Ready Steady Eddy

[EddyCurrent]

There are also 4 contactors which I haven't taken out yet. Are there any practical/safety differences between a relay and a contactor?

With electrical systems there are generally two main circuits, the 'control circuit' and the 'power circuit'. Contactors are regarded as components of the power circuit whereas relays belong to the control circuit, it's mostly to do with the current carrying capacity and the ability to break that circuit without arcing or at least controlling the arcing. There are relays with positive guided contacts and these are for use in safety circuits, I have not come across equivalent contactors but that's not to say they don't exist. I'm not 100% on this but I think relays originated in communications areas such as telephone exchanges. Contactors can have auxilliary contacts fitted which in essence are relay equivalents and are used in the control circuits for those contactors.