Up until 2 weeks ago my spot lights were working fine, switched on 1 day and they popped checked voltage at light point and it was 70v. Disconnected switch line at switch checked voltage on feed and it was OK at 235v .Whilst still disconnected from switch I send a live feed up switch line and got 235v at lighting point OK. Disconnected lights, reconnected switch line to switch checked voltage at lighting point and it dropped to 209v ,reconnected lights 1 by 1 (with a 12v transformer) and there was a voltage drop each time( there is 3 way switching for lights) can someone advise me ?

Having a difficult time trying to follow the circuit.

Can you list the devices in order from panel to switch to light, etc.

What is 235 volts?

Does the 235 volt feed go to lighting transformers?

Is this all underground wiring?

Having a difficult time trying to follow the circuit.

Can you list the devices in order from panel to switch to light, etc.

What is 235 volts?

Does the 235 volt feed go to lighting transformers?

Is this all underground wiring?

Hi from what I can see the feed comes from the panel to a terminal junction box which then splits and feeds other lighting circuits. One feed cable goes to another junction box which is where the spot lights are wired to, from this box a cable goes down to feed the switch and a return wire as the switch line, The power going to the switch is OK it's when it comes back on the switch line the voltage is lost. There are 3 switches as there are 3 points to switch the lights from. The 235v go to 12v transformers then lights. I have tested the switch line and there is no fault, could it be one of the switches?

Where are you located?
You may have a burnt or coroded buss where the breaker plugs onto, a loose wire or connection, If you keep applying a little more load each time and the voltage drops that much.
Are you sure the transformers Primary is 240(235) Volts?
And if you have 3 switches, you will need 2 to be 3 ways, and 1 4 way.
Are you using a low voltage dimmer with a relay box?