high readings (maybe)

[biglee1975]

hi all



just to let you know im still training as a spark after the last course i did turned out to be a piece of s**t with not much practical and today i was on a job with my uncle whos my mentor and we got a zs reading from a number of sockets of 106 ohms and when i questioned it i was told to google it by my uncle cause he seems to think i would learn better i just want to know is this acceptable for a tns supply from what i read in the regs book its not. any help would be glady helpful.

thank you

 

[Geoffsd]

The maximum Zs allowed for a standard ring circuit with a B32 MCB is 1.44 ohms, 230/(5x32).

Are you sure it wasn't 1.06 ohms?

 

[biglee1975]

there was no point in it its a megger 1502/2 just said 106 ohms and the pfc was 2 amps

 

[ipf]

there was no point in it its a megger 1502/2 just said 106 ohms and the pfc was 2 amps

That confirms the 106, then. I would have thought your uncle/mentor would be looking into the matter.

 

[Richard Burns]

As geoffsd said 106Ω as a Zs reading for a circuit protected only by a B32 is not acceptable and the value is so high that there is a serious lack of earthing for that circuit (though it could be a line conductor failure).

It might be possible that the TNS earthing has failed, you can check this by measuring the Ze, if this is high then you need to resolve that situation, if the Ze is less than 0.8Ω then the problem is in the circuit.

If it were a TT system then that Zs may be acceptable (not good but acceptable) but the circuit would have to have been protected by an RCD.

For the TNS system if there were RCD protection (as there should be for socket circuits) then nominally the Zs would be compliant with the regulations, but this would be bad practice as any basic circuit design should be able to get a Zs lower than the maximum 1.44Ω.

 

[Engineer54]

In other words, a reading of 106 ohms on a TN-S system is ''NOT'' acceptable!! So what's you're uncle now going to do about it??

 

[biglee1975]

spoken to dno about it will let you know the findings

 

[GMES]

spoken to dno about it will let you know the findings

Why have you spoken to Dno, have you got an high ZE at the mains, or is it just the socket circuit.
If it is the latter you may get charged by Dno if it is not their side at fault.

 

[Octopus]

hi all



just to let you know im still training as a spark after the last course i did turned out to be a piece of s**t with not much practical and today i was on a job with my uncle whos my mentor and we got a zs reading from a number of sockets of 106 ohms and when i questioned it i was told to google it by my uncle cause he seems to think i would learn better i just want to know is this acceptable for a tns supply from what i read in the regs book its not. any help would be glady helpful.

thank you

What was the scope of work you were doing?

Whe you got the high Zs did you check the Ze?

 

[biglee1975]

problem fixed down to a bad earth cable reading now down to 0.5 ohm ze 0.57 zs thanks all for the reply you found time to give me

 

[PEG]

...Parallels working a treat there...:stooge_curly: