Board questions!

[rob121]

Evening all!
Just completed one job for my DIS scheme. Planning on changing my nans CU for the other. Went to have a look the other day, not as bad as what I thought! No bonding in place and earthing conductor too small but gas and water right next to meter so all easy fixes. The board itself is the old wylex rewireable fuses, little bit concerned that it only has 4 ways for a 3 bed semi. One supplies garage (30A). One lighting circuit (5A). Two power circuits (Both 15A). I havent taken the unit cover off yet, but I can see it has one 6mm T+E , which I assume is garage supply. 3 2.5mm T+E, guessing either 1 ring, 1 radial or 2 rings (other cable perhaps runs behind unit?) and 2 1mm T+E for lights.
Supply is TN-S.
Look like 16mm Tails. Cut out fuse isnt labelled and is actually damaged, top casing is missing about 30mm round plastic, quite easily stick my thumb in and touch the brass inside, so will be informing DNO first thing tomorrow, need to fit an isolator and upgarde tails anyway so hopefully that will make them come out faster!
So heres the plan!
New board 8 way board for any future re-wire. Going to have a look at breaking the lighting circuit into 2. Its been wired as a ring so hoping I can remove the cable that joins upstairs to down and put them on 2 radials. Im not sure about the ring(s) yet, if it is 2 rings wired in 2.5mm T+E, is it worth sticking them on 32A or out them on 16A's? I cant understand why theyre on 15's atm which makes me a little suspicious! The garage unit im going to replace at the same time as its a similar board but its missing half the side of it so needs replacing. Its fed via 6mm clipped direct then runs over head. Wasnt sure whether to install a 2 way with RCD in garage or put it on one of the RCD's in the house? Im going round there first thing tomorrow to do Ze test and some quick IR tests as its not currently got any RCD protection.
Also last point, noticed 2 or three old wylex switches in her house, ones and isolator for garage, anothers for outside light, they look pre-historic, green metal with black plastic for the switch. Are they acceptable as long as theyre earthed or do they need replacing?
Any suggestions/help much appreciated as always!

Cheers,

Rob

 

[SimpleSimon]

Sounds like you've got your head screwed on Rob. Remember this work is notifiable.
Can't say much without seeing it, but think about a typical set up of a house such as your nans. You could have this

X3 32a (two rings and kitchen or cooker)
x2 6a (lights)
X1 15a (immersion, surprised thats not there)
X2 40a (shower and possibly cooker)

So just think if your Nans got this kind of setup and work out using diversity if the circuits can take the load.

When you say 6mm overhead fir the garage, is that outside? If so if it's t+e it's needs some protection over it such as conduit.

If the garage supply is in the wall at less than 50mm without mechanical protection than the RCD has got to be in the supply board rather than the dis. Board. If surface mounted and not outside than I'd put the RCD in the dis. Board.

 

[telectrix]

you may find the sockets are radials if so 16A or 20A MCBs. i very much doubt the lights will be a ring, but you can still split by installing a new feed to upstairs. make sure the lighting circuit/s have cpc's though. 1 problem you may find is that the L feed for the landing light is fed from the ground floor hall 2 way switch. if you split the lights you may end up with the dreaded "borrowed neutral"

 

[rob121]

Cheers for the replies Lads (or ladies, never know!)
Been to have a look today, didnt have long so will have to go back again, anyway good news is Ze is fine and dandy. Now for the bad points (you best put the kettle on):
1) Fuse for lights supplies 3 cables, all of which have silver conductors, look like tin maybe? could anyone enlighten me? Its inside a white sheathed cable, and includes a CPC.
2) IR tests werent less than pleasing. Tested at 250v, earth-neutral came back at 2.6mOhms, same for line-earth. Line-Neutral came back at 0! So disconnected each circuit individually and found the fault to be on the socket circuits. So immediately thought it would be something left plugged in, spent about an hour searching high and low for anything left plugged in, no LUCK. What concerns me is the N-E value. Will 2.6mOhms be enough to stop the RCD tripping? It must be something plugged in somewhere, perhaps behind a unit as L-N value of 0Ohms would blow the fuse is it was cable damage surely? The only thing I did see was the thermistat for the boiler, which I couldnt find a FCU for so perhaps its been spurred direct of the ring?
3) Went into her bathroom and found a socket in zone 1 above the bath! Couldnt believe it. Hoping its been supplied as a spur so I can just disconnect it and patch up, if its part of the ring I think my best bet is channelling down behind the bath (assuming the cables are run UP to the socket) and putting a JB under the bath and then screwing the front on, that way its classsed as outside the zones I believe, even so I would still fit an weatherproof one for peace of mind.

So the main concern is 1) and 2)
Does anyone have any ideas about what the lighting cable could be and whether its safe to put back into service?
And also any ideas about the low IR test results? Will go over saturday and break the ring in half at one of the sockets the IR test each half and then work backwards.

Anyways cheers again for the responses,

Rob

 

[Engineer54]

Well #1 is almost sure to be 3/029'' PVC imperial cable.... No problem putting back into service...

 

[rob121]

Thanks Engineer54, is it tin or something similiar though? I know copper does change colour but I did try scraping the surface but no change.

Rob

 

[telectrix]

probably tinned copper. try a file to get to the copper. your 2.6 Mohm will not trip thre rcd but needs investigating. as does the L/N of 0. that has got to be a load. try measuring with a multimeter. that will give you an idea of what sort of load it is.

 

[rob121]

Okay will try that at the weekend. Would you think the central heating system would be throwing it out if its been fed directly off the ring? Not exactly sure where I can isolate it seen as theres not FCU or central controller/JB. Assume it must be taken direct into thermostat/programmer.
Thanks teletrix, always good information on here and a great help to us youngsters and newbies trying to get started up. Have learnt a lot just sifting through old threads.

Cheers
Rob

 

[chronyx]

try measuring with a multimeter. that will give you an idea of what sort of load it is.

Can you elaborate please?

 

[telectrix]

your IR test will read 0 Mohms on a low resistance. you need to measure in ohms, not Mohms to see whastr sort of resistance you have. e.g. an immersion heater will read 0Meg. across L/N, but around 20ohms on a multimeter ( ohm meter ).

 

[SimpleSimon]

Okay will try that at the weekend. Would you think the central heating system would be throwing it out if its been fed directly off the ring? Not exactly sure where I can isolate it seen as theres not FCU or central controller/JB. Assume it must be taken direct into thermostat/programmer.
Thanks teletrix, always good information on here and a great help to us youngsters and newbies trying to get started up. Have learnt a lot just sifting through old threads.

Cheers
Rob

Perhaps a neon switch somewhere?

 

[chronyx]

your IR test will read 0 Mohms on a low resistance. you need to measure in ohms, not Mohms to see whastr sort of resistance you have. e.g. an immersion heater will read 0Meg. across L/N, but around 20ohms on a multimeter ( ohm meter ).

Gotcha - a low reading ohm meter vs high.

 

[rob121]

Ive got a megger 1553 so ill just measure the resistance. I did look for neons etc but couldnt locate any. Plus I wouldn't think a neon would give me a low n-e reading (im hoping what evers plugged in is giving me this reading, just hope the insulation isnt corroded/damaged. If I rectify the L-N by isolating the equipment but still get a low reading for the n-e, theres no issue with me going ahead with the unit change and making a note on the EIC is there? After all i've increased the safety of the installation by introducing an RCD. As ive said earlier on, she's planning on having the house rewired etc later on.

Thanks,
Rob

 

[telectrix]

a reading over 2 Mohms is acceptable. you would have to get down to kohms to trip RCD. that 2.6Meg. could be damp behind a socket.

 

[SimpleSimon]

The 2.6 is acceptable JUST by .6 but it would be strongly advised to rectify this as something will give. You don't want to leave it till it becomes an earth fault trips the RCD and you'd be buggered to find it. Best sort it whilst it's ok.

 

[telectrix]

The 2.6 is acceptable JUST by .6 but it would be strongly advised to rectify this as something will give. You don't want to leave it till it becomes an earth fault trips the RCD and you'd be buggered to find it. Best sort it whilst it's ok.

yep, does need investigating. possible damp or a leak across 2 cables behind a socket, trapped cable etc.