M
mbga9pgf
Hi all, very sorry to bother you with triv. I am in the process of sorting out some pretty shocking electics in a house that has been bodged at every stage.
Just so you all know, I am not on an approved scheme, however, I have a masters in electrical and electronic engineering. I am at the design stage and am trying to put as much of my home wiring right. To give you an idea of some of the things I have had to sort
6mm Twin and earth submain between 2 buildings left lying across the grass, protected by a 45A MCB. Terminated into a CU supplying amongst other things, a 10mm cable supplying a 9Kw shower and a 6mm halogen hob.The fact that it was left lying over the front lawn probably prevented it from overheating.
1.5mm T+E lighting cable wrapped round a 22mm copper central heating hot water feed pipe. He had installed a 16mm earth line to the ground spike (tt system), unfortunately, he hadnt bothered connecting the other loose end from the earth block by bonding the pipework. t+E showing signs of melting. I wonder how long before the rads became live?
no earthing in 2 way lighting switches. Metal fronted lighting switches may I add.
Anyways, those issues are now resolved. I managed to rewire the submain temporarily into the main CU, with a 16mm cable and a 50A MCB, works a treat and we no longer have wires in the garden.
Unfortunately, he did a DIY bodge job of the 17th edition split CU and has installed it in the meter box, outside. (See pic). I need to do a number of jobs which I am thinking through at the mo, most notably moving and upgrading the CU and building in a potential capacity increase into the future in the design. I am going to move the CU (via notification to the LABC) to the first floor, pretty much above its current location, on the back wall. Local BC dont have a single recorded submission of electrical work for the property.
Current issues:
1) Cables go from the current CU location, up through the cavity, to the first floor, and some go further upwards in the cavity to the loft (ceiling lights on 1st floor).
2) We have a pretty rubbish supply courtesy of the DNO. Its a 200 metre run from the nearest transformer pole. Voltage drop at 40A is around 20 volts. Ouch. DNO have been notified, however, until I have all the appliances chased and checked, I dont want them to get in, as I want a realistic demopnstration when they check the supply; all they will do is up the voltage to its upper limit and blow all my bulbs, whilst instead, a realistic load will demonstrate they need to relocate the transformer or up the cable capacity. We are currently scaled for 18KVa agreed capacity, according to the DNO paperwork, I very much doubt they can supply this, once we are renting the annexe out and living in the main house.
3) I am going to need either 25mm2 tails, or 25mm SWA cable to minimise volt drop in latter stages of the circuits. Longest submain circuit is going to be around 30 metres from the new CU location, cabled in 16mm2 twin and earth. I have to decide whether to split the tails at the CU, with 2 fused isolators, (both 60A), one supplying the main part of the house, the second the annexe, or, take the 25mm SWA up to the first floor then split the tails at that point. As we are renting the annexe, we need to add a meter to the split tails supplying the annexe submain at some point, probably at the meter box.
Now, heres the issue. The existing DNO supply cable looks gupping. Its right down the front of the house and looks like its only 10 or 16mm XLPE. With our existing voltage drop problems, it would be much easier if they moved the meter box and all to the new CU location. We all know this isnt going to happen however, instead, I am going to have to route 25mm SWA up the wall and at some stage bridge the insulated cavity to the new CU location on the back of the wall. I flipping hate the look of PVC conduit internally, and it would need to be in the kitchen. Wife would not be happy. I could chase, but I am guessing chasing 25mm SWA isnt much fun 15 feet up a ladder and its going to ruin the existing render.
As the existing wires in the cavity can removed and be hidden in the alcove in PVC trunking, this would solve the derating that should have been applied to the cable routed up the cavity. Fortunately, I have no cables routed underfloor on the ground floor, everything is on ring finals on the first floor and spurred down to the ground floor.
Bearing in mind we live behind electric gated access, up a 150m drive and they have no ready access to the meter anyway, whats the chance the DNO will move the meter and box indoors?
25mm SWA needs a min 160mm radius. How can I "bend" the cable through 90 degrees if I clip it externally, or choose to chase, to firstly get iot through the wall,secondly, going "Up" into the CU on t'other side of the cavity wall? Directly behind the CU we have our range cooker, so I cant use PVC conduit up to the first floor anyhow as the cooker is in the way.
Which would you all do? Split the Tails at the new CU location, and have the second fused isolator on the 1st floor, or split it down at the meter box, at the existing blocks, and somehow route/chase the submain (16mm T+E) to the first floor then off to the annexe?
Whilst I am making my mind up, I am getting on with drawing up plans of the existing wiring (flooring is alllifted at the mo anyhow), measuring PFC, Earth loop impedances, insulation resistances, checking ring final continuity and getting together a paperwork packup to hopefully ease the woes of any future owners.
Sorry I have overcomplicated, I will try and show you some pics if I have confused things to try and explain further.
Just so you all know, I am not on an approved scheme, however, I have a masters in electrical and electronic engineering. I am at the design stage and am trying to put as much of my home wiring right. To give you an idea of some of the things I have had to sort
6mm Twin and earth submain between 2 buildings left lying across the grass, protected by a 45A MCB. Terminated into a CU supplying amongst other things, a 10mm cable supplying a 9Kw shower and a 6mm halogen hob.The fact that it was left lying over the front lawn probably prevented it from overheating.
1.5mm T+E lighting cable wrapped round a 22mm copper central heating hot water feed pipe. He had installed a 16mm earth line to the ground spike (tt system), unfortunately, he hadnt bothered connecting the other loose end from the earth block by bonding the pipework. t+E showing signs of melting. I wonder how long before the rads became live?
no earthing in 2 way lighting switches. Metal fronted lighting switches may I add.
Anyways, those issues are now resolved. I managed to rewire the submain temporarily into the main CU, with a 16mm cable and a 50A MCB, works a treat and we no longer have wires in the garden.
Unfortunately, he did a DIY bodge job of the 17th edition split CU and has installed it in the meter box, outside. (See pic). I need to do a number of jobs which I am thinking through at the mo, most notably moving and upgrading the CU and building in a potential capacity increase into the future in the design. I am going to move the CU (via notification to the LABC) to the first floor, pretty much above its current location, on the back wall. Local BC dont have a single recorded submission of electrical work for the property.
Current issues:
1) Cables go from the current CU location, up through the cavity, to the first floor, and some go further upwards in the cavity to the loft (ceiling lights on 1st floor).
2) We have a pretty rubbish supply courtesy of the DNO. Its a 200 metre run from the nearest transformer pole. Voltage drop at 40A is around 20 volts. Ouch. DNO have been notified, however, until I have all the appliances chased and checked, I dont want them to get in, as I want a realistic demopnstration when they check the supply; all they will do is up the voltage to its upper limit and blow all my bulbs, whilst instead, a realistic load will demonstrate they need to relocate the transformer or up the cable capacity. We are currently scaled for 18KVa agreed capacity, according to the DNO paperwork, I very much doubt they can supply this, once we are renting the annexe out and living in the main house.
3) I am going to need either 25mm2 tails, or 25mm SWA cable to minimise volt drop in latter stages of the circuits. Longest submain circuit is going to be around 30 metres from the new CU location, cabled in 16mm2 twin and earth. I have to decide whether to split the tails at the CU, with 2 fused isolators, (both 60A), one supplying the main part of the house, the second the annexe, or, take the 25mm SWA up to the first floor then split the tails at that point. As we are renting the annexe, we need to add a meter to the split tails supplying the annexe submain at some point, probably at the meter box.
Now, heres the issue. The existing DNO supply cable looks gupping. Its right down the front of the house and looks like its only 10 or 16mm XLPE. With our existing voltage drop problems, it would be much easier if they moved the meter box and all to the new CU location. We all know this isnt going to happen however, instead, I am going to have to route 25mm SWA up the wall and at some stage bridge the insulated cavity to the new CU location on the back of the wall. I flipping hate the look of PVC conduit internally, and it would need to be in the kitchen. Wife would not be happy. I could chase, but I am guessing chasing 25mm SWA isnt much fun 15 feet up a ladder and its going to ruin the existing render.
As the existing wires in the cavity can removed and be hidden in the alcove in PVC trunking, this would solve the derating that should have been applied to the cable routed up the cavity. Fortunately, I have no cables routed underfloor on the ground floor, everything is on ring finals on the first floor and spurred down to the ground floor.
Bearing in mind we live behind electric gated access, up a 150m drive and they have no ready access to the meter anyway, whats the chance the DNO will move the meter and box indoors?
25mm SWA needs a min 160mm radius. How can I "bend" the cable through 90 degrees if I clip it externally, or choose to chase, to firstly get iot through the wall,secondly, going "Up" into the CU on t'other side of the cavity wall? Directly behind the CU we have our range cooker, so I cant use PVC conduit up to the first floor anyhow as the cooker is in the way.
Which would you all do? Split the Tails at the new CU location, and have the second fused isolator on the 1st floor, or split it down at the meter box, at the existing blocks, and somehow route/chase the submain (16mm T+E) to the first floor then off to the annexe?
Whilst I am making my mind up, I am getting on with drawing up plans of the existing wiring (flooring is alllifted at the mo anyhow), measuring PFC, Earth loop impedances, insulation resistances, checking ring final continuity and getting together a paperwork packup to hopefully ease the woes of any future owners.
Sorry I have overcomplicated, I will try and show you some pics if I have confused things to try and explain further.
Attachments
![[ElectriciansForums.net] Help required with tails/SWA routeing and DNO supply issues.](https://electricians.s3.eu-west-1.amazonaws.com/data/attachments/1/1954-b17266063ef533e4aad47193e5533e13.jpg)
Last edited by a moderator:
