Relay to protect timer from 120v converted chromega D

[Leigh]

This is not a transient or "spike" issue.
The load is resistive. Resistive loads don't generate spikes.

It appears to be an inrush current problem.

I had considered reversed hot/neutral as a possibility. It's a common problem.
But I can't come up with a good scenario to explain why that would blow a fuse, unless...

Perhaps the existing lamp socket will not handle 120 volts, given that the original part
was low-voltage (probably 24 volts).

If the socket is breaking down or has significant leakage to ground, it could blow
the fuse without leaving any visible indication of the fault.

- Leigh

[Len Middleton]

Given the price and availability of the RH Design unit, you might want a electro-mechanical relay for switching the lamps anyways just to keep it safe, unless of course its current configuration has its switching through a relay.

Leigh's comment regarding the voltage rating of the socket is reasonable, but then what is the voltage rating of the original wiring as well? You could be having a phase to ground or phase to phase fault blowing the fuse, if the voltage rating and condition (e.g. deterioration due to age) in the circuit is not up to your revised requirements.

Looks like you have more work ahead...