Air Con

[Robin Spark]

Hi there,

I have been asked to install power supplies and 3 ip65 rotary isolators for 3 LG air conditioning single spilt systems (manufacturer states 10amp supply each) into a small business premises that used to be a house.

I have done individual ones at other properties and each time installed a new radial circuit from 16amp CB in 2.5mm swa. On the Condenser unit it said something like 9amp starting current and 7.5 amp running current.

The guy installing the air con told me that all three at this other property could probably be taken as spurs from socket ring main and that i didnt need to install new radials.

Can anyone advise please

 

[Andy™]

they should be installed on their own circuit. you may be able to put 2 or maybe 3 on the same circuit

 

[benji]

seperate supplies for me ,but if it,s his show ask for it in writing

yours benji

ps it,s amazing how many air con. guys think they are qualified elects.

 

[Robin Spark]

Thanks for the quick replies, its just that i am sort of doubting the advice given bi air con guy as apparently another sparky had been to have a look with the aircon guy who said it was a load of tosh to install new circuits and he would spur off existing circuits and it could be done in flex as no need for armour.

Hence the original electricians quote seems quite low to me, however he has gone awol and they now need me to do install by end of this week.

What type of circuit would you instal Andy? Do you think 20 amp radial on 2.5mm swa would be ok for all 3? Dont think the cable run is going to be that long but will know better tomorrow when i go and have a look.

 

[PC Electrics]

I dare say he could spur off for one unit, but if he's proposing to create 3 spurs off one ring final then i'd say he's asking for trouble. Based on your OP you're looking at near 30A start up (I'll bet it's more than this for a short duration) and 23A running. This is too much to add to a ring unless the ring is extremely lightly used.

With a 23A running current surely a 32A/4mm radial with fcu for each unit?

 

[binky]

Installing off the ring would be OK if nothing else was using it, which i somehow doubt severly. Given the start up current you may get away with 2.5mm on a 20A, but would be inclined to go 4mm on a 32A as a radial. (or 2.5mm ring) if you want to stick with single circuit. Air Con will pull relatively high loads for long lengths of time so heating up of the cable becomes more of an issue, so I would prefer Andy's suggestion of individual circuit per unit, which is how I've seen every air-con unit installation done - bit like night storage heaters, or any other heating element unit such as immersion heaters and showers.

 

[Robin Spark]

thanks for the input, think i will have a better idea tomorrow once i have been to have a look and then should be able to decide on best option and I'll probably install new cct/s as pointless doing it the cheapest way if it isnt going to work properly.

 

[binky]

Concurr with PC who obviously types faster than me:^O

 

[ElectekAir]

I have spured one A/C unit off of a ring when I first started doing A/C...

Nearly every time the outdoor unit started under load (switching form heating to cooling) RCD went:_|

Had to install it's own supply now always do

 

[Robin Spark]

Been to look at the premises today and there is a spare way on non rcd side of crabtree split C/U. There are three identical air cons max load 6.5 amps each, normal running current 3.5 -4 amps.

Maximum cable run about 14 metres, which is going to be clipped above suspended ceiling so thats a bonus!

So thinking that I should be ok with 20amp rcbo and 2.5mm cable which will be fed to 3 individual isolators to the external units.

Is there any point in fusing down with 13amp SFCU's? The air con guy told me originally 10amp supply each but isnt this because its the next size protective device after max demand of 6.5amp running current.

NB feeling like i am being a bit thick at the moment asking these questionsheadbang

 

[initforthemoney]

The MCB is only protecting the cable so you can put in a 6mm with a 32 and run them all off that via 3 separate isolators.

 

[kme]

But he has 3 units with a max individual load of 6.5A

Why do you want to throw a 32A supply at it?

 

[Robin Spark]

No KME I'm putting in a 20amp radial which I know will protect the 2.5mm cable, was just thinking is there any reason I should fuse down for protection of the air con equipment or dont I need to be concerned with that?

 

[initforthemoney]

But he has 3 units with a max individual load of 6.5AWhy do you want to throw a 32A supply at it?

Why not?

Plenty of headroom, and the cost difference will be very little.

 

[kme]

No KME I'm putting in a 20amp radial which I know will protect the 2.5mm cable, was just thinking is there any reason I should fuse down for protection of the air con equipment or dont I need to be concerned with that?

Sorry Robin, I was aiming my comment at Initforthemoney. If the cable to the aircon is capable of carrying the 20A, no need to fuse down. However, as you will want local isolation, I`d be tempted to fit a fused spur anyway

Why not?Plenty of headroom, and the cost difference will be very little.

Headroom? He isn`t going to stand up inside the cable, is he??

If the circuit is a dedicated cct for the aircon, there is no necessity to "allow plenty of headroom". Even if there was a chance of another being added at some point; 4mm on a 25 would be perfectly adequate. Plus you would force local fusing, as the cable to the aircon is unlikely to be rated at 32A.

KME

 

[initforthemoney]

Headroom? He isn`t going to stand up inside the cable, is he??

If the circuit is a dedicated cct for the aircon, there is no necessity to "allow plenty of headroom". Even if there was a chance of another being added at some point; 4mm on a 25 would be perfectly adequate. Plus you would force local fusing, as the cable to the aircon is unlikely to be rated at 32A.

KME

I apologies for not being a little clearer.

Headroom is an expression used generally in the electrical industry to describe spare capacity in case of future expansion or even uprating.

Cookers are generally installed on to a 10mm T&E nowadays, to allow for larger appliances if the kitchen is refurbished at a later date.

Anyway, i didnt realise there were 25A MCB's available.

Everyday is a school day

 

[PC Electrics]

I'd still be tempted to put them on a 32A/4mm radial with an fcu for each. If you had no fcus (only an isolator) and one unit developed a fault the only available protection would be the MCB which would knock out all three units at once. With fcus each has fuse protection and will (hopefully) only 'blow' it's own fuse in the event of a fault and leave the other two running.

Also, compressors of any sort pull big start up current for short duration which in your case might be enough to trip a 20A mcb.

The cost of putting in 32A/4mm over 20A/2.5mm in this project is very small. I come from an industry (luxury 4x4 R&D) where over-engineering for the sake of it is taboo, but where sound engineering to give quality and reliability is the norm. If there is any risk of phone calls from the client because the mcb keeps tripping at start up, then go for the 'headroom'.

 

[Sidewinder]

Lode Lane was it?

 

[batty]

I would keep them seperate on 16 amp radial circuit on c type breaker no need for RCD protection as long as cables are not buried although swa can be as long as its earthed and as long as its not TT system.

 

[Robin Spark]

Completed the job today, blimey it was really hot and all I was thinking "Is this place needs air conditioning (as the sweat dripped off my nose into the consumer unit, crackle...fizz!! lol).

Bit concerned over the cutout, didnt think at the time to take a pic, TNCS supply, meter single phase in cupboard located within middle of the building, you have supply cable coming in to cutout and then there is another cable leaves bottom of cutout into a redundant cutout which has the fuse carrier missing? Hope you understand what I am trying to explain.