Perhaps a rather rudimentary question but what is “full mode” protection? I assume that it is a combination of common and differential modes but it seems to me that it is generally common mode that is provided.
I have took part in a couple of Webinars on the subject of SPD and tried asking questions to get a clear image of the connections in my head, didn’t quite get there. Reading that article last night I think I cut through the overload of information and got back to basics.
If the installation is TN-C-S with a hardwired link between neutral and earth at the intake and that is where the SPD is you don’t need a a device between the neutral and earth, because they are hardwired together.
If the installation is TT there is not a hardwired link between neutral and earth at the intake and you cannot install one, because you would be making a conversion to TN-C-S which is not permissible or good engineering, so you need a device between the neutral and earth to keep the separation between them, whilst allowing a discharge of electricity if required.
A TNS installation also requires a device between neutral and earth to keep the separation, so it is not converted to TN-C-S.
Does that sound like a reasonable summary?
Then there’s also the issue of blowing fuses or tripping trips that are protecting the SPD devices, the suppliers main fuse and/or additional over current protective devices installed in the enclosure with the SPD.
I have took part in a couple of Webinars on the subject of SPD and tried asking questions to get a clear image of the connections in my head, didn’t quite get there. Reading that article last night I think I cut through the overload of information and got back to basics.
If the installation is TN-C-S with a hardwired link between neutral and earth at the intake and that is where the SPD is you don’t need a a device between the neutral and earth, because they are hardwired together.
If the installation is TT there is not a hardwired link between neutral and earth at the intake and you cannot install one, because you would be making a conversion to TN-C-S which is not permissible or good engineering, so you need a device between the neutral and earth to keep the separation between them, whilst allowing a discharge of electricity if required.
A TNS installation also requires a device between neutral and earth to keep the separation, so it is not converted to TN-C-S.
Does that sound like a reasonable summary?
Then there’s also the issue of blowing fuses or tripping trips that are protecting the SPD devices, the suppliers main fuse and/or additional over current protective devices installed in the enclosure with the SPD.
