main earth

[VoltzElectrical]

I thought i'd chuck this in here as well (got it in regs section) to see if I get any responses from those who aren't checking out the regs section.
A large accommodation block has a main supply (3 phase) of 120mm. What size should the main equipotential bonding be?

7671 section 544 refers to main 'protective' bonding conductors. Do they mean 'equipotential bonding, as subsequently referred to in 544.1.2?


My reading of this is that the installation only needs bonding conductors of 25mm if copper.

If the installation is PME, then it could be 50mm??

Any help appreciated.

Cheers all

 

[rick.oshea]

Hia Voltz,

Just to clarify....

The term 'Equipotential bonding' normally covers Main protective bonding (E.g. gas & water) and supplimentary bonding..... i.e. it keeping everything at the same equal potential.

In the regs 544.1 refers to TN & TT and covers everything except PME.

If its PME then you use Table 54.8 and it goes off the size of the neutral conductor i.e. if your neutral is 35mm2 or less its 10mm2...35-50 = 16mm2 and so on...if your neutral on your incomer is 120mm2 then your main bonding will be 35mm2.

If its the Main earth we are talking about (from service head to MET), then you can calculate it with the adiabatic equation 543.1.3 or select it using Table 54.7 and this is saying 1/2 the size of the line conductor...... When you calculate it though, it normally comes out much smaller that the tabulated (and cheaper

The naked lady worked by the way!!!

 

[VoltzElectrical]

just working out size of bonding required to main water and gas. 120 mm 3 phase and neutral from local substation. Got 50 mm in but my mate saying needs to be at least half, I'm like err.. don't think so.

 

[VoltzElectrical]

there was a naked lady. I swear.

 

[rick.oshea]

If you've got 50mm and its PME, its all copper and your neutral csa is 120mm2, you're sorted....35mm2 would have done the trick (95mm2-150mm2, table 54.8)

When its not PME, you cant go less than half of the Main Earth...... up to a max of 25mm2 for main bonding (544.1.1)... its prob this he's thinking about? ..........Or may be he seen this 'naked lady' and its messed with his sanity??

 

[rick.oshea]

The main earth is half the line conductor if you use the table.....54.7, so he may be thinking about this?

 

[IQ Electrical]

I thought i'd chuck this in here as well (got it in regs section) to see if I get any responses from those who aren't checking out the regs section.
A large accommodation block has a main supply (3 phase) of 120mm. What size should the main equipotential bonding be?

7671 section 544 refers to main 'protective' bonding conductors. Do they mean 'equipotential bonding, as subsequently referred to in 544.1.2?


My reading of this is that the installation only needs bonding conductors of 25mm if copper.

If the installation is PME, then it could be 50mm??

Any help appreciated.

Cheers all

The main protective bonding conductors (formerly equipotential bonding conductors) are the usual gas and water etc. service bonding conductors.

If PME then the main protective bonding conductors are sized on the SUPPLIERS NEUTRAL (not your 'tails').
If the suppliers neutral is between 95mm and 150mm then your main protective bonding conductors will need to be 35mm minimum.

If TN-S then the main protective bonding conductor CSA must not be less than 50% of the earthing conductor CSA subject to a minimum of 6.0mm and need not exceed 25mm if it is a copper conductor.