I live in a small town where it is difficult to find certified electricians. In fact, electrician certification is not common for residential installations. I did find some experienced electricians but I don't think they are certified and know best practices in the installation.

I reached out to the company for support but the technical assistance on the products are limited and I need further clarification to make sure that I purchase the correct products and the installation is safe.

Here is the link to the thread about Relays, Contactors, and RCCBs in Picture 2 and Picture 3, which is related to this thread:

On-Delay, Under and Overvoltage Relay, Contactors AC-7a & AC-7b, Relay - Contactor compatibility, RCCB rated current higher than operational current


I WILL NOT do the installation by myself. I WILL CERTAINLY hire an experienced electrician after getting enough information.

I have questions on the surge arrester/surge protection device (SPD), contactors, and control relays. I will start with a post about the SPD.


I am going to install a surge arrester to the home main panel. I prefer not to break the concrete wall and not to change the existing wiring buried in it.

The voltage input ranges from 220 V to 230 V. The neutral line from the power meter does not light up the tester screw driver (it is grounded by the power company) and my house has its own separated grounding rod so I think it is the TT grounding system.

The wiring is shown in the picture below. Here are my questions:

  1. Schneider recommends that an external Short Circuit Protection Device (SCPD) (3), which has the rated current of 40 A, be installed with the surge arrester (5), which has the Imax of 40 kA. It is important to use the SCPD tested by the company as one of the essential characteristics of SCPD is that it withstands the lightning current and must not trip upon 15 successive impulse currents at the nominal current.

The MCB installed by the power company (1) has the nominal current of 20 A which is related to 4400 VA consumer power subscription. This MCB can be a product of Schneider or ABB depending on the stock.

If a lightning surge flows through the power lines and reach the 20 A MCB (1), considering that this MCB is not the one recommended by the company and it has a lower rated current compared to the SCPD (3), will this disrupt the function of the surge arrester(5)?

  1. The SPD installation must comply with the 0.5 - meter rule. To reduce the length of the wire conductors, a busbar rated 100 A is used to connect the SCPD (3) and the RCCB (4) so only the length of the wires labeled A and B are subjected to rule.

Can the length of A and B be as short as possible or there is a minimum safety distance between the bottom terminals of SCPD (3) and the top terminals of the surge arrester (5), likewise, between the bottom terminals of the surge arrester (5) and the top terminals of the ground terminal block (6)?

  1. Schneider mentions that the incoming polluted and the outgoing clean cables must be physically separated. Is there a minimum distance, labeled C, D, E, F, between cables to minimize the effect of the electromagnetic coupling in the event of lightning surges?

Picture 1

Picture 2

Picture 3

  • 1
    Caution, You come to a site that is almost exclusively non professionals and most on the other side of the pond so use caution with any answers. The basics are if the distance to your SPD then to ground are further than another device the devices that have a shorter path to ground may well blow before the SPD sees the spike, forget about coupling , with lightning strikes the voltage is high enough to jump the insulation and even feet away to find a lower potential path to earth. The best solution is to put the SPD as close to the incoming power as possible and have a solid path to earth
    – Ed Beal
    Dec 23, 2021 at 20:36
  • Thank your for responding to my post. I appreciate that. Do you have any views on the first and second questions? Dec 24, 2021 at 2:08
  • 1
    In your "New MCB Box" diagram, you define red as hot and blue as neutral. Are we to presume yellow is ground?
    – FreeMan
    Jan 21, 2022 at 13:41
  • @FreeMan Yes, yellow is ground. Thank you for your response. :) Jan 23, 2022 at 2:22

1 Answer 1


Wow, I would say you are taking the instructions much too literally, and also, expecting more than is realistic from a surge suppressor.

Surge suppressors do not stop lighting. They are not lightning arrestors; that is a totally different class of product that doesn't attempt to stop the lighting, but give it an easier route to earth. You need one of those. Trying to use a surge protector to suppress lighting will only make it catch fire.

Also you are building this system on the presumption that all the surges threatening your house are external to your house. Actually your own equipment is the source of many surges. So placing the surge suppressor distant from your breakers will leave it unable to protect your loads from each other.

As such, the box containing 3-4-5-6, I see no reason for that box at all. Get rid of it. I could see a separate box for a lightining arrestor but this is not that.

The surge suppressor belongs inside the MCB panel, within 0.5m of each and every circuit breaker in the panel.

On your questions, #1 it sounds like Schenider is just advertising their brand of breaker, the way cooking recipes often call out a specific brand of ingredient (when they know perfectly well that any will do).

#2 that long run between this special surge box and the MCB box will make the surge suppressor ineffectual at stopping surges coming from one of your appliances.

#3 Coupling can be reduced by using metal conduit and panel boxes, however a lighting hit is so destructive that it will simply travel down the wires.

  • Hi there, thank you for posting your views. I appreciate that. Dec 25, 2021 at 1:38

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