Zs too high at distribution boards

[knasher]

The boards i tested were none RCD protected, with 60A sub main protective device. Is the easiest way to solve the problem to install a main RCD incomer, eg 63A, 30mA at each DB? any advise?

 

[Guest123]

Was this found on a PIR???

 

[Deleted member 26818]

Would such a solution not fall foul of other Regulations, such as those in Section 314 Division of Installation?

 

[kmcgold]

what was it at the origin
could install new cpc

more info needed

 

[SirKit Breaker]

Check Ze at origin, if that is OK then you need to find problem further downstream. If its not OK and no obvious problem contact supplier.

Cheers...........Howard

 

[tonys]

What is the current earthing arrangement to each dis-board?

 

[knasher]

its TN-C-S supply

 

[Sintra]

What figures for Zs were you getting at the boards?


Sent from my iPhone using Tapatalk.

 

[kmcgold]

what's the ze
what's the zs of the db
length of runs,size of cable and type

 

[tonys]

its TN-C-S supply

What is the earthing arrangements to each dis-board? Type and Size of Earthing Conductor?

 

[knasher]

sorry just picked up all other responses to my query. Ze at origin is 0.08,(should be 0.35 shouldnt it for TN-C-S? Also, yes it was a PIR that picked up these issues. Also, re. your response (splindon), Yes, point taken re.sec.314.
Have read PIR further and looks like earthing conductor is too small 10mmcsa instead of 16mm. Supply conductors are 35mm. Could that be the likely cause?

 

[telectrix]

think you.ve answered your own question .10mmm way too small . Ze should be max. 0.35. anything under is good.

 

[tonys]

knasher - Are you an electrician?

 

[knasher]

Zs figures at DB's were 0.37, 1.13, 0.12, 0.95,0.13. overcurrent protective devices were 3871 mcb, 60A. some Zs figures seem acceptable, but not all (GN3 used)

 

[johnboy6083]

a 10mm earthing conductor instead of 16mm IMO wont cause a dramatic increase in ZS. when designing jobs, i would use the max Ze to workfrom, as its worst case scenario. it could be something simple like corrosion on the armour, or no link from the glandplate/banjos to the earthing bar in DB

 

[pennywise]

Is that 0.80 or 0.08

 

[knasher]

pennywise, Ze is 0.08.

 

[pennywise]

sorry just picked up all other responses to my query. Ze at origin is 0.08,(should be 0.35 shouldnt it for TN-C-S?

Sorry mate just got a bit confused with the wording.

 

[Deleted member 26818]

Not certain if the Ze of 0.08 is the measured value, or reference to the given value of 0.8 for TN-S systems?

 

[knasher]

thanks for all your input guys, this site is a great help to someone who is not ashamed to admit that I have only recently got my City & Guilds (In response to Tonys question, "am I an electrician?", no I feel as though I've still got a lifetimes learning ahead of me still, but find this whole subject fascinating. Cheers