Best option going forward. Install cert.

[ericmark]

If the electrician is a scheme member then likely he will do the notifying, if not down to you, in theory in England (Not Wales) some one can be qualified under the scheme to inspect and test other peoples work, since still not allowed in Wales I don't know the rules on doing this.

 

[JohnW2]

It absolutely is a Regulation that Earthing and bonding must be adequate before carrying out any work as these are necessary for the protective measure ADS.

I'm somewhat struggling to think of how bonding is necessary for ADS. Could you perhaps enlighten me?

Kind Regards, John

 

[ericmark]

I'm somewhat struggling to think of how bonding is necessary for ADS. Could you perhaps enlighten me?

Kind Regards, John

I do see that for either a fuse/MCB or RCD to operate current must return to the DNO by some route which does not involve the neutral, and to bond does not connect to earth, it just ensures all bonded conductors are at the same voltage.

But in general we are looking for items to be bonded to earth, not just to each other.

Although one could use a long wire and a low ohm meter to test bonding, so many times I read EICR where it says can't find bonding on gas or water pipe, and I wonder why it is not simply tested?

So the scenario. Dog knocks over lamp standard in bedroom, the bulb smashes as it hits the radiator so radiator becomes live, in the bedroom you can see the lamp on the radiator, so one can avoid touching the radiator, but in other rooms in the house the radiators can also be made live, however as long as all other metal in the room is also live there is no path so no danger, however that may be the theory, but in practice the is capacitive and inductive links to ground, so even wearing rubber shoes, if you touch a live part without first using a resistor to equalise the voltage you will still get a shock, so in real terms where pipes or other metal parts can transmit a voltage from one room to another, we want it earthed, so when the dog knocks over that lamp the power is auto disconnected.

I do see in certain places earthing can cause danger, I know in a fitters workshop I used 25 mm² earth cables to bond, as any earth cable smaller could melt if the welding set earth was not correctly attached to the work, but this is hardly a problem in a domestic premises.

The only problem with domestic is where the neutral is lost with TN-C-S however unless there is something unusual like a radio hams earth mat, the problems are not something the domestic installer can do much about.

 

[JohnW2]

I do see that for either a fuse/MCB or RCD to operate current must return to the DNO by some route which does not involve the neutral, and to bond does not connect to earth...

Well, we are presumably talking about main bonding, and that invariably does mean 'bonding to earth'.

What you say is true, but one should/must not rely on main bonding for ADS to work satisfactorily - which would be tantamount to the old (now outlawed) practice of using a water supply pipe as an installation's earth.

Given that, it would seem to me that not only is 'adequate bonding' not necessary to facilitate ADS via OPDs, but (if my understanding testing practices is correct) the presence of main bonding may 'mislead' one into thinking that ADS (via OPDs) would work satisfactorily (without the 'help' of extraneous-c-ps) when that was far from being the case.

My installation is a good example. My understanding is that standard practice is to measure Zs with main bonding present. If that is the case, then when one does that in my house, every one of the final circuits would show a Zs low enough for ADS via OPDs. However, if I disconnected the main bonding, the Zs of every final circuit would be at least 50Ω-75Ω (that being the resistance of my earth electrode), very very far from figures that would allow ADS via OPDs to operate.

Am I perhaps wrong in my belief that people would test my final circuits in my TT installation with main bonding connected?

Kind Regards, John

 

[securespark]

I'm somewhat struggling to think of how bonding is necessary for ADS. Could you perhaps enlighten me?

132.16 (from green book).

 

[JohnW2]

132.16 (from green book).

That's what we're talking about!

The question is ... what is that reg talking about when it says that bonding (as well as earthing) has to be "adequate' if the bonding is "necessary for the protective measure applied for the safety of the addition or alteration" ?? In other words, when/why is bonding necessary "for the protective measure applied for the safety of the addition or alteration".

Kind Regards, John

 

[ban-all-sheds]

Is it not to minimise the PD between the installation earth and e-c-ps at true earth?

 

[JohnW2]

That is indeed the (as far as I am aware, the one and only) intended purpose of main bonding. So in what way is it necessary "for the protective measure applied for the safety of the addition or alteration" (such as, in context, a replacement CU) ?

 

[ban-all-sheds]

The degree of necessity is of no relevance, given the wording of the regulation.

 

[JohnW2]

Slightly re-arranging the clause order, the regulation says that the earthing and bonding must be 'adequate' IF [that is] necessary for the protective measure applied for the safety of the addition or alteration". I still struggle to see how that IF clause would ever be satisfied in relation to bonding (earthing is a different matter).

 

[ericmark]

I would test the earth rod by disconnecting it from the system, I have always done that, I would not test the system, but just the earth rod or pit. The rest can change, so it does not really matter what the spot reading is.

When I see a reading of below 15 ohms on a TT it rings alarm bells.

 

[JohnW2]

I would test the earth rod by disconnecting it from the system, I have always done that, I would not test the system, but just the earth rod or pit. The rest can change, so it does not really matter what the spot reading is.

Yes - but, even with TT, if you were 'testing the installation' (e.g. in the name of an EICR), you would measure and record the Zs of each final circuit, wouldn't you - and, if so, I am right in my belief that this would be done with main bonding connected?

Kind Regards, John

 

[ericmark]

That is not how I was taught to do it. I do see that if the system I will trip a protective device it is save, however we are looking at 10 years, so relying on water or gas is not really on.

 

[JohnW2]

That is not how I was taught to do it. I do see that if the system I will trip a protective device it is save, however we are looking at 10 years, so relying on water or gas is not really on.

I agree with your reasoning, but was under the impression that the normal practice was to measure final circuits' Zs with bonding connected. Maybe I'm wrong? - somewhere I have a (probably not current) GN3, which might clarify.

Kind Regards, John

 

[securespark]

The question is ...when/why is bonding necessary "for the protective measure applied for the safety of the addition or alteration".

Can it depend upon supply type?