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Discuss 6mm main earth on tt system in the Periodic Inspection Reporting & Certification area at ElectriciansForums.net

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tc50

6MM MAIN EARTH on a tt system with 100 ohm ze at db ,it runs under patio to rod .do i have to upgrade it as it means patio has to come up ? old wylex 6 way rewireable fuse board protected by old crabtree 60amp elcb i have to add a spur for a stannah stair lift and upgrade the non existing bonding customer not happy where do i stand?
 
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A

Adam W

Without checking the regs and to my recollection the minimum CSA to a rod on TT is something really small like 2.5mm, so 6mm is fine.

... After checking the OSG 2.5mm is fine if protected against corrosion and mechanical damage, otherwise 16mm if protected against corrosion and buried, or 25mm if unprotected.
If not buried 2.5mm is ok if protected against corrosion and mechanical damage, otherwise 4mm, so again, 6mm is fine.
Table 4.2

So I suppose the question would be whether you would consider the main earth run under a patio to be 'buried'. Technically it is, but I can't imagine someone digging/drilling into it through the patio tiles.
 
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wirepuller

Forum Mentor
6MM MAIN EARTH on a tt system with 100 ohm ze at db ,it runs under patio to rod .do i have to upgrade it as it means patio has to come up ? The electrode should be visible for inspection,which it wont be under the patio.However as you are only undertaking minor works as long as the electrode Ra is ok you could just note it on your MW cert...(or install another rod elsewhere??) old wylex 6 way rewireable fuse board protected by old crabtree 60amp elcb i have to add a spur for a stannah stair lift and upgrade the non existing bonding customer not happy where do i stand?An ELCB is no longer an acceptable means of earth fault protection,either upgrade to RCD,or fit an RCD purely for the circuit you are altering....either way you cant use an ELCB for EFP for your alteration. Your call on main bonding,it should be in place...but if you consider that lack of bonding does not affect the safety of your install you may decide to omit it and note the reason on your cert....that would be a last resort.

..................
 
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malcolmsanford

Electrician's Arms
WP just for the sake of discussion, if that ELCB was current activated and you tested it, and if passed, would you still change it?
 

IQ Electrical

Electrician's Arms
WP just for the sake of discussion, if that ELCB was current activated and you tested it, and if passed, would you still change it?
That's a good point, there was an ELCB and a VOELCB-the latter of which is now deemed not to comply.

The main earth was usually taken to the VOELCB on a terminal labelled 'Frame' or 'F' whereas the ELCB will not usually have an earth terminal and will have an IΔn value on the front.
 

wirepuller

Forum Mentor
WP just for the sake of discussion, if that ELCB was current activated and you tested it, and if passed, would you still change it?
That's a good point, there was an ELCB and a VOELCB-the latter of which is now deemed not to comply.

The main earth was usually taken to the VOELCB on a terminal labelled 'Frame' or 'F' whereas the ELCB will not usually have an earth terminal and will have an IΔn value on the front.
Was taking ELCB to be a voltage operated trip....the old chilton one for example.....cant say I have come across any other sort apart from obviously RCD's.
 

malcolmsanford

Electrician's Arms


WP here is a current operated one, I managed to track down on wiki................. I have to admit they would not be found in numbers like the old VOELCB you mean mate, as very soon after they were introduced, the actual RCD was introduced.
 

wirepuller

Forum Mentor
Not come across one of those before malc......but I guess if it tripped within the required time it's ok to leave....??
 
E

Engineer54

Must admit, i can't say i've ever seen Matsu****a (Panasonic) protective devices used in the UK, especially at that time. Common as muck in the Middle and Far East.... and pretty decent too, apart from the protection curves offered, which are more akin to Yank curves!!!

That must be one of the first DP RCBO produced ...lol!! Looks like it has a breaking capacity to match the re-wirable BS 3036 fuse boards it was probably installed with too!!

Wonder what that ''Interchangeable type'' means ?? lol!!
 
A

Adam W

Judging by the black and white cables I would guess that that's not being used in the UK.
 
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tc50

Thanks for your response man thats exactly what i done fitted rcd to that circuit only and bonded water and oil pipes which brought zs at d.b. Down to 60 ohms from 100 so worth doing.incidently i got a pfc of 4amps at d.b. Is this acceptable
 

IQ Electrical

Electrician's Arms
Thanks for your response man thats exactly what i done fitted rcd to that circuit only and bonded water and oil pipes which brought zs at d.b. Down to 60 ohms from 100 so worth doing.incidently i got a pfc of 4amps at d.b. Is this acceptable
I'm guessing you mean 4000A ie 4kA?
Remember PFC is measured between L-E and L-N assuming a single phase supply.
 

wirepuller

Forum Mentor
Thanks for your response man thats exactly what i done fitted rcd to that circuit only and bonded water and oil pipes which brought zs at d.b. Down to 60 ohms from 100 so worth doing.incidently i got a pfc of 4amps at d.b. Is this acceptable
You've measured PEFC not PFC.......
 

rich.250

Electrician's Arms
For pefc 4 amps sounds alright.
I calculate 3.8 from your results.
Although the bonding will not reduce your Ze.
Make sure you test the pssc as this will be higher in your case,
And the highest result is recorded as your PFC.
 
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