quick test on a garage

[jimmylaud]

new to this so just looking for a bit advice and to see your thoughts had a quick test on a garage todayjust to check condition of wiring results i got were.

Tnc-s supply 6mm armour out to feed main board in garage

sockets zs- 0.56
R1-0.32
rn-0.32
R2-0.48
R1+R2-0.48

Insulation
L-N 82.6M
L-E 70.6M
N-E 0M

now my questions i thought R1,R2 was meant to be a quarter of R1+R2?
on the insulation test did i get a dead short due to earth and neutral having the same potential?
any help would be great

 

[Risteard]

now my questions i thought R1,R2 was meant to be a quarter of R1+R2?
on the insulation test did i get a dead short due to earth and neutral having the same potential?
any help would be great

R1 + R2 = (r1 + r2) / 4.

As for insulation resistance, how do you know it's a dead short?

0 million ohms isn't necessarily the same thing as 0 ohms.

 

[jimmylaud]

thanks for the reply so saying that R1+R2 should be 0.2 going with my results am i correct there?

as for the insulation i just tested N-E at 250v and it said 0.00 M ohms thanks again in advance

 

[Johno]

yep, R1+ R2 should be 0.2 and as for the insulation resistance, i would imagine there is a short, probably a socket pin through the neutral, is it not RCD protected?

 

[Johno]

you did disconnect the cables for the test didn't you?

 

[chris gray]

what earthing arrangement have u got?
+ how come u were testing n-e at 250v?

 

[jimmylaud]

hi its tn-s in the house, no the cables were not discotted at the garage cu didnt realise you had to do that, what are your thoughts on the R1+R2 thanks again

 

[jimmylaud]

chriss im aware neutral- earth is 0v but just assumed you still tested at 250v suppose its better to ask than guess thamks again

 

[Risteard]

If you tested the distribution board/installation as a whole then you need to disconnect the neutral/earth link for a TN system. Low Voltage systems should be tested at 500V d.c. (ELV 250V d.c.)

Yes, I make it 0.2 ohms as an expected approximate value for R1+R2.

 

[chris gray]

when you say your IR was 0ohms, where were u testing?

dont worry about asking questions, my mate stuck 500v across a 3ph board full of rcbo's and at the load side of a fire panel?

 

[pevvers]

R1-0.32
rn-0.32
R2-0.48
R1+R2-0.48

now my questions i thought R1,R2 was meant to be a quarter of R1+R2?
on the insulation test did i get a dead short due to earth and neutral having the same potential?
any help would be great

Well the calculation on a ring would work out at (r1+r2)/4, but if you have done the figure of 8 test then this could have been due to spurs. If the figure of 8 test was conducted the other way around, you could get spurious results.

The live neutral fault could be due to the main switch not being open. If this is the case, then you would be seeing the neutral-earth link the PME head if it's TN-C-S, or back at the star point of the transformer if it's TN-S.

Make sure you've isolated from the main switch, and left all MCB's on and fuses in place....

 

[Mr Mark Sparks]

Well the calculation on a ring would work out at (r1+r2)/4, but if you have done the figure of 8 test then this could have been due to spurs. If the figure of 8 test was conducted the other way around, you could get spurious results.

The live neutral fault could be due to the main switch not being open. If this is the case, then you would be seeing the neutral-earth link the PME head if it's TN-C-S, or back at the star point of the transformer if it's TN-S.

Make sure you've isolated from the main switch, and left all MCB's on and fuses in place....

for anyone like me who didnt know what spurious was

–adjective1.not genuine, authentic, or true; not from the claimed, pretended, or proper source; counterfeit.

 

[pevvers]

for anyone like me who didnt know what spurious was

–adjective1.not genuine, authentic, or true; not from the claimed, pretended, or proper source; counterfeit.

Sorry, should I just have said incorrect results?

My bad,

 

[Guest123]

for anyone like me who didnt know what spurious was

–adjective1.not genuine, authentic, or true; not from the claimed, pretended, or proper source; counterfeit.

lol.....:d

 

[Mr Mark Sparks]

its ok its my new word i will put it somewhere on my next periodic to confuse my manager

 

[pevvers]

Just pointed this out to the missus, and she doesn't know what it means either... So you're not alone!!

That'll teach me for reading the "improve your word power" section of Readers Digest in the bog for the last 25 years or so,

 

[Guest123]

I prefer to substitute the word spurious with "a bit iffy"

 

[jimmylaud]

thanks for all the replys so basically what i should have done was disconnected the ring from the board and then done the insulation tests? What do you mean by figure of 8 test pevvers? Has anyone got any thoughts on why my R1+R2 was higher than it should be thanks again

 

[Johno]

the R1+R2, if all sockets was on the ring,you would expect to be about 0.2 but if there was a spur off the ring then that would be added which would give a higher reading

 

[Johno]

as for the insulation resistance, if you are testing 1 circuit only, you must disconnect it, (L,N+E) and of course disconnect/unplug any appliances and remove any bulbs etc, but i find it is a good idea to test at 250v, to make sure nothing is still connected, before doing 500v