I have just been involved in a situation where temporary loss of neutral on a TNCS system caused thousands of pounds worth of damage. It seems this loss of neutral situation, either within or outside the installation, is occurring more frequently. SPDs are now commonly fitted but at DBS and generally with a Up in the order of 860v, so giving no protection on loss of neutral in a three-phase and neutral system. Cost benefit analysis across the national spectrum might not support a compulsion but is it time designers should be raising the issue with clients and at least offering a solution. On the other hand, is there a packaged solution?
Removing the main bonding won't achieve anything at all in an installation with internal conductive service pipes. The pipes throughout the installation would still import PEN voltage from other installations.
But would it not stop diverted neutral currents flowing in my bonding?
There have been cases in the past whereby a secondary effect of a broken neutral has been hot bonding conductors/gas pipes/water pipes etc due to them carrying (possibly very large) diverted neutral currents. Wasn't that unfortunate series of explosions in a terrace of houses put down to overheated bonding connections to lead gas pipes? If the bonding had been (automaticaly?) disconnected from the neutral/earth together with the phase conductor would this unfortunate outcome have happened?
You could just alter the pipe work in your installation, and ensure that it is all plastic, so that main equipotential bonding is not required. The gas main up to the house would be plastic in most cases, and just internal gas pipes would be metal. If all metal parts are NOT extraneous parts then main bonding is not required. Keep all pipes off ground to comply. That way you are not inviting diverted neutral currents into your home. There is no incentive for them to come.
Oil boiler pipes may also be metal and be extraneous conductive parts.
Of course appliances' exposed conductive parts connected to a P.M.E earth terminal can not be isolated. You would have to use all Class 2 (all insulated) appliances to avoid a Voltage rise if N rose to a high level above true earth.
Removing the main bonding won't achieve anything at all in an installation with internal conductive service pipes. The pipes throughout the installation would still import PEN voltage from other installations.
But would it not stop diverted neutral currents flowing in my bonding?
There have been cases in the past whereby a secondary effect of a broken neutral has been hot bonding conductors/gas pipes/water pipes etc due to them carrying (possibly very large) diverted neutral currents. Wasn't that unfortunate series of explosions in a terrace of houses put down to overheated bonding connections to lead gas pipes? If the bonding had been (automaticaly?) disconnected from the neutral/earth together with the phase conductor would this unfortunate outcome have happened?
You could just alter the pipe work in your installation, and ensure that it is all plastic, so that main equipotential bonding is not required. The gas main up to the house would be plastic in most cases, and just internal gas pipes would be metal. If all metal parts are NOT extraneous parts then main bonding is not required. Keep all pipes off ground to comply. That way you are not inviting diverted neutral currents into your home. There is no incentive for them to come.
Oil boiler pipes may also be metal and be extraneous conductive parts.
Of course appliances' exposed conductive parts connected to a P.M.E earth terminal can not be isolated. You would have to use all Class 2 (all insulated) appliances to avoid a Voltage rise if N rose to a high level above true earth.
