High Earth Fault Loop Imedance

[dazzo74]

Hi guy`s and gal`s Just a quicky really ....
Just tested my TN-C-S system for my external earth fault loop ,(Ze) and got a high reading of 6.92 ohms,which is obviously high compared to to stated 0.35 ohm maximum.
Noticed the original main earth is only 10mm. If i change it for 16mm will this bring my high reading down or should i conntact my local supplier?.

Also noticed the meter tails from meter to my old connsumer unit are of the old braided coated type and only look approx 10-12mm dia,so would this give me a high reading?.

 

[fireman22]

nothing to do with tails or 10mm, what meter are you using

 

[dazzo74]

Hi Fireman...
Im using a Metrel Installtest 61577.
Ive even tried carrying out Zs reading on my ring Using the supplied plug that came with the tester but i still get a reading of 5.84 ohms.
Any ideas ?

 

[RF Lighting]

Are you certain it is a TN-C-S system?

Are you certain you are testing it properly and on the right setting?

If so then contact the DNO and get it sorted. If it turns out the supply is fine then the DNO will charge you for the privelege of the visit.

 

[dazzo74]

Hi RF............
Yes Carried out first test with meter set on LOOP L-E to find my Ze reading, then press display to get my PEFC reading.

 

[RF Lighting]

Do you have access to a digital camera? If so could you post a picture of the supply head / cut out fuse.

I think a phone call to the DNO is the next course of action.

 

[dazzo74]

Hi again RF...

Going to try and get a camera sorted to give you some clue.

With this new house being terraced and the supply cables running along the back of all the houses on my row in now wondering if this is some sort of T.T system.....Hmmm think a call to united uttilities is now in order.

Cheers for the help guy`s.

 

[fireman22]

is it a multitest instrument that does all tests?
rcd loop ins. res. etc

 

[dazzo74]

Yes it is Fireman....
Think it`s a 14 in 1 ....set me back £500 as i got it while im waiting to sit my 2391 later this month.

 

[fireman22]

right i dont know the meter but a friend of mine phoned me with a simular problem he had ( i have three seperate meters) and it turned out the meter was set wrongly, check with the instructions you may be doing something simular. have you got a web site so i can look at the meter or instructions?

 

[RF Lighting]

aswell as a picture of the service head could you get us a picture of how you have connected your meter to the installation, and what setting it is on, just to be sure.

 

[dazzo74]

I certainly will Fireman
Cheers for the help .

 

[securespark]

Hi Daz

I use these machines day in and day out.

When you do Ze, are you disconnecting the main earthing conductor to the CU, and connecting the green lead. then putting black to the live and blue to the neutral of the main switch, with the switch in the off position?

Are you also doing test 7 AND test 8?

It doesn't really matter which supply you have. If you have tested Ze and it is greater than 0.35 for PME or 0.8 for TN-S, then the DNO should be notified as such. It is their responsibility to sort it out.

I come across at least 1 a week where the Ze is too high.


If, however it is TT (do you have a rod outside?), then you have up to 200 Ohms to play with (or 100 if you subscribe to NIC thoughts).

5/6 Ohms on TT is very good.

HOWEVER, you MUST have an RCD on a TT install or it is AT RISK!

Preferably on TT you need a min 100mA S type incomer and a 30mA on the split side.

 

[Adam_151]

What to you get for the PSCC? presumably more than 33A ?

Not sure whether your can do it or not (secure?) but if you are doing a two wire EFLI test, do it with neutral instead of earth and tell us what you get

 

[securespark]

Well, that's the idea behind test 7 and test 8. Forget which way round it is ( ), but one does one and the other the other, IYKWIM....

And of course, the PSCC will get higher the lower the Ze.