Using relays at their rated current?

[cpitman]

In the US, the NEC requires wiring/breakers/etc to be rated for 80% of the current for continuous loads (3+ hours). So if I want a 12A load on a circuit, I need the wiring/breaker to support 15A.

Does any of this apply to electrical components? The main example I have now is relays. If I need to switch a 12A load (and keep it closed for 3 hours or more), would a relay rated for 12A work? Or do I need one rated for 15A and have it loaded at only 80% of capacity?

[BrokenYugo]

I'm not qualified to answer regulations wise, but it is generally considered poor form to run any electrical component at or near it's maximum rating.

[bdunham7]

The NEC does not apply to electrical components other than those used in your building wiring.  How much you derate a relay or other component in your device is an entirely separate question and the answer could range from 'none' to 'a lot'.  80% is not a good universal answer.  Also the NEC 80% rule only applies to standard configurations and breakers--there are systems and breakers that are rated for use at 100% continuously. 

[cpitman]

Thanks, "derating" is the keyword I needed! Is there a resource you would recommend for understanding derating?

I see quite a few "high spec" standards like NASA and the military, are those considered "standards"? Or are they more conservative than needed for normal commercial uses?

[floobydust]

First classify the relay's load - is it resistive, tungsten lighting, inductive ballast or an electric motor etc. ? You have to take into account the inrush currents.
There are UL and IEC approvals for relays as a component for use in a product. Not at the NEC level unless it's a device like a motor starter I believe.
Many relays have no formal approvals and a "12A" rating is vague for how long it will last with certain loads or if it's fit for purpose.
Example part to look at is popular T9, T90 appliance relay approvals. It's current rating varies depending on the load/lifetime.