Help, cu change cert and advice......

[Tarzan]

I was thinking about it last night when i should of been trying to get to sleep,

2.1 ohms end to end of L-L & N-N

cannot remember cpc resistance.

I will ask the spark for the test results.

Trailer boy.....

Was asked by client to change cu

Asked tutors at college if they could recommend a qualified part p spark (nic)

One was recommended and a phone no supplied

I gave the guy a call and as i am studying at the same college as he qualified from he accepted the job of testing and certing the job for me.

I changed the cu as the installation looked sound enough, and called the spark in.

As far as im concerned this was a formal arrangment and test.

He came and tested. 3 out of 7 circuits failed.

I paid him his fee which i dont mind and it has hit home the importance of testing an installation before any work commences............

I need to obtain the test results i think.

He was testing all circuits to issue a EIC.

At college we have covered testing, IR, continuity, earth fault loop impedence , rcd, couple of (basic) cable calcs, zs=ze+(r1+r2) but not form filling yet or evaluation of test results and to be honest i would not attempt a house without someone qualified and good at their game next to me. To date i have only done the dead test on college practical assessments. In september i start my third year and will be covering in great detail test and inspect, 17th edition wiring regs and i have started my nvq level 3.

hope this helps

 

[green-hornet]

Ok the picture is a little clearer now. We all learn from our mistakes and often do not make the same mistake twice.

The work you have done ie replace the CU is notifiable, you would be allowed to do this work under the guidance of a suitably qualified and registered electrician who will issue the certificate and notify building control.

The certificate will be a multi signature EIC, you will be responsible for the design and installation and he will be responsible for the testing and commisioning.

When a CU is fitted you can not simply fail a circuit, everything has to be safe and put right for the additional protection to work safely.

The reading you have for end to end are very high and would suggest some irregularities with connections, many old properties have this problem when additions are made by poor joints or cables of different sizes.

The only advise I can give is to study the EIC and find out all the readings has the electrician has found.

There could be some reference with maximum tested Zs levels and the R1+R2 readings which along with the tested Ze could throw some more light on this problem.

Another problem for a high reading is at some point there is a continuity leak over, which would normally show on any IR test, and individual continuity testing. I think you may have to verify the ring, and then find all the spurs which I would suspect there is a few.

I would have a talk with the electrician who did the testing and try to solve this problem together.

 

[PC Electrics]

Are you absolutly sure you've got metric 4.0/1.5 t&e there? Check out my imperial cable guide here (scroll down for a link to a suitable micrometer):

http://www.talk.electricianforum.co.uk/showthread.php?t=7583

You can measure the diameter of a strand and check that it's defo metric too.

If you a certain that this is 4mm cable, are you certain it's a ring?

It may have started life a two radials and been "converted" later. Also look out for spurs on spurs with 2.5 t&e - if you have got this you either need to repair (costly) or put the circuit on 20A (cheaper).

Also watch out for any 2.5/1.0 - ie 2.5 t&e with a 1.0 cpc. Although this is okay on a 32A 60898 you need to ID it on the cert.

Seems to me, you should have attended site with the tester. You could have watched and learned. He could also have explained his findings as he went along.

Is the testing spark also expected to notify? Is he going to inspect the final installation?

 

[Tarzan]

Thank you so much chaps for your genuine advice!

The ring does have spurs, in 4mm and 2.5mm. It also has been extended in 2.5mm. It serves 26 points. ground floor, 1st floor, kitchen.

Is it worth splitting into two 20amp radials?

I will go through every socket and jb checking connections as i go.

I was with the spark whilst he tested however no cert was issued.

I will phone him monday for a copy of results.

 

[PC Electrics]

Thank you so much chaps for your genuine advice!The ring does have spurs, in 4mm and 2.5mm. It also has been extended in 2.5mm. It serves 26 points. ground floor, 1st floor, kitchen.

Is it worth splitting into two 20amp radials?

I will go through every socket and jb checking connections as i go.

I was with the spark whilst he tested however no cert was issued.

I will phone him monday for a copy of results.

So, who's issuing the EIC here?

 

[green-hornet]

Tarzan I would be very interested in what the client is thinking about all this, this situation can become a very good learning excersise for you, or something that will haunt you forever.

Let us have an update when you speak to the spark on monday.

There are a few forum members close enough to do a hands on assistance just to get to the bottom of this if needed.

 

[Tarzan]

So, who's issuing the EIC here?

The nic spark who tested it said he would be happy to issue a EIC once the problem causing the high readings have been corrected.

I am worried about the client too as I must be looking a bit of an arse........ headbang

 

[Tarzan]

Tarzan I would be very interested in what the client is thinking about all this, this situation can become a very good learning excersise for you, or something that will haunt you forever.Let us have an update when you speak to the spark on monday.

There are a few forum members close enough to do a hands on assistance just to get to the bottom of this if needed.

I will post an update tomorrow. Good suggestion will regard to hands on assistance.......Its good to know you boys are so approachable and thank you for your advice.

T

 

[Tarzan]

test results for failed circuts

1.ring, 4mm t&e LL .66ohm

NN .66ohm

EE 1.71 ohm

r1+r2 .6 ohm

loop .23 ohm

Lighting 1.5mm r1+r2 2.37ohm

loop 1.57 ohm

lighting 1.5mm r1+r2 1.01ohm

loop 1.13 ohm

psc 1.83ka

ze .13

Any advice??

 

[green-hornet]

test results for failed circuts1.ring, 4mm t&e LL .66ohm

NN .66ohm

EE 1.71 ohm

r1+r2 .6 ohm

loop .23 ohm

Looks like this could be imperial sizes and not metric

Lighting 1.5mm r1+r2 2.37ohm

loop 1.57 ohm

The high reading can be down to loose connections, the Zs will probably be about right

lighting 1.5mm r1+r2 1.01ohm

loop 1.13 ohm

This looks ok to me

psc 1.83ka

I have not calculated the PFC but looks about right given the Ze

ze .13

Any advice??

I can not see how these readings have failed these circuits

 

[Tarzan]

Thanks GH>

So should I try a different Part P Spark?

 

[Tarzan]

I can not see how these readings have failed these circuits

Thanks GH

Should I try a different Part P Spark

 

[green-hornet]

I would think this customer is probably getting worried at this point, I would ask the electrician who failed them to state why.

 

[Tarzan]

I would think this customer is probably getting worried at this point, I would ask the electrician who failed them to state why.

Very understanding customer, lucky really, and the house is empty.

Asked electrician and he said values are to high. He wants the values to be lower???????????

As previously mentioned I am inexperienced in testing but im under pressure to get the job finalised as the house owner needs the safety cert.

 

[kme]

I`ve so far kept out of this, but.....

+1 to GH above. None of those rewadings scream "fail" to me. A couple are slightly out from what I`d expect on paper......but this is real world.

Why does your guy say they "fail"??? I`d love to know.

KME

 

[SPECIAL LOCATION]

test results for failed circuits1.ring, 4mm t&e LL .66ohm

NN .66ohm

EE 1.71 ohm

r1+r2 .6 ohm

loop .23 ohm

Lighting 1.5mm r1+r2 2.37ohm

loop 1.57 ohm

lighting 1.5mm r1+r2 1.01ohm

loop 1.13 ohm

psc 1.83ka

ze .13

Any advice??

Well......

I am bu99erd if I can see what the blokes fussing about!!??**

Excused my astonishment please ladies & gents! :O

Working backward through your figures....

---------------------------------------------------------------------

[1] Ze & psc

V=IxR or Voltage = psc x ze

so 0.13ohms x 1830amps = 237.9volts

As GH saids these all look good! :Applaud

so lets continue to assume Ze most definitely IS 0.13ohms

----------------------------------------------------------------------

[2] lighting 1.5mm r1+r2 1.01ohm loop 1.13 ohm

1.5m T&E with 1.0mmCPC is 30.20miliohms per meter (from Table 9a pg 166 OSG)

so (1.01ohms / 30.20) x 1000 = a radial approx 33.4meters long..

33m sounds a reasonable figure to have in a domestic property! :Applaud

AND as we know Zs=Ze+(R1+R2)

as per guidance points 10.3.6 on page 87 of OSG.

so your man gets Zs 1.13 ohms

and Ze+R1+R2 = 0.13 + 1.01 = 1.14ohms

0.01ohms discrepancy!?

thats about as close as a gnats crotchet as you can get IMHO

AND I assume this is on a "type B 6amp 60898" breaker?

which allows a max permissible Zs of 7.67ohms from table 41.3 in Big red page 49..

Allow for the 80% rule of thumb this drops down to 6.13ohms!

AND table 7.1 pg 44OSG onward suggests 3% voltdrop light circuits on 6A will go up to the 90meter length range!

So on that circuit I can find nothing wrong there! :|

------------------------------------------------------------------

[3] Lighting 1.5mm r1+r2 2.37ohm loop 1.57 ohm

1.5m T&E with 1.0mmCPC is 30.20miliohms per meter (from Table 9a pg 166 OSG)

so (2.37ohms / 30.20) x 1000 = a radial approx 78.4meters long..

NOW...

this would be theoretically longer but is still within the 90m length

HOWEVER...

by a process of deduction and the formula from pg 87 OSG

Zs=Ze+(r1+r2) your blokes numbers don't add up proper...

i.e... 1.57 = 0.13 + 2.37 clearly does NOT compute!

lets assume you man has made an error with one of his readings..

or written a number down wrong...

either:-

R1+R2 = 1.57 - 0.13 = 1.44ohms

OR

Zs = 0.13 + 2.37 = 2.5ohms

(may be a bad connection with the meter probes while doing R1+R2?

or did he forget to zero the meter leads on this reading?)

Even so... Whichever way you try and look at these numbers taking the largest options possible they are still within the spec for a 6a type B 60898 circuit IMHO!!!!

Which figures does he say they exceed?

----------------------------------------------------------------------

[4] ring, 4mm t&e LL .66ohm NN .66ohm EE 1.71 ohm

r1+r2 .6 ohm loop .23 ohm

from page 82 of OSG we know R1+R2 on a ring is (r1 + r2)/4

so (0.66 + 1.71) / 4 = 0.59ohms

which is about as close as you can get to the 0.6ohm figure you have been given... (assuming that is a meter reading not a calc!?)

so if R1+R2 = 0.6ohm... Zs should be 0.6+0.13 = 0.73ohms

your man has 0.23ohms?

could be some parallel paths coming into play with FCU's supplying heating system maybe?

even so the max permissible Zs on a 32A type B 60898 is 1.44ohms

then take the 80% rule of thumb.. gives us 1.15ohms

so even the 'my expected higher calculated value (0.73)' is within the limits!?

So in what way is this a non-compliant circuit???

Reconsidering the cable lenghts.....

As has been mentioned already is this actually a 4.0mm/1.5mm T&E

or is it imperial

or a bit of mix and match?

think you said earlier its got bits of 2.5mm in as well???

SO first of all assuming it is 4.0mm L & N with 1.5mm CPC

4.0mm conductor is 4.61miliohms per meter

1.5mm conductor is 12.10miliohms per meter

.66 / 4.61 x 1000 = 143.16 meters long

1.71 / 12.1 x 1000 = 141.32 meters long!

1.84meters difference between the two conductors going around the ring...

In my book thats quite reasonable!

NOW lets assume it is 2.5mm L & N with 1.0mm CPC

2.5mm conductor is 7.41miliohms per meter

1.0mm conductor is 18.10miliohms per meter

.66 / 7.41 x 1000 = 89.06 meters long

1.71 / 18.1 x 1000 = 94.47 meters long!

5.41meters difference between the two conductors going around the ring...

again overall for an older installation thats not too bad!

ANYWAY..

If your ring is a mixture of 4.0mm & 2.5mm around its length

I would be guessing the real cable length is anywhere between 90m & 140m long... which could be feasible in a domestic property...

you would need to verify this based upon the size of the building and what you estimate the cable runs to be?

The recommended max lengths from table 7.1 in OSG are typically between

106 & 176 for RCD protected circuits on 32A breakers for 2.5mm & 4.0mm rings...

SO..

In summary I am at a loss to suss out why this guy has some concerns?

unless theres other info or readings we haven't been told about?

Anyway..

Assuming you can get your head round my ramblings and number crunchings...

and you can follow the references to the OSG & Big red book...

I would suggest you ask if your other guy could explain his reasonings for why he is concerned about the circuits?

and if he can point to any relevant tables etc.. in the books..?

:C

 

[green-hornet]

I would copy and paste Special locations answer and show the guy who tesred for you, he may learn something and become a better electrician for it.

Scoob for you Special

 

[Tarzan]

Well......I am bu99erd if I can see what the blokes fussing about!!??**

Excused my astonishment please ladies & gents! :O

Working backward through your figures....

---------------------------------------------------------------------

[1] Ze & psc

V=IxR or Voltage = psc x ze

so 0.13ohms x 1830amps = 237.9volts

As GH saids these all look good! :Applaud

so lets continue to assume Ze most definitely IS 0.13ohms

----------------------------------------------------------------------

[2] lighting 1.5mm r1+r2 1.01ohm loop 1.13 ohm

1.5m T&E with 1.0mmCPC is 30.20miliohms per meter (from Table 9a pg 166 OSG)

so (1.01ohms / 30.20) x 1000 = a radial approx 33.4meters long..

33m sounds a reasonable figure to have in a domestic property! :Applaud

AND as we know Zs=Ze+(R1+R2)

as per guidance points 10.3.6 on page 87 of OSG.

so your man gets Zs 1.13 ohms

and Ze+R1+R2 = 0.13 + 1.01 = 1.14ohms

0.01ohms discrepancy!?

thats about as close as a gnats crotchet as you can get IMHO

AND I assume this is on a "type B 6amp 60898" breaker?

which allows a max permissible Zs of 7.67ohms from table 41.3 in Big red page 49..

Allow for the 80% rule of thumb this drops down to 6.13ohms!

AND table 7.1 pg 44OSG onward suggests 3% voltdrop light circuits on 6A will go up to the 90meter length range!

So on that circuit I can find nothing wrong there! :|

------------------------------------------------------------------

[3] Lighting 1.5mm r1+r2 2.37ohm loop 1.57 ohm

1.5m T&E with 1.0mmCPC is 30.20miliohms per meter (from Table 9a pg 166 OSG)

so (2.37ohms / 30.20) x 1000 = a radial approx 78.4meters long..

NOW...

this would be theoretically longer but is still within the 90m length

HOWEVER...

by a process of deduction and the formula from pg 87 OSG

Zs=Ze+(r1+r2) your blokes numbers don't add up proper...

i.e... 1.57 = 0.13 + 2.37 clearly does NOT compute!

lets assume you man has made an error with one of his readings..

or written a number down wrong...

either:-

R1+R2 = 1.57 - 0.13 = 1.44ohms

OR

Zs = 0.13 + 2.37 = 2.5ohms

(may be a bad connection with the meter probes while doing R1+R2?

or did he forget to zero the meter leads on this reading?)

Even so... Whichever way you try and look at these numbers taking the largest options possible they are still within the spec for a 6a type B 60898 circuit IMHO!!!!

Which figures does he say they exceed?

----------------------------------------------------------------------

[4] ring, 4mm t&e LL .66ohm NN .66ohm EE 1.71 ohm

r1+r2 .6 ohm loop .23 ohm

from page 82 of OSG we know R1+R2 on a ring is (r1 + r2)/4

so (0.66 + 1.71) / 4 = 0.59ohms

which is about as close as you can get to the 0.6ohm figure you have been given... (assuming that is a meter reading not a calc!?)

so if R1+R2 = 0.6ohm... Zs should be 0.6+0.13 = 0.73ohms

your man has 0.23ohms?

could be some parallel paths coming into play with FCU's supplying heating system maybe?

even so the max permissible Zs on a 32A type B 60898 is 1.44ohms

then take the 80% rule of thumb.. gives us 1.15ohms

so even the 'my expected higher calculated value (0.73)' is within the limits!?

So in what way is this a non-compliant circuit???

Reconsidering the cable lenghts.....

As has been mentioned already is this actually a 4.0mm/1.5mm T&E

or is it imperial

or a bit of mix and match?

think you said earlier its got bits of 2.5mm in as well???

SO first of all assuming it is 4.0mm L & N with 1.5mm CPC

4.0mm conductor is 4.61miliohms per meter

1.5mm conductor is 12.10miliohms per meter

.66 / 4.61 x 1000 = 143.16 meters long

1.71 / 12.1 x 1000 = 141.32 meters long!

1.84meters difference between the two conductors going around the ring...

In my book thats quite reasonable!

NOW lets assume it is 2.5mm L & N with 1.0mm CPC

2.5mm conductor is 7.41miliohms per meter

1.0mm conductor is 18.10miliohms per meter

.66 / 7.41 x 1000 = 89.06 meters long

1.71 / 18.1 x 1000 = 94.47 meters long!

5.41meters difference between the two conductors going around the ring...

again overall for an older installation thats not too bad!

ANYWAY..

If your ring is a mixture of 4.0mm & 2.5mm around its length

I would be guessing the real cable length is anywhere between 90m & 140m long... which could be feasible in a domestic property...

you would need to verify this based upon the size of the building and what you estimate the cable runs to be?

The recommended max lengths from table 7.1 in OSG are typically between

106 & 176 for RCD protected circuits on 32A breakers for 2.5mm & 4.0mm rings...

SO..

In summary I am at a loss to suss out why this guy has some concerns?

unless theres other info or readings we haven't been told about?

Anyway..

Assuming you can get your head round my ramblings and number crunchings...

and you can follow the references to the OSG & Big red book...

I would suggest you ask if your other guy could explain his reasonings for why he is concerned about the circuits?

and if he can point to any relevant tables etc.. in the books..?

:C

I truly hope I can provide a explanation to this standard in my career after I am qualified!

Thank you so much.

The question is, what do I do now?

Would any body like to do a EIC for me?

 

[green-hornet]

Copy the answer Special Location gave and show the electrician who tested the results.

He should then issue the certificate you have paid him for without any circuits as failed.

Then get him to sign up on this forum so he like I and others can be educated in the right and wrong ways to do things.