TESTING RCD SUPPLIED BY A GENERATOR

[Ahr35181]

When testing a 240V 30mA portable generator supplied RCD I was unable to make it trip even at 500mA, other than with the RCD test button. With the RCD unit removed it tripped at 24mS with a 30mA test current. My RCD tester is a Seaward with 15th Edition instructions!!! Any ideas why this is?

Thanks Alan

 

[resqcapt19]

Is the generator "neural" bonded to the frame? Some portable generators here in the US do not have this bond and there is no current path to operate the RCD.
Don

 

[Ahr35181]

Thanks for your reply, I'll have to have a closer look at the generator.

The generator in question is an emergency generator for an asbestos decon mobile caravan. What puzzles me is why do some portable generators not have the supply neutrul bonded to earth to maintain an earth fault path?? If this is the case, protection against indirect contact is solely provided by the 30mA RCD.

Thanks,

Alan

 

[RAMConsult]

This is a leftover from the time before GFIs and RCDs were widely available. The generator neutral was left floating so that the only current flow from accidental contact with the hot conductor would be through the capacitance of the windings, worked fine until some insulation wore off somewhere in the windings. Then thankfully OSHA came along.

 

[sparksski]

Ahr35181

I was always under the impression that portable generators relied upon thier own earth spike/rod to provide an earth connection and as such could not be relied upon for a good earth loop impedance path during a fault. This is then the reason that the RCD is used to provide protection against indirect contact as disconnection within 0.4 secs could not be garaunteed for portable equipment.

The RCD does not rely upon an earth connection and usually there is no provision to connect an earth as the fault monitoring is purely done with the phase and neutral imbalance.

As an aside is the Seaward tester 15th edition as per the instructions as we have been working to the 16th edition for years now in the UK.