SPD arrangement

lyledunn:

The above follows manufacturers instructions. Am I right in assuming that the neutral module is not used as protection is afforded by the N/E bond on a TN-C-S system? 

There are only 2 types of connection in BS 7671 for three-phase systems with Neutral - CT1 (Fig 534.3 in BS 7671) and CT2 (Fig 534.4 in BS 7671).


What is shown in your picture appears to be neither of those, if the system has a Neutral ... but yes you are correct, in this case if the N and PE are bonded close to the SPD the N-PE for CT1 may not be necessary.


In TN-C-S systems, because the Neutral separates from PE downstream of the service head, especially in premises with LPS, there may well be impulses between N and PE by the time you get to the distribution board / switchboard. It may therefore be OK to use this at the main switchboard / distribution board, but Type 2 or Type 3 SPDs downstream would need all 4 SPDs.


I still think connection of the N-PE SPD would be the best approach (since it's been provided), as shown in Fig 543.3 and Fig 16A5 in BS 7671 - but the OSG says refer to manufacturer's instructions !

 

lyledunn:

The above follows manufacturers instructions. Am I right in assuming that the neutral module is not used as protection is afforded by the N/E bond on a TN-C-S system? 

There are only 2 types of connection in BS 7671 for three-phase systems with Neutral - CT1 (Fig 534.3 in BS 7671) and CT2 (Fig 534.4 in BS 7671).


What is shown in your picture appears to be neither of those, if the system has a Neutral ... but yes you are correct, in this case if the N and PE are bonded close to the SPD the N-PE for CT1 may not be necessary.


In TN-C-S systems, because the Neutral separates from PE downstream of the service head, especially in premises with LPS, there may well be impulses between N and PE by the time you get to the distribution board / switchboard. It may therefore be OK to use this at the main switchboard / distribution board, but Type 2 or Type 3 SPDs downstream would need all 4 SPDs.


I still think connection of the N-PE SPD would be the best approach (since it's been provided), as shown in Fig 543.3 and Fig 16A5 in BS 7671 - but the OSG says refer to manufacturer's instructions !