Can a SPD be installed in a domestic installation without an earth conductor connecting it to the MET, because it will discharge the surge from the live line conductor to the neutral conductor?
If it is TNC-s and you are within a few feet of the N-E bond in the service head, then there is not really much scope to excite a large N-E voltage, and voltages L-N and L-CPC are more or less the same.
However, if there are other items earthed, so the MET is more than just a second neutral connection, and also as the separation from the NE bond increases (allow about a micro-henry per metre ) then the voltages on N and E will diverge. How much divergence is serious enough to warrant a break-over device to clamp the voltage is an 'interesting' question. I'd suggest a few metres.
I'm sure there will be some maker's advice based on very generic assumptions that are intended to sells slightly more SPDs than we really need that contradicts this.
If it is TNC-s and you are within a few feet of the N-E bond in the service head, then there is not really much scope to excite a large N-E voltage, and voltages L-N and L-CPC are more or less the same.
However, if there are other items earthed, so the MET is more than just a second neutral connection, and also as the separation from the NE bond increases (allow about a micro-henry per metre ) then the voltages on N and E will diverge. How much divergence is serious enough to warrant a break-over device to clamp the voltage is an 'interesting' question. I'd suggest a few metres.
I'm sure there will be some maker's advice based on very generic assumptions that are intended to sells slightly more SPDs than we really need that contradicts this.
