It trips when the test button is pressed, but I can't fire it off with my Megger MFT1741.
When these were being installed they were being tested by applying voltage without recording a trip time, rather than applying current and recording the trip time.
So is expecting to test it as I would a modern RCD appropriate?
I have advised that replacement is required, being a 500 mA device in a domestic property, utter regardless of if I can get it to trip with a Megger MFT or not, but stand to be corrected if need be.
is it the only RCD ? it would be OK as the front end of a TT, if the 30mA protection is done circuit by circuit further down, to see a 500mA or 300mA is a common starter RCD for some of the older farms round here before any submains or boards, serving to provide some fire prevention and a last ditch protection if something bad happens further in.
Of course if you cannot make it fire on a proper RCD test, you should treat it as faulty & replace. It should fire on LN imbalance, just like a modern one.
On some early current mode RCDs, they were re-using bits from the voltage operated models so the test button is not (I think) introducing a fault like a modern RCD - it is just operating the firing solenoid, so they may past self test even if the pick up winding comes detached. Is that flat enamelled wire on the core or a trick of the camera and lighting ?
I suspect JP will want you to post it to him as a museum of interesting parts if it is surplus to requirements
