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Topic Title: Air Con DB question
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Created On: 01 April 2014 05:54 AM
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 01 April 2014 05:54 AM
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Tailz

Posts: 8
Joined: 11 October 2012

Hi, have been asked to quote for fitting sub DB for air con. Can anyone offer any advice?

There are 16 units total, with currents and manufacturers recommendations as follows;
3 units@ 9A (20A MCB)
3 units@ 8.6A (20A MCB)
4 units@ 4.4A (10A MCB)
2 units@ 4.8A(10A MCB)
1 unit@ 6.5A (16A MCB)
3 units@ 5.7A(16A MCB)

I cannot find anything on discrimination, so assuming 100%, I have three phase. Nowhere suitable to fit big ugly 3ph DB in new offices, so thought three no single-ph DBs with balanced loads, fed via split con would be suitable as running over suspended ceiling, no insulation (not used split con before)

Now AC guy says, due to the way he has sited the units, there will be two boards running load of 7kW with one (furthest away from main DB) running at 12kW. Approx cable runs will be 20, 25 and 35m.

Any advice, re: economical installation or general thoughts welcome!
 01 April 2014 09:24 AM
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AJJewsbury

Posts: 11498
Joined: 13 August 2003

I guess you mean diversity rather than discrimination.

I'd be wary of split-con - I reckon the separately insulated N strands put you in appendix 10 territory - which I suspect you'd prefer to avoid! SWA instead perhaps?

- Andy.
 01 April 2014 10:44 AM
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OMS

Posts: 19690
Joined: 23 March 2004

Don't undersize the sub mains - it sounds like someone is installing a load of really horrible split DX units rather than a sensible VRF system.

All of the single phase units will have horrible harmonics associated with them - so you need plenty of copper to compensate.

Like Andy, I'd caution against split con. If you don't want to use armoured, think perhaps of CY or SY. I would size it for at least FLC of the relevant machines plus a 25% margin (including the CPD, to accomodate starting conditions and the harmonic heating)

I guess you are where you are, but a simple TP external condensor and a number of indoor units powered from a dedicated ring final fused at 20A within the spaces would be a far better solution electrically (and mechanically)

Regards

OMS

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Failure is always an option
 01 April 2014 05:54 PM
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mapj1

Posts: 2853
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Another curveball, not all 3 phase DB have to be ugly - there are some rather nice domestic looking 3 phase CUs that use a 4 pole isolator and an odd-tooth dinrail arrangement that connects every third prong. Only really enough space for small stuff line T+E inside, but I've seen it done for things like lots and lots of lighting circuits in an office setting. About the same size as a rather long domestic consumer unit, with 15 or eighteen out bound circuits from memory. Now if I had a more useful memory, I could tell you who makes them, but right now I can't.
regards
Mike.

-------------------------
regards Mike
 01 April 2014 09:41 PM
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peteTLM

Posts: 3167
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Originally posted by: Tailz

Hi, have been asked to quote for fitting sub DB for air con. Can anyone offer any advice?



There are 16 units total, with currents and manufacturers recommendations as follows;

3 units@ 9A (20A MCB)

3 units@ 8.6A (20A MCB)

4 units@ 4.4A (10A MCB)

2 units@ 4.8A(10A MCB)

1 unit@ 6.5A (16A MCB)

3 units@ 5.7A(16A MCB)



I cannot find anything on discrimination, so assuming 100%, I have three phase. Nowhere suitable to fit big ugly 3ph DB in new offices, so thought three no single-ph DBs with balanced loads, fed via split con would be suitable as running over suspended ceiling, no insulation (not used split con before)



Now AC guy says, due to the way he has sited the units, there will be two boards running load of 7kW with one (furthest away from main DB) running at 12kW. Approx cable runs will be 20, 25 and 35m.



Any advice, re: economical installation or general thoughts welcome!



Please dont use 3no. single phase boards on a 3 phase supply supplying 3 phase loads

As Andy has said, split con is out of the window.

-------------------------
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Lack of planning on your part doesn't make it an emergency on mine....

Every man has to know his limitations- Dirty Harry
 01 April 2014 10:22 PM
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jamieblatant

Posts: 513
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Why do people with 3 phase supplies like to use single phase equipment with single phase motors in as apposed to 3 phase equipment with 3 phase motors in

IT MAKES ME SOOOOO MADDDDD

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 02 April 2014 05:46 AM
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Tailz

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Joined: 11 October 2012

Thanks AJ, Pete, Jamie - so single phase DB option, and split con cable are out.

OMS - Like the CY/SY, good idea! Unsure of the air con design, but they are installing Daikin units.

Mike - I'd like to find one of these units, but no luck so far... any ideas at all where I could find one?


So, given the above advice, I'm considering this:
Dedicated ring final for 10no smaller units, fused at 20A
Pretty looking (hopefully!) local TP DB for 6no larger units, fed via CY/SY.
 02 April 2014 09:36 AM
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mapj1

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]Hmm,
Well I hd a dig about and for a while I thought they must have stopped being made as the only ones I could see searching for 3 phase CU were very much build to order on Ebay, and no obvious reputable maker's mark.

like this chap ;-)3 phase CU on Ebay
But if one serches the ABB catalogue for 'single row distribution' and 3 phase, you get the top row in this link 3 phase consumer units
which I think are the sort of thing I'm talking about, but I'd be happier if they were shown with a photo - the key to the ones I'm thinking of is that it looks like a normal CU, if rather a large one, except for the use of the 3 phase comb bus bar inside instead of a normal one..
Probably worth a phone call or two to see if it really is what it appears to be, and if they really exist or are just vapourware from the sales folk. I must admit I'm not totally sure as I'm confused by the stated module widths - I'd have expect a multiple of 3, mabe plus one for the neutral on the far end of the incomer.
I hope I'm not wasting your time with a blind alley.
Best regards .

-------------------------
regards Mike

Edited: 02 April 2014 at 09:59 AM by mapj1
 02 April 2014 09:57 AM
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tattyinengland

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Are there any units sited particularly far away from the DB? With all those units going in, some are sure to be a fair old run away from the DB position.

Watch out for the volt drop.

Some air con units require an outside supply only and some units require and indoor supply too - check that the indoor units don't have a requirement for an individual supply, because then the job is twice as big as what you have quoted for.

Regards
Tatty
 03 April 2014 11:24 AM
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AJJewsbury

Posts: 11498
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majp1 - I think Proteus do the kind of thing you're thinking of: http://www.proteusswitchgear.c...ucts.asp?category=580
Like you, I've seen plenty of 3- and 4-pole bus bars in catalogues, but pictures of complete assemblies are a bit rare! (The French seem particularly prone to using 3-phase on horizontal layouts, but seem to prefer lots of little wires rather than a bus-bar to connect things.)
- Andy.
 03 April 2014 11:45 AM
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Zs

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Andy J I wag my finger at you most firmly Sir....Proteus???.

Tailz have a look at Hager Invicta because they are gorgeous.

http://www.hager.co.uk/news-ex...oards/14086.htm


ah, that's a link to the little 'style of' boards but you'll find your way to the Invicta TPN ones from there.

Zs
 03 April 2014 12:34 PM
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OMS

Posts: 19690
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Originally posted by: jamieblatant

Why do people with 3 phase supplies like to use single phase equipment with single phase motors in as apposed to 3 phase equipment with 3 phase motors in



IT MAKES ME SOOOOO MADDDDD


What, like luminaires, desktop PC's, water heaters, beverage units, small fans, hornby train sets etc etc

OMS

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Failure is always an option
 03 April 2014 12:40 PM
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AJJewsbury

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Andy J I wag my finger at you most firmly Sir....Proteus???.

I know, I know, sorry! But it was the only thing I could find through Google this time. I'm sure I've seems something nicer when I was looking at ABB's unifix L bus-bar system, but I can't find it now

Your link seems only to be only SP type A boards though (just the case shaped to match their type B offering) - so not a horizontal layout 3P as far as I can see.

- Andy.
 08 April 2014 06:14 AM
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Tailz

Posts: 8
Joined: 11 October 2012

I was thinking of the six smallest units wired in 2.5mm on a 20A radial. Cable length of 40m max.
Was going to put the six larger units on a TP local DB, so should be fairly central. Each run will be less than 15m, wired in 2.5mm as 20A radials.

As for size of sub main DB cable, 16mm 4C was my calcs - had a look on Doncaster cable website, which suggested 4.0mm for YY flexible cable???

(Used this for sizing guidance - 400v, 12.3kW (22.19A ph) 30m length, installed on tray)

Edited: 14 April 2014 at 10:06 AM by Tailz
 08 April 2014 07:01 AM
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Tailz

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Joined: 11 October 2012

Update of information. Just to avoid any unintentional confusion, all of the AC units are SP. The reason behind a local TP DB was to balance the load.

It now appears that the three large 'cassette' units to the first floor (9A each) and those to the second (8.6A each) need to be on the same phase - apparently due to communication between three units? AC guy can't give me a definite answer!

Need to call Daikin to confirm, unless anyone here knows?

Edited: 14 April 2014 at 01:41 PM by Tailz
 16 April 2014 10:38 AM
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Tailz

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Okay, so according to manufacturer, the two sets of three large units (one for each open office space on each floor) don't have to be on the same phase, so that's good news.

Three SP boards are looking favourite for aesthetic reasons for client.

Full loads are 90A, 80A and 60A, what's best option??
 17 April 2014 06:26 PM
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peteTLM

Posts: 3167
Joined: 31 March 2005

Whats the best option?

A nice looking 3 phase TPN board.

Look at some of the Hager boards as Zs has suggested, or schneider/MG do some half decent looking ones.

-------------------------
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Lack of planning on your part doesn't make it an emergency on mine....

Every man has to know his limitations- Dirty Harry
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