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https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Electrical Questions >> DB https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1089194736 Message started by jaja on Jul 7^th, 2004, 11:05am

Title: DB
Post by jaja on Jul 7^th, 2004, 11:05am

I need to install a new 4 way sub board for a 6KW electric heating system in my flat, the board will consist of 1 x 32 amp mcb- bolier 1 x 16amp mcb- imersion 1 x 5amp- clock, complete system running at 45-50 amps. Im going to install a 10mm T+E supply cable, Is this big enough. And can wire the supply cable direct off of the henly block at mains or should i wire it from consummer unit with a 45 amp mcb for protection. Do i need to install an isolator inbetween the mains and sub DB. Also do you think theres a chance of over loading the mains by doing this ,considering that i have an 80 amp supply to the flat, with 1 x 32 amp cooker, 1 x ring -kitchen 1x 32amp- ring main 1 x 5 amp-lighting. Any adice would be appreciated!

Title: Re: DB
Post by plugwash on Jul 7^th, 2004, 3:22pm

45A seems a bit on the light side

i would use a 50A mcb in the existing CU with 16mm twin and earth

Title: Re: DB
Post by jaja on Jul 7^th, 2004, 4:01pm

The reason i chose a 45 amp mcb is because The existing CU is an old wylex rewirable, and i think the max MCB i can get for it is 45 amp (mini trip) without replacing the CU . So you dont think that a 10mm isn't sufficient enough to handle the load?

And coming straight off of the henly block and into an islolator and then into the Sub DB is out of the question?

Title: Re: DB
Post by plugwash on Jul 7^th, 2004, 4:46pm

10mm on 45A sounds ok it dpends on exactly how much each appliance draws

also if your wylex board only has a 63A main switch then you should not fit any breakers above 32A

you can henly into the tails and i will post the procedure below but the new board should be close to the henlys and should be wired in with 25mm tails

Title: Re: DB
Post by plugwash on Jul 7^th, 2004, 4:48pm

adding a shower CU is not rocket science but you must work carefully and make the connections well

remember bad connections on a 50A cuircuit can be bad enough and this is 100A wiring so take care

this is a shower CU
http://www.screwfix.com/app/sfd/cat/pro.jsp?ts=05435&id=69659

(you can change the mcb to a 40A if suitable)

you will need to henly block it into the tails this is done as follows
fit a double pole henly block to the fuseboard
http://www.screwfix.com/app/sfd/cat/pro.jsp?ts=05950&id=14850

turn off the main switches on both the existing CU and the new CU

PULL THE SERVICE FUSE (TAKE CARE SOME OLDER SERVICE FUSE UNITS LEAVE AN EXPOSED LIVE WHEN YOU PULL THE FUSE)
remove the tails from the meter to the existing cu
use fresh 25mm red and black double insulated tails to rewire the cu's

connect meter to henly block
conenct henly block to main cu
connect henly block to shower cu

conenct the earth from the new CU to your main earth terminal
http://tlc-direct.co.uk/Products/TLEB8.html

useing 16mm earth cable if you do not have one install it between the main earth and the CU useing 16mm cable from the main eart to the main earth terminal and from the main earth terminal to the cu and move main equipotential bonds to it

put the service fuse back
turn back on main switches

Title: Re: DB
Post by L.Spark on Jul 7^th, 2004, 5:00pm

jaja, I strongly recomend getting some advice on this from an electrician if you are not electricaly minded, it is not a minor job, you will need to properly assess maximum demand of each of them circuits, also having BS 3036 semi enclosed fuses will create problems.

I am presuming you have to have these electricaly heated system, electrical heating systems are very expensive to run, and waste alot of electricity, but if gas central heating system is not an option then ok.

If you can properly assess all that is needed then there is no problem, but I cannot recomended doing this yourself.

Title: Re: DB
Post by Lectrician on Jul 7^th, 2004, 7:27pm

umm, 40amp supply and DIY=burnt out connection in no time :-(

I would use a 50amp breaker in a new one way board from the henly (or fit a new board), and then 16mm split concentric (yes you lot, i know!) to a new board adjacent to the heating system.

What is the 6kW heating, one of those electric boilers?? Ummm......go for LPG or Oil mate, lectric is sooo expensive as heating :-)

Title: Re: DB
Post by HandyMac on Jul 7^th, 2004, 7:38pm

wrote on Jul 7^th, 2004, 5:00pm:

Can I reinforce what's being said here?

I was a pretty competent DIYer before last year, a qualified and experienced electronics engineer and all that, so what could some simple electrickery teach me? Hell, I knew red was live and black was neutral, and the funny green and yellow wire was earth - it don't get any more complicated than that does it? I thought I would get a tick in the box by acquiring my 2381 certificate (which I have). Hell, I was unemployed at the time and this was a tyre-kicking exercise that seemed like a good idea.

The one thing 2381 taught me above all else is that I'm not the dogs reproductive assets I thought I was. Previously I'd have been up for a full rewire and so on, but 2381 taught me no way, best left to the professionals. I really had no idea what TT, diversity and other terms meant for example.

These days, even though I could do many of the jobs myself and have done in the past, I'm very happy to pass on work to others who have been at the sharp end long enough to know how to do things properly. I'll do the occasional change of a broken 13A socket, install a loft light and replace a light fitting, but aside from that I consider it out of my domain.

Andrew

Title: Re: DB
Post by L.Spark on Jul 7^th, 2004, 8:50pm

And id like to use that as a perfect example of Responsibility, it would not be responsible to carry out such works without due knowledge, and it's totally irresponsible to try and advise to do such things too.
There are some tasks which are minimal and present very low risk, this is not one of them!

Title: Re: DB
Post by HandyMac on Jul 7^th, 2004, 10:01pm

wrote on Jul 7^th, 2004, 4:48pm:

adding a shower CU is not rocket science but you must work carefully and make the connections well

Sorry about my blatant honesty which is known to take no friends, but I do feel this is out of the league of a DIYer because the end result could be a limp expired body lying on the shower floor.

This ain't a job I would take on - even in my own home, even though I believe I am more than competent to do the job.

Water and electricity don't mix, and especially if there is a moist body in the vicinity. I wouldn't want that moist body to be one of my family, or that of someone I know (Tony Bliar excepted).

So you do this super-duper wiring job. Great, wonderful, excellent news! Now what are you going to test it with to make sure it's safe? Everything is earthed right? Everything bonded equipotentially? The fault current is definitely gonna trip that connection if there's any stray current isn't it? Your RCD's are actually working within specification aren't they? You do have the 16th edition testing kit to hand and know how to use it?

There are too many variables in this situation for my liking.

Andrew

Title: Re: DB
Post by big_all on Jul 7^th, 2004, 10:49pm

andrew you have my complete respect
you realised your shortfall and admitted it
it takes a brave man to admit any shortfall
and you have taught us all a good lesson there

Title: Re: DB
Post by HandyMac on Jul 8^th, 2004, 5:57am

Apologies, I discovered that soapbox mode got inadvertently switched on...... ;)

Andrew

Title: Re: DB
Post by Beanzy on Jul 12^th, 2004, 2:25am

Now then andrew we've caught you out here!

"Apologies, I discovered that soapbox mode got inadvertently switched on..."

Who wired the SoapBox?, was it a DIY job or did you get a pro in to do it? I hope it's got the correct IP (Indexfinger Pointing) rating and a RCD (Rant Ceaselessly Detector) if you're going to take it outside the main equipotential zone.

;)

Good advice BTW.