Surge / Lightning Protection

[nstoker]

I have an engineering degree - but I only took one electrical course. I sure could use some help with a surge protection design.

I pump water from a lake for irrigation. At the home site I send a 24 volt signal to a relay to trigger a 240 volt pump. It is about 800 yards to the relay. It is about 8 feet from the relay to the pump.

I have blown 3 relays and I do not know why or where the surge is coming from. These cost ~$50 each so I am tired of doing this.

I would like to fuse everything and try to determine where the spike is coming from. I'd even like to fuse the line from the relay to the pump in case I am getting a reverse voltage.

Is there someone who can design such a circuit for me? I can probably build it - but if they want to build it that would be great as well.

Thanks in advance for your assistance and I hope I don't insult anyone.

[I_Daniel]

Just a query - do you have a diode across the coil of the relay?
If not then using a diode (plus to plus side of the coil) will stop the "flash back" a 1N4007 should do it
Yes a bit over overkill because a 1N4007 is rated at 700 volt RMS (1 000 Peak), 1 amp-(surge 30). If I recall correctly it has a rather good response time and also frequency is above the other 1N400x.

You could also try a VDR (Voltage Dependent Resistor) across the 240V AC