A couple of questions on SPD's
I am specifying an SPD for a house supplied with overhead lines. Already know I need a type 1, will actually be a type 1/2 at the origin and considering a type 2 in the main DB.
Then comes the question of maximum discharge current required. I think where there are lightening conductor systems involved this is calculated, but for a domestic property without such a system, overhead lines and singe phase supply I expected to just find a number I have to comply with, but couldn't find anything in BS7671? Am I just missing the obvious.
Second part of the question. I noticed in table 3.7.3 of the on site guide that maximum cable length for spd connections is only defined for a type 1 SPD. Other parts of the osg and BS7671 extrapolate this to type 2 spd's as well. The cable length is to reduce ringing generated by large spikes. I was wondering if this limit was only intended for type 1 spd's dealing with very large spikes and has been incorrectly extended to any spd installation unnecessarily. Your thoughts.