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?

 

[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/