Ordered this relay rated at 10A, 240V and it arrived today. I bought it on the rating without really looking at the size, it is tiny, about the size of the end of my index finger. Have I failed to understand the meaning of 10A contact rating or is it really up to the job. I want to drive motor (workshop vacuum) rated at 1.1kW so only looking for 4A really

 

Its going to be fine,if you search for 240V-10A relay you will see that they are going to be in same size as yours.

 

Ordered this relay rated at 10A, 240V and it arrived today. I bought it on the rating without really looking at the size, it is tiny, about the size of the end of my index finger. Have I failed to understand the meaning of 10A contact rating or is it really up to the job. I want to drive motor (workshop vacuum) rated at 1.1kW so only looking for 4A really

Make sure it can handle the locked-rotor current.

 

There are several different contact rating specs, most of the time the amperage quoted is for an AC resistive load, deratings occur for AC inductive or DC loads.
A universal motor such as your has considerable inrush current at switch on.
The life expectancy is most likely less than expected.
Max.

 

I'm not so sure that this will last long switching a reactive load such as a vacuum cleaner motor. I would use something a little more robust and ideally one that fits in a base which allows connection via screw terminals. There are a few on ebay.

 

Personally I would pick up a contactor off ebay, they go as low as $10, the coil can be changed if necessary for the right voltage, they would last you many years.
Or you could use the small one to pick it up if you need low coil current.
Max.

 

Thanks guys, knew it didn't look right. I'll get a big fat one that goes "clunk"

 

I once used a 10 amp rated switch on the primary of a transformer, with a 3 amp load on the 55 volt secondary, switching the switch welded the contacts closed. I suspect your relay will do the same.

 

I might have a suitable relay laying about but it will be alot bigger..