A question about CU Earth (and others random wonderings...)

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My main question is, where is (or should) the CU earthed? The supply comes over head line (L & N wires I believe) to the CU and the only earth wire goes to the water main (which I assume is for the earth bonding of the copper pipes?) but there doesn't appear to be an earth rod going into the ground. Any views on this?

My other source of puzzelment comes from a friends (rented) house where the upstairs mains power circuit controls the downstairs lounge and dining room sockets as well - and also appears to control the bathroom light (the power circuit that is) with no visible source of a fused connection. The outside security light has no isolation switch (ie its premanently live) however this, I believe, is on the correct lighting circuit.

Lastly - should a power shower have its own RCD, or, is a 45amp wired fuse acceptable? The house has the old style fuse box (fuse wire + push fit fuses) and I thought an RCD would be the safer option.

This is more for the sake of my own curiosity rather than an upcoming DIY project
 
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You should very definetly have an earth stake and rcd at the source of the installation. By the sounds of it an old installation so you may have an elvb installed which looks like an rcd but isn't.

There is no reason why upstairs and downstairs skts should be on seperate circuits

The security light should be on it's own isolator depending on wattage. A 1000 watt light would be better via a switched fuse spur off the ring, 300w ok on lighting circuit, but should be switched.

Power showers are usually via a 3a fuse, or do you mean electric shower?
 
HWatts, could you post a picture of the consumer unit and the mains incoming (meter and service head)?

Its possible you have a PME (protective multiple earth) installation, with the earth being carried on the neutral cable.

The way to tell is to look at the big fuse block (cutout) next to the meter and see if there's an earth wire coming out of it somewhere.

If there's no earth wire there, you NEED an earth rod. Water mains is not good enough for earth - there may be plastic sections on the pipe.

Do try to post a picture though!
 
Thanks for the explainations.

The outside light is less than 300w but curcuit isn't switched and I meant electric shower rather than power shower. Thats got a 30amp (wired cartridge) fuse. I just thought that might have been safer if it had an RCD

Whats an "elvb" - I assume your refering to the consumer unit, which is old style (post 1960's but pre 1980's) with the plug in 'fuse wire cartridge' style fuses?

Cheers Hywel
 
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You dont seem worried about the earth issue. You NEED an earth. without it, your fuses are HALF as likely to blow when a fault occurs, therefore a fire and/or electric shock is TWICE as likely.

That old fuse box could do with replacing.

And the shower doesn't have to be on an RCD, with no earth an RCD is nearly useless.
 
Earth leakage voltage breaker, the predecessor to the rcd Looks pretty much the same.
Do you have a box inbetween the incoming main fuse and the fuseboard with a PRESS TO TEST button on it? that will be either a elcb or rcd, If you think it could be over 20yrs old it will almost certainly be an elcb, and ought to be upgraded to rcd

If you do not have such a box then check as crafty said to see if there is a largiish earth wire coming out of the box your main fuse is in .
 
crafty1289 said:
And the shower doesn't have to be on an RCD, with no earth an RCD is nearly useless.

That is correct, the shower doesn't HAVE to be on an RCD but it is a good idea to have one on a shower. To say that without an earth the RCD is nearly useless is not true as it functions just the same regardless, tripping when it senses leakage to earth through some undefined path.

You original earth was probably through the water main and may still be working but it should be earth staked or PME'd ASAP high priority.
 
Sorry crafty1289, I didn't ignore your concern in previous post, I'd already clicked on the reply link prior to seeing it!

Anyway, there are two seperate installations involved that I had questions for. The most important, the earth rod query is at my parents house. It was built in late 1960's and passed the standards then.

setup_1.jpg

This is the setup here. There is no RCD between the fusebox and meter, there is an earth out of the fusebox, but it is wired to the water main where it enters the house.

As for the shower query, that was a different installation. The second (rented) house does have an RCD (it's an 63A RCCB 30mA Trip) between the fusebox and meter, though it also has the old style (cartridge fuse) box. This was what I was thinking about with regard to the shower having a RCD. This installation is earthed to the armoured cable.

setup_2.jpg

This image refers to the setup in the second installation (rented house)
 
The first one - this needs sorting ASAP. ring your electric supplier and ask them if they could upgrade the earth at that property. Ask them if a PME earth is available. If it isn't, you will have to get an electrician to fit and test an earth rod for you. It met the standards in 1960, but there's been a lot of change since then. And if the fuse box and wiring is also that old, it could do with replacing too.

We aint trying to drum up business for sparks in your area, just stating facts, 40 year old wiring is getting on a bit. I heard the average life span for houehold wiring is 20 years.

The second picture - Is this a modern installation? Is it proper armoured cable? or is it lead and paper? If it feels like lead, get an electrician to test this too, lead sheaths have a nasty habit of shrinking when the earth clamp is tightened, thus reducing the effectiveness.
 
The fuse box, I had wonderd about the possibility for replacement for a while now with a modern circuit breaker one. I will let them know about the earthing situation too.
The wiring on the other hand appears fine. Did some work a while back and what I saw it was as good as the new stuff - not brittle or anything.

Pretty sure the second property has a lead/paper sheeth cable. It looks a fairly old installation. Fusebox (not circuit breakers), analogue meter the exception being the main RCD which seems to have been added as an afterthought, it looks a lot newer than the rest of the equipment. Have to get the landlord to deal with anything here though.
 
lead and paper cable will last forever so i heard, thats nothing to worry about, but the integrity of the earth on its sheath is.
 
while the water main may actually be quite a good earth you can't rely on it anymore because more and more of our pipework is being replaced with plastic.

so as others have said you either need to get the electricity board to supply an earth or fit a rod and 100ma type S RCD. Fitting a rod is not something i reccomend a diyer to do because if you get it in the wrong ground it can be totally ineffective and without proper test equipment you just can't tell. Neither is fitting the 100ma type S RCD (because you'd need to pull out the service fuse first).
 
:eek: I had completely forgotten about this post. So I never did get the spark out in June to sort it! Thanks for reminding me. Thats been moved to the front of the to do list ASAP
 
So, in essence, you need an earth connection to the install.

You could ask the DNO to convert your TT supply to TN-C-S. That way you would not need a split-load board with TD or S type RCD.

But, either way, you need a MET, and bonding to service pipes, whatever your supply.
 
HWatts said:
It was built in late 1960's and passed the standards then.

Sorry to hijack this thread but I'm intrigued by this comment.

Was an electrical installation certificate issued when it was built? I'm curious because, to this day, regardless of the latest provisions of the building regulations, it is quite common for new houses not to have an EIC.
 

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