Improve a bodged garage supply.

[SparkusMaximus]

Hi all,

My mother in law has a gagarage converted into an annex, a lot of bodging has taken place all before I knew them.

Inside the flat conversion we have a 9.5 kw shower on a 32a, a ring on a 32, light circuit on a 6a and a water heater on a 16a,

Now the SWA supplying this is 6mm protected by a 32a mcb on the rcd protected side of the CU.

I said I would sort it out for them as when they have the shower it will trip sometimes as they use a plug in heater.

I want to obviously change the cable, but working out my MD its looking like I need a 16mm this will be a nightmare so can 10mm be justified?

CC of 10mm swa ref method C is only 58a table 3 (three core as I need to transport the earth)

Do I need 16mm or will 10mm sufice.

Thanks guys I really appreciate your help as I want to be able to work things out the BRB way.

 

[Guest 004]

look up cable clacs, there is a thread going

 

[malcolmsanford]

So your thinknig is that you will need a 60amp supply to feed thse 4 circuits .................... I would say that 40 amps would be more than efficient, if you don't think it is then you could get a 50amp, but remember entirely houses run quite happily on just 60amps.

 

[Guest 004]

Just done a quick calc on Amtech, it is coming back at 35mm, that 9.5 Kw is the problem, plus another 13Amp heater

 

[telectrix]

10mm XLPE SWA has a ccc of 81A ref. method C , clipped or buried. will be adequate for your needs, ( ref. AEI Cable Finder , online )

 

[SparkusMaximus]

Well thats what I am thinking logically, but when I do the MD it comes out at about 90a, I know they will not pull that but and a 10mm will be an improvement but, shower will be 41a although its on a 32a mcb which never trips only the the mcb in the house goes for the whole lot.

and I don't think I can put it on a 63 as the ccc is only 58 for a 3 core swa ref c or have I got that wrong?

 

[SparkusMaximus]

Thanks telectric I did see the XLPE thread but thought that value was only burried, didn't realise it was for ref c too.

 

[telectrix]

as i said 10mm XLPE on a 63A be fine.

 

[Guest 004]

Volt drop!!

 

[SparkusMaximus]

TBH I have not done any volt drop calcs yet run will be about 15m

 

[Guest 004]

View attachment Garage Supply.pdf

Print out from Amtech, with 3% VD, you will need a 25mm, for a 50 Amp supply
2% gave a 35mm

Shower has no diversity allowed 41 Amps @ 9.5Kw
and you have a 3 kw heater as well

 

[Guest 004]

so you 80 meters to the DB, and 15m to the shower?

 

[SparkusMaximus]

SWA supplying the annex from the main CU is about 15m.

 

[Guest 004]

ouf, dont know where I got 80 metres from, BRB with a calc for 15m

 

[Guest 004]

10mm for 15 m

 

[SparkusMaximus]

lol, I wonderd what I had said to give the 80m, yes I would like to go 10mm 3 core for 15m on a 63a but was thinking I might need a 80a with a 16mm.

 

[malcolmsanford]

Hi all,

My mother in law has a gagarage converted into an annex, a lot of bodging has taken place all before I knew them.

Inside the flat conversion we have a 9.5 kw shower on a 32a, a ring on a 32, light circuit on a 6a and a water heater on a 16a,

Now the SWA supplying this is 6mm protected by a 32a mcb on the rcd protected side of the CU.

I said I would sort it out for them as when they have the shower it will trip sometimes as they use a plug in heater.

I want to obviously change the cable, but working out my MD its looking like I need a 16mm this will be a nightmare so can 10mm be justified?

CC of 10mm swa ref method C is only 58a table 3 (three core as I need to transport the earth)

Do I need 16mm or will 10mm sufice.

Thanks guys I really appreciate your help as I want to be able to work things out the BRB way.

Should we not be addressing other things in this post ie why we have an inductive load of nearly 42amps on a 32amp MCB. That should be addressed first off. So unless that is wired in a 10mm^ cable he may find that fitting the correct protection device for the load be another issue to deal with.

As it is 4 circuits two inductive the shower and the water heater..............and the other 2 sockets and lamps. If we think logically here the shower may very well be on with the water heater and they may very well plug in a heater while both of these are on, which would be the worse case scenario, but let's use a little diversity here and say the shower maximum 45 mins a day, the water heater will be on thermostat if not a timer, and the heater ...well any ones guess.

So what size protection device would we choose for this .................

 

[Guest 004]

No diversity allowed for showers!

 

[SparkusMaximus]

Should we not be addressing other things in this post ie why we have an inductive load of nearly 42amps on a 32amp MCB. That should be addressed first off. So unless that is wired in a 10mm^ cable he may find that fitting the correct protection device for the load be another issue to deal with.

not sure if I understand what your getting at but I have stated its bodged, and I said I would rectify it, I am asking if 10mm would be suitable or do I need to go bigger. There are numerous bodges, but this one is the one I can't work out the size of cable needed, as I work it out to need a 16mm but I am hopping that I have done something wrong and can get away with 10mm.

 

[malcolmsanford]

No diversity allowed for showers!

Not for inductive loads like showers or water heaters as a final circuit, but when we are doing an installation like this with other types of circuits then I would take diversity into account ................otherwise most modern homes would be having 150+amps supplies to them all.

 

[SparkusMaximus]

and this is why MD is such a mystery to me, on one hand its a science on the other its all a bit wooo and a bit waaay.

 

[malcolmsanford]

not sure if I understand what your getting at but I have stated its bodged, and I said I would rectify it, I am asking if 10mm would be suitable or do I need to go bigger. There are numerous bodges, but this one is the one I can't work out the size of cable needed, as I work it out to need a 16mm but I am hopping that I have done something wrong and can get away with 10mm.

You have a load on that shower of nearly 42amps, but have a protection device of 32 amps, As an MCB will run at 1.45 times it's rated value for a short period of time, an hour is the norm then it will not trip, what it is doing though is everytime you take that shower your asking that MCB to perform at it's over rated load, and therefore subjecting it to at the very least a shorter life, at it's worse overheating and a chance it will burn out and cause damage.

 

[SparkusMaximus]

And thats why I said I would sort it out, although I am starting to wish I didn't. I think I am just going to go with a 63a on 10mm XLPE clipped direct, can anybody see that as not a good idea.

Is there a CCC page for XLPE in the BRB I can't fathom if there is.

 

[Guest 004]

50 Amp MCB fromthe DB
40 Amp for the shower
16 Amp for the sockets
16 Amp for the heater
6 Amp for the lighting

will be fine

 

[Guest 004]

View attachment Garage Supply.pdf
Done all the calcs for you now, hope you can understand it

 

[SparkusMaximus]

50 Amp MCB fromthe DB .
40 Amp for the shower,
16 Amp for the sockets
16 Amp for the heater,
6 Amp for the lighting,

will be fine

Agree with that apart from the fusing down the ring to a 16a as if I go 63a from the DB I don't need to.

 

[Guest 004]

What is the main switch size at the DB 100 or 63?, and more importantly what have the DNO supplied at the head?

 

[SparkusMaximus]

main cut out 100, 63 main switch, however if I go for 63a I Will put in 1 way board more than likely, but didn't think about that I don't think I can put a 63mcb in with a 63 main fuse can I.

Thanks very much MrEnigma for you help here, much appreciated.

 

[Guest 004]

main cut out 100, 63 main switch, however if I go for 63a I Will put in 1 way board more than likely, but didn't think about that I don't think I can put a 63mcb in with a 63 main fuse can I.

Thanks very much MrEnigma for you help here, much appreciated.

no probs, just pm me your details, so I can forward the invoice for the consultancy

 

[malcolmsanford]

What is the main switch size at the DB 100 or 63?, and more importantly what have the DNO supplied at the head?

100 I would imagine as not many 63 amp main switches made .

main cut out 100, 63 main switch, however if I go for 63a I Will put in 1 way board more than likely, but didn't think about that I don't think I can put a 63mcb in with a 63 main fuse can I.

Thanks very much MrEnigma for you help here, much appreciated.

So you have a 100 amp main fuse ..................63 amp main switch ??/..........................you want to fit a 63amp MCB...................with a 63 amp fuse ..................think we have covered every kind of protection device here now .....any MCCB here.

Sit down son and tell us exactly what you have got.

 

[SparkusMaximus]

cut out 100a, main switch in CU 100a, but was thinking of putting in a little 1 way garage supply, However I think I will jsut keep it in the mian C/U.

 

[andyb]

Not for inductive loads like showers or water heaters as a final circuit, but when we are doing an installation like this with other types of circuits then I would take diversity into account ................otherwise most modern homes would be having 150+amps supplies to them all.

Malcolm, I think you must be getting too much sun in Saudi Arabia.

Showers & water heaters are resistive loads.

 

[malcolmsanford]

Malcolm, I think you must be getting too much sun in Saudi Arabia.

Showers & water heaters are resistive loads.

quite right I have inductive on the brain ................... unless the shower as a big motor pump in it ...........teach me to be working on motor design and skiving off on here

 

[malcolmsanford]

cut out 100a, main switch in CU 100a, but was thinking of putting in a little 1 way garage supply, However I think I will jsut keep it in the mian C/U.

To be honest if I don't like putting 50amp or 63amp MCB into a domestic board, IMO it is loading them up.

I would personally henly block the tails from the meter to the CU and fit a 60 amp switch fuse and if you wanted to you could fit a smaller fuse. Then run your 10mm^ SWA into a small garage CU with a 63amp 30mA RCD protecting the circuits there.