old CU, bad earth, fused neutral (photo) advice

[aspeakman]

Hi All,

I have just moved into a house in suburban Leeds that is about 100 years old. Although the house has been re-wired in the last 20 years, it's not been a good job. I am weighing up the work that needs doing. My first concern is the earthing. It appears that the only earthing is a 6mm wire going to incoming the cold water pipe. there are two other earth wires to the CU, both disconnected. The supply to the house is obviously very old, it comes in underground on two core armoured cable that is bitumen wrapped. There is no earth provided. I contacted YEDL about the earth and they said they could come and check it and install an earth if necessary. This may be free or cost £30 + VAT. My question is, will they just expose the armour and put a strap or similar round it for the earth, or will they convert it to TNC-S, or provide an earthing rod? I have heard that there can be problems with TNC-S earthing and tripping RCCDs.

I am also concerned about the main fuses - I understand that having a fused neutral is bad practice, and they are only rathed at 60A, which might be a litte low for a large house. I assume that YEDL would say that this needed changing, who would be responsible for paying for this work?

Any comments appreciated

 

[JohnD]

TNC-S is a very good thing to have, they will probably fit it.

Supply your own Earth Block and some 16mm G&Y ready for then to connect to their new earth terminal. You can connect your Consumer Unit to this in 16mm (you will probably have to split the copper into a fork and use two holes in your old Wylex fuseboard as the holes will probably only take 10mm. Use the end holes as they are the biggest) and 10mm for Main Bonding to your Gas and Water pipes (you are allowed to do that yourself, it is not notifiable). The Earth Block needs a permanent label; you get one of these with each Pipe bonding clamp, so get one extra and fasten the metal label using the earth block fixing screw. Main bonds must be in unbroken lengths of 10mm without joins; and made to rigid metallic services (water, gas, oil) within 600mm of their entry into the house, and on the consumer's (your) side of the meter or stopcock.

You can get a 4-way Earth block but I prefer the 8-way, it gives room for expansion, and I expect you will soon want a rewire.

The main fuses are the responsibility of the supplier. It might not be YEDL; but write (don't phone) to the address on your electricity bill; it is their responsibility to know the company that maintains these, not yours. It is possible that the Neutral fuseholder contains a solid link, but I'm sure thy will want to change it. It may be done in the same visit as your new earth but there are some interesting demarcations between the various companies in the electricity industry.


BTW close that cover, and do not touch the fuseholders - old ones often crack or break. Tape the cover to prevent anyone else fiddling with it, especially if there are ever children in the house.

p.s. I don't believe it was rewired 20 years ago. The old brown Wylex was replaced by a Cream model in the early 1970's

 

[Adam_151]

All good advice by John D, but when you're buying the 16mm Earth and the MET, get a 100A DP isolator, an enclosure for it and some 25mm², and then when the guy comes to replace the service head ask if he would mind if while he has the fuses out if you could drop the tails out of your CU and install the isolator between the meter and the CU, if you make him a coffee and offer him a biscuit or two he might even do it for you, this will make changing the CU when doing the re-wire easier.

You can see if you can get him to fit a bigger fuse than 60A, but in reality you are quite unlikely to even pop a 60A one with a house, make sure he replaces the old cloth tails between service head and meter tho...

As said, don't touch the fuses, sometimes the older ones can break and go bang (and when the fault level is likely to be a quite few KA and the next upstream device is likely to be around 400A and at your local substation, could be quite nasty .... the DNO guys have full face shields, etc) also the clips can weaken over time, if a fuse is pulled and re-fitted it may become a fire risk due to high resistance connections when re-fitted

TN-C-S is not a bad system (though it does have some drawbacks), this is what they will probably provide, I'm not sure what RCD issues you have heard about, but I haven't heard of any

 

[Adam_151]

*Waits for dingbat*

(He seems to specialise in re-wireing houses in suburban leeds that have four way wylex standard boards and dodgy earthing arrangements )

 

[JohnD]

Good point, I was toying with the idea of an isolator.

If you screw the DP isolator into place, and fit the 25mm tails to the Supply side (top) having cut them to a length that will comfortably reach the meter terminals, he is even more likely to agree as it will only take half a minute. You can then connect your old CU tails to the load (bottom) of the isolator after he's gone (though it is preferable to do it while the fuse is out).

If you get a MEM Isolator and enclosure, it has a very cunning "hatch" at the bottom that allows you to access the load side terminals and fit new tails, without taking the rest of the cover off and exposing the live Supply terminals. Provided you have remembered to switch it off, that is very safe.

 

[aspeakman]

Thanks for all the useful information, John, you are probably right about the age of the wiring, I think different parts have been upgraded at different times.

What is the advantage of TNC-S over TNS? Is it that you will have a lower impedance between earth and neutral? Are there any disadvantages to TNC-S cf TNS?

I just opened the fuse lid for the photos, I made sure it was closed straight after.

Yes, the CU will be upgraded at some point soon, good idea about the separate isolator. I have seen good prices on Protek CUs, which come complete with RCD and your choice of MCBs. Anyone have experience with Protek, or is it should I go with someone like MK?

http://www.qvsdirect.com/10-Way-Spl...nswitch-RCD-MCB-s-of-your-choice-p-21883.html

 

[JohnD]

Crabtree or MEM for choice. MK used to be excellent but seem to have dropped off. Sockets and switches still good though.

My preference is MEM.

Buy on quality first, ease of fitting second, price third.

 

[jj4091]

I would suggest you enclose a photograph when you write to your suppliers there will probably not be anyone there who has seen a set up that old.

 

[aspeakman]

jj4091 - it seems that Leeds is pretty notorious for ancient set-ups like this.

Been doing a bit of reading up on brands of CU, JohnD - a lot of people seem to agree with you that MEM is the way to go, with some recommendations for Hager as well

 

[JohnD]

A nice big one with room for future expansion
http://i113.photobucket.com/albums/n228/JohnD_UK/POL_0123-1.jpg?t=1166634289

 

[JohnD]

... get a 100A DP isolator, an enclosure for it and some 25mm²...

And here's an example of the MEM one in a comparable situation.

Not sure if you can make out hatch at the bottom in the pic.

Good grief, I spy an 8-way earth block as well

 

[aspeakman]

Thanks JohnD, you have an extensive library of photos

 

[RF Lighting]

I would suggest you enclose a photograph when you write to your suppliers there will probably not be anyone there who has seen a set up that old.

You'd be amazed.

One of the houses I was in today had a cutout of a similar age, as do probably 1/3 of all houses around here.

Not sure if you can make out hatch at the bottom in the pic.

It is a bit clearer in this picture

 

[plugwash]

btw what does the message on that isolator say?

 

[securespark]

p.s. I don't believe it was rewired 20 years ago. The old brown Wylex was replaced by a Cream model in the early 1970's

Good point John.

However...I have come across quite a few installs where they have actually been rewired, but for some odd reason, the spark has decided to re-instate the old CU......