Earh loop problem

[james the spark]

I replaced a fuse box last week and when i did the earth loop on the circuits it came up with around 114-ohms yet the ZE was only 0.75-ohm can anyone explain this

 

[StuSpiers]

Was it a true ZE test? - (did you remove parallel paths before test?)

If that was a clean ZE reading then you have a poor L - E loop (loose connections dodgy cable etc etc)

Again also you could be getting parallel path on your ZS and the cpc not connected at all.

I assume you did r1 + r2 dead test?

 

[james the spark]

yes all parallel earths removed and all r1+r2 tested fine and it is on every circuit so i dont think its a loose connection

 

[StuSpiers]

It may sound stupid but did you check the connections from MET (if there is a seperate MET) to the CU earth bar?

If it is on every circuit you are getting a breakdown some where between MET and CU

Do you have any pics of the earthing arrangements/connections.

 

[james the spark]

it is a tns system and i tested at the db on just the main earth and the sheath of the supply and reading was the same 0.75ohm. the only odd thing about it was there was some damage to the sheath of the supply and the original earth clamp had signs of arcing perhaps a previous fault and a loose clamp but still came up with a ok reading with a new clamp.

asked several electricians i used to work with and non of them could give me answer as what could be causing the high reading.

 

[truckster]

Are you testing through any RCD.s? they can throw a spanner in the works with loop tests. I normally bridge them out or calculate Zs with Ze and R1/R2 results.

 

[james the spark]

yes the readings are through rcds though i have never had this problem before when doing so. this may be a stupid question but how do u calculate that ?

 

[telectrix]

Zs = ( R1+R2) + Ze. as truckster said, could be RCDs/MCBs cocking it up. try taking a Zs reading on the busbars. if that is ridiculously high, you know it's not a problem with the circuits.

 

[james the spark]

cheers for that amazing what you forget from you college days such a simple calculation and could i hell think how to do it.

yea il give that a go hopefully that will be all it is, on another note have any of you ever seen damage to the main earth clamp/sheath before from arcing?

 

[richy3333]

If you've forgotten such a simple calc what sort of electrical work do you normally do?

As your post indicates you don't normally do domestic work, dare I mention notification to BC & Part P (on the basis you're in E&W)?

 

[james the spark]

I notify all of my jobs i do domestic and commercial mainly domestic actually just the fact that i haven't used that calc in a while. and E&W?

 

[telectrix]

i assume he means england and wales. part p does not apply in scotland, southern ireland, outer mongolia, kazeckstan, '''''''''''''''

 

[Engineer54]

i assume he means england and wales. part p does not apply in scotland, southern ireland, outer mongolia, kazeckstan, '''''''''''''''

Or China!! Though you did include Outer Mongolia lol!!!

 

[Amp David]

I'd test on each side of the rcds to see what if any the difference is. Also your saying that every circuit is around 114 ohms?

Is your tester working properly, as every domestic job i've done, measured Zs values differ quite a bit between say a lighting circuit and a shower or cooker radial

 

[jumpin jax]

Do an R1+R2 test with the insulation resistance test at 25a, that will determine wether you have a good circuit for Zs.

 

[mechelec]

it is a tns system and i tested at the db on just the main earth and the sheath of the supply and reading was the same 0.75ohm. the only odd thing about it was there was some damage to the sheath of the supply and the original earth clamp had signs of arcing perhaps a previous fault and a loose clamp but still came up with a ok reading with a new clamp.

asked several electricians i used to work with and non of them could give me answer as what could be causing the high reading.[/QUOT

Who fitted the new clamp and what sort did they fit????