Earth Fault..RCD after meter

[AlanWirral]

Hey Guys,

Just a quick one. Recently dealt with a problem at a relatives home in Anglesey.

Basically the polish maintenance guy got a shock off the outside water tap and then off the kitchen one! He turned the main switch off but it happend again:ack2:

I went along and with my voltstick started touching the metal light switches and taps and low and behold it lit up like a xmas tree. I quick polarity check proved my suspicions of an external earth fault.

I left the building and after getting in touch with Scottish Power they confirmed the 'Stay' on there mast had come into contact with the Line and caused the fault. This was rectified and the house was checked..Ze etc.

Now the owner obviously doesnt want this to happen again so i've said we need to fit a RCD. Bearing in mind the board is metal with only the rings protected by 30ma RCBO's and no main RCD. Is the best practice here to get SP to fit an RCD before the meter or should i go ahead and fit one after the meter and before the CU. Finding an old contactum main RCD to swap with the main switch might prove a struggle.

Haven't had the pleasure of dealing with this fault before so could do with some advice please boys :frown2:

Thanks in advance

Alan

 

[alarm man]

Basically the polish maintenance guy got a shock off the outside water tap and then off the kitchen one!

id just leave it as it is to be honest....:devilish:

 

[telectrix]

can't see how an RCD can protect against this. what you are saying is that the earth is being taken to line voltage outside. the |RCD will only break L and N. you'll still have a line potential to earth and hence into the house via water pipes etc. this is something scottish power have to remedy.

remember the nags at newbury the other month. voltage gradient through the ground.

 

[Knobhead]

Electrocute a polish though, now there’s a thought! Do they need any more handy men?

And before I get jumped on again it says polish not Polish, consult the OED!

 

[telectrix]

well i'm just about to polish off a pint.

 

[Paul.M]

If I've read the op correctly this could be rectified by a plumber installing a few foot of pvc poly pipe just after the incoming supply of gas and water therefore taking away the potential difference to the taps from an outside supply of current until the DNO can fix their end.

 

[Paul.M]

CCan't believe I've just said that a plumber can sort out an electrical fault!

 

[telectrix]

course he can. you get the plumber to act as a spacer between the line conductor on the pole and the earthed stay. sssimmpples

 

[Paul.M]

This thread reminds me of another thread about a year ago where the neighbours TT rod was tripping next door neighbours circuits, similar in principle?

Ground is conducting current to the taps, isolate by using poly pipe (water does not conduct electricity that well contrary to believe) problem solved for a short, cheap fix until the main issue can be addressed.

 

[AlanWirral]

Sorry telectrix I have sounded a bit thick here thinking an RCD would 'Stop' the problem!

Basically apart from the water/Gas issue what can actually be done my end to stop the problem entering the house? A switch to cut off just the earth? The DNO just said it can happen anytime and basically tough! Surely tthis isn't right?

 

[spark 68]

You are not allowed to have a switch on a protective/earthing conductor.

I would, as others leave it as is, as the fault was external, and there is not a lot you can do about it, other than maybe plastic pipes etc. as others have already suggested

 

[AlanWirral]

Right

Well surely in cases like this then safe isolation should apply to the earth? A conductor is a conductor at the end of the day and with the potential to become live as easily as this it should be switchable.

I'll put the ball in there court and see what they say. Thanks guys

 

[Engineer54]

Sorry telectrix I have sounded a bit thick here thinking an RCD would 'Stop' the problem!

Basically apart from the water/Gas issue what can actually be done my end to stop the problem entering the house? A switch to cut off just the earth? The DNO just said it can happen anytime and basically tough! Surely tthis isn't right?

To be honest, the chances of this situation ever happening again, is so remote i wouldn't even give it a first thought, let alone a second. And the last thing i would want in my house, is to lose those solid earth connections that those copper gas and water pipes afford to my installation...

Leave well alone, is my advise to your relative!!!

 

[WayneL]

Alan,

All you can do is make sure that all exposed conductive parts inside the house are 'earthed' and all extraneous conductive parts inside the house are 'bonded'.

This will ensure that should something similar happen again all metalwork inside will be at the same potential and so minimise the risk of a fatal shock.
Other than that, there's not much you can do in the way of 'protection'.

You should fit a length of plastic in the pipework that leads to the outside tap in order to insulate it from the interior bonded metalwork - the same would apply to any other metalwork that extends from the 'equipotential zone' to outside - as this is the biggest risk because it can be touched whilst standing on (in contact with) 'true' earth.

 

[AlanWirral]

Thanks guys. With a ZE of just 0.2 and checking all bonding/earthing is constant throughout there isn't much else I can do. I suppose this truly shows the need for earthing.

I shall instruct the owner to sort the outside water pipe asap also.