Bonding of metal trunking and metal encloseres

[zsoltimatrix]

Hi guys,

Does anybody knows that in an industrial area bonding of the metal trunking parts and the metal enclosures counts as the main equipotential bonding? Becaouse this would effect bonding cable size.

Thanks!

 

[Jurasic Spark]

Hi guys,

Does anybody knows that in an industrial area bonding of the metal trunking parts and the metal enclosures counts as the main equipotential bonding? Becaouse this would effect bonding cable size.

Thanks!

Well, Extraneous conductive parts are connected to the MET with Main Protective BONDING conductors and Exposed conductive parts to the MET with a CPC.

In some instances Supplementary Bonding is also required.

 

[zsoltimatrix]

Well, Extraneous conductive parts are connected to the MET with Main Protective BONDING conductors and Exposed conductive parts to the MET with a CPC.

In some instances Supplementary Bonding is also required.

So, a metal enclosure and a metal trunking is which one? Extraneous or exposed?

 

[Jurasic Spark]

Exposed.

 

[zsoltimatrix]

From BS 7671:

Exposed-conductive part: Conductive part of equipment which can be touched and which is not normally live, but which can become live when basic insulation fails.

Extraneous-conductive part: A conductive part liable to introduce a potential, generally Earth potential, and not forming part of the electrical installation.

By BS7671 protective earthing is required for exposed conductive parts, and protective equipotential bonding is required for extraneous-conductive parts.

So, the metal trunking and metal enclosure is part of the installation so protective earthing is to be used. So it is not necessary to use 6mm2 cable for this.

Thanks guys for pointing me in the right direction!

 

[Jurasic Spark]

From BS 7671:

Exposed-conductive part: Conductive part of equipment which can be touched and which is not normally live, but which can become live when basic insulation fails.

Extraneous-conductive part: A conductive part liable to introduce a potential, generally Earth potential, and not forming part of the electrical installation.

By BS7671 protective earthing is required for exposed conductive parts, and protective equipotential bonding is required for extraneous-conductive parts.

So, the metal trunking and metal enclosure is part of the installation so protective earthing is to be used. So it is not necessary to use 6mm2 cable for this.

Thanks guys for pointing me in the right direction!

Correct, like I said EXPOSED

 

[zsoltimatrix]

Correct, like I said EXPOSED

Yes.

 

[zsoltimatrix]

Is there any rule for sizing the protective earthing conductor which connects the exposed-conductive parts to the earthing terminal?

 

[gaulty]

it's in the regs book mate. mines in the work van or i'd look it up for you, near sure it depends on whether it's protected (in conduit etc) and also what resistance reading you get? has to be under a certain resistance think but not 100% sure it's around 5 megohm like i said if i had my book i could find out.

If your getting to high a resistance your cable is too small. Usually! The main reason it needs to be under a certain resistance is so that if there is a fault it flows through the earth and not your body.

 

[GStueyXR]

The main reason it needs to be under a certain resistance is so that if there is a fault it flows through the earth and not your body.

That aint so accurate.... Low resistance earth is to maximise fault current to achieve I2 (operating current of overcurrent protective device)

Your explanation is sooo wrong, whether the earth is low resistance or not, if you offer a parralel path, an inversely proportional current will flow through you relative to your natural resistance.

 

[Jurasic Spark]

Is there any rule for sizing the protective earthing conductor which connects the exposed-conductive parts to the earthing terminal?

You can calculate it (reg 543.1.3) using the Adiabatic Equation.
or
You can select it (reg 543.1.4)