More building regs questions v.2

[ppelec100]

So having a look at the electricians guide to the building regulations, section 7 safe working.
7.3 is about pre work tests and is states that electricians should carry out the following test before any installation work is carried out including additions and alterations to existing installations also rewires and new installations...

a) polarity
b) effectiveness of earthing
c) operation of RCD's

My 2 questions are as follows:

Q1) Why is the insulation resistance test not included? I know if the IR was 0 ohms it would be tripping, but lets say if it was like 1 mega ohm... surely this should be investigated as it is low and additions and alterations will be affected if that 1 mega ohm then went below?

Q2) How far do you go with the effectiveness of the earthing? Is it just an R1+R2 test for continuity of cpc or is it also a Zs reading?

Thanks for any answers once again, just trying to learn for the future. ?

 

[telectrix]

IMO the 3 things mentioned are more to do with ensuring your safety before starting work. Other testing comes later.

 

[snowhead]

As Tel, the clue is in the title of the chapter,
section 7 safe working

Subsequent chapters will have different procedures to conduct

 

[telectrix]

just to expand.....

a) polarity........ ensures that if you switch a MCB off to work on a circuit, you are switching L and not N
b) effectiveness of earthing. .....ensures that you aren't going to get a belt off metallic enclosures etc.
c) operation of RCD's. will save you life if you make a cock-up.

now where's my tinfoil hat to ensure the aliens can't suck out my brain?

 

[pc1966]

Those 3 items are all about ensuring that fault protection works. Not that the installation is free of faults!

a) Goes beyond the MCB being a means of isolation. Correct polarity is critical (in the UK for sure) so that your OCPD is in the line conductors (not neutral) otherwise you have no meaningful over current protection to earth. A fault very likely will cause a fire as your 2.5mm or whatever is trying to take out the DNO's 100A fuse. That is why incorrect polarity is a C1 for EICR.

b) Effective earth is also fundamental to safety. Even with RCD protection you must have a usable earth otherwise the RCD is not "additional" protection, since it won't trip on a typical fault until some poor sod completes the circuit. Should that be in somewhere like a shower the resulting shock current/time even from a 30mA instant RCD is getting in to the dangerous region.

c) Is kind of self-explanatory. But you also have to remember in a TT system you are almost certainly dependent on the RCD action to clear a fault as your earth rod is unlikely to be low enough impedance to trip the MCB action. RCD are far more complicated than a fuse, or thermal-magnetic MCB, so testing them under simulated leakage conditions is needed as you can't be sure they are working simply because you can manually flip the breaker on/off.

But you are right that you should also be testing the insulation out before energising final circuits in all cases.

 

[telectrix]

basically, broken down into 3 sections.
1. before working.
2. before energising.
3 . after energising.

 

[Lister1987]

just to expand.....

a) polarity........ ensures that if you switch a MCB off to work on a circuit, you are switching L and not N
b) effectiveness of earthing. .....ensures that you aren't going to get a belt off metallic enclosures etc.
c) operation of RCD's. will save you life if you make a cock-up.

now where's my tinfoil hat to ensure the aliens can't suck out my brain?

Waste of tinfoil Tel ?

Goes back to way tests are done on the prescribed order; to ensure the following test has a safe way of going wrong

 

[ppelec100]

IMO the 3 things mentioned are more to do with ensuring your safety before starting work. Other testing comes later.

As Tel, the clue is in the title of the chapter,
section 7 safe working

Subsequent chapters will have different procedures to conduct

Those 3 items are all about ensuring that fault protection works. Not that the installation is free of faults!

basically, broken down into 3 sections.
1. before working.
2. before energising.
3 . after energising.

Okay thanks I should of noted that the section 7 is about safe working and this is mainly for the safety of the person carrying out the work.

So where will I find info on the pre-checks to do on a circuit to determine if the circuit is adequate to carry out any alterations or additions to?

I'm assuming an R1+R2 test should be done as a pre-check which is basically part of the 7.3 as well as after works being carried out to make sure there is a continuity of CPC.

For a ring circuit the end to end test will need to be done too? Will the step 2 and step 3 test need to be done (figure of 8 of end to ends)?

Should an IR test be done a as a pre-check to ensure the circuit is adequate enough for additions or alterations too? As I wouldn't feel too keen on making an alteration or addition to a circuit which has a IR of 1M ohm, although it satisfies the minimum requirement, it would still require some investigation right?

 

[Lister1987]

Okay thanks I should of noted that the section 7 is about safe working and this is mainly for the safety of the person carrying out the work.

So where will I find info on the pre-checks to do on a circuit to determine if the circuit is adequate to carry out any alterations or additions to?

I'm assuming an R1+R2 test should be done as a pre-check which is basically part of the 7.3 as well as after works being carried out to make sure there is a continuity of CPC.

For a ring circuit the end to end test will need to be done too? Will the step 2 and step 3 test need to be done (figure of 8 of end to ends)?

Should an IR test be done a as a pre-check to ensure the circuit is adequate enough for additions or alterations too? As I wouldn't feel too keen on making an alteration or addition to a circuit which has a IR of 1M ohm, although it satisfies the minimum requirement, it would still require some investigation right?

Sequence of tests will be on part 6 or big blue, or in GN3 and on-site guide.

 

[pc1966]

I'm assuming an R1+R2 test should be done as a pre-check which is basically part of the 7.3 as well as after works being carried out to make sure there is a continuity of CPC.

For a ring circuit the end to end test will need to be done too? Will the step 2 and step 3 test need to be done (figure of 8 of end to ends)?

Should an IR test be done a as a pre-check to ensure the circuit is adequate enough for additions or alterations too?

Short answer is yes - test first or repent later when problems come up!

Never assume something is correct before you start, otherwise you might make a change and then spend your time trying to fix your work when really the fault was elsewhere.

As I wouldn't feel too keen on making an alteration or addition to a circuit which has a IR of 1M ohm, although it satisfies the minimum requirement, it would still require some investigation right?

I would agree with you there, anything below a few Meg is suspect unless you have a very good reason why it might be like that (e.g. very extensive industrial circuit with lots of dust and damp).

 

[ppelec100]

Sequence of tests will be on part 6 or big blue, or in GN3 and on-site guide.

The sequence of test is for AFTER the work has been carried out (dead test and live tests)... Or I'm guessing it would be used to check the adequacy of the circuit too, prior to carrying out works? But it seems excessive to carry out ALL the tests, so which ones are necessary?
Isn't there info on ONLY circuit testing prior to carrying out works? If so, which book and what section could I find this info?

I'm just trying to finish the building regs book before I make a start on the guidance note 3. So if its in there let me know and I'll refer to it once I start.

Thanks for answering

 

[ppelec100]

Short answer is yes - test first or repent later when problems come up!

Never assume something is correct before you start, otherwise you might make a change and then spend your time trying to fix your work when really the fault was elsewhere.


I would agree with you there, anything below a few Meg is suspect unless you have a very good reason why it might be like that (e.g. very extensive industrial circuit with lots of dust and damp).

Where would I find the info for the test to carry out PRIOR to carrying out works to ensure the circuit is adequate?

Which test would you carry out then prior to carrying out any works on a circuit?
Let's say an existing lighting circuit, and someone wanted an extra light with a switch for that light and also a ring circuit which they wanted to add an extra socket to.

 

[DPG]

Where would I find the info for the test to carry out PRIOR to carrying out works to ensure the circuit is adequate?

Which test would you carry out then prior to carrying out any works on a circuit?
Let's say an existing lighting circuit, and someone wanted an extra light with a switch for that light and also a ring circuit which they wanted to add an extra socket to.

I would definitely recommend GN3.

 

[Lucien Nunes]

The tests and test sequences specified in regulations (and guides to same) are all about ensuring that completed installations achieve a recognised and agreed level of safety. How you tackle a job in a way that makes your time usage efficient, your business profitable and your customers happy is more of a commercial strategy than a technical requirement, provided you always leave the installation safe and compliant.

You might choose not to bother testing anything at the beginning, then pay for any remedials yourself at the end out of the time saved and extra jobs you won by cracking straight on and getting a good reputation for not being fussy or awkward. Or, you might test the hell out of everything, put in pessimistic quotes, insist on extra work being done that the customer wasn't expecting, lose some jobs but never have to cover the cost of remedials yourself. Between the two extremes is probably an optimum point for the type of installations and customers that you have to deal with.

 

[ppelec100]

I would definitely recommend GN3.

Okay thanks, I will start reading the GN3 after I finish the building regs book

 

[pc1966]

Where would I find the info for the test to carry out PRIOR to carrying out works to ensure the circuit is adequate?

Which test would you carry out then prior to carrying out any works on a circuit?
Let's say an existing lighting circuit, and someone wanted an extra light with a switch for that light and also a ring circuit which they wanted to add an extra socket to.

As Lucian says, there is a certain business trade-off in how you should best tackle a job, and some of that will come with experience as you get to know the range of customers and the sort of installations you are going to work on.

It is quite risky to quote time & cost without seeing the installation, but often when you take a quick look (or get the customer to send some photos of the supply/CU and the bits they want changed, etc) you will have an idea if it is risky to offer without testing or not.

So for a big job like a CU change you really want to know what you are getting yourself in to, so many electricians would insist on an EICR first, either as a step before quoting (if it looks like a troublesome job) or as the initial stage of the work if it looks routine.

A very good guide as to what things might be wrong that would need rectification as part of any work (big or small) is available for free as the Best Practice Guide #4 here:

Best Practice Guides | Electrical Safety First

Electrical Safety First produces, in association with other industry bodies, a range of Best Practice Guides which provide definitive information and guidance on a range of technical subjects.

www.electricalsafetyfirst.org.uk

For smaller jobs, such as a light change or extra socket, you probably don't need to test before quoting, unless the age or general condition/abuse over the years gives you cause to worry. But it is best to do at least a quick check before you start in case there are surprises, then the customer does not get the impression you are trying to make up for mistakes you made. I.e. you can be up front if you discover a problem that is possibly costly to fix (e.g. open or missing CPC on lighting where it might be in a hidden junction box somewhere).

It may not change the job outcome/cost. But at least they should feel you are doing it professionally by checking for safety first and letting them know, rather than doing the work and then trying to explain why it was actually broken before you touched it.

 

[ppelec100]

Hello again,

For any more questions I have on the building regs, I will just post here rather than constantly creating new post... I hope it doesn't break any electriciansforums regulations

Reading through section 8.4.2 page 133, near the bottom of the page where it gives examples of c1 c2 c3... C3 (b) states: no supplementary bonding in bathroom where it is required.
Now I think I know why it would be required... because if plastic pipes are used and the bonding would not be continuous from the water stopcock position? So you would have to bridge the copper pipe (before it converts to plastic) to any metal bathroom taps, showerheads etc (after the plastic pipe)??

This is more of a confirmation question
Thanks for any answers

 

[westward10]

See Regulation 132.16 where you are required to carry out some basic checks before additions or alterations are carried out. The checks you have quoted are likely to satisfy this Regulation.

 

[ppelec100]

See Regulation 132.16 where you are required to carry out some basic checks before additions or alterations are carried out. The checks you have quoted are likely to satisfy this Regulation.

Thanks