The MOV is being installed across Line and Neutral which is correct. Since this is a single phase socket array, all the 3 (Line Neutral and Ground) are shorted together via the copper busbar. Therefore the potential differences between the sockets should be negligible.

More expensive surge arrestors will have MOV across line-line, line-neutral, neutral-ground and line-ground. Obviously this Mr DIY is just a extra precaution instead of full protection~ better than nothing i suppose haha

Except electricity doesn't work that way. It will always travel along the path of least resistance. What the MOV does is to give it an easy alternative so the MOV burns up instead of your load. So essentially electricity doesn't really care whether it is 'nearer' or 'further' UNLESS there is added impedance which I don't believe to be the case because your power switch is barely 1' long...

Try taking a multimeter and measure the resistance between your proposed location and the actual location. Probably u get less than 50ohms. When the surge comes in at 1,000 volt, it probably isn't going to care about the 50ohms haha.

Well the truth about surge protection is electrical surges are kinda unpredictable in terms of amplitude (peak to peak volt) or duration (surge time) so designing a perfect surge arrestor is close to impossible. Even industrial surge protector guys such as Emerson etc usually do not offer any sort of guarantee.

In fact some manufacturers put multiple MOVs across the same system in hopes that one of them 'catches' the strike. Theoretically installing a MOV at the 'entrance' is a good industry practice but there is no concrete proof that installing elsewhere along the PCC (Point of common coupling) affects the efficiency of the surge arrestor system.

If you have an expensive equipment, investing in a proper surge arrestor instead of Mr DIY is highly recommended

Mr DIY surge arrestor also can spark discussion LOL

Using back your diagram,



If the impedance between the 2 points are negligible, then these 2 points are at the same electrical potential. I guess manufacturers don't know this value that's why they recommend putting at the 'entrance'? And Mr DIY probably installed it at whichever cheapest location

I not sifu la lol. If you paranoid then make a trip to Jln Pasar, buy another MOV with same part number and stick it to the entrance also can.

What makes u consider surge arrestors at the first place? If your lights dim while your neighbours wash their car it's better to check grounding instead