Testing the lighting circuit

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A question on the "Continuity of CPC and Polarity" test using the Megger MFT.

I've recently purchased the Megger MFT and been using this for multiple tests.

On lighting circuits, the above is very easy when we are looping at the switch and there is only one wire going to the light. You can easily locate the Switching Line and Earth for the purposes of the test - at ceiling.

This is not so easy when you are looping at the ceiling and potentially have the following cables:
- Line In
- Line Out
- Switch
- Additional Light Feed
- Smoke Detector

In the above situation I tend to use Ideal Connectors which I shove above the ceiling plasterboard and only have two wires coming down to the light: Switching Line and Neutral (Earth is not required for this light fitting)

Similarly, my external light is also assembled in a series of Ideal connectors inside an adaptable box.

I suppose it's a case of performing these tests before fixing wires into the Ideal connectors or always ensure that an earth is also coming down to the light fitting?

I would appreciate your advice around how and when these test are handled. Thanks in advance.
 
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In the above situation I tend to use Ideal Connectors which I shove above the ceiling plasterboard and only have two wires coming down to the light: .
Point of order. The connectors above the ceiling MUST be inside a proper enclosure. Not just shoved up there hanging in the breeze.

All tests must be carried out to ensure polarity, Zs etc are correct. These tests need access to the relavent connections.

Your copy of Guidance Note 3, or the on site guide, tells you the process
 
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Do Ideal Connectors need to be in a box when they are accessible?
Practically, if I am fitting a light pendant, the hole for the box (to fit above ceiling) will be bigger than the radius of the pendant and hence, not hidden away when fitting the light pendant. Unless, it’s put away and plastered over.
 
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Practically doesn’t come in to it. The regulations state that every junction must be enclosed. That means that the cable outer sheaths should be fully inside the enclosure. No inner conductors can be outside the enclosure.

The enclosure itself must be secured to backgrounds and (of course) the cables supported, to prevent the cables being pulled out of the box. Or the enclosure must provide strain relief - typically cable clamps etc.

It is wrong to do otherwise. The best solution is for the junction to be within the ceiling lamp base.
Otherwise another method needs to be found, access from above, or relocate the junction to a location that is compliant. I know it’s inconvenient and often difficult, but electrical work can be like that sometimes.

For lighting circuits this is where loop in at the switch wins every time.

EDIT. These may be a solution for you

A bit dated (some of the reg numbers have changed) but this gives you some more info. https://www.tlc-direct.co.uk/Technical/DataSheets/Hager/JB_Guide.pdf
 
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Do Ideal Connectors need to be in a box when they are accessible?
Practically, if I am fitting a light pendant, the hole for the box (to fit above ceiling) will be bigger than the radius of the pendant and hence, not hidden away when fitting the light pendant. Unless, it’s put away and plastered over.
YES
 
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Loop at the switch is the way to go these days. If you need a permanent live at the ceiling, you can send up a 3C&E. Live, switched live, neutral and earth.
 
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A small point of "discussion".

I have come across the term "CPC" in this and another "discussion", where I did not understand it - at first!
I have ascertained that "CPC" may mean "Circuit Protective Conductor" - for which the more "usual" term is PE (Protective Earth) or PEC (Protective Earth Conductor).

To me, it seems that the term "CPC" is somewhat unorthodox - and "weird", since it does not reference "Earth" or "Ground" in its "name"
(I do know that connection to Earth or Ground is not the point but connection to the "neutral" source is the real point - for "Equipment" Earthing/Grounding..)

I wonder what "authority" recognises "CPC" - as opposed to the "recognition" of PE, PEC, Earthing Conductor, Grounding Conductor etc. - or just "Earth" or "Ground".
 
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To me, it seems that the term "CPC" is somewhat unorthodox - and "weird"
It's not unorthodox in the UK because that is the term we use.

Do you dispute that it protects the circuit?

I wonder what "authority" recognises "CPC" - as opposed to the "recognition" of PE, PEC, Earthing Conductor, Grounding Conductor etc. - or just "Earth" or "Ground".
'The' Earthing Conductor is the conductor from the supply earth to the MET.
 
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Re " the term "CPC", as an acronym for "Circuit Protective Conductor"
It's not unorthodox in the UK because that is the term we use.
OK.
However it was not familiar to me
Do you dispute that it protects the circuit?
If one wishes to be a bit technical, a CPC/PE/Earthing Conductor/Grounding Conductor does not "protect" the circuit (wiring).
However, it should provide a low resistance "path" for the return to the "Neutral" source of the "Supply" of any "Overload" (fault) current, which then "causes" the "Protection Device" (Circuit Breaker/MCB/RCBO) to operate.
'The' Earthing Conductor is the conductor from the supply earth to the MET.
Now you have introduced another acronym (MET) unknown to me, which may one of these https://acronyms.thefreedictionary.com/MET - or some other.

Please explain !


A "Supply Earth" (PE/CPC) is provided only with TN-S Systems.
In a TN- C System, it is "provided" along with the Neutral (PEN)
In a TN-C-S System, it is provided "locally", via a "Earthing/Grounding Electrode" connected to the "Neutral" Supply at the first "point of connection" (only).

(In a TT system, the PE is provided only "locally".
Good luck with that "connection" being of low enough resistance to be able to supply the current required to operate a "Circuit Breaker" for "Equipment Protection" ! )
 
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In a TN-C-S System, it is provided "locally", via a "Earthing/Grounding Electrode" connected to the "Neutral" Supply at the first "point of connection" (only).

In a TN-C-S there is no requirement for an "Earthing/Grounding Electrode" at the premises. In some network fault situations a local ground electrode ( at the house ) can introduce significant risks of high currents from Neutral to Ground electrode.

What do you mean when you say ""the first "point of connection" (only). ? Where is this first point ?
 
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In a TN-C-S there is no requirement for an "Earthing/Grounding Electrode" at the premises. In some network fault situations a local ground electrode ( at the house ) can introduce significant risks of high currents from Neutral to Ground electrode.

What do you mean when you say ""the first "point of connection" (only). ? Where is this first point ?
While I do not wish to argue with you - in North America and in Australia/New Zealand - the TN-C-S systems installed there do require a "local" Earthing/Grounding Electrode.
This "electrode" does not provide any extra benefit for "Equipment Grounding/Earthing" but it is there to provide (local) "System Grounding/Earthing"

This also becomes a part of the Multiple Earth System (MEN)

If the need to provide local "System Earthing" in the UK is not seen to be significant, that is another matter, but it is seen to be significant in North America/Australia/New Zealand etc.

"The first point of connection" is at the CU/Panel, where the "Supply Authority" "Neutral Bar" is "linked" to the local "Earth Bar" and the "Earth Bar" is connected, via a "High Capacity" conductor (6 mm² CSA in Australia), to an Earthing Electrode - to provide "System Earthing".

Much of this is discussed in
which I invite you to view.

The different requirements of "Equipment Earthing" and "System Earthing" are often not understood - even by "Electricians"

See https://commons.wikimedia.org/wiki/File:HomeEarthRodAustralia1.jpg
Note that "The coiling of the conductor in the manner shown, provides an Impedance, which defeats the purpose of this Earth/Ground connection for "System Earthing/Grounding"."
 
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@FrodoOne I will admit that CPC and MET are abbreviations, but these terms are in common use and defined in the Wiring Regulations, the OSG and elsewhere. I can’t think of a day at college when both weren’t used all the time (except down the pub).
Maybe time to have a read?
 
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The different requirements of "Equipment Earthing" and "System Earthing" are often not understood - even by "Electricians"

True. Earth that protects the cable and Earth that protects the equipment need not be the same

13 Apr 2018
There is often confusion between a "high integrity earth" and a "clean earth".

High integrity earthing involves one or more alternative earth cables from sockets to the main Earth terminal at the consumer unit. The earths in sockets connect to this earthing system,

Clean earthing involves two separate earthing systems. The cable and metallic fittings ( back boxes etc ) are protected by the standard earthing system of a conductor in the cables. The earths in the sockets connect to a separate earth system which is grounded to a clean ( free of electrical noise ) earth. Often a ground rod or rods.

mk clean earth.jpg


1656496870139.png



The link is cut if a clean earth to sockets is required with a separate CPC earthing to the fixing screws and ( in this socket ) the metallic front plate

The terminals with the half circle are for a clean earth that protects the equipment plugged into the socket. A clean earth is NOT the CPC and should NOT be connected to it. A clean earth uses a separate wire which connects to a local Ground and as such is not affected by electrical noise that is present on the CPC

Where there is no provision or need for a clean earth then the two earth terminals must be linked so that the CPC is connected to both the Clean Earth terminal and the CPC earth terminal in the socket.

Clean earths are used for sensitive equipment and for communication equipment where the case / frame of a machine must be at true ground potential to avoid potential differences along communication cables that connect the frame of one system to the frame of another system at a remote location.
 
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Re " the term "CPC", as an acronym for "Circuit Protective Conductor"
That is not an acronym.

OK. However it was not familiar to me
So what? You are on a foreign site.

If one wishes to be a bit technical, a CPC/PE/Earthing Conductor/Grounding Conductor does not "protect" the circuit (wiring).
However, it should provide a low resistance "path" for the return to the "Neutral" source of the "Supply" of any "Overload" (fault) current, which then "causes" the "Protection Device" (Circuit Breaker/MCB/RCBO) to operate.
The CPC does not come into it when an overload occurs.
In the event of an earth fault, by disconnecting the supply, it might prevent someone getting a shock (or the line conductor melting) so could be termed 'circuit protection' - or even protection in the circuit, if you will.

We use lots of words that are not really suitable for the specific usage.
Portuguese would be much easier to learn if only they didn't have different words for everything. I shall complain.

Now you have introduced another acronym (MET) unknown to me, which may one of these https://acronyms.thefreedictionary.com/MET - or some other.
Please explain !
Main Earthing Terminal.

Once again, you are on a foreign site - although you have been here for five years and don't seem to have learned much.

While, obviously, you may ask what terms mean, I do not understand your belligerent attitude.
 

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