dbuckley
Senior Member
- Location
- Canterbury, New Zealand
Another good reason for keeping current off the grounds is to reduce interference breakthrough on audio systems; dimmers that use the ground as a neutral for their contreol electronics are particularly obnoxious in this regard.
The other thing I'd note is that ther is nothing wrong with TN-C(-S) distribution, it works well in many contries of the world. However, there are times when other systems are much better, like marinas, milking sheds, and entertainment stages in the middle of fields, and the NEC is quite rigid in its enforcement of TN-C-S for pretty much everything. And especially in forcing SDSs to be TN-S bonded to the installation ground.
The American MGN thing is a unique twist on TN-C-S scenario; in (most of the populated bits of) the USA there is a primary neutral in the MV distribution, which most countries don't have. On top of that, the primary neutral (where present) is bonded to the secondary neutral. This arrangement creates all sorts of... (looking for the right word...) situations that the rest of the world doesn't suffer from, mainly relating to stray current shocks from somewhere down the road...
The other thing I'd note is that ther is nothing wrong with TN-C(-S) distribution, it works well in many contries of the world. However, there are times when other systems are much better, like marinas, milking sheds, and entertainment stages in the middle of fields, and the NEC is quite rigid in its enforcement of TN-C-S for pretty much everything. And especially in forcing SDSs to be TN-S bonded to the installation ground.
The American MGN thing is a unique twist on TN-C-S scenario; in (most of the populated bits of) the USA there is a primary neutral in the MV distribution, which most countries don't have. On top of that, the primary neutral (where present) is bonded to the secondary neutral. This arrangement creates all sorts of... (looking for the right word...) situations that the rest of the world doesn't suffer from, mainly relating to stray current shocks from somewhere down the road...