10mm meter tails 60amp fuse 6mm bond

[simpson93]

Afternoon all been a while since I've posted.


at today's job I noticed 10mm meter tails with 6mm bonding and although my first thoughts were tails should be min 16mm and bonding 10mm

so at the risk of sounding stupid I couldn't find the exact reason why this was wrong as the 10mm would take 61amps

could anyone clear this for me?

 

[Deleted member 26818]

Bonding is under sized, though it probably complied at the time of design/construction.
Nothing wrong with the CSA of the tails as far as BS7671 is concerned, though they are probably not double insulated.

 

[Risteard]

they are probably not double insulated.

I would suggest that they definitely are not double insulated.

 

[Deleted member 26818]

I would suggest that they definitely are not double insulated.

Who knows?

 

[Risteard]

Who knows?

I'd be pretty confident that they aren't as I am not aware of any cable which is.

 

[Deleted member 9648]

PVC insulated and sheathed I think you'll find, often referred to as DI though, but not strictly correct. A bit like calling a vacuum cleaner a hoover....everyone knows what it means even if it's not strictly correct.

 

[HandySparks]

I'd be pretty confident that they aren't as I am not aware of any cable which is.

https://www.tlc-direct.co.uk/Products/CA10TBRslash50.html

(I bought some a while ago for my temporary board.)


Perfectly acceptable on a 60A fuse or if the load is limited to less than 60A.

 

[Risteard]

https://www.tlc-direct.co.uk/Products/CA10TBRslash50.html

(I bought some a while ago for my temporary board.)

Indeed, but that cable is not double insulated.

 

[HandySparks]

Indeed, but that cable is not double insulated.

OK, insulated and sheathed, then.

 

[Deleted member 26818]

Whether a cable is described as being double insulated, has no bearing on whether it is or isn't as far as BS7671 is concerned.
What matters is whether the cable complies with the requirements.
As cables with insulation and sheaths, and cables with reinforced insulation satisfy the requirements for double insulation, such cables are deemed as being double insulated.

Risterd despite your obsessive compulsion to disagree with me at every opportunity, I suggest that if you do not like my use of the term 'double insulation' for cables that satisfy the requirements for double insulation, that rather than continue this childish sniping at me across various forums, you take this particular matter up with the JPEL 64 committee.
By all means continue chasing after me, if that floats your boat.

 

[simpson93]

The cable is double insulated

 

[simpson93]

Gunna be replacing to 25 and redo earthing.

 

[J.C.E]

Whether a cable is described as being double insulated, has no bearing on whether it is or isn't as far as BS7671 is concerned.
What matters is whether the cable complies with the requirements.
As cables with insulation and sheaths, and cables with reinforced insulation satisfy the requirements for double insulation, such cables are deemed as being double insulated.

Risterd despite your obsessive compulsion to disagree with me at every opportunity, I suggest that if you do not like my use of the term 'double insulation' for cables that satisfy the requirements for double insulation, that rather than continue this childish sniping at me across various forums, you take this particular matter up with the JPEL 64 committee.
By all means continue chasing after me, if that floats your boat.

girls,girls!

 

[Leesparkykent]

What is the board supplying? what is the earthing arrangement? What's the installation method of the tails?

 

[davesparks]

Afternoon all been a while since I've posted.


at today's job I noticed 10mm meter tails with 6mm bonding and although my first thoughts were tails should be min 16mm and bonding 10mm

so at the risk of sounding stupid I couldn't find the exact reason why this was wrong as the 10mm would take 61amps

could anyone clear this for me?

Why do you say minimum 16mm tails and 10mm bonding?
The minimum size for bonding is 6mm unless PME conditions apply.
There is no lower limit on tail size, other than the availability factor.


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[davesparks]

Bonding is under sized, though it probably complied at the time of design/construction.

It is only guaranteed undersized for a PME supply, it may be correct for TNS or TT or other TNCS supplies.



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[davesparks]

What matters is whether the cable complies with the requirements.
As cables with insulation and sheaths, and cables with reinforced insulation satisfy the requirements for double insulation, such cables are deemed as being double insulated.

.

Well if you want to be pedantic then technically speaking an insulated and sheathed cable may be considered to afford equivalent protection to DI subject to some stipulations (which I can't remember) rather than actually being deemed to be double insulated.

Plus reinforced insulation is a separate thing to DI, although the regulations consider them to be equivalent.

 

[7029 dave]

If my memory is still good, in trunking singles, you can reduce the csa of a conductor as apposed to multi conductors.

 

[simpson93]

Tn s supply

 

[Leesparkykent]

Tn s supply

Except where PME conditions apply, a main protective bonding conductor shall have a CSA not less than half the CSA required for the earthing conductor of the installation and not less than 6mm.

 

[simpson93]

So the install is fine than

 

[davesparks]

So the install is fine than

Is it? What size earthing conductor is required?


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[Leesparkykent]

So the install is fine than

depending on the installation method of the tails and the PEFC of the installation.

 

[Leesparkykent]

what's the Ze?

 

[marconi]

Why do you say minimum 16mm tails and 10mm bonding?
The minimum size for bonding is 6mm unless PME conditions apply.
There is no lower limit on tail size, other than the availability factor.


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Do you not mean to say 'demand factor' or 'load factor'?

 

[simpson93]

0.3 ze

 

[Leesparkykent]

0.3 ze

V/Ze= 766A

I=766
T=0.16
K=143 (not incorporated in a cable or bunched)

766x766=586756

586756x0.16=93880

square root of 93880=306

306/143=2.13mm for your main earthing conductor.

Taking reg 544.1.1 in to account the 6mm bonding conductor is adequate.

Edit: Based on a BS1361 fuse

 

[Deleted member 26818]

A Ze of 0.3 Ohms suggests that PME conditions apply.

 

[davesparks]

Do you not mean to say 'demand factor' or 'load factor'?

No I mean to say availability factor, tails smaller than 16mm are not commonly available as a lot of wholesalers don't keep them.


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[marconi]

No I mean to say availability factor, tails smaller than 16mm are not commonly available as a lot of wholesalers don't keep them.

Thank you for clarifying. I thought you might have been using 'availability factor' as used to describe sources of electrical energy see https://energymag.net/technologies/availability-factor/

 

[JohnS888]

V/Ze= 766A

I=766
T=0.16
K=143 (not incorporated in a cable or bunched)

766x766=586756

586756x0.16=93880

square root of 93880=306

306/143=2.13mm for your main earthing conductor.

Taking reg 544.1.1 in to account the 6mm bonding conductor is adequate.

Edit: Based on a BS1361 fuse

Hi Lee or anybody else. Can you confirm what the T value of 0.16 relates to with this calculation?

Thanks

 

[JohnS888]

V/Ze= 766A

I=766
T=0.16
K=143 (not incorporated in a cable or bunched)

766x766=586756

586756x0.16=93880

square root of 93880=306

306/143=2.13mm for your main earthing conductor.

Taking reg 544.1.1 in to account the 6mm bonding conductor is adequate.

Edit: Based on a BS1361 fuse

Hi Lee or anybody else. Can you confirm what the T with value of 0.16 relates to here?

Thanks

 

[ronalsparks]

The supply authority and utility provider will expect to see 16mm tails and therefore a 10.0mm bond is required to satisfy their requirements also. The regs and calculations can determine other values but to ensure you meet the minimum requirements of the energy supplier this is what I would install as a contractor.