Supplementary bond or main bond?

[electrospark]

Hi,

Just a quick question. i'm running some 10mm piros on some traywork. Is the bonding to the tray main bonding of supplementary bonding? The head is 3 phase rated at 200A but the piros are from a 3 phase ryefield board with 60A single phase supplies leaving to supply flats. I was advised by someone to fit a 4mm bond to the tray but this seems to be very small for it. I'm not sure how you go about sizing the bond for traywork and trunking???
Thanks for any advice.

 

[ricicle]

The tray work will not need bonding unless it could introduce a potential from outside the equipotential zone. If the tray enters a flat then it will require bonding with 10mm² within the flat (ie from that flat's CU) as it becomes an extraneous conductive part to that flat.

 

[ban-all-sheds]

Is the bonding to the tray main bonding of supplementary bonding?

Surely it's neither?

If you've got Pyro in contact with it then it'll be an exposed-conductive-part, won't it, and require earthing, not bonding?

 

[electrospark]

Is the bonding to the tray main bonding of supplementary bonding?

Surely it's neither?

If you've got Pyro in contact with it then it'll be an exposed-conductive-part, won't it, and require earthing, not bonding?

Ok earthing then. So what would csa of the earth cable depend on? The pyro has a pvc sheath so not directly in contact with the tray.

 

[ricicle]

Is the bonding to the tray main bonding of supplementary bonding?

Surely it's neither?

If you've got Pyro in contact with it then it'll be an exposed-conductive-part, won't it, and require earthing, not bonding?

I would not earth it either - the Pyro sheath is earthed (or should be we hope !)

 

[electrospark]

The tray work will not need bonding unless it could introduce a potential from outside the equipotential zone. If the tray enters a flat then it will require bonding with 10mm² within the flat (ie from that flat's CU) as it becomes an extraneous conductive part to that flat.

The tray is only in the communal area of a block of flats and will not enter any flat. So are you saying that it is not necessary to earth it at all???? Surely it would need some degree of earthing?

 

[ban-all-sheds]

Ok earthing then. So what would csa of the earth cable depend on?

Same as any other cpc. 543.1.

The pyro has a pvc sheath so not directly in contact with the tray.

OK, so the tray isn't an exposed conductive part after all.

 

[electrospark]

Is the bonding to the tray main bonding of supplementary bonding?

Surely it's neither?

If you've got Pyro in contact with it then it'll be an exposed-conductive-part, won't it, and require earthing, not bonding?

I would not earth it either - the Pyro sheath is earthed (or should be we hope !)

of course the sheath will be earthed.... So even with pvc covered pyro the tray need no be earthed providing the tray does not enter a flat?

 

[ban-all-sheds]

I would not earth it either - the Pyro sheath is earthed (or should be we hope !)

But if (here it isn't, but it could have been) the Pyro wasn't PVC covered, the cpc would have been making contact with the tray, possibly dodgy/intermittent contact.

Wouldn't ensuring the tray was properly earthed have been a good idea?

 

[electrospark]

I would not earth it either - the Pyro sheath is earthed (or should be we hope !)

But if (here it isn't, but it could have been) the Pyro wasn't PVC covered, the cpc would have been making contact with the tray, possibly dodgy/intermittent contact.

Wouldn't ensuring the tray was properly earthed have been a good idea?

Yes so we are saying that if fact it should be earthed in this case. So how do you determine the size of the earth to the tray or trunking?

 

[ban-all-sheds]

Yes so we are saying that if fact it should be earthed in this case.

I thought we'd established that as the pyro is coated the tray won't need earthing?

So how do you determin the size of the earth to the tray or trunking?

Same as any other cpc. 543.1.

 

[ricicle]

Even if the Pyro was not pvc covered the sheath would be earthed. It would not be possible for the tray to become live via the line conductor without it penetrating the earthed sheath, and the fault cleared. The tray would obviously rise in potential with the earthed sheath during the fault but would clear within allowed times if the circuit is designed correctly.
If your assessment decides that you do want it earthed then you would have to choose in line with table 54? or the Adiabatic equation.