Relay Current 10A: Nominal or Maximum Current?

I wouldn’t try to push more than 10A and if you planned on running close to 10A most of the time I would go with a higher current relay.

Ideally I would look for the datasheet for the relay in question and see what it has to say about current and different temperatures.

Sometimes the current rating will change based on the voltage your feeding through it. The data sheet will show that also.