In answer to your concern Khonwan.

If you earth the pump directly to an individual electrode or in your case use the surrounding mass of earth in the bore hole, in the event of the cable becoming damaged or an earth fault developing in the motor the resulting earth fault current would not be sufficient to operate the protective device, in this case an MCB. If the touch voltage exceeds 50VAC automatic disconnection must occur. Any voltage above 50VAC is potentially hazardous.

Installing a 30mA or a 100mA DIN rail RCD would operate in less than 0.4secs, in practice 20 to 30 milli secs.

It would then comply with the automatic disconnection requirements of the AS and BS standards.

In your case you would just fit an RCD as the pump motor is not readily accessible to indirect contact.

SPDs should be installed in the switch board for the very reason that they will be near the neutral link and earthing bar, in your case you could mount them in an enclosure adjacent to the switch board the total length of the earthing conductor should be kept as short as practicable.

The MCB is to protect the SPDs from short circuit fault. You could connect the SPDs to the load side terminals of the motor MCB and save the expense of an additional MCB.

In the case of your socket outlets in your house, the installation of an RCD (which you have wisely carried out) will give additional protection if the MEN system is used (and will be the primary source of protection if the TT system is used) in the event of an earth fault.

Most deaths and serious injury from electric shock are caused by indirect contact.

One is fully aware that overseas standards are not legally enforceable in Thailand but they can be used as a guide so as to achieve a safe electrical installation.

　

　

Look at the picture provided by Naam, Post #11, you can see the surge protectors (red blocks marked L, L, L, N) installed in his pump starter panel. The surge protection should be located as close to your submersible pump as possible.

incorrect assumption. there is no such thing like a pump starter panel in this picture. separate breakers and pump start relays are located somewhere else. the picture shows my setup of phase protection (individual phases are switched off when voltage too low or too high) as well as additional lightning protection for the main house.

Look at the picture provided by Naam, Post #11, you can see the surge protectors (red blocks marked L, L, L, N) installed in his pump starter panel. The surge protection should be located as close to your submersible pump as possible.

incorrect assumption. there is no such thing like a pump starter panel in this picture. separate breakers and pump start relays are located somewhere else. the picture shows my setup of phase protection (individual phases are switched off when voltage too low or too high) as well as additional lightning protection for the main house.

Interesting application. At least I got the surge protector part correct.