So, to answer the question about the 30mA RCD device upstream going off when it shouldn’t. Yes, you could have this problem if you don’t use harmonic filters. I realise this is not the only problem that harmonics can cause. They can also damage other parts of the power system and make it less efficient. But the circuit breaker not working is not one of them.

inclined to agree - I cannot see a situation where a peaky waveform causes something to not trip when it should, but a higher peak to average may lead to both breaker and circuit being more stressed than the nameplate rating based on averages or RMS values suggests. And there lies one of the reasons that large loads without power factor correction either by L-C filters or switch mode active methods are not permitted ;-)

More on those active methods is described here.

https://www.st.com/resource/en/application_note/an523-understanding-power-factor-stmicroelectronics.pdf

Mike

A 300 mA type B 4 pole 100 Amp RCD that was protecting an industrial batch washer tripped unexpectedly after 2 days of operation today. The RCD was faulty and could not be reset even with the load disconnected. I replaced it with a new one today and it resumed normal operation. There was no clear indication of what caused the tripping. It could have been harmonics? Probably more likely a short circuit or a voltage spike.

Given that the RCD was faulty, did it need anything to cause the trip?

Would not reset after the trip had occurred 

without opening it it would be hard to say - but an RCD that size probably has electronic amplification between the sense coil and the trigger mechanism, which is probably firing a fairly bosky solenoid actuator  with a triac or power transistor. I'd bet, but not very much that most likely a mechanical issue, followed as next likely by the trigger electronics having failed dead short, so the actuator fires as soon as power is applied. The latter sort of fault is more likely to be spike induced.
Mike.

or premature aging of the circuit breakers only?

Or perhaps it might be fairer to say that the circuit design should take account of any and all effects so that all components are employed within their capabilities? (like we do with conventional power factor - circuits are sized for the apparent current not just the real current).

  - Andy.

I agree with you. You have stated a very important and sensible engineering principle. It is essential that the circuit design considers all the possible effects and ensures that all the components are used within their limits, a good way to achieve a reliable and efficient system.

However, I also realise that the circuit design is influenced by other factors, such as cost, quality, and safety. These factors are based on the client’s needs and expectations, who may have different objectives and options. Therefore, I consider it important to balance these factors and communicate clearly with the client to ensure that the circuit design satisfies their needs and expectations.