None of the RCBO (with width of 1P MCB) in our market is of VI type. All the cheaper ones is VD and the more expensive one is VD with FE. Most of 2P RCCB in our market is VI type (less prone damaged by surge than RCBO) with exception of old or cheapo obscure brand (that you only see used by cheapo developer). VD type will not function if floating neutral (loss of neutral before RCD), which is why the more expensive RCBO is VD with FE.

This post has been edited by jio: Sep 20 2023, 06:50 PM

1. The internal circuit for the RCD function will stop working. If that circuit ended up having shorts it may pop when you switch it back on. If you have lightings and electronics stop working after lightning storm, I would suggest you test all the RCDs as well.

2. VD type RCDs require sufficient voltage between L & N in order to work. In fact it will draw a couple mA current when switched on even without load. Floating neutral in single phase, there isn't sufficient voltage between L & N so VD RCDs won't work. In 3 phase it may ended up being overvoltage, VD RCD may trip or stop working temporarily due to overvoltage protection or pop due to lack/failure of overvoltage protection.

No, there is no fail safe protection and the power to the circuit won't cut off if the RCBO doesn't trip unless the breaker upstream tripped. The overload/overcurrent protection of the RCBO might still work if it is not damaged by the blown RCD circuit (failed RCD frequently still continue being used by the owner not aware or care enough to test it) , but don't take risk. VD with FE will still work without neutral as it will use the earth as fallback. VI type will still work without neutral as it is powered by the CT secondary winding, even if it less prone to surge damage it could still be damaged.

For water heater it is less of a risk as it rely on control circuit (which will have some sort of under/overvoltage protection) and power relays to turn on the high current circuit. It is when RCBO used with other circuit (especially socket outlets) in wet areas that VD type is not safe during loss of neutral.