Electrician used wrong cable size

[portlouis]

Hi all,
I had an split air conditioner installed last week by an electrician and commissioned by a Fgas Engineer.

The engineer who commissioned it was also an electrician and said that the electrician has used the wrong cable size.I am not sure who is correct specially when both of them are electricians.

The air conditioner specs from the manufacturer are:
7.1 kw (24000 BTU)
Fuse Required: 16A

#Rated Capacity(W) : Cooling:6810 (1830-7810) Heating 6870 ( 1850-7930)

#Power Input (W) : Cooling : 1980 (410-2800) Heating 2050 (420-3000)

#Current Input (A) :Cooling (8.9) Heating (9.0)

#Nominal Load (kw): Cooling (6.81) Heating (6.87)

The electrician has used 4mm twin earth and core and the total run of the cable is around 20 metre run through the floorboards and insulated roof. He has installed the cable directly from the consumer unit with a Type C Wylex mcb which is rated at 32A. This then goes in red rotary isolator outside near the external compressor.

The F-gas engineer said that the electrician should have used 6mm or even 10mm as there will be a voltage drop when the the compressor kicks in.When i spoke to the electrician he said that the air conditioner is inverter compressor(whatever that means) and the cable he has installed is ok.

I just want to know if the cable is at risk of burning down eventually due to it being wrong size, before asking the original electrician to come back and rectify the work.

 

[Taylortwocities]

I assume the system is working?

Looks fine to me. Cable and MCB rated at 2x the requirement. Any kick in surge Will be fraction of a second and won’t cause anything to happen to the cable.

MCB is C curve to prevent trips on start up surge. All good. Don’t worry.

 

[bernardgreen]

Putting the figures into https://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html indicate 6mm² is required

Maximum current in 4mm² cable is 27 Amp hence the 32 A MCB is wrong for 4mm² cable. It should be a 20 Amp MCB

 

[portlouis]

I assume the system is working?

Looks fine to me. Cable and MCB rated at 2x the requirement. Any kick in surge Will be fraction of a second and won’t cause anything to happen to the cable.

MCB is C curve to prevent trips on start up surge. All good. Don’t worry.

Thanks.The system works fine and no problems with it.However with the money paid to the electrician i would have assumed that the other electrician would not have made any comments about the quality but how neat and good the job is.

 

[Taylortwocities]

Maximum current in 4mm² cable is 27 Amp hence the 32 A MCB is wrong for 4mm² cable.

Not correct. 27A is max for 2.5mm
4mm is 37A (subject to Installtions method).

If your statement were correct then every (standard) 4mm radial with a 32A MCB needs to be ripped out!

 

[bernardgreen]

4mm is 37A (subject to Installtions method).

Only if Reference method C* (clipped direct)

http://www.batt.co.uk/upload/files/currentratingstable4d5_1312876143.pdf give the follow maximums for various methods

4mm² 27 22 27 17.5 37 26

 

[SUNRAY]

I haven't done the calcs, my gut feeling is clipped direct 4mm² but 6mm² for pretty much anything else, especiall if it goes under/through insulation.

 

[EFLImpudence]

OP - Fuse Required: 16A

 

[AndyPRK]

It draws less than 9A so 4mm is plenty.

you could in theory lower the MCB rating to protect the cable