Hello,
I have a question regarding the current-specification of a typical “Arduino”-Relay, which I want to use for switching lights. Is the current given (10A at 250VAC) the nominal or the maximum current? This matters for me to know how much power I can switch with this relay.
Thanks for your help!
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.
This is what the data sheet says. It should show the nominal current, but I am not exactly sure then what the maximum would be. Another thing is that the count of operations seems to be dropping pretty significant when operating at a higher current.
It gets complicated real quick 
I would contact the guys over at www.controleverything.com and tell them what you’re doing and ask for a safe relay for that application.
Hi @izmevid
When a relay spec says that it is a 10A rated relay, that is the absolute maximum current allowed and larger currents will immediately damage the relay. As you noticed, the contacts are degraded by switching higher currents, so if you also want long life, you need to substantially overrate the relay switching current.
Another problem that shows up in your datasheet above is the ability to switch inductive loads like motors. Your 10A maximum relay can only safely switch a 3A motor (and this another absolute maximum). If you are switching a motor, the best spec to check is your motor’s LRA or locked rotor amperage. This is the current that is drawn briefly when the motor starts up and you want to handle that full current with your relay. Not being careful here will cause the relay contacts to weld together and you will not be able to shut the motor off with the relay, which can be dangerous.
The best way to approach this is to figure out what load current you are switching and then select a relay that is spec’ed to handle 3-4X that current. Working backwards is more difficult.
If your load is inductive such as a motor as mentioned by @bko, then you should consider using the relay to control a Contactor, and then have the Contactor control the motor. Contactors are designed to handle those motor start-up loads. Check you local electrical code; a Contactor might be required even if your relay is capable of the job.