Electrical Loadings - Why is such a large supply required by Fujitsu?

[Canopyman]

Hello,
New to the forum and thanks for any replies.
I am looking to install either a Mitsubishi Floor Mounted Unit SRF35ZJX-S (4.5kW heating) or a Fujitsu AGYG12LVCA (also 4.5kW heating). This is for my house.
Both units run at around 1.1-1.2kW electrical loading in heat mode. The Fujitsu units requires a 20A supply. The Mitsubishi unit indicates a max running current of 8A.
The Fujitsu unit indicates a running current of 5.5A and a start current of 5.5A.
If I need to provide a 20A supply, that's a substantial job in it's own right. If I only need to provide 8A, that should be fine from a ring main?......
I'd prefer the Fujitsu, but can't see why the high requirement of a 20A supply.
Does the inverter cycle to a point where it might actually need 20A? :confused:
Any insight appreciated.
Regards
Gordon
Dorset

[r.bartlett]

13a fused spur off a ring main will be more than enough

http://www.ambientcontrol.co.uk/content.cfm?cID=203

[Tayters]

Hi Gordon,

Not sure on the MHI unit but the Fujitsu spec states max current of 11.5A (which will be in heating). From memory the 3.5kW units I've commissioned will be 5-7A on a heating test run.
The outdoor unit where the power goes to has a 20A fuse. Off on a tangent but if this has reason to blow then something has gone seriously wrong like a compressor to earth and you'd be looking at a new outdoor unit, compressor/PCB etc and a smaller fuse in the power supply is unlikely to help avoid this.

As Richard says a fused spur from indoors should work fine, make sure the mains cable you use is of a suitable size. Perhaps not for the purist but there are countless units installed this way.

The only point to watch out for is that with the unit at full peg the electrical load on the circuit is such that it isn't above that of the breaker and if the breaker is on an RCD there is a slim chance that you will get nuisance trips from the inverter operation. Only seen it happen twice and like I say unlikely to happen but the chance is there all the same.

Cheers,
Andy.

[Magoo]

generally based on LRA ( lock rotor amps ) of compressor plus a margin of safety.