Incoming Gas cross bonded off cold water

[sparksburnout]

Nothing to do with fault currents,on a TNCS system the bonding conductors may carry a significant current under normal load conditions,thats why there is a requirement for 10mm.

come on then W/P, how under normal conditions can a TNCS system have "significant" current flowing through the EB?

 

[Deleted member 9648]

come on then W/P, how under normal conditions can a TNCS system have "significant" current flowing through the EB?

Because main bonding is connected to a metallic service at or near earth potential, and is electrically connected to the neutral terminal. Therefore a parallel path is created through which a proportion of the neutral current may divert. Do you think the required CSA of TNCS/PME bonding conductors are increased over TT/TNS for fun?

 

[davesparks]

come on then W/P, how under normal conditions can a TNCS system have "significant" current flowing through the EB?

Diverted neutral currents, which is the reason that PME supplies require larger main bonding and that the bonding size be maintained back to the PME terminal at the cutout.

 

[sparksburnout]

Because main bonding is connected to a metallic service at or near earth potential, and is electrically connected to the neutral terminal. Therefore a parallel path is created through which a proportion of the neutral current may divert. Do you think the required CSA of TNCS/PME bonding conductors are increased over TT/TNS for fun?

A proportion yes, but I don't think the word significant is particularly apt under normal conditions?

 

[davesparks]

A proportion yes, but I don't think the word significant is particularly apt under normal conditions?

Why not significant? If an old iron water main feeds a row of houses and each one has main bonding connecting that water main to the supply neutral then it will see a significant proportion of the neutral current

 

[Deleted member 9648]

A proportion yes, but I don't think the word significant is particularly apt under normal conditions?

Obviously no point in a 10mm bond then, do it in 6.0mm. No reason at all for the main bond on larger installations to be up to twice the CSA required on a TNS.

 

[Deleted member 26818]

Significant as in virtually all.
Problem with TN-S supplies, is that most are now PME, just not been upgraded to TN-C-S yet.

 

[sparksburnout]

I'm not questioning your knowledge w/p, just trying to get this straight. I understand how some current will flow through the EP, obviously it is a parallel path, but under normal conditions, on an average (let's say domestic) installation, it's not going to be large, certainly no where near that requiring 10mm? For example I just tried my own installation - with the shower and other stuff running I have a current draw of 41A through the tails, 40mA through the water bond and *****all through the gas, which is not surprising as it is plastic outside.(maybe come back to that just thinking about it). Am I, therefore, incorrect in thinking that the increased EP bond for TNCS systems is nothing to do with fault conditions including possible loss of neutral then?

 

[Deleted member 26818]

Due to the fact that the network neutral and earth are combined, any neutral current from the installation, will also be present in the earth conductors.
If incoming services are metallic and bonded, then diverted neutral currents from other installations that are bonded to the same services will also be present in the earth conductors.
A break in the Combined Neutral and Earth network conductor is another kettle of fish.

 

[sparksburnout]

Due to the fact that the network neutral and earth are combined, any neutral current from the installation, will also be present in the earth conductors.
If incoming services are metallic and bonded, then diverted neutral currents from other installations that are bonded to the same services will also be present in the earth conductors.
A break in the Cobined Neutral and Earth network conductor is another kettle of fish.

cheers Spin, I wasn't thinking of the bigger picture here. Methinks I might get me a copy of GN7

 

[Barrie Patrick]

I know what to do here. Install a bonding clamp on gas pipe with a short piece of 1mm connected to it. Tell kitchen fitter it is an aerial for your wireless bonding arrangement back to MET. He will definately believe you as he does not understand electrical type stuff thingys. Then tell customer it is free. Everyone will love you.

ROFLMAO :sorcerer: