skts x 2 earth terminals

[driverman]

Been 2nd fixing today, which i've not done for many years. I've noticed that both Volex 13A twin & single sockets have 2 x earth terminals. Is that now standard? I thought that requirement was only applied to sockets that served a lot of IT equipment. Even years ago i would sleeve the earths separately, but then into one terminal. Is there any electrical reason for the change? Thanks

 

[UNG]

ugh, twisted earths, the bane of fault finding / testing!

You forgot the twisted live and neutrals for extra grief just weakens the cable IMO

Exactly, never have liked twisting conductors together. As an apprentice years ago, it was the norm to twist (was imperial then) conductors together. When metric cables came out, many electricians still twisted conductors together. In my opinion very bad practice. I doubt if many twist conductors together nowdays! Or do they ?

There are people who still do it they should have their pliers confiscated

There are arguments for both.
Twisting together would allow for continuity of the conductors, if the terminal became loose.
Twisting together restricts the number of conductors that can be terminated.
Twisting together is a pain when it comes to testing.

I think people who do are just twisted

i can't see it making any difference what so ever. However, as not in the game as such I just wondered why the introduction. Surly must be more expensive to produce, therefore there must be a reason why. Could it be an EU instruction?

It probably won't make much difference to the Bob's in the factory whether it has one earth terminal or two

EU are not interested in UK sockets....the reason is manufacturers dont have to manufacture both types....cheaper to tool for one only,and the extra cost of the two terminals is sneaked onto us.

The mouldings on a lot of sockets these days universal so they can have one or two earth terminals, the extra cost of the second earth terminal is probably only a few pence

In fault-finding an RFC with a higher-than-expected value for r2, on at least a couple of occasions it has turned out to be due to relying on the socket internal metalwork.

One end of the RFC into one terminal, the other end of the RFC into the other terminal. Screws done up tight. But the sockets had riveted bits of metal work, not always making good contact. I've seen sockets with the best part of an Ohm measured between the two terminals.

Had this a few times I also find the switches can be a bit hit and miss when doing R1 - R2 tests

 

[Deleted member 9648]

You forgot the twisted live and neutrals for extra grief just weakens the cable IMO



There are people who still do it they should have their pliers confiscated



I think people who do are just twisted



It probably won't make much difference to the Bob's in the factory whether it has one earth terminal or two



The mouldings on a lot of sockets these days universal so they can have one or two earth terminals, the extra cost of the second earth terminal is probably only a few pence



Had this a few times I also find the switches can be a bit hit and miss when doing R1 - R2 tests

Those few pence per socket add up when you are mass producing.

 

[Tidy Max]

Im not sure what your saying Spin?
Are you saying the image (for example) in Guidance note 8 page 132 is incorrect!
As it says on page 131 that if the ends of the protective conductor are separately terminated at DB & sockets then Reg 543.7 will be met as shown in image

That is specifically for circuits that have high protective conductor currents. Which is what Spin is saying.

In the post that you quoted he is saying in a normal RING circuit there is only ONE cpc.

 

[Simlec]

That is specifically for circuits that have high protective conductor currents. Which is what Spin is saying.

In the post that you quoted he is saying in a normal RING circuit there is only ONE cpc.

​Are you sure?

 

[Tidy Max]

Yes i am sure! You may have two ends but its two ends of the same cpc! There aren't two seperate circuit protective conductors! Once again i will totally hold my hands up if i am getting the wrong end of the stick which is usually the case!

 

[Simlec]

Ring circuits, by their design, provide duplication of all conductors, including the protective conductor unless this is formed by metallic conduit and/or trunking. Regulation 543.7.1.104 requires that each protective conductor is terminated separately at each connection point; the regulation also requires that each wiring accessory has two separate earth terminals. At socket-outlets, this is a very easy requirement to meet – simply select accessories with dual earth terminals.

 

[Deleted member 26818]

As far as I can recall, the requirement is for a CPC with a minimum CSA of 4mm, or for there to be 2 CPCs both of which must satisfy the requirements to be considered as a CPC.
RFCs are effectively a circuit with conductors run in parallel so in a standard RFC run in 2.5mm T&E the conductor sizes can be considered as 4mm line, 4mm neutral but only 3mm CPC.
3mm as I am sure you are aware, is less than the 4mm required.
Some people say that because it's 2 conductors, it is therefore 2 CPCs.
That's ok, as long as both of the conductors would satisfy the requirements to be considered as CPCs.
When RFCs are run in singles, all of the conductors are usually the same CSA, so if the CSA of the CPC is 2.5mm, then when doubled, we have 5mm which is greater than the minimum 4mm required.

 

[Silly Sausage]

Ring circuits, by their design, provide duplication of all conductors, including the protective conductor ..................

It's not though, is it?!?! The conductors carry differing currents along their lengths.

Also, if you whip out a section of the ring (or get a break ), what do you get????
Two undersized Radials!

Yes i am sure! You may have two ends but its two ends of the same cpc! There aren't two seperate circuit protective conductors!

I completely agree!

 

[Guest55]

It's not though, is it?!?! The conductors carry differing currents along their lengths.

not being balanced with regards to load carrying doesnt exclude them from being duplicated........

;-)

edit ;

if you break a ring at any point , you have 2 radials , thereby you must have 2 cpc's.......

 

[Maddison]

i was always taught one cpc from each leg into each terminal then link between the two so not relying on the socket as the link, that way if one comes loose there is still another terminated and socket is still protected rather than losing both earths.

 

[Deleted member 26818]

not being balanced with regards to load carrying doesnt exclude them from being duplicated........

;-)

edit ;

if you break a ring at any point , you have 2 radials , thereby you must have 2 cpc's.......

If when testing an RFC you discover the CPC is not continuous, what code would you apply and why?

 

[UNG]

Those few pence per socket add up when you are mass producing.

How many times have manufacturers tried to save a few pence that have ended up costing them millions
There are so many factors to consider in mass production a few pence for an extra terminal is only one of them

i was always taught one cpc from each leg into each terminal then link between the two so not relying on the socket as the link, that way if one comes loose there is still another terminated and socket is still protected rather than losing both earths.

I've done that a few times to get round a resistance problem on the socket link

 

[shanky887614]

How many times have manufacturers tried to save a few pence that have ended up costing them millions
There are so many factors to consider in mass production a few pence for an extra terminal is only one of them



I've done that a few times to get round a resistance problem on the socket link

why would you do that except on it installations?

you want the conductors together or your just adding more resistance for no reason

 

[Guest55]

If when testing an RFC you discover the CPC is not continuous, what code would you apply and why?

firstly , why would i bother giving a reply to that question when you were unable to answer in your own words why you would issue a C2 for 3.5mtr tails in yesterdays meter thread ?

secondly , your question has no relevence to the statement i made above.

 

[Deleted member 26818]

To be honest, if the socket has that high a resistance between the two terminals, it sounds faulty, and could probably do with being returned to the supplier/manufacturer.

 

[Deleted member 26818]

firstly , why would i bother giving a reply to that question when you were unable to answer in your own words why you would issue a C2 for 3.5mtr tails in yesterdays meter thread ?

secondly , your question has no relevence to the statement i made above.

I have answered that question.
Here is the answer again:
It does not comply with BS7671 and it is potentially dangerous.

Why is it not relevant?
You are suggesting that an RFC if split is two Radials, therefore there are two CPCs.
If that's the case then a discontinuous CPC on an RFC should have no code.

 

[Guest55]

I have answered that question.
Here is the answer again:
It does not comply with BS7671 and it is potentially dangerous.

Why is it not relevant?
You are suggesting that an RFC if split is two Radials, therefore there are two CPCs.
If that's the case then a discontinuous CPC on an RFC should have no code.

your original answer consisted of nothing more than a link to a meter operators code of practice , which is completely irrelevent with regards to an inspection conducted to bs7671

and youre still not making it clear how we go from no code for 3mtr tails to C2 for 3.5mtr and a discription of the hazard posed to incur such a code.

yes , i said a rfc split is 2 radials with 2 cpcs.

the reason you would issue a defect code for a break in cpc continuity on a rfc is because a circuit designed to operate as a rfc is no longer functioning in the manner that it was originally intended , which in no way contradicts my statement that a split ring contains 2 cpc's.

 

[Simlec]

I'm not sure where the 4mm CPC comes into play other than the flex from the sockets above 16a.
the min size of CPC for the two individual conductors on a ring final circuit is 1.5mm

My maths must not be upto much if there is only one CPC in a ring circuit...

 

[Deleted member 26818]

The 4mm requirement is for where high integrity earthing is required.
I believe the minimum CSA is 10mm if not copper, and 4mm if copper.
I don't know about your maths.
As for there being 2 CPCs in a RFC, fine, I imagine that they both connect to every point served on the circuit as per the requirements of BS7671?
As I said earlier an RFC is effectively a circuit supplied using parallel conductors.
Unless the combined CSA of the CPC conductors is greater than 4mm, a separate CPC will be required.
That separate CPC is required to be such that fulfills the requirements that pertain to CPCs.
In other words, you can't just run in a 1mm conductor to take the total CSA of the CPC conductors to 4mm.
If the RFC is wired in singles and the CPC conductors are 2.5mm, then the combined CSA of the two CPC conductors is 5mm, which exceeds the 4mm minimum, and another separate CPC is not required.

 

[Deleted member 26818]

your original answer consisted of nothing more than a link to a meter operators code of practice , which is completely irrelevent with regards to an inspection conducted to bs7671

and youre still not making it clear how we go from no code for 3mtr tails to C2 for 3.5mtr and a discription of the hazard posed to incur such a code.

yes , i said a rfc split is 2 radials with 2 cpcs.

the reason you would issue a defect code for a break in cpc continuity on a rfc is because a circuit designed to operate as a rfc is no longer functioning in the manner that it was originally intended , which in no way contradicts my statement that a split ring contains 2 cpc's.

Not stating that your statement is contradicted.
I did ask what code you apply.
I would also remind you that BS7671 only requires us to comment and code instances which may give rise to danger. The're is no requirement to make observations or apply codes to instances that do not give rise to danger.

So to repeat my question:
What code and why would you apply to a discontinuous CPC in a RFC?