First thing, I'll reiterate what several others have already said - for transformerless inverters, always try to "design-out" or mitigate the requirement for an RCD in the first place.
All transformerless inverters will have a degree of inherent leakage current. I think that G83/2 requires that the tested/reported leakage current is no greater than 0.25% of the max AC current. For a 16A/3.68kW (G83 limit) inverter, this equates to 40mA, most decent units will rarely leak more than 5-10mA.
A 30mA RCD can trip from an AC leakage current value greater than 15.1mA (I stand to be corrected on that exact figure though).
As has been stated already, a TypeAC RCD's trip coil will saturate (and never trip under AC ground fault conditions) if any component of the leakage current is pure or pulsed DC. A TypeA RCD will still operate under AC ground fault conditions even if a pulsed DC component of the leakage current is present. It's trip coil will saturate if any pure DC component is present. However, if the amplitude of the pulsed DC leakage current is greater than 6mA then the Type-A RCD cannot be guaranted to operate within its certified scope of operation - this is an important point (can you or the inverter manufacturer guarantee that the 6mA limit will never be exceeded?). A TypeB RCD will operate under AC ground-fault conditions without being compromised by either pulsed or pure DC components of the leakage current.
Hypothetical (but also very real) scenario - TL inverter, requirement for RCD protection under BS 7671 (for whatever reason), TypeAC RCD installed. RCD never "nuisance" trips, just sits there looking pretty. Subsequent AC ground fault occurs (for whatever reason) but the RCD still doesn't trip. Too late to realise that the reason it never "nuisance tripped" is that the trip coil was saturated with DC and became about as useful as a chocolate fireguard. In that scenario, the end customer has been sold/supplied with a circuit protective device that will not operate as intended. It is worse than not fitting an RCD in the first place.
If there is no simple separation (ie, a galvanic transformer) between the DC and AC circuitry within the inverter, and an RCD is required on the AC output of the inverter (due to consideration of BS 7671) then a TypeB RCD is the required solution to provide ADS/ground-fault protection. However, many TL inverter manufacturers certify their product to VDE 100-712 in that it is, by design, unable to inject DC to ground. If the inverter manufacturer states this, then they typically go on to say that if an RCD is required then it need not be a TypeB (ie, a TypeA is ok to use).
There are some transformered inverters still around, although not many. The difference it makes is that, if an RCD is required on the AC circuit, then the inverter alone will not cause nuisance tripping of the RCD, and there is no scenario where a DC leakage current component might compromise the normal function of such an RCD, regardless of what type of RCD is fitted.
Completely agree with the various previous comments/advice about never sharing an existing RCD - a big no-no. "Nuisance tripping" and DC impact on RCD selection/function are two completely different considerations.
Just my tuppence...
All transformerless inverters will have a degree of inherent leakage current. I think that G83/2 requires that the tested/reported leakage current is no greater than 0.25% of the max AC current. For a 16A/3.68kW (G83 limit) inverter, this equates to 40mA, most decent units will rarely leak more than 5-10mA.
A 30mA RCD can trip from an AC leakage current value greater than 15.1mA (I stand to be corrected on that exact figure though).
As has been stated already, a TypeAC RCD's trip coil will saturate (and never trip under AC ground fault conditions) if any component of the leakage current is pure or pulsed DC. A TypeA RCD will still operate under AC ground fault conditions even if a pulsed DC component of the leakage current is present. It's trip coil will saturate if any pure DC component is present. However, if the amplitude of the pulsed DC leakage current is greater than 6mA then the Type-A RCD cannot be guaranted to operate within its certified scope of operation - this is an important point (can you or the inverter manufacturer guarantee that the 6mA limit will never be exceeded?). A TypeB RCD will operate under AC ground-fault conditions without being compromised by either pulsed or pure DC components of the leakage current.
Hypothetical (but also very real) scenario - TL inverter, requirement for RCD protection under BS 7671 (for whatever reason), TypeAC RCD installed. RCD never "nuisance" trips, just sits there looking pretty. Subsequent AC ground fault occurs (for whatever reason) but the RCD still doesn't trip. Too late to realise that the reason it never "nuisance tripped" is that the trip coil was saturated with DC and became about as useful as a chocolate fireguard. In that scenario, the end customer has been sold/supplied with a circuit protective device that will not operate as intended. It is worse than not fitting an RCD in the first place.
If there is no simple separation (ie, a galvanic transformer) between the DC and AC circuitry within the inverter, and an RCD is required on the AC output of the inverter (due to consideration of BS 7671) then a TypeB RCD is the required solution to provide ADS/ground-fault protection. However, many TL inverter manufacturers certify their product to VDE 100-712 in that it is, by design, unable to inject DC to ground. If the inverter manufacturer states this, then they typically go on to say that if an RCD is required then it need not be a TypeB (ie, a TypeA is ok to use).
There are some transformered inverters still around, although not many. The difference it makes is that, if an RCD is required on the AC circuit, then the inverter alone will not cause nuisance tripping of the RCD, and there is no scenario where a DC leakage current component might compromise the normal function of such an RCD, regardless of what type of RCD is fitted.
Completely agree with the various previous comments/advice about never sharing an existing RCD - a big no-no. "Nuisance tripping" and DC impact on RCD selection/function are two completely different considerations.
Just my tuppence...
