Another take on bonding for TNCS

[davetheglitz]

I'm sure this is obvious to a lot of you - but I've just got this straight in my mind and thought I ought to share it!

I have trouble explaining bonding to customers as to quantify the chance of your water pipes going live is a million to one.

However - with TNCS if the neutral connection goes open circuit before the incomer - then if any appliance is on - even a low wattage light - the earth connection then effectively becomes live. If bonding isn't in place then if you touch a kettle body and a tap for example you will get a nasty shock. If not on an RCD it could kill.

I've seen loads of main switches where the neutral connection has burnt out. For this to happen before the incomer to my mind could easily occur as human error or a limp wristed electrician. Far easier to quantify than someone shorting line to the water supply with a mechanical digger!

Perhaps this is the justification for 17th edition using RCDs everywhere - makes more sense to me.

Is this new to people or am I just a thicko!

 

[Andy™]

TT and RCD it

PME has too many safety problems. even if it does raise all pipework to 230V (so there is no PD between anything in the house), there is still a serious fault and anyone out the zone can easily get a fatal shock

 

[Apache]

so - why don't we all have our own rod and TT everything?

Is there a disadvantage?

 

[Andy™]

so - why don't we all have our own rod and TT everything?Is there a disadvantage?

there would be a lot more advantages than disadvantages

And it may do a better job at making things safer than part p ever will!

 

[steptoe]

Dave,

welcome to roysten vasey

you'll never leave,

 

[Apache]

Dave,welcome to roysten vasey

you'll never leave,

didn't think you'd be far away......

 

[batty]

With pme all your bonding should be up to scratch before it is connected.

Batty

 

[sparkyork]

there are limiting factors tho, for example if you got plastic incoming water supply, and copper pipework within the house after the stop cock, then you could do with varifying that this water supply needs a bond or not, a reading below 22k ohms from metal work to MET would require bonding to be completed, if its above this figure then its not an ECP and does not require bonding. how many houses are potentially at increased risk with the neuytal going open, when they prob dont even need this water bond.

 

[sparkyork]

ps i agree with above comments about tt ruling, id rather have a tt at home than this pme

 

[Jono Pashley]

Called DNO to come fit a Isolator this morning, Woman asks if i want to be put onto PME also...No Ta you can keep that thanks .

 

[spinlondon]

Don't see the problem with PME if you are going to instal RCDs everywhere.

There's nothing preventing you from using a rod as well.

 

[davetheglitz]

The point is that there are loads of houses out there with PME systems with no RCD protection and no bonding. Trying to persuade some customers to have a new board can be hard, as as far as they are concerned their electrics have always worked - so 'why do I need a new board and why do I have to have this bonding thingy!'. Using this as an explanation may persuade them to do the right thing and get things safe.

I agree that I can't see what is wrong with an RCD protected PME system - and perhaps this is what the new 17th boards are addressing via the back door! Who would admit to coming up with such a seriously flawed method in the first place!

Only thought I've got is that for an inspection you can only inspect to the regs at the time the installation was made. Personally I would now say that no RCD on a PME system should be a code 2 - but obviously it must go as a code 4.

 

[ianmacd]

Elecsa have a leaflet (as a pdf download) for it's members about bonding that seems to be geared towards the cusomers.

I am sure (although can not find the thread) that andyc posted a similar one from a different source. I beleive it was this one: http://www.esc.org.uk/pdfs/safety-in-the-home/Earthing-bonding-ESC.pdf

 

[ianmacd]

There maybe some others on this page that could be useful too:

http://www.esc.org.uk/safety-in-the-home/safety-leaflets.html

Ian.

 

[Apache]

Don't see the problem with PME if you are going to instal RCDs everywhere.There's nothing preventing you from using a rod as well.

you don't mean that, do you?

 

[spinlondon]

you don't mean that, do you?

Of course.

 

[ianmacd]

So, if the DNO lost their neutral, the premises would be drawing all those little electrons from the earth rod and not from the DNO's Neutral instead?

 

[Apache]

So, if the DNO lost their neutral, the premises would be drawing all those little electrons from the earth rod and not from the DNO's Neutral instead?

and the neighbours premesis too :|

To me, the ammature, it didn't sound like a good plan?

Where's Steps when you need him?

 

[ianmacd]

Where's Steps when you need him?

Too busy banging in earth rods converting his town to TT.

 

[davetheglitz]

and the neighbours premesis too :| To me, the ammature, it didn't sound like a good plan?

Where's Steps when you need him?

If you and your neigbours house are both bonded correctly to common metal services then in principal you won't initially notice a problem. However - now your neighbours neutral cable will be taking your current as well as your neighbours!! You have successfully exported your problem - and how long before his neutral burns out?.

Nice!