Larger installations, what to inspect

hightower · Jan 5, 2017

Before adding anything to a circuit it is necessary to ensure that main bonding and earthing are up to standards. This is fairly straight forward for a domestic property, but what does it mean for a larger property.

The example I'm thinking of is the school I work in (part-time now, slowly making the transition!). Let's say I'm to add a spur to an existing RFC. Okay, I'm going to do my usual MWC tests of Zs and IR etc, and I'll obviously do a RFC 3-stage test to ensure it is indeed a ring. But what do I have to do in terms of checking earthing and bonding?

Is it just a case of making sure the DB supplying the RFC gets a good Zdb reading? Or do I have to go back to the origin of the install and inspect the earthing arrangement there (even if it's 200 yards away in another part of the building?)

What about bonding, do I just have to ensure that bonding is carried out in the area I'm making the addition (so proximity of the RFC)? Or do I have to check bonding is carried out in all areas that the DB supplies? Or do I have to check bonding in all areas for the whole school?

The Ghost · Jan 5, 2017

First port of call imho is to inspect existing tests and records for that circuit and hopefully they are in date so you can rely upon them as to the state of bonding and existing circuit then MEIWC for the spur addending that to the current tests records. If there are no records then you have a problem. But its a school so I expect the records will be there and show what you need to see.

hightower · Jan 5, 2017

Vortigern said:
First port of call imho is to inspect existing tests and records for that circuit and hopefully they are in date so you can rely upon them as to the state of bonding and existing circuit then MEIWC for the spur addending that to the current tests records. If there are no records then you have a problem. But its a school so I expect the records will be there and show what you need to see.

I'd probably expect the records to exist too, but I've been here 10 years and not seen a single cert. I'm sure EICRs exist in some dark cupboard. We've had large firms come in for power installs etc (before the days of me beginning my training, so excuse my, then, ignorance) and never been issued an EIC for any work. Funny, because we are issued test results for Cat5e but the same firm offered no EIC.

The Ghost · Jan 5, 2017

There is no way a school can be without PIR surely! I think you need to get to the bottom of that and flag it with the responsible person. This is a normal school we are talking about yeh? Any person coming in doing work in a school MUST issue certs for work done Maybe the council hold them? Either way a copy must be available at the premises for exactly what you are doing to show that you are extending a circuit that is safe to extend. Otherwise an EICR must be done on the premises if it hasnt within regs time periods. (5 years with 6 month routine checks)

westward10 · Jan 5, 2017

The premises officer will know the location of the incoming services to verify the bonding. The only snag may be where the school has expanded to additional buildings, from experience of testing lots of schools the bonding to these buildings is often undersized and the armour of the supply cable is used to support the bonding which is nearly always inadequate for purpose. Earthing conductors from the DNO supply can greatly vary for these installations and this is what you need to verify to confirm bonding sizes. Don't forget the MWC only asks to comment on the adequacy of these provisions and that is another can of worms.

hightower · Jan 5, 2017

Vortigern said:
There is no way a school can be without PIR surely!

I haven't said it is without a PIR, just that I've never seen them - but then again I've got no business seeing them unless I'm going to be doing work here (which I'm not, this is just a scenario). As for the 5 year checks, I'm not sure this is mandated in BS 7671, and more a recommendation in GN3. That said, I can recall the council sparks coming about 4 years ago to carry out some sort of tests - I wasn't involved in this so can't say the extent of them.

westward10 said:
The premises officer will know the location of the incoming services to verify the bonding. The only snag may be where the school has expanded to additional buildings, from experience of testing lots of schools the bonding to these buildings is often undersized and the armour of the supply cable is used to support the bonding which is nearly always inadequate for purpose. Earthing conductors from the DNO supply can greatly vary for these installations and this is what you need to verify to confirm bonding sizes. Don't forget the MWC only asks to comment on the adequacy of these provisions and that is another can of worms.

The MWC might only ask us to comment, but BS 7671 tells us the earthing and bonding must be up to scratch before carrying out additions.

westward10 · Jan 5, 2017

It states they should be adequate hence the can of worms. If bonding is absent then this will require additional works. If it is there, but undersized then a judgement needs to be made on it's adequacy and this may be dependent on other factors such as earthing system, whether it complied at the time etc.

hightower · Jan 5, 2017

westward10 said:
If bonding is absent then this will require additional works. If it is there, but undersized then a judgement needs to be made on it's adequacy and this may be dependent on other factors such as earthing system, whether it complied at the time etc.

Okay, we're getting somewhere now. So back to my very first question and the point of my post. Where does this bonding need to comply for me to carry out an install? Just the bonding of the area of the circuit I'm working on? The bonding of the area of the DB I'm working on? Or the bonding of the whole installation from origin on?

Risteard · Jan 5, 2017

westward10 said:
whether it complied at the time etc.

Certainly the adequacy could be dependant on a number of things, but whether it was permissible at the time or not couldn't possibly have any bearing on whether or not it is adequate.

Wilko · Jan 5, 2017

hightower said:
Where does this bonding need to comply for me to carry out an install? Just the bonding of the area of the circuit I'm working on? The bonding of the area of the DB I'm working on? Or the bonding of the whole installation from origin on?

I think the answer will depend on the earthing system at the building DB. If the building was TT then (with my tin hat on) perhaps just that building would suffice, but other systems would need further verification back to the installation DNO connection and MET