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

 

[Silly Sausage]

Hi Paul,

You seem to have become a very serious individual recently.
Where's all the good old banter gone? I hope you're not having some serious grief elsewhere.

 

[i=p/u]

I'm laughing.. Ty 10mArcd and ram it up clerks .,.,

 

[i=p/u]

And as the 4mm would be providing additional mechanical protection, just record your normal R1R2..

 

[Chr!s]

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?

You dont nee the 4 mm, though it wont do any harm, are you expecting greater than 10 mA per circuit?

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?

The idea is to duplicate the CPC so best to put in seperate terminals.

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.

Well if the 4mm is ran as a Radial then at the last outlet in effect you have three CPC's back to the MET, so R2 is the paralell resistance of the three cables.

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

May be worth speaking to the Designer.

 

[Nic Norwood]

I may be very very new at the game, but as I've come to understand it the reason the c.p.c's are termintated seperately at the socket outlet and at the consumer unit is to reduce the high earth leakage current down each leg of the ring during the start-up or banks of computer's psu's? therefore reducing liklyhood of nuisance tripping? =/

 

[kingeri]

The extra CPC is nothing to do with 'safety', it provides an additional 'fail-safe' route for any additional earth leakage from the numerous switching PSUs used in PCs.

You need to test with the 4mm in place, as it is just as much a part of the circuit as the CPC in the T&E. I don't see any logic in the idea of testing without it in place. You can't cherry pick what you want to test because it's what you're used to, you test what is there and what will be in service long after you've gone.

 

[Chr!s]

I may be very very new at the game, but as I've come to understand it the reason the c.p.c's are termintated seperately at the socket outlet and at the consumer unit is to reduce the high earth leakage current down each leg of the ring during the start-up or banks of computer's psu's? therefore reducing liklyhood of nuisance tripping? =/

Are the cpc's at each socket not eletrically connected? Its just for strength and to improve the integrity of the cpc.

The RCD will just see all the leakage, not that its been split down several legs.

 

[Paul.M]

Hi Paul,

You seem to have become a very serious individual recently. Other people call that professionalism lol

Where's all the good old banter gone? It will be back shortly.

I hope you're not having some serious grief elsewhere. Nope, life is good and I'm building a better future

Thanks Archy for your kind questions but I'm fine mate. Just needed a bit of a break from the forum for a few months. Think I've turned into one of those old members that has seen everything (almost) on here and just sits back and watches. Thank God I'm not a Mod because there would be 50+ members banned straight away lol.

I'll post up some funny stuff soon. The Elex show is 3 weeks away and I have'nt thought of a funny name badge yet :rofl:

 

[Elmer BeFuddled]

At the end of the day a HI circuit doesn't need a second cpc to follow the first. The continuation of the cpc from outlet to outlet needs to have a separate termination, as it does in the CU.

 

[Silly Sausage]

Paul, glad to hear all is well!
I (generally) treat these forums as chatting down the pub, occasionally a serious topic comes up to to be discussed.
I'll keep any professionalism to the work I occasionally do!

Please don't turn into another Tony, one is more than enough!

 

[D Skelton]

Dunno bout anyone else but I'm learning.

Turns out what I was taught wasn't 100% accurate.

Thanks kingeri

 

[Elmer BeFuddled]

Dunno bout anyone else but I'm learning.

Turns out what I was taught wasn't 100% accurate.

Thanks kingeri

Does that mean my last statement (as I was taught) is wrong? I'd ask for a rebate if it was but I didn't pay!!

 

[Sintra]

The 2 cpc's definitely have to be tested as 1. Been thinking about this for a while and if they are joined throughout the circuit they are performing the same function.

 

[D Skelton]

Does that mean my last statement (as I was taught) is wrong? I'd ask for a rebate if it was but I didn't pay!!

Mate my college education was shoddy at best! The only saving grace was in my final year we had what you might say was an electrical guru at the front of the class, thank god this was when we were learning the important stuff! It was in this final year for example that we also had to re-learn almost everything from year two because we were taught most of it either wrong, or we weren't taught it at all! The muppet that was teaching us in year two was one of these "We do it like that coz it says so in the regs book, now no more questions" types, frigging infuriating!

I have learnt my trade mostly in my third year at coll, on site, through research and through knowing some pretty clued up sparks. I'm confident I know my stuff but I don't trust everything I learned at college, hence my carefully worded reply to paul.m's OP.

 

[Paul.M]

The 2 cpc's definitely have to be tested as 1. Been thinking about this for a while and if they are joined throughout the circuit they are performing the same function.

Sintra I cant be 100% sure that the 4mm earth single is touching the T&E on its entire run so I dont know that I would call it a cpc. Think I've just stated another question???

 

[D Skelton]

We need a guruuuuuuuu!!!!

Where are they when you need one most 'ey paul?

 

[Engineer54]

My solution would be to connect the 1.5mm CPC's in one of the socket outlets earth terminals, and the 4mm earthing conductors to the other socket earthing terminal!! At the CU/DB connect the 1.5mm CPC's in one termination on the earth bar and the 4mm earthing conductors into a separate termination next to the 1.5mm!!...Sorted!! As this is for IT purposes, the socket outlets will require 2 No's of earthing terminals at the socket outlet accessories (which most do these days).

 

[kingeri]

My solution would be to connect the 1.5mm CPC's in one of the socket outlets earth terminals, and the 4mm earthing conductors to the other socket earthing terminal!! At the CU/DB connect the 1.5mm CPC's in one termination on the earth bar and the 4mm earthing conductors into a separate termination next to the 1.5mm!!...Sorted!! As this is for IT purposes, the socket outlets will require 2 No's of earthing terminals at the socket outlet accessories (which most do these days).

That's exactly what I do, and on the last IT install I did, this is what was specified.

D Skelton - I only learned this myself whilst on a job - it was the way the (more experienced) guys did it, so I can't claim any special honours.

 

[Chr!s]

Sintra I cant be 100% sure that the 4mm earth single is touching the T&E on its entire run so I dont know that I would call it a cpc. Think I've just stated another question???

The 1.5 will termimate on one side of the socket, the 4 mm the other, i think you are missing the point of what it is your trying to acheive.

You need a hoigh integrity connection for the Protective Conductor of the final circuit, this is due to the risk of electric shock if the earth connection it lost.

The 1.5 terminated in two sepertate terminals on the socket would acheive this. You have added a 4mm into the design also, not needed but no problem. As i stated earlier and as E54 stated, 1.5 one side 4mm the other, the 4mm will be in paralell with the 1.5.

Take the furthest point where the 4mm Radial ends, that will be you R2, the three cables in paralell.

 

[KAS1]

Perfect interpretation of 543.7.1.103 (iii)

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.