Seeking Valves

[Nowhere-Man]

While I was at it, I wired in an RCD closer to my supply and that should trip out at 0.03 amp.

While an RCD is a very good thing to have in the mains supply of an old radio I'm sorry to say that represents a misunderstanding of what an RCD can do. An RCD does NOT trip on overcurrent. What it does is detect whether the current in the live and neutral are the same. If they differ by more than the (usually) 30mA rating then it will trip. If the current that's going astray is passing through you, then it can save your life. If you have a faulty mains transformer (or rectifier or smoothing cap for that matter) and things start to get hot in the set then an RCD will not trip. Except if things get bad enough for the insulation between the primary and frame of the mains transformer fails, and only then if the frame of the transformer is earthed.

I'm sure there's a tutorial thread on RCDs somewhere on GVR.

The whole subject of RCDs, fuses and isolating transformers is quite complex and prone to a lot of misunderstanding.

Additional special note about electricty afloat. If you're connected to a shore based supply then that should be protected by a 30mA RCD as well as overcurrent protection by fuse or MCB. If you're using an onboard supply (generator or inverter) the generator neutral should be connected to the hull (assuming it's metal) and that will give an excellent earth. Then protection can be as per usual for a domestic supply. If the neutral is NOT connected to the hull then this is a specialised arrangement (known as a IT supply, nothing to do with information technology) which could be very hazardous.

My understanding of RCD's is that under normal conditions the voltages between live and neutral cancel and the vector sum is zero. If there is some leak between live and neutral, the vector sum isn't zero. In the device is a toroidal transformer that will detect and trip the circuit.

On boats, there are significant misunderstandings of electrical systems. I am currently rewiring a boat the electrical system of which has had me baffled. The shore line supply was actually taken to an inverter/charger and then the A.C. from the inverter was taken to the Consumer Unit. What happened was the inverter blew (I guess the internal fuse) and that disconnected the entire supply. I couldn't get the inverter out to inspect the fuse as it has been cabled into a small cupboard and couldn't be freed up. So, I took it out of circuit and connected shoreline straight to the Consumer Unit.

The kicker was the lighting system functioned as follows: DC from battery bank fed to Inverter/Charger and emerges as 260 A.C. 260 AC then fed to Consumer unit and to lighting MCB. Outgoing circuit wire then fed to a drop-down transformer and back to 12 volts again. With 6 amps current draw on the batteries just to have the inverter on, result is a huge loss of battery amps reserve. What could have been simpler than just taking 12 volts from the batteries to the halogen lights?? Household cable was also used but on boats we use arctic cable which is more resistant to vibration (domestic cable isn't allowed on boats).