R1 + R2

[securespark]

Lots of testing related queries & comments from me tonight!

I saw an EIC for a customer's installation & couldn't work out the figures:

Zs = Ze + R1 + R2, right?

So, Ze-.32.

R1R2 for lighting = 1.18. Zs = 1.24.

None of the figures on the EIC add up.


Also, the figures entered for a ring final are

R1 0.24

Rn 0.24

R2 0.38

then R1+R2 0.18.

 

[Spark123]

Ze is without any parallel paths i.e. through MEBs etc which may have an influence to a neighbouring property

Ring final max R1+R2 could have been a spur?

 

[equitum]

Could be that the measured Ze is greater than when Supplier Earth is combined with water/gas main bonded services which are effectively reducing the impedence when tested ? (as these are providing parallel paths when live testing EFLI)

 

[DESL]

SS

My understanding is you can calculate Zs from Ze+R1+R2 or by measuring EFLI with a Loop tester which will include capacitive and inductive reactance as it tests cct live with AC whereas R1+R2 is measured with DC.

 

[securespark]

So assuming this spark has tested R1 & R2 for continuity with DC, how can the sum of those figures equal 0.18?

 

[equitum]

SS

sorry not up to speed with the lingo yet, "SS" ?

 

[Spark123]

I'm taking it
r1=0.24
rn=0.24
r2=0.38

r1+r2/4 = 0.155

This is the figure which give or take a teeny bit for different conductor sizing should be the same around the sockets on the ring (R1+R2)
Any spurs from the ring will have higher readings.

SS = Simon Securespark!

 

[Adam_151]

So assuming this spark has tested R1 & R2 for continuity with DC, how can the sum of those figures equal 0.18?

Talking about the ring final now?

end to end are r1, r2 and rn (not R1 R2 and RN)

R1+R2 = (r1+r2)/4

(0.24 + 0.38)/4 = 0.62/4 = 0.155 , this doesn't take spurs into account, so 0.18 would be reasonable I'd say

Its late, so sorry if I've miss-understood....

 

[equitum]

SS - ah ha !

Thought it might have meant "spose so!"


Back to R1+R2 business, yes agree as phase-phase n-n cpc-cpc measurements are end to end, when cpc and phase are combined its back to the maths of resistances in parallel , so yes, looks about right to me.

 

[securespark]

Thanks guys!

I had, rather stupidly, forgotten about the effect of spurs on the calcs...

 

[equitum]

Spurs will have no effect on the calcs for the ring as it equates to a half of half of the loop formed by p1 +cpc2 + p2 + cpc1. But agree the measured value may be higher at a spur as you then have the additional single length on cable to add on, and of course you record the highest value on the EIC.

 

[Paul Barker]

The main point is you take your ze with the supply isolated and the main earth conductor disconnected, you take your zs with these things connected. So the external element of zs with all these things connected won't be the same as ze therefore zs will not be ze plus R1 + R2 (just an approximate double check that's all), despite what the books say.

Another mistake people make is measuring pfc straight after measuring ze. No, ze is the only test in which the main earth is removed, it has to be put back for pfc measurement, (because you want to know what the pfc is likely to be in real conditions, or why bother finding out what it is at all?)and therefore will be different.