amperes break costs around two hundred dollars. "It Works!" is probably the biggest screw-up in the English language. It leads to "It Doesn't Work!" and that is guaranteed to happen at the worst freakin' possible time.
Do it right por favor. Find the ratings and obey them. BTW a hot non gear reduction starter motor starting say a 454 Chevrolet engine at 20 degrees can draw in excess of 400 amperes inrush and break. Guesswork leads to disappointment.
