My CU must be earthed...but where ?! (with pics)

[mikej2005]

Hi,
I bought a house last year and this is the electricity meter/CU set-up in the garage :

The house was built in 1972 and I've so far been unable to locate where the supply is earthed. All the house circuits exit the CU at the rear and disppear into the wall, but there is no obvious earthing point to any nearby supply pipe.

Mains water enters the house in the downstairs toilet through a plastic pipe so there is no bonding there. The gas meter is on the opposite wall to the CU in the garage and there is no obvious earthing connection to that either, unless it's buried in the concrete floor.

I've even looked under the suspended floor of the room the CU backs on to and there are no cables beneath, so the only possible route would be down in the wall cavity.

Does anyone have an explanation as to what's going on, or am I missing something obvious ?

Would it be normal for a house of this age to have a hidden main earth connection within a cavity wall ?

Thanks in advance for any help or advice.

 

[ricicle]

It looks a possibility that you have a PME supply there, if that's what that white label by the cut-out says.What I can't see though is any main earthing conductor coming out from that terminal on the side of the cut-out.(It is partly obscured by the mains tails)
There is a possibilty that it is a TT system (using an earth rod) and the earth wire is hidden behind the boards and goes to ground out of sight.Have you looked for a rod of any sorts?
The PME could have been provided at a later date and has not yet been utilised.
Your best course of action would be to get a Ze test done on the incoming supply by a competant electrican, this would go some way to providing the answer.

EDIT:If it is TT then there is no main RCD (or old voltage trip).
This needs looking at ASAP for your own safety to check the integrity of the earth to your property.

 

[Steve]

OK, open up that main fuse box, the brown/black one.

BEWARE THE MAIN INCOMING WIRES WILL STILL BE LIVE AND MAYBE EXPOSED.

If the only earth wire is the one that I can see going to the other 2 mini CUs, then the installation is NOT EARTHED and this needs rectifying ASAP.

If there is another earth wire, you need to trace it.

Also look on that black box to the left of the meter - this is the main incoming fuse cutout. DO NOT ATTEMPT TO OPEN IT. On the RHS of it, there might be an exposed terminal. If this is the case, you might have a PME earth terminal provided. You need an electrician to tell you if this terminal is in fact connected to the neutral/earth in the cutout.

 

[kai]

Can you take a closer photo of the black box to the left of the meter?

(It is the main service fuse block) - as the last post pointed out - there may be an earth lead coming out of the right hand side of it, and tucked behind the mounting board, and then onto the black Wylex fuse box above it.

 

[mikej2005]

Spot on guys - I had a closer look and it is in fact a PME supply and the earthing cable that exits the CU from within at the rear does indeed appear to emerge further down and is attached to the main terminal, as in the photo :

I take it this means that my CU is earthed properly, at least as far as it's possible to tell just by looking at the layout ?

 

[davy_owen_88]

The main earthing conductor between the cut-out and the main CU is undersized and should be replaced with 16mm² g&y cable. While you are at it check how many large earth conductors are present at the wylex board. If there are just two then the metal service pipes entering your property require bonding with 10mm² g&y cable and suitable clamps.

 

[mikej2005]

The main earthing conductor between the cut-out and the main CU is undersized and should be replaced with 16mm² g&y cable.

Thanks for your reply - is it safe and/or am I allowed to do this myself, provided the main CU is switched off ?

 

[davy_owen_88]

It's safe enough but isn't to current standards. You can change the main earthing conductors yourself and it isn't notifiable work, but if you are removing the connection to earth, make sure you isolate all circuits while you are working.

To upgrade the cable you will need to go inside the consumer unit so remember that even after switching off the main switch the tails entering the top of the main switch will still be live - there should be insulating covers over them but there may not so be very careful not to touch them.

 

[nozspark]

To be honest, whenever I see one of these wooden framed wylex boards I recommend a CU change at least. This would have the added benefit of having MCB's and a RCD on the socket/shower circuits.

If you got a spark in to do this then you should expect to pay somewhere in the region of £300 and this should include new CU, main earth and main equipotential bonding to water, gas etc. Obviously if there were any other problems then this would have to be reflected in the price.

 

[sparkydude]

How can you give a price of £300 Noz when you dont know how far away from the incomer the main service entry pionts are, and does your £300 include for a full inspection report on the installation? Round here a periodic inspection costs around £100-£150 so thats a very cheap fusebox change you would have then . Judging by the age of ther old wylex board could be anykind of wiring inside there, maybe even Rubber cables.

Nick

 

[Doctor Drivel]

How can you give a price of £300 Noz when you dont know how far away from the incomer the main service entry pionts are, and does your £300 include for a full inspection report on the installation? Round here a periodic inspection costs around £100-£150 so thats a very cheap fusebox change you would have then . Judging by the age of ther old wylex board could be anykind of wiring inside there, maybe even Rubber cables.

Nick

Rubber cables in 1972? I doubt it. If this was fitted in a new build the wiring would be most probably be well installed and PVC. He can do the earthing wiring himself quite easily, linking to the metal gas pipe - although plastic gas service pipes were coming in, in 1972. The old cartridge fuses can be replaced with plug-in MCBs to improve safety and convenience.

 

[sparkydude]

Sorry did not realise the installation was from 1972. True you can just change the fuses for plug in MCBs, but if we were to do that as an NICEIC approved contractor we would have to test the installation as we would be changing the overcurrent protective devices characteristics and would need to verify the protective device would trip in the recommended time.

Nick

 

[nozspark]

Sparkydude

Obviously if there were any other problems then this would have to be reflected in the price.

Right here goes for what I would charge (assuming this is a normal 3 bed semi)

All pricings approximate
PIR = £80 (half day)
Replace CU (split load) including tails, ME & MEB's (if close & easy) = £220

Now also assuming that this would take maybe just over a day to do then if you take the parts out of it you would be clearing about £200, any other problems found during the PIR would have to be costed as extra and rectified before the CU swap..

 

[mikej2005]

Thanks for your comments guys.

I has a boiler installed recently and the installer identified that the incoming gas pipe near the meter needed bonding with 10mm2 earthing cable to the CU. He also spotted that the main earth cable needed upgrading to 16mm2 as mentioned above.

Thankfully, I don't have rubber cabling and the existing cable, whilst 35 years old, is in good condition.

I will consider a CU replacement soon. I'm starting to wonder whether the main 60A fuse and undersized tails would cope if the 10.8kW and 9.5kW electric showers were used at the same time, along with the electric fan oven !

 

[Adam_151]

good condition.
I'm starting to wonder whether the main 60A fuse and undersized tails would cope if the 10.8kW and 9.5kW electric showers were used at the same time, along with the electric fan oven !

In reality...it probably would, the 60A BS1361 should hold 100A for a good 10 minutes or so, and while a shower could sometimes last over 10 mins, its unlikely both will overlap for more than 10 mins (...and... if it is over 10mins for a shower, that must mean the missus is in the same shower, rather than the other one, right? )

Oh, and on a cold day where you stay in the shower a little longer... the fuse will be a little colder as well

Not good design practice, and I wouldn't install it, but I wouldn't be putting money on needing a replacement fuse anytime soon unless you set out to do it!

Anyway, do you have enough water pressure to use both at once?