Wow, can't believe this thread is still going strong.
Just to update you all, I'm still no further on. I've tried my hardest to give as much detail of my installation as I possibly can. Had a friend come round tonight to inspect my lighting work so far. He's experienced with electrics and he said my lighting spurs are correct, even though I already knew. The fact he's Bulgarian, he seemed rather surprised at how the cables were running vertically and horizontally, instead of diagonally!! Regarding the sockets (on a separate cicuit obviously), he suggested that I use 4mm cable to wire them instead of 2.5mm incase we have oil radiators on in the winter which makes sense, but I'm still not sure whether to do this or to keep the spurs at 2.5 in keeping with the rest of the sockets on the circuit so its consistency is maintained.
I took the fuse board cover off and noticed the beginning of the circuit starts with 4mm cable and then appears to spur off to a couple of sockets via a junction box using 2.5. As I say, i wanted to spur off one of the sockets, but even now i don't know whether the cable sizes can be changed like that. I just wish I didn't have OCD about the whole thing, I'm getting nowhere fast. I suppose it's only to make me cautious and make me sure of what i can and can't do but i must say, i never thought adding a couple of sockets to an existing electrical circuit could be so damn complicated . Is there really noone who can help me? I don't need people to tell me how to do this, I just need to know where I'm going wrong.
Joined: Nov 20, 2007 Posts: 1177 Location: Vinarsko, BG
Posted: Wed Aug 08, 2012 7:21 am Post subject:
If you do not know how to calculate the total load in the circuit or the size of cable to use, then on your own head be it. Your information regarding the circuit you have in place uses the words 'appears to'. Giving you any information that is not based on the full facts regarding your circuit, could be quite dangerous.
It would appear that your problem is in fact quite simple, but given your lack of knowledge it could be quite a different problem to the one you stated. Your friend has seen the installation, but for some reason you do not trust his opinion. So why would you expect someone who has not seen or tested your circuit to supply information?
To answer your specific question, you are going wrong because you do not have enough basic knowledge to be able to use any of the answers. I am sorry if that sounds a bit blunt, but your life could depend on getting the correct installation.
seathrift thanks for your reply. I understand what you're saying. I agree I have very basic knowledge at the moment but I feel I just need a little bit more to be able to tackle this job successfully and safely. At the end of the day it is a simple job, but I'm only losing confidence because of some of the comments I'm reading, not to mention confused because there are people saying you don't need to be a qualified electrician etc and people saying I do in order to add some sockets to a circuit. I have 3 weeks left to carry out this work until my family return so in that time, I'm hoping to gain as much knowledge as possible. If I really thought I couldn't do this, I would get someone to help me, but I know everyone who knows me would say: You got an electrician in just to add some sockets to your installation?? Couple of years back, I asked my local electrician to come in and change some light switches for me because at the time I was TOTALLY clueless on electrics and he didn't feel it was worth the time and money so he called my friend who isn't an electrician to come and do it instead of him!!
OK, maybe it's best to start from scratch. Lets start from the main consumer unit. I have a 25A MCB and the circuit cable going from that is 4mm. Now I have to check all the sockets yet again to confirm they are also wired in 4mm as you would assume they would be. I still believe they are 2.5mm but until i check again i won't be 100% sure. Not going to be easy to check either. Only way is to hold some scrap cable to it and compare.
Is this a good starting point? Am I on the right track?
BTW, I do know how to calculate the total load but I'll mention more on that later. Basically for now, lets say a circuit wired in 2.5mm cable rated at say, to be on the safe side, lets assume rated at 18.5A instead of 20A. That's 4255W in total to play with for all of the appliances on the circuit. The total load for all the appliances on the circuit must not exceed the total load rating of the cable. To protect the cable we use a 20A MCB which trips when excessive current is being drawn from too many appliances on the circuit. If it trips, you must not change the MCB on the 2.5mm circuit to a higher rated one such as 32A as it won't offer any protection to the cable, ok maybe after the house has burned down it will begin to operate .
My friend by the way I don't trust him a lot because once i asked him to wire up my cooker and he didn't have a clue and ended up doing it myself lol.
The MCB in the board is to protect the cable. If the cable is rated at 18 amp it must be protected by a MCB smaller than 18 amp (ie 15 amp). Although the sizing of the cable should take into account the length of cable run, ambient temperature etc.
A 4mm cable should be sufficient for a 25 amp MCB as long as the cable run (from board to furthest point) is not to excessive.
All cables in a circuit need to be protected by the correct size MCB to prevent any over loading of the cable in a circuit. The size of MCB to protect the circuit will be determined by the smallest cable in that particular circuit.
Its all very entertaining but for the hazard of electricity, firstly wire diameter is not the be all and end all when taking into account allowable current through the wire of we expect to be with sufficient copper, also quoting the above post what really is excessive? Once the fire occurs?
And ambient Temp in Bg! Whats the temperture during the summer months, it aint Britain...
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