Computer RFC Testing???

[Paul.M]

I'm scratching my on this because I've never done it before. I'm on a new build school wire with quite a few computer RFC's using 2.5 T&E + a 4mm single Earth that we are just pulling in now. When it comes to us testing these circuits, how do I/we record the results?

Both the 1.5mm CPC and the 4mm Earth will be in the same terminal at each socket therefore creating a parallel path with a higher resistance if only one of them is tested, but these are going to always be like this, so do I record the combine findings or test for continuity on each of the R2's then record the R2 of each on one cert or make another page for one of the findings?

I've got it in my head that we need to do 3 lots of R2 tests and put them all on paper:-

1.5mm CPC
4mm Earth
Combined CPC + separate Earth.

Or is it just me + the QS + another very qualified spark that is having a blond moment???

 

[D Skelton]

Am I right in thinking that your 4mm is for HI earthing, if so it needs to be in a seperate terminal at each socket. I may be wrong but I was taught that you need to carry out the usual r1 + r2/r2 tests with the CPC only. Record the value of the HIEC but don't use it as part of your calculation when working out/measuring Zs.

Like I said, I may be wrong and need correcting but I remember this is the way I was taught.

 

[Guest55]

only 1 reading is to be recorded , and as the 4mm is performing the role of cpc as well as the t&e , then take measurement of both combined would be my solution.

 

[Top Cat]

Cut the 4.0mm earth out, problem solved!:54:

 

[Elmer BeFuddled]

Daft Q #3 (there will be loads more!!) I thought a separate earth was only needed on the end of a radial (i.e. L&N are radial, earth is a ring) back to the CU and at each socket the in and out earth (in the t+e) should use the separate earth terminals to ensure if one drops out there will still be a path to earth?

 

[Paul.M]

Am I right in thinking that your 4mm is for HI earthing, if so it needs to be in a seperate terminal at each socket. Yes it is

I may be wrong but I was taught that you need to carry out the usual r1 + r2/r2 tests with the CPC only. Record the value of the HIEC but don't use it as part of your calculation when working out/measuring Zs. This is my dilemma, what do I put on the cert? A normal R1 + R2 (or a R2 only [accetable btw]) on the 1.5mm CPC or the 4mm Earth (not the CPC due to routing) or the combined reading of the the two?

Like I said, I may be wrong and need correcting but I remember this is the way I was taught.

Thanks mate, good in put. Makes me think more about it. Is there, or should there be more in the regs (GN3) about this?

After all, this is for a school and I'm not the type of man to cut corners. I'm going to every test and bang everything down on paper, then let the XXXXXXX city council Clerk of Works question me about it.

 

[D Skelton]

I was taught r1+r2 or r2 value recorded for CPC (1.5mm) only is to be your actual value, this being the value you would put down on the cert. The value measured on the 4mm HIEC is to be measured and recorded but not as part of the r1+r2/r2 on the certificate.

With regards to HIECs check out section 543.7.1, in particular 543.7.1.104.

 

[Paul.M]

only 1 reading is to be recorded , and as the 4mm is performing the role of cpc as well as the t&e , then take measurement of both combined would be my solution.

Thats my point Biff. Both CPC and Earth conductor will be the return path on a R1 + R2 test as well as a Zs which would be lower resistance (on the R2) than the R1 due to the combined CSA of the CPC and Earth.

To late tonight, I'll do some maths tomorrow.

 

[Paul.M]

I was taught r1+r2 or r2 value recorded for CPC (1.5mm) only is to be your actual value, this being the value you would put down on the cert. The value measured on the 4mm HIEC is to be measured and recorded but not as part of the r1+r2/r2 on the certificate.

With regards to HIECs check out section 543.7.1, in particular 543.7.1.104.

You are a star. Book reading tomorrow for me. Too late tonight. Cheers for that.

 

[Guest55]

Thats my point Biff. Both CPC and Earth conductor will be the return path on a R1 + R2 test as well as a Zs which would be lower resistance (on the R2) than the R1 due to the combined CSA of the CPC and Earth.

To late tonight, I'll do some maths tomorrow.

CPC & earth ? i'd say CPC & CPC.
if the 4mm isnt performing the function of a cpc whats it doing ?
if it is considered as a cpc why not include it in the R2 / Zs measurement ?

 

[i=p/u]

You actually don't need it on a ring just in and out on diff terminals of each socket1.5mm is enough

hope this helps wee man.

 

[D Skelton]

if it is considered as a cpc why not include it in the R2 / Zs measurement ?

Because you're taking into account worst case scenario

 

[Guest55]

Because you're taking into account worst case scenario

which is what ?

 

[D Skelton]

which is what ?

4mm falls out?

 

[i=p/u]

Just for you Paul m. You've been helpful to me I'm sure b4

 

[Guest55]

4mm falls out?

eh ? what the hell you on about ?
why would a loose connection be a reason not to include the 4mm in the tests ??
its just as likely a 1.5mm could pop out in which case you'd be relying on the 4mm to help clear any fault current as well as the remaining 1.5.
totally lost me there.

 

[Paul.M]

CPC & earth ? i'd say CPC & CPC.
if the 4mm isnt performing the function of a cpc whats it doing ?
if it is considered as a cpc why not include it in the R2 / Zs measurement ?

When is a CPC not a CPC?

A. When it is an Earth.


CPC protects the cable and provides an Earth return path.

An Earth is the return Earth path for the appliance/s.


Now the repeated question:- Which one do I write down on the cert? Both doing the same job, but both are are doing a different function.

I pretty much know the answer but I'm asking for your opinions and some where that I've got it in the regs (thanks Jim).

What would you write on a cert???

 

[Guest55]

is that directed at me paul or just in general ? lol.

 

[D Skelton]

eh ? what the hell you on about ?
why would a loose connection be a reason not to include the 4mm in the tests ??
its just as likely a 1.5mm could pop out in which case you'd be relying on the 4mm to help clear any fault current as well as the remaining 1.5.
totally lost me there.

Why else would the regs specifically ask for the conductors to be terminated seperately? My guess is higher than average earthing conductor currents means expansion and contraction of terminations (even a miniscule amount) that have to be taken into account. As it is an earthing conductor extra precautions are there to ensure fail safes.

To be honest, I'm not sure, and I may be barking completely up the wrong tree but I was taught to install and test the way I said, but why? I've never really given it a thought until now. It would seem that none of us so far are 100% sure

 

[Paul.M]

You actually don't need it on a ring just in and out on diff terminals of each socket1.5mm is enough

hope this helps wee man.

Yes I know that IPU but the pr**k from the council clerk of works wants everything extra, extra, extra safe for the school.


And yes I have been helpful to you in the past but when you first joined you were a rounded door handle and you got on my ---- on a few occasions. After about your 1000 post you became an Electrician and posted better posts. You've become a sparky and you have the correct attitude now. You've become a valuable member of this forum over the years and well done to you.

Paul M