Help identifying earth type

[Darren Blake]

My girlfriend is in the middle of a kitchen refit and has uncovered a bit of a mess of a CU installation behind a removed cupboard.

It's what I shall call an "old style" CU with twin blade type modules that look like they used to have rewirable fuses. These have all been retrofitted with MCBs. Tracing back from the CU, there is a bakelite connection block where a second live and earth feed has been taken off and into a mini CU with an RCD (I don't rememeber the spec - maybe 40A / 30mA) and a 32A MCB. This was installed by a proper certified sparky just before Part P landed and feeds her power shower (7.5kW). Going further back, there a the meter and finally a 60A main fuse housed in a greay plastic box.

Now, apparently just after she moved in, she "had an earth installed" by the same guy, and I'm trying to work out what kind it is. Here is what I know:

There is a small earthing block mounted to the board, external to the CU.
There is a conection from the earth block to the CU and from the earth block to the same grey box that the 60A fuse is in.
There is another earth connection that runs from the earthing block, up into the loft and then back down into her bathroom where it dissappears behind some panelling with a load of water pipes and doesn't re-emerge again.
There is a sticker on the board that says "Protective Multiple Earth System Installed".

Now, I'm assuming that since she has overhead power cables (live and neutral only) coming into the house, she had a PME system installed (hence the sticker). However, from browsing these forums, I thought that this required a time-delay RCB on the main feed? Also, does the earth bonding to the water pipes sound right (assuming that's what it is)?

Anyway, the upshot of this is that rightly or wrongly I don't quite trust her sparky at the moment, and I'm urging her to have the whole CU replaced so it would be nice to be able to talk sensibly to someone about what would be required, but I'll come onto that next once the earth thing is sorted out.

 

[WSDLTD]

everything sounds fine with the earthing the earth is fetched from the outer sheath of the armoured cable, consumer unit would be a good idea to change though for safetys sake but hang on till about feb at least because the 17th edition wiring regs are out so things will be changing

 

[JohnD]

Now, apparently just after she moved in, she "had an earth installed" by the same guy, and I'm trying to work out what kind it is. Here is what I know:

There is a small earthing block mounted to the board, external to the CU.
There is a conection from the earth block to the CU and from the earth block to the same grey box that the 60A fuse is in.
There is another earth connection that runs from the earthing block, up into the loft and then back down into her bathroom where it dissappears behind some panelling with a load of water pipes and doesn't re-emerge again.
There is a sticker on the board that says "Protective Multiple Earth System Installed".

OK

Now, I'm assuming that since she has overhead power cables (live and neutral only) coming into the house, she had a PME system installed (hence the sticker). However, from browsing these forums, I thought that this required a time-delay RCB on the main feed? No, it doesn't. PME is a good method of earthing. the time delay RCD is needed on installations without a good earth Also, does the earth bonding to the water pipes sound right (assuming that's what it is)? Incoming main services - water, gas, oil must all be bonded to the installation's earth to prevent any difference in voltage with risk of shock

Anyway, the upshot of this is that rightly or wrongly I don't quite trust her sparky at the moment, I haven't heard a good reason for that and I'm urging her to have the whole CU replaced Wouldn't hurt, I expect she's got an old Wylex. Is it Brown or Cream? so it would be nice to be able to talk sensibly to someone about what would be required, but I'll come onto that next once the earth thing is sorted out. The earth sounds OK provided the PME on the Service Head is connected to both CUs and all incoming services

Best way to find a good local electrician is to ask friends, neighbours and other local tradesmen who they recommend, then ring them and ask if they are members of a self-certification scheme (correct answerr is "yes")

 

[JohnD]

... the earth is fetched from the outer sheath of the armoured cable

Not on PME it isn't

 

[WSDLTD]

dont worry to much about the suplimentary bonding, 17th edition has done away with it, everything in the entire house will soon have to be covered by a rcd

 

[sparky40]

Hello.
A TT system, not PME , uses earth rods/mats etc 100mA/30mA RCD's or time delayed RCD's.
A PME system uses the neutral.
Many local distributors change existing TT systems over to the TN-C-S system.(PME )

The other 'larger' ( 10mm ) earth cables are your MEBC's. They should go to your gas/water services at thier intake positions. (within 600mm of meter/stopcock and before any branch in the pipework ( if metal ), or on entry to the dwelling)

Does this help at all ?

 

[WSDLTD]

thanks so much for correcting me,silly old me thought i read PE

 

[Adam_151]

... the earth is fetched from the outer sheath of the armoured cable

Not on PME it isn't

Well if its straight concentric cable....


Anyway, next version of BS7671 isn't due for proper reease for another year, and an extra few months after that before it starts getting used properly

And it unlikely we'll need to RCD everything (although John D might be in favor of that...) everything in the bathoom looks liely though, as does doing away with sup. bonding

 

[Darren Blake]

Cheers for the replies so far. SO... just to labour the point, can I be resonably certain that the earthing system is PME (which I believe uses the neutral incoming wire - hence the connection to the 60A fuse)?

 

[Adam_151]

I'd definatly put my money on TNC-S (PME), but can you get a picture?

 

[JohnD]

...There is a conection from the earth block to the CU and from the earth block to the same grey box that the 60A fuse is in....

...There is a sticker on the board that says "Protective Multiple Earth System Installed"...

50p says it is

 

[Darren Blake]

LOL - well, I know it might sound a silly question, what with the sticker and all, but it is just a sticker. I just wanted to confirm it from first principles because the electrical history of the house is a bit shady.

Some of the wiring in the loft is (forgive the pun) shocking.

I'll try to post up a pic.

 

[JohnD]

What colour is the old CU (this is a serious question)? Is it a Wylex? If the installation is old it will not be enough to put a new CU in, the wiring and accessories will also need renewing.

I like a nice big new CU, with room to replace both the old ones and space for future expansion. RCBOs are better than Split.

 

[securespark]

...There is a conection from the earth block to the CU and from the earth block to the same grey box that the 60A fuse is in....

...There is a sticker on the board that says "Protective Multiple Earth System Installed"...

50p says it is

Sorry, John, not necessarily!

I do a lot of work in S-o-T area, and there, some idiot has seen fit to go round putting "P.M.E. SYSTEM" stickers on every head, but they are invariably TT. Sometimes, the TT supplies are even underground.

UPSHOT: Never take anything for granted..

 

[JohnD]

Ahhhh, them Northern folk...