RCCB - Type A vs AC

Question

I would like to install an RCCB at the electrical point that will power a few devices that are going to be in my fish pond. Documentation and general info online say that Type AC RCCB can work with resistive loads but will not detect DC leakage currents or is not advisable for DC loads. I'm not sure if the devices in my pond could cause DC leakage current back into the AC line. The devices that will be downstream from this RCCB are an AC powered submerged pond pump (85W), a 12v/16A LED controller with dimmer.

I would also appreciate it if someone could explain what DC leakage current means and in what scenario a type A RCCB will work while type AC won't. Would this be a correct example: if the part of the wiring/circuit that comes in contact with a person (i.e. trigger a leakage current scenario) is the AC (alternating current) carrying part, then both the RCCB types will trip/work and if the part of the wiring/circuit that comes in contact with people is DC, then a Type AC RCCB will not work?

Answer 1

Type A RCCB means they can protect when the output of a device, typically electronics, is "pulsed DC", meaning what's called a "PWM output" (PWM stands for Pulse Width Modulation). Things like Solar Inverters and UPS systems create an "approximation" of AC power by pulsing DC (from batteries for instance) to make it look like AC, called "pseudo AC".

The type AC RCCB can only be used on "regular" AC power, like what you get from a utility or local generator.

In your case, the pump is AC, the LED light controller is possibly PWM on the OUTPUT, but because that is actual DC, not pseudo AC, and that portion of the circuit is 12V, it would not count. So a type AC is fine.

Answer 2

The pump is unlikely to add a DC fault. But the LED controller could.

Almost all electronic devices convert the AC into DC internally using a rectifier. If the rectifier goes bad, then it may draw the full current on one half of the AC waveform, and nothing on the other. So instead of drawing a steady AC current, it's now drawing pulses of DC.

This can "blind" a Type AC breaker, so that it will no longer detect any earth leakage faults.

Type AC devices are now pretty much obsolete. The only reason you might consider using them is that they are cheaper.