I am thinking of starting a project where I will need to interface a microcontroller output and mains for a lighting system. My question is about relays. I have found this one. And I am wondering will it be ok to put 230v through the switch of the relay? Also what am I looking for in the data sheet to tell me what is the maximum voltage that the switch will take?
The relay is a good one for resistive loads like incandescent lamps. The AgSnO2 contacts can handle higher inrush currents than AgNi.
Note that all given currents refer to cos(\$\phi\$) = 1, i.e. fully resistive loads. If you want to switch reactive loads like fluorescent lamps you're limited to a fraction of the given maximum current. You also want a safety margin for the inrush when switching a cold incandescent lamp when the voltage is maximum.
Your 10 A then become 1 A. Since a 60 W bulb draws 0.25 A at 230 V you should be able to switch up to 4 lamps with 1 relay.
Forget I mentioned incandescent lamps. I was in the supermarket today and I needed a replacement bulb. While in the past there was an offer of at least 30 or 40 different incandescent bulbs in all sizes and shapes today they were all gone! Same variety in CFL (compact fluorescent), so that's no problem, but I didn't think the incandescent effectively would be gone before 1st January 2011.
Anyway, for your relay. Relays like the resistive load of an incandescent bulb much better that the reactive load of a (compact) fluorescent lamp. While in theory you should derate the relay further for the changed load, in practice CFLs are only 20% the power of incandescent lamps, so your load will remain within the limits set earlier: you should still be able to switch 4 CFLs with 1 relay.
If you are in any doubt about dealing with mains power - don't do it.
You might want to consider a ready made unit like this one from Adafruit:
If money is no object, then the first thing I go to is a solid state relay (SSR), instead of the mechanical switch variety. I've had to switch 120VAC with a DC control voltage many times in the past, and I've alwyas started with Crydom SSRs. SSRs make interfacing with AC voltage really, really simple. Crydom has several models that can switch 230VAC.
That said, everything I have used them in is for prototype and R&D automation. It would be interesting to hear how others here feel about it.
I've done this kind of thing before, and it worked fine. The relay you've chosen looks about right, and as long as your not switching a huge load it will be fine.
If your unsure about the load, then do a simple calculation, for example if your switching a 100w bulb on and off, then 100w divided by 230v = about 0.4 amps. The datasheet says that the relay is rated at 10A... so its way more than enough.
If your calculations are out, and things go wrong the worst that can happen is it burns out a cheap relay, or blows a fuse or MCB or something... it's not the end of the world.
The Max. switching voltage is apparently 277V AC and 30V DC. What you should be asking however, is how much current you need to be rated for. This is not a simple thing to answer because depending on the type of load you are switching, you actually need to derate the current differently to account for inrush current.
I suggest reading through Agilent Application Note 1399 - Maximizing the Life Span of Your Relays to give you an in depth idea of what I'm talking about. Don't mess around with this stuff without taking appropriate precautions. You will note that for incandescant lighting, you need to derate by a factor of 10%. That means if your lighting draws 5 amps, you better get a relay that can switch 50 amps.
I think the reason that incandescent lighting is derated so much is because when the filaments are cold, they have much lower resistance than when they heat up, and so draw a huge amount of current from a cold start. I'm really just guessing at this though.