advice

[Lenny07]

Hi, just needing sum advice on cu change.

Q1. No cont of cpc on down ring, is it k to disconnect damaged cable from each relevant sckt and have 2 radial circuits?

Q2. Cont of L - L on up ring 17.9 ohms, is ti ok to do the same as above?

Q3. Landing light has borrowed neutral, can i put both lighting circuits on same mcb?

I only ask these questions as client wants min disruption as they have decorated the house, we know there is jbs under floor as old colours at cu and new colours in skts. Thanx.

 

[Theorysparky]

Q1 Yes 20amp radials

Q2 I would do more testing/investigation and narrow it down. it sounds like a poor termination.But if thats not conclusive then radials again

Q3 Yes thats fine

typical customers decorate then get electrics updated !!!!! muppets

 

[Apache]

yes X3, so long as the remaining radials in 1 and 2 test out ok

 

[batty]

I am sorry but cannot see you can have two radials when lives are connected or am I reading this wrong.

 

[Theorysparky]

er......

i assumed that he was going to disconnect the cable between the sockets that had the cpc fault..

high L-L continuity the same..

 

[Lenny07]

Thanx guys. I forgot to mention, no main bonds in which i am upgrading as part of the cu change anyway but i can only ascertain that the main water comes in property in plastic and comes out the top of the stop cock in plastic, un usual in the area. Client says its the only 1 he knows of, the boiler, gas, main stop cock and cu is under the stairs, i know u can only bond whats there but wud u advise bonding gas and boiler (overkill i know), also i was guna upgrade the main earth from 6mm to 16mm (tns system) am i right in believing 6mm is adequate or is that a tt? thanx for your help guys.

 

[kme]

Main bond - at least 50% of incoming consumer`s tails - if they`re 16, 10 is ok; if they`re 25 you should be looking at 16mm.

Gas bond is fine - no need to bond at boiler.

KME

 

[Lenny07]

Thanx kme

 

[ADS]

Main bond - at least 50% of incoming consumer`s tails - if they`re 16, 10 is ok; if they`re 25 you should be looking at 16mm.Gas bond is fine - no need to bond at boiler.

KME

16mm Bonding - Where does it say this?

 

[spinlondon]

16mm Bonding - Where does it say this?

Nowhere, for TN-S the requirement is to size according to the earthing conductor, must be a minimum of half the CSA of the earthing conductor, and not less than 6mm

 

[Sidewinder]

Spin,

No where as I can see is TN-S specified.

The sizing as I can see is as follows:

Table 54.1 specifies buried main earthing conductors.

Table 54.7 specifies main protective conductors.

Table 54.8 specifies main protective bonding conductors.

As no presentation is specified, we MUST take the worst case, that is PME & TN-C-S.

This directs us to 54.7.

KME may have had a lapse, however, up to 16mm sq 16mm sq copper equivalent is allowed for main protective conductor.

Up to 35mm sq 16mm copper equivalent is required for same.

In table 54.8 main protective bonding conductors.

Up to 35mm sq 10mm sq is allowed.

Up to 50 mm sq it is 16mm sq.

Up to 95mm sq it is 25mm sq.

Up to 150mm sq it is 35mm sq.

Above 150mm sq it is 50mm sq.

I suspect that he has either had a typo moment or a genuine lapse!

Admittedly you can always size according to the adiabatic if you have sufficient data.

Will you?

Always?

In the future?

In compliance with CDM etc... ?

Which is statutory... !

 

[spinlondon]

Post No. 6

Table 54.7 refers to protective conductors other than protective bonding conductors. See Regulation 543.1.1.

Table 54.8 refers to protective bonding conductors where PME conditions apply.

 

[Sidewinder]

Sorry Spin missd the little (tns system)!

---------- AUTO MERGE Post added at 22:51 ---------- Previous post was at 22:51 ----------

I would still probably size for PME/TN-C-S though.

 

[kme]

`Twas an "artois" moment..............

I beg your indulgence. I`m probably not in the best position to be posting technical comments "off the cuff" at the mo.........

I`ll probably be stupidly wrong a few times over the next few months. Apologies in advance. Blame old age or summat!

KME

 

[ADS]

Sorry Spin missd the little (tns system)!---------- AUTO MERGE Post added at 22:51 ---------- Previous post was at 22:51 ----------

I would still probably size for PME/TN-C-S though.

There's a lot of going off track here.

The OP is talking about a domestic CU change - so it's 10mm bonding.....TN-S or TN-C-S.

He's not likely to have 'incommers' of 10mm or less and he's not likely to have 'incommers' of 50mm or bigger - so it's 10mm Main Protective Bonding.

And it's 16mm Earthing Conductor.

I would always bring 'Earthing and Bonding' up to current Regs on a CU swap - none of this..... 'will a 6mm do?'

ESC Best Practice:

6. Main earthing and bonding and meter tails

6.1. The installer must verify, as a minimum, that:

a) the main earthing terminal of the installation is

connected to an adequate means of earthing

via a suitably sized earthing conductor,

B) the main protective bonding is adequate, and

c) the meter tails and the distributor

 

[spinlondon]

The minimum CSA required by BS7671 for protective bonding conductors is 6mm

 

[ADS]

The minimum CSA required by BS7671 for protective bonding conductors is 6mm

 

[ianmacd]

The minimum CSA required by BS7671 for protective bonding conductors is 6mm

 

[spinlondon]

ON SITE GUIDE PG 28 TABLE 4.1This table gives the minimum CSA of the 'Earthing Conductor' and 'Main Protective Bonding Conductors' for TN-S and TN-C-S systems.

As you can see from the table - unless you have an incomming 'Line' conductor (Neutral for PME), of less than or equal to 10mm or more than or equal to 50mm, then the 'Earthing Conductor' is required to be 16mm and the 'Bonding' conductors are required to be 10mm.

And if I am installing a '17th Edition' board, (and the additional protection it provides), then I certainly wouldn't be cowboyish and not upgrade the earthing and bonding to the same, 17th Edition, Regs.

I honestly don't know what you've been reading, Spin.QUOTE]

I've been reading BS7671, which the OSG is not, I suggest you do the same.

Following the OSG will ensure compliance with BS7671, however the guide does not list every manner in which compliance with BS7671 can be met.

BS7671 requires that earthing conductors meet the requirements of Section 543 and where PME conditions apply also meet the requirements of Regulation 544.1.1 (Regulation 542.3.1).

Section 543 gives requirements for selection of protective conductors in general, this can be achieved either by using the adiabatic equation or using Table 54.7 (Regulation 543.1.1).

Other than in the Table 54.1 there is no actual reference to a minimum CSA for an earthing conductor. Table 54.1 indicates a minimum CSA of 2.5mm

 

[ADS]

Sorry - Ignore the OSG Pg 28 Table 4.1 everyone - apparently these minimum CSAs for 'Earthing Conductor' and 'Protective Bonding Conductors' are wrong.

I hate argumentative people who do it for the hell of itX(

OK Straight Question, Spin -

Is the information in the table on pg 28 of the OSG incorrect?

No hummin or hahin or excuses and explanations - simple Yes or No!

What exactly is a 17th. edition board, is it any different to a 16th. edition board?

In my mind, a board containing RCDs/RCBOs that goes some way to complying with the requirement to not allow a fault on one circuit to interupt the supply to the whole installation..............

....but you know what I meant - you're just being pedantic.