remedial works after a periodic???

[Andy™]

I have read it somewhere ( i can't recall just now) that if the 6mm bonding does not show signs of any heat damage, then it will be fine.

i can remember reading something like that, but cant remember where either!

i think it may have been on a guide recommended PIR codes, something like 4 if no sign of damage, and 2 if sign of damage

 

[Nicky Tesla]

So will this now be OK if mentioned as a departure, seen as it is a code 4 when replacing the DB

 

[Andy™]

So will this now be OK if mentioned as a departure, seen as it is a code 4 when replacing the DB

i think it was more of a guide for PIR's. For alterations/new install i would upgrade it to 10. could possibly note as a departure if the customer wont allow you to replace and your sure (in your opinion) that it will be safe to leave as is.

 

[Nicky Tesla]

absolutely sure, when all mcbs are protected by an rcd

 

[green-hornet]

I have been doing work for the electrical safety council (grants scheme).

This is how they word a cu change.

Replace consumer unit with dual split unit each section 30mA RCD protected.

Circuits are to be arranged if possible so that RCD(a) controls one first floor lighting and one ground floor sockets circuit. The reverse being for RCD(B).

Renew meter cables, Renew main earthing lead.Renew bonding to gas and water services.

Bathroom supplementary bonding.

Apply continuity test between extraneous-conductive parts in bathroom and the main earth terminal in order to establish continuity through the water system. Where the measured resistance value is <0.05 ohms and all circuits in the bathroom are additionally protected by 30mA RCD(s) no supplementary bonding is required.

and so on and so on.

I have to work to those specs on all the works.

I just price for all the work to be done!

 

[Nicky Tesla]

from above post.....Where the measured resistance value is <0.05 and all circuits in the bathroom are additionally protected by 30mA RCD(s) no supplementary bonding is required.

If there is <0.05ohms then there is no need for supp bonding even if there are no rcds

and if there are rcds, then it doesnot matter if it is >0.05ohms

 

[green-hornet]

Like I said I work to the spec that they give, not what I think it should be.

Under the 17th edition supplementary bonding may be ommited providing that.

All circuits comply with the requirements for disconnection times

All circuits are RCD protected by a 30mA device maximum

All extraneous conductive parts in the location are effectively connected to the protective equipotential bonding.

So a continuity check should be the least you are required to do.

 

[steptoe]

a few points

1 its a CU change so an EIC and not a PIR

2 ALL earthing must meet the current regs, (unless you wish to deviate and prove with some other method the install is still safe)

3 it is NOT the "main earth" , it is simply the "earthing conductor", the term main implies a secondary one as well.

4 in TNCS it must be half size of neutral, minimum 16mm earthing conductor, 10mm meb

NT , you need to understand the principles of a TNCS system before you can justify that statement of having a max 30mA flowing through the system, it simply doesnt work like that, as I have pointed out before the reason for earthing conductors and MEB on TNCS being so apparently oversized is to allow for the carrying of imported fault currents.

 

[Nicky Tesla]

valid point steps

 

[Nicky Tesla]

just been thunking......if the water supply has a plastic incomer and is proved not to be earthy, but is still bonded (which I still think is odd, because it would not be an extraneous part) due to the system being in copper. Then TNCS fault currents will not flow along that bonding cable. Therefore 6mm will be fine IMOA

At least steps made a valid point and didnot simply say "that is not regs" you have to know why the regs are the regs.

 

[berlingo2]

quote from berlingo above....The new 17th edition consumer units are pre wired so that both RCD units will not trip at the same time.( the whole point of using a 17th board and splitting up circuits as per reg 314.1 on page 39)yes agreed, but it will not stop both RCD's tripping at the same time if there are two faults on seperate ccts at exactly the same time. As i said above not much chance of that happening.

Bonding cables exist to minimise the touch voltage between conductive and extraneous parts etc etc. They do this by keeping the voltage between parts below 50v, that is their job. Now if all the ccts in the house are protected by an rcd, then a max of 30mA could be flowing through any conductor be it conductive or extraneous. Therfore why on earth do we need bonding cables of 10mm in this situation really. What is the Prospective maximum current to pass through a bonding cable.

In fact any cpc on the whole system.....For me all the t&e cables should be fine with just 1.0mm cpc even 10mm.

broken neutral (PME)

 

[SPECIAL LOCATION]

Im about to carry out a change of consumer unit as a major job for the nic domestic installer inspector... now what i need to know is do i need to upgrade the supp bonding conductor from its original 6mm to 10mm for the installation to pass??? answers on a post card please...

how would you answer the inspector if he asked you to justify your choice with reference to 131.8 BS7671 and On-Site table4.1 Guide pg 28? ?:|

 

[steptoe]

hi Nicky, its not just about pulling in a fault through the water main/or gas, but on a TNCS you can actually pull in a fault through the neutral/earth, as it is also spiked in numerous places along its length, usually reasonably close to where it enters the property, thus enabling a fault in your neighbours property to easily jump across to yours as well.

earthing I think, as most of us are well aware, is somewhat of a major inconvenience, it must be the only thing we ever do that we hope is a total waste of time and never used!!!!

but, its all about ass covering, maybe sometimes Im OTT with it, but I think we all realise that to err on the right side of caution is the only way to ensure we stay separate from the bobs out there.

 

[green-hornet]

For measurement purposes, the Earth serves as a (reasonably) constant potential reference against which other potentials can be measured. An electrical ground system should have an appropriate current-carrying capability in order to serve as an adequate zero-voltage reference level. In electronic circuit theory, a "ground" is usually idealized as an infinite source or sink for charge, which can absorb an unlimited amount of current without changing its potential. Where a ground connection has a significant resistance, the approximation of zero potential is no longer valid. Stray voltages or earth

potential rise effects will occur, which may create noise in signals or if large enough will produce an electric shock hazard.

Not my words, they are taken from wikipedia just to clarify what earth is.

 

[ianmacd]

So with a TN-S system when working on a remote CU (garage/shed/etc..) would you have to bring the main bonding up to 10mm if its not currently (as per OSG table 4.1)?

Also is that a mistake in table 4.1 where it says the "Line conductor or neutral conductor of PME supplies"? Should that include TN-S too?

Ian.

 

[green-hornet]

TN-S systems export earths very well and bonding would be required to be upgraded as per current regs.

Table 4.1 refers to pme supplies because the TN-S systems are being replaced by pme.

It does include TN-S and is not meant to exclude it.

 

[PC Electrics]

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