main bonding jumper

[shoaib]

do we need a main bnding jumper to bond neutral and earth at main panel for all earthing systems i.e. TN-S, TN-C-S, TT.
i believe that neutral and earth are bonded at transformer in TN-S, whereas at main panel in TN-C-S and neither bonded at transformer or main panel in TT.
please correct me.

 

[hbendillo]

OK, I'll bite. To what does "TN-S" and all the other letters you posted refer?

 

[Smart $]

Those earthing systems are IEC designations. There is no direct correlation to NEC requirements.

Under the NEC, the main bonding jumper must be installed at service disconnecting means, bonding the grounded [neutral] conductor to the equipment grounding system (load-side grounding). Earthing systems, grounding electrode system (GES) under the NEC, can be connected to the grounded conductor anywhere from the service point (utility-consumer demarcation) to the service disconnecting means.

Where the system is ungrounded, there is no main bonding jumper... and IIRC, the GES has to be connected to the equipment grounding system at the service disconnecting means. In this case, it's for both line and load sides.

 

[GoldDigger]

See http://en.wikipedia.org/wiki/Earthing_system for more information and to get an idea of what US equivalents are. US POCOs use Multiple Grounded Neutral as the standard for most systems.