New Wiring

[aidan1979]

Hi All

My sister asked me to change one of her double light switches to a double dimmer switch. Her house is a new build which she bought off-plan, was completed about 18 months ago and had the electrics signed off by a qualified electrician that worked for the construction company.

I thought it would be relatively straightforward but when I took her light switch off the wall i noticed the following:

1. There were 4 different wires coming into the box even though the switch only controls 3 lights (1 in the centre of the room and two wall lights).

2. All of the neutrals went into a separate plastic block (like the ones used to join wires - not a JB) and all the lives went into the switch itself. None of the neutrals went into the switch.

3. The metal box was not earthed (i.e. mains earth wire went straight into the earth connection in the light switch).

4. One of the neutral wires had a little damage to the blue insulation which had not been covered with insulating tape).

I had no idea what to do with it and thought it looked quite dodgy so I told my sister to speak to the construction company and get someone in to look at it. She did and they sent an electrician round. Unfortunately my sister lives a couple of hours from me so I couldnt be there but he said that they had correctly signed off on the electrics as it was all fine:

1. He didn't give a reason for the four wires.

2. He said that the neutrals did not have to go into the switch as this was a not so normal but perfectly fine and within electrical regulations way of wiring the lights.

3. He said that the metal box was earthed by a screw into the wall.

4. He didn't address the damaged insulation on the neutral (albeit that it is very small).

Can you guys please advise as to whether you think you've seen this kind of wiring before as I am still not convinced that the electrics should have been signed off.

Thanks a lot!!!

Aidan

 

[Adam_151]

1. He didn't give a reason for the four wires.

Either one in, one out to the next room, one to the ceiling lights and one to the wall lights, or its the one at the end of the line and one in, one to ceiling light and one to each wall light

2. He said that the neutrals did not have to go into the switch as this was a not so normal but perfectly fine and within electrical regulations way of wiring the lights.

Thats correct, you don't switch neutrals unless its a double pole switch

3. He said that the metal box was earthed by a screw into the wall.

The earth in the cable is attached to the switch front, right?...acceptable as long as at least one lug of the metal pattress is fixed and non-adjustable, however many people would fit a link across

4. He didn't address the damaged insulation on the neutral (albeit that it is very small).

If it is truely damaged then most people would do something with blue tape or heatshrink, are you sure its not just lost a very tiny bit of the outside, and makes it look white on some cables? or can you see bare copper

Can you guys please advise as to whether you think you've seen this kind of wiring before as I am still not convinced that the electrics should have been signed off.

Looping through the switch is perfectly acceptable and in compliance with BS7671, however some people would argue that the neutral block should be secured in some way, it makes it easier for you to fit new ceiling lights that might have very little room for terminations in comparison to 3 plate at the ceiling. Some older electricians however dislike the practice of neutrals at switch positions, that is just a personal perference however.

 

[aidan1979]

Thanks a lot Adam. That will put all our minds at rest. BTW is there anywhere online that will show a diagram of this type of wiring for my info?

On the neutral you can see copper but its only a couple of mm. I'll put some tape on it for her when i'm netx down.

 

[luminaire]

Hi Aidan
There are basically two ways of wiring found on light circuits today.
One is using the ceiling rose as a junction box and is the one that most people are more familiar with. This means there are no neutrals at the switch. Black cables are in fact switch cables and should be sleeved red or brown.
The other method is to bring the live and neutral direct to the first switch, keeping the neutrals separate using a connector block, then continuing to the next switch and so on.
Some electricians fit an earth cable within the box, but strickly speaking it is not necessary to do so. However, I do as it happens because then it is there if you want to replace your switch with a chrome one for example.

If there was a nick in the cable and you could see the copper then he should have taped it over.

Incidently if you are switching over to dimmers you may need to fit a 25mm box rather than the standard 16mm box used for light switches.

 

[Adam_151]

BTW is there anywhere online that will show a diagram of this type of wiring for my info?

//wiki.diynot.com/_detail/elec...rics:lighting:single_way_lighting&cache=cache

-From the diynot wiki at //wiki.diynot.com.