can i use 12VAC 60w transformer for 12VAC 30w (3 10W) light?
Yes. 60 watts is the MAXIMUM you can use with that transformer.
Transformer rating is 60 watts ~ don't use total wattage over that. So with your three 10 watt bulbs, that totals 30 watts. Will be okay. You can actually use up to six 10 watt bulbs, or a total of 60 watts max. Been using light bulbs for 65 years !
