New Wiring Regulations

[NT]

Blue/brown wiring was in use before Part P came in, and still under 1% of diy electrical work is jumping through the part p hoops.

The whole thing is a minefield of silliness really.


NT

 

[Penners]

I hope Flyfisher will forgive a modest hijack of his thread, but while all you electrical experts are tuned in, I have a related question on the subject of earth bonding.

The more that I investigate the plumbing in my house, the more of a hotch-potch I'm finding. I've got areas where plastic tube has been used with brass compression joints; areas where copper tube has been used with copper Yorkshire joints; but mainly I've got copper tube with plastic pushfit joints. And the whole system connects back ultimately to the rising main in alkathene.

So what do I do about earth bonding? Obviously there's no electrical continuity anywhere in the system, so do I just forget about it? Surely I'm not expected to connect a bonding "bridge" across every plastic component to the next bit of copper, am I?

In the bathroom, I could still connect the bath (steel) to the radiator, and in the utility room I could connect the steel sink to the radiator to the washing machine. But is there any point?

Many thanks for any advice.

 

[Lime]

I think your system Penners is exactly what 'equi-potential bonding' is for.
It is designed to ensure that every metal part in the bathroom is at the same potential (hopefully earth).
Just think what might happen if the electrically-isolated copper or iron pipe feeding your bath tap was made live by, for instance, a water leak onto a ceiling rose or a frayed cable next to it.
That could lead to the bath being live but the nearby hand basin's cold tap being earthed for instance. Touch the two with wet hands and bingo "frying tonight".

So to answer your question it does make sense to connect all the metal in the bathroom together but it must be earthed directly to the main earth terminals near the supply by a completely separate cable.
Do not take the earth from any electrical equipment.
Connecting the bath taps etc to a radiator to obtain an earth is unsafe.
However if a metal radiator is in the bathroom that should be equi-potential bonded too.

Further text added to to clarify points made.

 

[NT]

In the bathroom, equipotential bonding means connecting all the exposed metalwork together to ensure that if one bit goes live, they all go live. There is no need to earth or equi bond the rest of the house.


NT

 

[Moo]

All this talk of earth-bonding plumbing is making me feel really nervous. Who should I get to check that my (and our son's) plumbing isn't a potential death-trap? Would a decent electrician do?

 

[NT]

Most houses today dont have bathroom equipotential bonding, and it has no realistic safety benefit in most cases. The regs have mandated it for all newly wired bathrooms now, but it is a decision that invites controversy.

Unless you've got PME or TT, there is really no case at all for retro-fitting bathroom equi bonding. People in the trade like to try and present one, but I've yet to hear one that stands up to scrutiny.

If you have a TT system, equipotential bonding in the bathroom is certainly a safety feature and worthwhile including at rewire time, if you have a TT earth system. Its one of various small safety features that older installations lack.


In the case of bonding incoming services, which is earth bonding rather than equipotential, it has a clear although small safety benefit. Old installations may lack this one, although most are bonded via CH piping anyway, but its not a cause for worry as the safety benefit is small, its just one more way in which new installs are a bit safer.

Most of our houses are NTCS in many respects.

Theres rarely any need for a householder to consider the question of equipotential bonding or earth bonding, and if youre worried you can happily go back to sleep.


NT

 

[Lime]

I would agree with you NT to some extent.
If a system of plumbing and wiring has not been altered since it was installed some time ago the likelyhood of problems is small.
However with the advent of plastic water pipe connections and plastic baths many systems have been altered as far as their electrical properties are concerned.
I think there is a very strong argument to ensure that the hot and cold supply to the bathroom are electrically connected to each other if nothing else, particularly if an immersion heater is fitted.

 

[NT]

I think there is a very strong argument to ensure that the hot and cold supply to the bathroom are electrically connected to each other if nothing else, particularly if an immersion heater is fitted.

Would you like to share with us what that argument is?


NT

 

[tony]

Main Equipotential Bonding.

bonding or equipotential bonding is a electrical connection between various exposed conductive parts and extraneous conductive parts at the same potential
the purpose of bonding is to reduce any risk of electric shock by connecting together mettalic parts with bonding conductors


Supplementary Equipotential Bonding

This involves connecting together the conductive parts of electrical and non electrical item such as radiators, baths, sink etc, all the associated pipework and metal baths for example

Means of earthing in older installation

Older installation may use a gas, water or other metal service pipe as means of earthing. This is not permitted.
It has never been permitted to use a gas pipe as a means of earthing and since 1966 it has not been permitted to use any other service pipe either.
Equipotential bonding must me made to the gas water and any other metal service pipe

BS951 earth clamps( as found on copper pipework) must not be used on cables especially at the cutout( where the electricity suppliers fuse is ) this clamp is designed to provide a good connection when tightened around a pipe, as a cable is not pipe this will damage the conductors possibly by squeezing them together,this is found on many tns systems


Main equipotential bonding not provided.
Prior to 1966 the wiring regulations contained no requirements for main equipotential bonding

where protection against indirect contact( getting a electric shock from something that is not normally live except in a fault condition) is provided by EEBAD(earthed equipotential bonding and automatic disconnection of supply)
The installation of main bonding has been a requirement since 1966
During the 1980's new regulations were introduced requiring the minimum soze of conductor to be larger than previously called for now main conductors should be 10mm2( depending on length of cable)

supplentary bonding to a metal sink is not required, it is required in areas of increased shock risk ie bathrooms , saunas, swimming pools etc

A kithchen is not defined in the regulations as a special location

Local supplementary bonding shall be provided connecting the terminals of the protective conductors of each circuit supplying class 1 and 2 equipent in zones 1,2, and 3 and extraneous conductive parts in these zones

regards

tony

 

[Lime]

I think there is a very strong argument to ensure that the hot and cold supply to the bathroom are electrically connected to each other if nothing else, particularly if an immersion heater is fitted.

Would you like to share with us what that argument is?


NT

I feel sure you are aware of the arguments that I could make.
Two conductive pipe systems running throughout a house that are isolated from each other are vulnerable to accidental (or on purpose) connection to the electricity supply in some way.
The isolation can come about with the changing of a cold water tank, single bath taps, modernising the shower or any change where metal is not used where it once was.

I speak from some experience. I once lived in a terraced cottage with a shared cold water lead plumbing system.
It was supplied by Anglian Water in plastic pipe fitted just before I moved in.
8 doors along an elderly couple bought an old washing machine from an auction and used it when they got home.
(The machine was wired with the black and green wires transposed.)
They tripped my ELCB off and caused all the cold water mains supply to the cottages to become live as I discovered when investigating the fault.
(They were completely unaware of this problem)
My hot water was heated by an immersion heater supplied by an addition fusebox with it's earth taken directly from an earthing rod and not through the old trip fitted on the older circuit.
All the cottages except one were TT. (The exception was a TN-C-S)
They relied on the shared lead water pipe for an earth which had become isolated.
That day was not a good one for taking a bath (plastic of course).

 

[Flyfisher]

While equi-potential bonding seems like a good idea, is it not almost certain that, in these days of modern plastic plumbing, it is almost inevitable that such bonding will be compromised sometime, somewhere?

Isn't it fair to assume that by far the best protective measure for any installation is the provision of RCDs to prevent people from receiving fatal shocks in cases where a fault arises? I particularly like the idea of RCBOs fitted to every circuit, as previously suggested, and I assume that these devices can be selected with a tripping sensitivity lower than the 'normal' 30mA I've seen and used.

Would it be correct to say that, yes, loads of earth bonding is a good thing (if in doubt, earth it?) but the RCD is the thing that will actually save you if, heaven forbid, circumstances arise whereby mains current starts to flow through your body?

 

[tony]

rcbo 's can be purchased with ratings of 10ma

Not a good idea due to leakage current.

Put most of your circuits on individual rcbo's, its more expensive, ive done that.

regards

tony

 

[tony]

but if your plumbing is electrically isolated and it does become live a result a rcd wont be then be all and end all.

After all bs clamps can be purchased for £5 for 25 and a drum of 4mm2 for under £10.

So just do it yourself its pretty easy.

After all who will know if its been in for 20 years or 2 months as the green and yellow colour has been use for donkey years.

If you did get a pir and didnt have bonding it would be marked down as a code 2 as requires improvement

regards

tony

 

[Lime]

Would it be correct to say that, yes, loads of earth bonding is a good thing (if in doubt, earth it?) but the RCD is the thing that will actually save you if, heaven forbid, circumstances arise whereby mains current starts to flow through your body?

No.
RCDs and RCBOs protect against an imbalanced current between the live and neutral.
They require an electrical current to pass through some other connection (the earth) to give the imbalance.
If you are unfortunate to touch both the live and neutral you will not trip the RCD because the current will be the same in either conductor.
In many situations that is the most likely form of electrocution.
For instance in a bedroom twin flex is often used with no earth connection anywhere.
If anything happens to expose the wires the RCD will not operate if the wires are touched.

Also any situation where the safety electrical earth is compromised is not protected by RCDs or RCBOs either.

However even if the RCD operates correctly, 30mA (the common compromise current setting of RCDs) is very unpleasant even if felt for a short time.
Remember the current passing through you can be anything until the RCD trips.

 

[Flyfisher]

All good points.

I understand a very sensitive RCBmight result in nusiance tripping due to 'normal' leakage currents. If 10mA is too low what would be a better figure, or is the standard 30mA adequate?

I also take the point that connecting yourself to live and neutral is a potential recipe for disaster than an RCD can't help you with. I always remember the old lab rule of keeping one hand in a pocket when doing any electrical work, although this is hardly useful advice in normal circumstances.

As for a 30mA RCB still allowing a 'very unpleasant' shock, it's the fatality of it that concerns me more than the unpleasantness :wink:

 

[NT]

I think there is a very strong argument to ensure that the hot and cold supply to the bathroom are electrically connected to each other if nothing else, particularly if an immersion heater is fitted.

Would you like to share with us what that argument is?

I feel sure you are aware of the arguments that I could make.

(Snip argument for ease of reading.) What you say is a common argument for the need for supp equi bonding, but only applies to ancient installations that are grossly unsfe, as yours clearly was. It is not an argument for fitting supp equi bonding to new installs or modern wiring systems.

And frankly, retrofitting it to installations that unsafe brings as much risk as it abates. If you live with a dangerous installation like that, the only real solution is to sort it out.


NT

 

[NT]

While equi-potential bonding seems like a good idea, is it not almost certain that, in these days of modern plastic plumbing, it is almost inevitable that such bonding will be compromised sometime, somewhere?

I dont know if you mean bonding of incoming services or bonding of metalwork in bathrooms.

Isn't it fair to assume that by far the best protective measure for any installation is the provision of RCDs to prevent people from receiving fatal shocks in cases where a fault arises?

There are several safety barriers to electrocution, RCDs just add one more. Best, I dont think so, no. Insulation, double insulation, earthing and fuses are much more effective safety barriers.

I particularly like the idea of RCBOs fitted to every circuit, as previously suggested, and I assume that these devices can be selected with a tripping sensitivity lower than the 'normal' 30mA I've seen and used.

Not recommended, 30mA RCDs/RCBOs are bad enough wrt nuisance trips.

Would it be correct to say that, yes, loads of earth bonding is a good thing (if in doubt, earth it?)

Its widely accepted that many items are slightly safer left unearthed. Earthing is not perfect, especially on TT systems where the CPC (earth wire) voltage can rise to high voltage during a fault.

but the RCD is the thing that will actually save you if, heaven forbid, circumstances arise whereby mains current starts to flow through your body?

If all other safety measures have broken down, then the last remaining one will probably save your bacon, whichever one it may be, so the question confuses 2 things there.

RCDs are not 100% reliable, do not limit shock current (as is often fondly imagined), and do not act at all on the minority of L-N shocks. However they still offer a magnitude of safety improvement under identical conditions.

One of the problems with them is that conditions are not identical, as users too often take full advantage of this apparent extra safety, and start doing things they never would have before, like using power tools outdoors in mild drizzle etc, thus negating any safety benefit and more.


NT

 

[NT]

I understand a very sensitive RCBmight result in nusiance tripping due to 'normal' leakage currents. If 10mA is too low what would be a better figure, or is the standard 30mA adequate?

30mA is a pretty good compromise for individual circuit RCBOs. Its a poor figure for whole system RCDs, where 100mA is better. With your large property you really do need RCBOs, putting such an acreage of wiring onto one RCD would be begging for trouble.

As for a 30mA RCB still allowing a 'very unpleasant' shock, it's the fatality of it that concerns me more than the unpleasantness :wink:

yes, and its been found that cutting the shock time, which is what an RCD does, has a real benefit in preventing death.


NT

 

[Lime]

And frankly, retrofitting it to installations that unsafe brings as much risk as it abates. If you live with a dangerous installation like that, the only real solution is to sort it out.

I agree with your post in general.

Unfortunately grossly unsafe situations can occur in new installations too if alterations are made with no thought to the consequences.
Small apparently insignificant changes can be potentially disastrous to the integrity of an electrical safety system.

What I wish to emphasize is that nothing should be taken for granted.
Even the water supply pipe coming into the house can be a source of danger.
Ensuring the bathroom metal fittings are all at the same potential (even if live) is a sensible precaution for safety.

 

[Lime]

One of the problems with them {RCDs} is that conditions are not identical, as users too often take full advantage of this apparent extra safety, and start doing things they never would have before, like using power tools outdoors in mild drizzle etc, thus negating any safety benefit and more.

Don't they just!
Split cables run through puddles to cement mixers and power tools used in pouring rain.
Far too many people think the RCD makes anything electric safe.
It does not!