Have you tried testing the RCD on ramp and without the device connected

I couldn’t even get it to reset. I disconnected the load cables and it stills Tripped.

It’s been sent back to China for tests. Despite what you all might be thinking, this is a reputable brand.

If you cannot test it when disconnected i’d guess it’s beyond use.

Yep. Needs replacing. It has been suggested to bypass the RCD. I’m not ready to do this. I believe there’s a problem rather than nuisance tripping 

How old is the circuit and why has it now started operating under no load?

How old is the circuit and why has it now started operating under no load?

Two weeks old. Was tested and inspected and commissioned by the manufacturer 

At a guess, you have a NE fault or your device is at fault. Really hard to say without looking at the circuit 

I installed the final circuit. C50 mcb,100 Amp 300mA type B RCD to the machine isolator. To cause a 300mA RCD to trip o would expect 200mA as a minimum to be leaking out somewhere.!

No NE fault on the supply but possibly on the machine. . >999 on all IR tests up-to the isolator 

300mA type B. Does the type B pick up frequency as well as DC leackage? Have you got an inverter connected that is faulty? Type B’s do DC and frequency. 

Yep, 3 inverters. Motor overloads st at 8 Amps

Good question. The speed has been played around with (Frequency) 

You can adjust the speeds at the HMI

Its very hard to say without looking at it. If it fails under no load and the neutral is disconnected I’d go for the device. But if neutral is connected and it has loads attached i’d look at the load. I am not an expert RCDs have always been neutral issues in my previous experience 

If you do find the fault I interested