MCB Rating for Daikin & Mitsubishi

[mick2me]

Reading the installation instructions for my Daikin,
It does not state the rating for the MCB?

Should I fit 15a or 20a

I have a Daikin
FTXS25CVMB INTERNAL
RXS25CVMB OUTSIDE UNIT (3Kw)

I am also planning to buy a further unit
Mitsubishi SRK25-ZD (3Kw)

Im off for two weeks,:) so will pick up replies on my return, Thanks

[marc5180]

I have a daikin ftxs50 installed in my conservatory which is run from a 15amp fuse spare from my cooker
Hope this helps

[mick2me]

I have a daikin ftxs50 installed in my conservatory which is run from a 15amp fuse spare from my cooker
Hope this helps

MCB's offer much closer protection than fuses.
Therefore need to be more accurately calculated.

Wonder what MCBs installers are using?

Right, I'm off on me olidays, better put the laptop
away before SWMBO returns from the kennels....


Eyup she's here already :eek:

[davej]

hi Mick2me
my daikin book says the unit rxs25cv reqiuresa 15 amp fuse. start and run current show 4.4amps.

[mswinman]

Hi Mick.
Not sure if your 3KW is input or output but from somebody else's post it would appear to be output. So from that, what size of cable are you running to it, and how far do you have to run it? Would suggest you run it 2.5mm2 and use 16a Type C breaker. A type B breaker may trip on motor start up, as start current is much more than run current. Ensure your breaker is to BS60898 as you should not use earlier types ( type1, type2, type3)and if it's fed from a TT supply You must install an RCD between the consumer unit and the service blocks.

[DEVIL]

mswinman not realy, RXS25CVMB are inverter units so they start getel, so ... no shoc at starting a 16 amp, should do it, and 1.5 mm cable should be ok, and, yes RXS25CVMB has a'n nominal output of 2.5Kw, and max 3 Kw of cooling, and 3.4Kw nominal, and max 4.5 heating

[daddymac]

The primary job of the fuse is to protect the cable, it offers no real protection to the unit!
For myself, I'd avoid 1.5mm cable for this job unless you're right near the Dist Board as the voltage drop could adversely affect your unit's performance!
If you're running 2.5mm cable, then a 16a MCB will adequate. Non-inverters (fixed-speed) would need a C-type, but if this is an inverter, a standard B-type should do the trick!

Hope this helps!

Richie (aka Daddymac):D

[frank]

The primary job of the fuse is to protect the cable, it offers no real protection to the unit!
For myself, I'd avoid 1.5mm cable for this job unless you're right near the Dist Board as the voltage drop could adversely affect your unit's performance!
If you're running 2.5mm cable, then a 16a MCB will adequate. Non-inverters (fixed-speed) would need a C-type, but if this is an inverter, a standard B-type should do the trick!

Hope this helps!

Richie (aka Daddymac):D

Even a 16A mcb will protect a 1.5mm cable which is rated at 19A.

The RXS25 runs at 4.4A so 1.5mm2 cable will be sufficient :)

[DEVIL]

so, let's talck some math , the unit whe are talking abaut is rated at max 1.46Kw so .... 14600 / 220 = 6.6 Amp ok, next Volt Drop formula per m is like this :

voltdrop over length = length X volt drop X amps

where 1.5 mm2 whorst cable is 28 mV /amp/m resulting from this

11.000 mV (11 V) = 59 m X 28 mv X 6.6 Amp

so a 11 volt drop (0.5% that is recomended by daikin) mens u can have a conductor of 59 m , do u thing he is havin a whire of 59 m ??? highly improbabal , and let's be serios when is it working at that loud

[mswinman]

Sorry! Didn't realize they were inverters so B curve breakers are fine. I'd still use 2.5mm cabling though, 1.5mm cabling is at its upper limit at 16A even though the unit only draws 4 amps you have to consider fault/overload conditions, I've seen a 16a breaker connected to a load drawing 28A! and no trip. 2.5mm cable has an upper limit of 25A. There are other factors to consider such as thermal insulation, If you bury the cable in any insulation you have to derate the whole cable run depending on how much is buried in insulation and of course theres that other unit to consider that may be installed later.Just for the record, voltage drop for 1.5mm is 29mv per amp of load per metre and 2.5 is 18mv per amp of load per metre. Something else springs to mind, if your consumer unit/dist board does not have an RCD, and as you're connecting to an outside unit it should have. You might consider fitting an RCBO, These are the same size as normal MCB's and offer the same O/L protection but also detects earth leakage.
Regards Paul.

[DEVIL]

so , judginh by what u say :

"I'd still use 2.5mm cabling though, 1.5mm cabling is at its upper limit at 16A even though the unit only draws 4 amps you have to consider fault/overload conditions, I've seen a 16a breaker connected to a load drawing 28A! and no trip. 2.5mm cable has an upper limit of 25A.
"
, 2.5mm2 it whuldnt be enought because

"'ve seen a 16a breaker connected to a load drawing 28A! and no trip."

"2.5mm cable has an upper limit of 25A."


and still if that unit whould drain more 16 amps it whould burst in flames, and it whoult make a big short cirrcuit that whoul for shore make it trip, orr make the MCB burst in flames, so 2.5 mm2 whould be too mutch and not a real use

[mswinman]

I'm taking into account the second unit to be fitted later. If it was one unit 1.5mm would be fine, this second unit is only mentioned in the original post. the volt drop calcs were posted whilst I was writing my answer so sorry for the apparent duplication.

[Makeit go Right]

1) Daikin-FTXS25 inverters are suitable for the general power ring main, surely.

Run a separate 15A circuit from the consumer unit/power distribution board if you like but, well, sounds a bit unnecessary.

2) As for a 5kW system in the conservatory, well I would have thought that system should be on its own circuit, probably a 20A type-C MCB (check with the manufacturer). Being a conservatory, one would also have that circuit protected with an RCD (Residual Current Device).

(I’m not a sparkie, though, so don't listen to me, eh.)

[mick2me]

Well I've just returned from Las Vegas/Los Angeles, Family visit, not gambling.

Let me tell you thats the place to be to sell Air!:p
8pm and 108f!:eek:

Anyways thanks for the replies.

The Unit and second unit are mounted externally on the opposite side of the wall from a split load consumer unit. there is no power point anywhere near. Direct feed from MCB's (1 per unit) is the easy option.

Route ... MCB-->2.5mmT&E(3m)-->20a double pole external disconnector switch-->Outside unit-->1.5mm 3core&e(6m)-->Inside unit.

The only issue is what size MCB to run the Daikin only? bearing in mind the close protection of such an animal.

[Brian_UK]

The only issue is what size MCB to run the Daikin only? bearing in mind the close protection of such an animal.May have been asked before - but - (RTFM) what does the installation manual recommend ?

[mick2me]

May have been asked before - but - (RTFM) what does the installation manual recommend ?

It does not say Brian?

[Brian_UK]

It does not say Brian?AH!!? Frank, one for you here:cool:

[frank]

240V single phase 16A :)

[mick2me]

240V single phase 16A :)

Thanks Frank

Exactly what I bought today.

16a Wylex MCB's (B) @ £4.45 each inc vat.

Good old Screwfix.com

http://www.screwfix.com/app/sfd/cat/pro.jsp?id=79276&ts=55741

http://www.screwfix.com/sfd/i/cat/07/p2477607_l.jpg

[frank]

Thanks Frank

Exactly what I bought today.

16a Wylex MCB's (B) @ £4.45 each inc vat.

Good old Screwfix.com

http://www.screwfix.com/app/sfd/cat/pro.jsp?id=79276&ts=55741

http://www.screwfix.com/sfd/i/cat/07/p2477607_l.jpg

Hi Mick

For any motor - inverter driven or not I would recommend a type C breaker.

[mick2me]

Bu**er:(

I am sure they will change them.:D