For SPDs, in terms of preventing damage from induced voltages, the hard part is not voltage spikes between the cores of the incoming supply cables, but the voltages that exist between the incoming supply cable considered as a group, and other things, such as telephone lines, plumbing, structural steels, and if you have one, the lightning protection system- equipment that straddle pairs of such things (phones, cable TVs, fax machines etc ) are especially at risk.
If you like imagine the pick-up working rather like a crude dipole antenna, with the mains wiring as one limb, and the phone lines or the plumbing or whatever as the other.
Cheers Wikipedia for the image ... Note that a surge is more of one or two isolated cycles, not a continuous wave, and the sort of SPD we can buy only work for a few microseconds at their rated current - if there really was a continuous over-voltage, they would simply catch fire without ADS.
A real radio dipole is laid out with the limbs carefully balanced in a straight line and away from obstructions, but the same pick up effect still occurs if neither condition is met, just less efficiently and with more interference picked up- the older ones among us will have seen a coat hanger and a car body used as as the two parts of a medium wave and VHF radio antenna and also working - though that is so unbalanced you may prefer to think of that as a monopole and a pseudo 'earth', the pick-up mechanism is the same.
In more rambling installations, the 'other limb' of the "diplole antenna" may well just be the wiring of the rest of the installation.
However, any device connected L-N cannot do much about that, unless L and N part company and are forming the antenna, but usually they are really the same limb, having stayed side by side for most of the route,
I suspect a lot of SPD will not quite work as expected, as they are not across the actual pair of things that form the dominant pick-up mechanism.
For SPDs, in terms of preventing damage from induced voltages, the hard part is not voltage spikes between the cores of the incoming supply cables, but the voltages that exist between the incoming supply cable considered as a group, and other things, such as telephone lines, plumbing, structural steels, and if you have one, the lightning protection system- equipment that straddle pairs of such things (phones, cable TVs, fax machines etc ) are especially at risk.
If you like imagine the pick-up working rather like a crude dipole antenna, with the mains wiring as one limb, and the phone lines or the plumbing or whatever as the other.
Cheers Wikipedia for the image ... Note that a surge is more of one or two isolated cycles, not a continuous wave, and the sort of SPD we can buy only work for a few microseconds at their rated current - if there really was a continuous over-voltage, they would simply catch fire without ADS.
A real radio dipole is laid out with the limbs carefully balanced in a straight line and away from obstructions, but the same pick up effect still occurs if neither condition is met, just less efficiently and with more interference picked up- the older ones among us will have seen a coat hanger and a car body used as as the two parts of a medium wave and VHF radio antenna and also working - though that is so unbalanced you may prefer to think of that as a monopole and a pseudo 'earth', the pick-up mechanism is the same.
In more rambling installations, the 'other limb' of the "diplole antenna" may well just be the wiring of the rest of the installation.
However, any device connected L-N cannot do much about that, unless L and N part company and are forming the antenna, but usually they are really the same limb, having stayed side by side for most of the route,
I suspect a lot of SPD will not quite work as expected, as they are not across the actual pair of things that form the dominant pick-up mechanism.
