code for undersized main earth?

[nicks electrix]

Evening all,

What code is given for 4mm/6mm(not sure what size it is) main incoming earth cable for a PIR? It is a TN-S.

Thanks

 

[Andy™]

unless there is signs of thermal damage, i would go with 4 for 6mm

 

[sparkytim]

Concur with above

 

[PC Electrics]

http://esc.org.uk/pdfs/business-and-community/electrical-industry/BPG4_08.pdf

says 2

 

[ian3012]

guys, i don't do pir's so help me understand here please....

i can't remember why i think this or where i got it from....

tncs.... = 16mm minimum csa earthing conductor... no exceptions

tt & tns = 6mm minimum csa

i thought you could use the adiabatic to calculate whether an earthing conductor was of sufficient csa for tt and tns??

and if you can do the adiabatic.... and it checks out that your 6mm earthing conductor is sufficient.... then why would you give it a code 4 ?

have i got this all wrong? i'm really confused now.

 

[sellers]

Main earth CSA shall be no less than half the CSA of the incoming tails.

 

[spinlondon]

http://esc.org.uk/pdfs/business-and-community/electrical-industry/BPG4_08.pdfsays 2

Only for less than 6mm

 

[ian3012]

sellers... that may well be a rule of thumb.... but i bet you can't show me that in the brb.....

c'mon guys... someone must be able to answer my question... :Blushing

 

[spinlondon]

There is no definitative answer to your question, you should write the report according to your opinion, and code according to whether you consider each situation to be safe or unsafe.

Main protective bonding conductors, should have a CSA not less than half the CSA required for the main earthing conductor, and they should be not less than 6mm

 

[sparkytim]

Concur

BRB 542.3.1 AND 544.1.1

 

[ian3012]

thanks spin, i agree with 99% of that..... what i was asking is....

why, (when you've established by adiabatic equation that the csa of your conductor is fine) ... would you then give it a code 4....

by using the adiabatic, you've just confirmed it complies with 543.1.3

then in the next breath, saying it doesn't comply by giving it a code 4.

 

[batty]

thanks spin, i agree with 99% of that..... what i was asking is.... why, (when you've established by adiabatic equation that the csa of your conductor is fine) ... would you then give it a code 4....

by using the adiabatic, you've just confirmed it complies with 543.1.3

then in the next breath, saying it doesn't comply by giving it a code 4.

Code 4 means does not comply with current wiring regulations but not neccessarily is unsafe which will be the majority of electrical installations everytime a new wiring regulation is brought out almost all installations will not be to that standard so they are not to that regulation but not unsafe. If an earthing conductor is not to current standard that is not to say installation is unsafe it just means it does not comply with current standard so a code 4 is given.

 

[Risteard]

I agree with ian. If it satisfies the adiabatic equation then it cannot be a non-compliance.

 

[spinlondon]

Would a 4mm

 

[ian3012]

hi spin ....i don't know if a 4mm(2) EARTHING CONDUCTOR would satisfy the adiabatic equation because you don't give the req'd info to be able to work it out..

but i'm guessing you're gonna refer us to a reg that says a 4mm(2) wont suffice?

(osg 4.3 suggests the min to be 6mm(2) csa, but i assume your talking about an old installation from a pir point of view)

ok. i give in... i can't find a reg.... :|

 

[spinlondon]

hi spin ....i don't know if a 4mm(2) EARTHING CONDUCTOR would satisfy the adiabatic equation because you don't give the req'd info to be able to work it out..but i'm guessing you're gonna refer us to a reg that says a 4mm(2) wont suffice?

(osg 4.3 suggests the min to be 6mm(2) csa, but i assume your talking about an old installation from a pir point of view)

ok. i give in... i can't find a reg.... :|

What info is required?

 

[ian3012]

ok spin ... i know you like a game.... lol.... i need to know the size of your tail.. ROTFWL

i'll assume the size of your tails... is 4mm(2) (how do you do squared?)

then i'll state that your 4mm earthing conductor is just fine. :innocent

 

[binky]

ok spin ... i know you like a game.... lol.... i need to know the size of your tail.. ROTFWL i'll assume the size of your tails... is 4mm(2) (how do you do squared?)

then i'll state that your 4mm earthing conductor is just fine. :innocent

Oh no it isn't (is panto season over yet?) cos if I remember rightly the main earth has to be a minimum 6mm, unless it's been changed in the 17th. (think I better go check in case I've got that wrong :innocent )

 

[ian3012]

let me know what you find binky... i don't know a reg that says 6mm minimum size, but i'm happy to be shown.(i have already mentioned osg 4.3)

this thread has continued because i keep asking how you can use the adiabatic equation to prove that:

a) an earthing conductor complies with the current regs....

and then....

B) give it a code 4... (obviously thats saying it doesn't comply.)

(that just doesn't make any sense to me)

it has further developed into a game of cat and mouse between me and spin, where he's trying to catch me out... (and of course it amuses me and i'm willing to play)

spin and i both know that in reality a 4mm(2) earthing conductor will never carry a pfc of minimum 287.5 amps for however long it takes for the main fuse to blow at that current...... or will it? :^O

 

[Andy™]

i agree with Ian here. if its proven to adequate by adiabatic, then its compliant with 7671. if its compliant with 7671, then it cannot be coded