Main Earth & bonding again

[cliffed]

just wondering what you guys reckon.
Main Earth tns,95mm conductors,50 mm Earth,bonding conductor 35 mm.
Sub main to other building,Swa 70 mm 4 core ,c/w 35mm Earth conductor.
Main bonding required in building to usual utilities,what code would you give.

 

[Ian1981]

just wondering what you guys reckon.
Main Earth tns,95mm conductors,50 mm Earth,bonding conductor 35 mm.
Sub main to other building,Swa 70 mm 4 core ,c/w 35mm Earth conductor.
Main bonding required in building to usual utilities,what code would you give.

In a TN-S if copper the protective bonding conductors need not exceed 25mm2.
Need to be no less than half the required size of the earthing conductor and a minimum of 6mm2
Are you saying there is no bonding in place to other building to extraneous parts?
Is it an eicr you are doing?

 

[Richard Burns]

This seems to be a compliant installation as Ian has said, why do you wish to code it?

 

[cliffed]

Yea it's a Eicr,bonding is present but not to the size needed.
Thinking all earth's need to be sized to the intake position,exporting the main Earth to the building,meaning a 50 mm Earth cable.
Also this Swa supplies a Main panel Db,which then supplies other DBS.
My query is ,will the 35 mm c/w the swa be ok for Earth & main bonding,I don't think so.

 

[Ian1981]

Yea it's a Eicr,bonding is present but not to the size needed.
Thinking all earth's need to be sized to the intake position,exporting the main Earth to the building,meaning a 50 mm Earth cable.

Nope.
If you have a 70mm 4 core feeding the other building then if using table 54.7 the cpc required is half the size of the live conductors so 35mm cpc or calculate it using the Adiabatic equation.
Note this is for a cpc not bonding conductors.
As I've already said on tns if the bonding conductors are copper then they need not exceed 25mm2 regardless of size of main earthing conductor or live conductors at the supply end.

 

[cliffed]

Yea,so where would you connect the bonding conductors,25mm being correct.
Thinking if you exported the original 50 mm Earth,then bonding conductors would be ok to connect to this MP DB.Now there's a problem.

 

[Ian1981]

Yea,so where would you connect the bonding conductors,25mm being correct.

Bonding conductors need to be connected back to the MET to which there is only one.
An cpc can be used as a combined bonding conductor and cpc if it satisfies both requirements what size does the cpc actually need to be and what size do the bonding conductors need to be.
You could calculate what actual size the main earthing conductor needs to be from the Adiabatic equation and work out that the bonding conductors need only be not less than half required size and not less than 6mm
I would say the existing 35mm can be used as both so in the other building the extraneous parts are bonded back to the db containing the 35mm conductor with in turn is connected to the MET.

 

[westward10]

Quite simple this your main protective bonds need not exceed 25.0 and a separate 35.0 earth has been installed, I see no problem.
Did you get that motor running Cliff.

 

[cliffed]

Yes thanks,it's works ok direct on line,but with the inverter No.
Not sure what the company's are going to do with that,will let you know when all done,thanks all for your guidance.

 

[cliffed]

Quite simple this your main protective bonds need not exceed 25.0 and a separate 35.0 earth has been installed, I see no problem.
Did you get that motor running Cliff.

Yes agree,but wondering about the other sub mains running from that MPDB,Earth can be used for main bonding,but originally installed for main Earth.
Will the other Swa's comply using the 70 mm swa sheath for their main Earth
Am I overthinking.

 

[cliffed]

Bonding conductors need to be connected back to the MET to which there is only one.
An cpc can be used as a combined bonding conductor and cpc if it satisfies both requirements what size does the cpc actually need to be and what size do the bonding conductors need to be.
You could calculate what actual size the main earthing conductor needs to be from the Adiabatic equation and work out that the bonding conductors need only be not less than half required size and not less than 6mm
I would say the existing 35mm can be used as both so in the other building the extraneous parts are bonded back to the db containing the 35mm conductor with in turn is connected to the MET.

Cpc half the swa,35 mm,bonding needs to be 25mm.
Agree what you say,but there are other Db's in that area,supplied by swa cables,does that the interfere with those main earth's,if using that 35 mm for main bonding.
The actual main Earth is 50 mm,hope I've explained myself ok.

 

[Ian1981]

Cpc half the swa,35 mm,bonding needs to be 25mm.
Agree what you say,but there are other Db's in that area,supplied by swa cables,does that the interfere with those main earth's,if using that 35 mm for main bonding.
The actual main Earth is 50 mm,hope I've explained myself ok.

Your swa armour size is irrelevant if it's not being used as a cpc, you are just supplementary bonding the swa to earth as it's an exposed conductive part.
Your 35mm is being used as the sub circuit cpc to the other building with the 70mm 4 core and can be used as your main protective bonding conductor combined so there is no issue in that respect.

 

[cliffed]

Yea I see,meaning the 35 mm complies with that installation,bonding conductors can be installed at that point,these will be 25 mm,thanks.

 

[Ian1981]

Yea I see,meaning the 35 mm complies with that installation,bonding conductors can be installed at that point,these will be 25 mm,thanks.

Yes.
I would install an earth marshalling bar in the other building and take your 25mm bonding conductor back to that along with the 35mm (which also connects to the sub board feeding external building)which should connect back to the MET at the origin, with it suitably labelled as to what it is and noted on any test certificate.
Sounds like a nice job.

 

[cliffed]

Cheers,will do,will finish the Eicr sometime next week,& give all results & recommendations to our company,passing on to client.
Obviously if this would of been a Tncs Earth,things would be a bit different,regarding main Earth?

 

[Ian1981]

Cheers,will do,will finish the Eicr sometime next week,& give all results & recommendations to our company,passing on to client.
Obviously if this would of been a Tncs Earth,things would be a bit different,regarding main Earth?

Main earth no it can be still sized as per table 54.7 or calculation.
The bonding conductors however need to be sized on the DNOs supply neutral not the neutral size of the 'tails as it were.

 

[westward10]

GN8 is very informative on this well worth the investment.