possibly stupid qustion(s)

[stringman]

Hi
I have been asked to look at some electical issues in my new partners house ( more investigate than cure!!)

first one- bedroom

there seems to be only 2 double sockets in the master bedroom- neither in a usual place. So one socket has a 4way going to the other part of the room, it also has a plug but with flat twin and earth which i presume runs to another socket.
so this leads to 2 questions:

1) why run twin and earth to a socket - would it not be safer to run a 4way extention?

2) could I run a spur of this socket? I seem to remember (years ago) that you could run a spur (single socket?) of a double socket is this still the case ? if so is it per socket on a ring or just one spur per ring?

Next scenario

in the airing cupboard there is powerr to the hot water tank and there is also power ( dropping down from the loft in twin and earth cable 32a rated) to power the power shower unit.

she has asked if there is a way to get power into the loft so that we can put the old clunky pc in the loft as a media server and possibly run a small stereo (seperate issue regarding speakers in the bathroom)

without any investigation ( so please dont flame me) could i tap off fromthe hot water tank power supply? ( dont think i can)
or could i do it fromthe power shower feed? (dont know why but i get the feeling this is on a separate "ring" so may be able to cope with a socket that pulls no more than 4a

.
sorry its loads of questions

 

[Iggifer]

First question:

I don't really know you mean. There's a 4 way extension lead:

with t+e connected to it which then connects to a plug?

if that's the case, t+e isn't designed for 'flexible' applications, it's designed for fixed wiring, as the cores are solid. You're better off replacing this with some 1.5mm flex, such as this

Second Question:

It's impossible for anyone to know the answer to this question without more information; actual cable size, breaker rating, rating of shower / immersion heater

The answer is more than likely a no anyway. You're better off spurring from the upstairs ring socket to the loft. I did this myself recently and took me maybe an hour from start to finish, including chasing out the wall, running the cable and re-plastering (roughly) over the chase.

The other option is to run the cable up to the loft in conduit / trunking, which is easier than chasing and makes removing the cable much easier, but leaves a protrusion.

 

[ban-all-sheds]

1) why run twin and earth to a socket - would it not be safer to run a 4way extention?

It would. Not because of electrical loading - everything is supplied by a plug, and so is limited to 13A, but because twin and earth is not meant to go into a plug. There is no way to clamp it properly and it's not meant to be moved around like flex is.

Seeing that sort of bodge would ring huge alarm bells for me - if the electrics have been fiddled with by someone that incompetent who knows what else they might have done that you can't see?

2) could I run a spur of this socket?

Which one?

The one with the 4-way and the plug-with-twin&earth-in?

In general, yes, as long as it itself is not a spur, but in this case I would advise against it until you know where that twin&earth in the plug goes because you might be at risk of overloading the ring at that point.

I seem to remember (years ago) that you could run a spur (single socket?) of a double socket is this still the case ? if so is it per socket on a ring or just one spur per ring?

One per socket, but remember that the whole existence of a ring final, which is essentially a circuit wired with cable which is too small, is predicated on not having any segment of the ring exposed to long overloads. So sockets which are empty most of the time, and used occasionally for portable appliances are one thing - once you get into permanently connected loads you need to exercise more care.

twin and earth cable 32a rated

Not really any such thing - cable ratings depend on how they are installed:

http://www.tlc-direct.co.uk/Book/4.3.2.htm

without any investigation ( so please dont flame me) could i tap off fromthe hot water tank power supply? ( dont think i can)

Personally I don't regard that as a cardinal sin, provided the circuit can cope with it. Is it on a dedicated circuit? What rating is the MCB? What size is the cable? Is the circuit on an RCD?

or could i do it fromthe power shower feed?

Far less likely.

(dont know why but i get the feeling this is on a separate "ring" so may be able to cope with a socket that pulls no more than 4a

The circuit won't be on a ring, and it may have no spare capacity.

sorry its loads of questions

Here are loads of answers, including loads to questions you've not asked yet

• http://www.google.co.uk/search?q=electrical+circuits+101
  
  
• http://kevinboone.net/electricity.html
  
  
• http://web.archive.org/web/20080213151445/http://www.kevinboone.com/domesticinstallations.html
  
  
• //www.diynot.com/wiki/electrics:books
  
  
• //www.diynot.com/wiki/electrics
  
  

 

[ericmark]

There are two places where a automatic disconnection device can be fitted on a circuit. At the origin or at the destination if within 3 meters of the origin and the cable is unlikely to be damaged.

The ring is two cables in parallel so all sockets on the ring are protected at the origin with a 30A/32A Fuse/MCB which will automatic disconnect should there be an over load.

From the ring we can take a spur to a single device where there is an automatic disconnection device (fuse) built in. i.e. fuse in the plug. In theroy the cable should be limited to 3 meters although I have seen much longer spurs. When a fuse is fitted for example a fused connection unit (FCU) then there is no real limit to how many sockets can be connected to it. In the same was as with extension leads which could have 10 sockets on it.

The problem is working out if the socket you are looking at is directly on the ring or if some time in the past some one has broken the rules and taken an unfused spur from an unfused spur. In both cases there will be two cables so you have to test it.

As well as testing to see if part of a ring you also need to test the loop impedance in real terms using a FCU you are reasonably safe but where directly connected to a 32A MCB then one does have to be careful there is a limit to cable lenght permitted.

Add to this not all houses have rings. Radials both with thicker cable and 32A MCB or with 2.5mm and 20A MCB with the latter extending is easy just test the loop impedance but with the thicker cable very hard to get 3 x 4mm cable in the terminals of the socket so hard to extend.

The regulations say over 2kW fixed appliances should have a dedicated supply. So you should not tap onto either shower or immersion heater circuit. But in real terms most immersion heaters use 13A and have a 16A MCB so tapping of that circuit no great crime. But with the power used by a shower you should not tap into that.

Any new sockets should be RCD protected and if you don't have a RCD at the consumer unit then to comply easy way is to use RCD FCU then power all new sockets from that.

I have seen some real dangerous wiring. And it is always the last person to work on it who is blamed. If you think there may be faults which only an electrician using his meter will find you may be better not touching it. You should use the loop impedance meter and insulation tester etc. And we all know you will not. If the installation is sound to start with then likely no problem. But if not sound to start with you could be held libel because you failed to test for something you did not do.

As to PC in the loft I don't like the idea of something not designed to run unattended to run in that way. You will need to take fire precautions.

 

[viewer]

Not part of your question or an answer, but relevant.
Does she own the house? If rented/ joint owned/etc you could be in an awkward position if you carry out work not agreed by all owners.

 

[stringman]

1) why run twin and earth to a socket - would it not be safer to run a 4way extention?

It would. Not because of electrical loading - everything is supplied by a plug, and so is limited to 13A, but because twin and earth is not meant to go into a plug. There is no way to clamp it properly and it's not meant to be moved around like flex is.

this is what i was thinking, I can easily change the cable so that it is the correct cable
Seeing that sort of bodge would ring huge alarm bells for me - if the electrics have been fiddled with by someone that incompetent who knows what else they might have done that you can't see?

I have since found out that my partners ex did this "extention" and was too tight to buy the correct cable. he has done nothing else with the electics in the house

2) could I run a spur of this socket?

Which one?

The one with the 4-way and the plug-with-twin&earth-in?

In general, yes, as long as it itself is not a spur, but in this case I would advise against it until you know where that twin&earth in the plug goes because you might be at risk of overloading the ring at that point.

the twin and earth extention runs to a cupboard that has a pc in it ( which is never used so will soon be stripped out

I seem to remember (years ago) that you could run a spur (single socket?) of a double socket is this still the case ? if so is it per socket on a ring or just one spur per ring?

One per socket, but remember that the whole existence of a ring final, which is essentially a circuit wired with cable which is too small, is predicated on not having any segment of the ring exposed to long overloads. So sockets which are empty most of the time, and used occasionally for portable appliances are one thing - once you get into permanently connected loads you need to exercise more care.

Ok That makes sense, I am not to worried about the loading as its in the bedroom and the 4way thats been run ( not the twin and earth) powers a bedside lamp, alarm clock, cordlesss phone and occasional hairdryer.

with the spur can it only be a single socket or can it be a double socket?

twin and earth cable 32a rated

Not really any such thing - cable ratings depend on how they are installed:

http://www.tlc-direct.co.uk/Book/4.3.2.htm

without any investigation ( so please dont flame me) could i tap off fromthe hot water tank power supply? ( dont think i can)

Personally I don't regard that as a cardinal sin, provided the circuit can cope with it. Is it on a dedicated circuit? What rating is the MCB? What

from what i can see there are breakers for lights up and lights down, cooker and ring so i think that hot water tank is on the main ring
and the switch is wall mounted with no signs of cables so i think i will give up on that idea

or could i do it fromthe power shower feed?

Far less likely.

(dont know why but i get the feeling this is on a separate "ring" so may be able to cope with a socket that pulls no more than 4a

The circuit won't be on a ring, and it may have no spare capacity.

The power to the shower pump comes from a seperate breaker unit which has been installed next to the main breaker- this is rated at 40a. so i was still hoping i could "tap" off this with a rcd double socket which would power a PC and a light in the loft. I appreciate i need to find the rating for the pump first.

sorry its loads of questions

Here are loads of answers, including loads to questions you've not asked yet

• http://www.google.co.uk/search?q=electrical+circuits+101
  
  
• http://kevinboone.net/electricity.html
  
  
• http://web.archive.org/web/20080213151445/http://www.kevinboone.com/domesticinstallations.html
  
  
• //www.diynot.com/wiki/electrics:books
  
  
• //www.diynot.com/wiki/electrics
  
  

 

[JohnW2]

From the ring we can take a spur to a single device where there is an automatic disconnection device (fuse) built in. i.e. fuse in the plug. In theroy the cable should be limited to 3 meters although I have seen much longer spurs.

I'm not so sure about that. I think that 433.1.103 (and Appendix 15) of the regs allow unfused spurs without the usual 3 metre limit when there is a downstream OPD. Neither 433.1.103 mention any length restriction and, indeed, FWIW the OSG suggests a rule of thumb of limiting the length of unfused spurs to one-eighth of the distance from the spur to the furthest point of the ring (which could be more than 3 metres in some situations).

Add to this not all houses have rings. Radials both with thicker cable and 32A MCB or with 2.5mm and 20A MCB with the latter extending is easy just test the loop impedance but with the thicker cable very hard to get 3 x 4mm cable in the terminals of the socket so hard to extend.

True, but if one extended the end of a 4mm² radial circuit, one would only need 2 x 4mm² cables. Also,of course, one can add 2.5mm² unfused spurs to a 4mm² radial circuit (per Appendix 15).

... and a very happy, heathy and prosperous 2013 to all!

Kind Regards, John

 

[stringman]

I have had a look at the shower pump.
it is an aquilisa quartz a2
on the panel it says 250w /240v which is about 1 amp isnt it.

http://www.aqualisa.co.uk/upload/INSTALLATION GUIDES/Install_QtzDigExp_adj.pdf

the feed is from its own 40a breaker so i am thinking that i could put a couple of sockets on that feed?

 

[Simon35]

I have had a look at the shower pump.
it is an aquilisa quartz a2
on the panel it says 250w /240v which is about 1 amp isnt it.

http://www.aqualisa.co.uk/upload/INSTALLATION GUIDES/Install_QtzDigExp_adj.pdf

the feed is from its own 40a breaker so i am thinking that i could put a couple of sockets on that feed?

What size is the cable to this shower controller? If its 2.5mm T+E that breaker is too big.