R1 + R2

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Does it matter what circuit you take the R1 + R2 measurement to add to Ze for your EFLI?
GN3 methods show the R1 + R2 value taken at each ceiling rose in a lighting circuit and to record the circuit extremity reading then add to Ze. I understand this, however, what about R1 + R2 on other circuits, ring/radial circuits etc....do i need to record these values aswell and take the higest reading across all circuits?

Little bit of guidance would be really appreciated. :confused:
 
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ricicle said:
You should do an R1 + R2 for every circuit you are testing. ;)

Ok, let's say i had done some minor work on a lighting circuit. The Minor Works Certificate asks for EFLI. Because the work was only completed on the lighting circuit would you only use R1 + R2 from the lighting circuit to add to Ze?

I need to get this clear in my head.
 
Yes, but its generally the accepted way to note measured EFLI values on certs as opposed to calculated ones
 
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EDIT: I'm sure there was a question above about the difference between calc'ed and measured Z's

None in theory, but chances are Ze+(R1+R2) will be a little higher than measured Zs in reality due to parallel paths, etc
 
R1 + R2 is measured using a low-ohm meter. EFLI is measured with voltage present. So measure R1 + R2 as normal, but then measure Zs and Ze separately. It's a very easy test to perform.
 
Mikey, (R1 + R2) is a characteristic of a final circuit. It will be different for each circuit.
Ze is a characteristic of the supply.

Zs, therefore, will be different for each circuit, but, as suggested, you should be measuring this value - if you can measure (R1 + R2) you can [even more easily] measure Zs.

You only have to measure Ze once.

You measure the other values for every circuit worked on and enter their values in the schedule of test results. The Zs for each circuit is compared to the Zs(max) for the protective device for each circuit.
 
Adam_151 said:
EDIT: I'm sure there was a question above about the difference between calc'ed and measured Z's

None in theory, but chances are Ze+(R1+R2) will be a little higher than measured Zs in reality due to parallel paths, etc

There was, sorry Adam. I took it out as it was a pretty dumb question. I was hoping i'd of deleted it in time before someone read it. :oops:

Thanks for the replies though fellas, it's lot more clearer in my head now. ;)
 
Sorry to be a pain with this.

I've measured Zs for my downstairs ring using the socket method (Megger 1552). The result is 0.26 ohms. The circuit is protected by 32A MCB to BS60898, so according to GN3 the result is ok. However, my supply is TN-S, which would mean my Ze is approx 0.8 ohms. So, why is my Zs measured at a socket lower?

Tell me if i'm talking crap.
 
Have you actually measured the Ze.(I assume you know the correct way to do this) :?:

Zs in reality will nearly always be lower than Ze + (R1+R2) due to parallel paths through MEBs etc
 
ricicle said:
Have you actually measured the Ze.(I assume you know the correct way to do this) :?:

Zs in reality will nearly always be lower than Ze + (R1+R2) due to parallel paths through MEBs etc

No i've not actually measured Ze yet. I've just assumed that Ze is up to 0.8 ohms with it being TN-S.

My house has no MEB, it's something i need to do asap.

Again, thanks for your help with this.
As you've probably noticed i'm still training. I've just bought my tester and i'm trying to get my head around the testing aspects. We havn't touched on testing in college as much as i'd like to so i'm trying to educate myself as much as possible.

I'll get there eventually.
 
even with no MEB's, there are still lots of parallel earth paths..

if your bathroom is bonded as it should be then there's a few.

every metal back box sunk into a wall with an earth connection ( or even the screws ) also provide a parallel earth path..
 
Ze on TNS could be as high as 0.8 but in actual fact is often less than this.
Yours might for example be 0.23 say.
Your R1 + R2 value might be 0.14 say
so you add 0.23 + 0.14 to calculate as 0.37
(Ze + R1 + R2) = Zs (calculated).

Now then you might actually then measure Zs as 0.37 and bingo.

However each measured reading might be a little more or a little less depending upon the accuracy of your testers and also the temperature and also how tightly you clamp the croc clip/probe on yer test leads etc.
So errors creep in.

Adding bonds to do a measured Zs might actually bring the apparent Ze down and therefore the Zs reading.
supplementary bonding/parallel paths might also bring your effective R2 down also lowering the measured Zs.
So errors creep in.

Hope that`s clearer but I might have complicated it even more
 

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