Discuss pir code for undersizes water bond in the Periodic Inspection Reporting & Certification area at ElectriciansForums.net

Status
Not open for further replies.

sid578

EF Member
Messages
6
hi .doing a test on a complex where the tails are 25mm ..main bond 16mm ..but the cable bonding main water is only 6mm..think the tails have been upgraded from original but not water bond (not a easy run) .there are 30 flats in complex ..what pir code would i put fo this
 

Murdoch

Regular EF Member
Messages
26,648
Location
Woking
Potentially no code. Can't remember the new reg number but it was 131.8 in the BRB!
 

telectrix

Disrespected Scouser
Electrician's Arms
Trainee Access
Messages
63,525
Location
cheshire/staffordshire
use adiabatic equation to determine the min. reqd. size for main earthing conductor. ( irrespective of the fact that the re is a 16mm there). then the main bonding conductor/s need to be at least 50% of that size.
 

topquark

Electricians Arms Member
Mentor
Electrician's Arms
Trainee Access
Messages
3,377
As there's existing bonding, assuming it's metal and extraneous. TNC-S = minimum of 10mm, it is potentially dangerous, so code 2.
 

topquark

Electricians Arms Member
Mentor
Electrician's Arms
Trainee Access
Messages
3,377
The reason for the minimum sizes (and why they must be updated before any work is done) is to ensure that fault current can be handed in the event of a fault. It would depend on where the fault was (which circuit/ocpd etc) to actually cause a real issue.

If it isn't potentially dangerous, why would it need to be upgraded before any work was done?
 

Murdoch

Regular EF Member
Messages
26,648
Location
Woking
The reason for the minimum sizes (and why they must be updated before any work is done) is to ensure that fault current can be handed in the event of a fault. It would depend on where the fault was (which circuit/ocpd etc) to actually cause a real issue.

If it isn't potentially dangerous, why would it need to be upgraded before any work was done?
Not picking a fight BUT if it was this important why don't those who make the rules, make any attempt to educate the public. More often than not Joe Public thinks that the sparkie is trying it on with unnecessary work.

Joe Public would say his cables on his final ring have 1.5mm earth so what's wrong with his 6mm bonding.
 
OP
S

sid578

EF Member
Messages
6
many thanks guys .the ze was 0.11. just worked it out to 4.6 .. prob put as a c4 just to cover my self
 

telectrix

Disrespected Scouser
Electrician's Arms
Trainee Access
Messages
63,525
Location
cheshire/staffordshire
that's 4.62 for the main earthing conductor. you can divide that by 2 for bonding. for pme, though 10mm is specxified, so a C3, IMO. there's no code 4 now.
 
G

Guest55

In comment to telex and top quark i'd split the difference
C3 if undamaged and soundly connected , C2 if heat damaged and badly connected.
This is new diplomatic biff.
;-)
 

telectrix

Disrespected Scouser
Electrician's Arms
Trainee Access
Messages
63,525
Location
cheshire/staffordshire
agreed. but if clipped onto pipework with a rusty croc clip, i might go as far as a C1.
 

oldtimer

Regular EF Member
Messages
4,313
Location
Edinburgh
Me thinks there has to be a bit flexability here and they realise this so say you go to a 25 yo installation in a flat the DNO fuse is 60A it is a TNS with 6mm to the water and gas and the customer wants a new CU fine but you aint going to rip the flat up to put 10mm in and when I moved into my house there was a bit of stranded 1.5 unsheathed wrapped around the main stop cock so me thinks we need to get real here as I think 10mm is fine for a 100A supply with 25mm tails.
 
E

Engineer54

25mm tails and a 16mm earth for a service supply of 60A?? Bit of an overkill to say the least!! ...lol!!!
 

telectrix

Disrespected Scouser
Electrician's Arms
Trainee Access
Messages
63,525
Location
cheshire/staffordshire
considering that i've had 16mm tails running at 95A for an hour and just managing to reach 40deg.C.
 

topquark

Electricians Arms Member
Mentor
Electrician's Arms
Trainee Access
Messages
3,377
The discussion was about the adequacy of the 6mm bonding on TNC-S! I think you've just made my point for me Tel!
 

oldtimer

Regular EF Member
Messages
4,313
Location
Edinburgh
25mm tails and a 16mm earth for a service supply of 60A?? Bit of an overkill to say the least!! ...lol!!!
Yep seems to be urban myth that the tails must be 25mm and the earth 16mm but for a flat with a 60A fuse then I would say 16mm tails 10mm earth and 6mm water/gas remember I have seen jobs lost because the customer wanted a new CU but did not want to upgrade the earth I think they call this common sense and why is it all of a sudden a safety problem when older installations have either no earth on the gas water and are borrowing one from the guy upstairs (work it out) or the earth is a 2.5-6.0
 

telectrix

Disrespected Scouser
Electrician's Arms
Trainee Access
Messages
63,525
Location
cheshire/staffordshire
amazing we never had loads of deaths under 13th. 14th , 15th editions. we didn't have the digital test equipment to read to 0.01ohms, >299Mohms. no RCDs, very rare to see MCBs, yet the human race survived. wonder how.........
 

topquark

Electricians Arms Member
Mentor
Electrician's Arms
Trainee Access
Messages
3,377
Because power requirements were not as large and the scope for electrical failures much less likely, and yes the systems WERE adequate at the time they were installed. We did still have the 10mm minimum size main bonding requirement for TNC-S in the 16th though, hmmm I wonder why? ;)
 

telectrix

Disrespected Scouser
Electrician's Arms
Trainee Access
Messages
63,525
Location
cheshire/staffordshire
because when the 16th came out, we had test gear that could measure an EFLI of less than an ohm, accurately, so then the IEE as was could come up with some fancy new regs.
 

Snapester

Regular EF Member
Messages
357
Location
Birmingham, UK
I have just done CU upgrade in a flat, 16mm & 6 earth with
6mm bonding. I feel 6mm is adequate for the installation even thought he main earthing system is TNCS. There is no damage or signs of overheating on earth conductors and disconnection times are good. Using ESC guidelines I've left 6mm in.
 
Status
Not open for further replies.

Permanent unswitched live colour?

  • Brown

    Votes: 63 67.0%
  • Black

    Votes: 31 33.0%

Electrician Talk

Top