R1+R2 and Zs calculate acceptable?

[NEBITOMI]

hello
1.is that acceptable if i do only Zs test last point of the lighting circuit and on scoket!
instead of measure R1+R2?
i can caluclate R1+R2 ACTUALY!
ZS-ZE=R1+R2 is it acceptable to write the value on certificate?

2. as i know the maximum Zs by rcd (rcbo)protected circuit 1667 ohm!
but if the measured circuit is wery high value ,but not reach 1667 ohm ,then is it still acceptable ?

IM new to testing learning currently!

 

[buzzlightyear]

regs book page 61 BBB .

 

[NEBITOMI]

regs book page 61 BBB .

sorry not understand ! i checked the page and understand that but i sitll have not got answer to my question!

 

[buzzlightyear]

ZE is your external loop impedence measure at the point of origin

ZS is you highest measured earth loop impedence (usually at the furthest socket outlet)

So as you say ZS = ZE + RI +R2 or R1 + R2 = ZS -ZE

If you need the actual R1 and R2 reading induvidually it can be worked out on the basis that your R2 reading will be 1.67 times greater than your R1. This is due to the earth conductor being smaller than the phase and thus has a larger resistance.

For example if ZE measures 0.2 ohms and your maximum measured ZS is 0.734

Then R1 + R2 = 0.734 - 0.2 = 0.534

R1 = 0.2
R2 = 0.2 X 1.67 = 0.334

All that said these figures dont prove very much. A ring circuit needs to be tested as per the IEE Regs, which I could explain if you wish.

We do now have an R1 R2 reading but we havent proved ring continuity!

 

[Blissof89]

It depends on the installation. If you are doing a periodic inspection on a property that you have access to old test records for if there is no sign of any modifications and the Zs is as previously recorded it would be safe to assume that R1+R2 is as previous.

It is not good practice to always assume that Zs-Ze=R1+R2 as there may be parallel earth paths, like a copper gas or water pipe connecting to a boiler. If that pipe work was ever removed or altered the parallel path may be lost, and your Zs will rise.

 

[NEBITOMI]

ok! thanks ! but problem is only in the ring circuit actualy!?!/
but the lighting circuit is ok if i write that value what i calculated then?

 

[NEBITOMI]

also measured Zs also can confirm the conductor contunuity no? test instrument will sign that ,if any conductor not connected well!
if the plarity is not good then the rcd will trip anyway!
im i wrong?

 

[Blissof89]

A parallel earth path can exist on any circuit, I was just using the boiler as an example. Lighting may have parallel earth paths via supplementary bonding in a bathroom.

I tested a place the recently where someone had borrowed an earth from downstairs lights for a few of the rooms upstairs, if the downstairs lighting circuit was ever modified this could cause the upstairs lighting to loose its connection to earth and it could go un noticed.

It had been tested 5 years ago, but I didn't have the test results. Last guy to do an EICR had just calculated R1+R2=Zs-Ze I guess.

 

[NEBITOMI]

but in new installation is acceptable?for initial verification!
mi right?

 

[Silly Sausage]

but in new installation is acceptable?for initial verification!
mi right?

For an IV, I would say, ensure that the cct is totally isolated from the rest of the installation and take a measurement.

Periodics, depends who you're working for! Sometimes it was a question of getting a Zs somewhere and a Ze and leave the rest to the company. It wasn't my name going on any certificates!

 

[Blissof89]

Not really, you should do the full tests, especially for IV.

What I have said above, applies to an IV just as mush as it does an old property with no test records.

If you have miss terminated one of your CPC's, or builder has struck a nail right through the center but missed the live conductors completely and you have a good parallel earth path you aren't going to notice.

And if you don't notice and next guy comes to test it in 10 years and he calculated as well from your results he isn't going to find it either. Then a couple years down the line the boiler is relocated and all of a sudden your circuit has no connection to earth.

 

[NEBITOMI]

ok! good! thanks!!!!

 

[ChrisElectrical88]

I always calculate (R1+R2)+Ze for my Zs values on all tests. Zs-Ze isnt accurate enough for me. Including on a ring main.

Ill also Zs all sockets and random poibts on other circuits as im sampling just to make sure nothing stands out.

 

[Blissof89]

I always calculate (R1+R2)+Ze for my Zs values on all tests. Zs-Ze isnt accurate enough for me. Including on a ring main.

Ill also Zs all sockets and random poibts on other circuits as im sampling just to make sure nothing stands out.

I was interested to read that GN3 actually seems to recommend this method over live testing for Zs now. Safer I suppose.

 

[ChrisElectrical88]

I was interested to read that GN3 actually seems to recommend this method over live testing for Zs now. Safer I suppose.

Its also the most accurate way to test.