For a Ring Main, then there is no limit, probably 1000 amps is enough. Though you mean a ring final circuit, not a Ring Main. Presumably this will be a standard circuit with a 32 amp Type B circuit breaker with 2.5mm T+E cabling?

What is the load of the appliance, and will it run at that load all the time, or is that the start up current?

I'd be happy to fit an air con on an existing 32 amp circuit if I knew it would typically be running at 5 amps or less, with a 15 amp inrush to start the motor. Also, the existing appliances need to be taken into account. If there's already an oven, microwave and kettle on it, then I'd be reluctant to add to the circuit, but if, say, its feeding bedrooms, which have a maximum demand when the hoover is plugged in, then it may be fine to tap off that circuit.

How do you cope with start up/inrush currents? I know some Heat Pumps require a type C circuit breaker to account for the inrush, so does yours need a type C circuit breaker?  If so, will the existing circuits characteristics be able to satisy the requirements to be able to fit the tybe C?

It isnt easy, and no one can give you an answer without looking at the circumstances, it could be fine in the real world by tapping off an existing circuit, but it could cause numerous problems too, so I can see why your Electrician is not keen on using the existing circuit, as it will be him who is liable for the repairs/hassle/replacement if it does not work. To be fair, virtually every air con unit I've seen/fitted have their own circuit, so I can see his reluctance to fit it to your requirements.

For a Ring Main, then there is no limit, probably 1000 amps is enough. Though you mean a ring final circuit, not a Ring Main. Presumably this will be a standard circuit with a 32 amp Type B circuit breaker with 2.5mm T+E cabling?

What is the load of the appliance, and will it run at that load all the time, or is that the start up current?

I'd be happy to fit an air con on an existing 32 amp circuit if I knew it would typically be running at 5 amps or less, with a 15 amp inrush to start the motor. Also, the existing appliances need to be taken into account. If there's already an oven, microwave and kettle on it, then I'd be reluctant to add to the circuit, but if, say, its feeding bedrooms, which have a maximum demand when the hoover is plugged in, then it may be fine to tap off that circuit.

How do you cope with start up/inrush currents? I know some Heat Pumps require a type C circuit breaker to account for the inrush, so does yours need a type C circuit breaker?  If so, will the existing circuits characteristics be able to satisy the requirements to be able to fit the tybe C?

It isnt easy, and no one can give you an answer without looking at the circumstances, it could be fine in the real world by tapping off an existing circuit, but it could cause numerous problems too, so I can see why your Electrician is not keen on using the existing circuit, as it will be him who is liable for the repairs/hassle/replacement if it does not work. To be fair, virtually every air con unit I've seen/fitted have their own circuit, so I can see his reluctance to fit it to your requirements.