Low insulation resistance on remote hager rcbo board and effect on upstream devices.

Were you measuring L-N or live&N to Earth.  The first is not surprising and does not affect the Earth leakage. The second says there is a fault somewhere.

30K to ground - assuming at 500vdc, is not that unlikely from those designs of active RCD designed to get the power to trip from L-E if power from L-N is interrupted. I'd be wary of doing that insulation test sustained, but it does not sound like real fault.

And yes if you had enough of them to draw a significant chunk of 30mA then you could not have an upstream RCD of that rating. (and 24K is perhaps 10mA RMS so you are certainly well on the way to eating into the trip reserve.)
Mike

As the issue went away when the RCBO (functional) earth leads were disconnected, I guess you were testing L-PE or L&N-PE.

Assuming that 0.03MΩ is accurate - that's 30kOhms - whereas (in simple terms) you'd need it to be down to 7.66kΩ to get 30mA - so you'd need around 4x the number of boards/RCBOs to have any risk (although it would lower the "headroom" making unwanted tripping due to leakage from appliances more likely).

I am a little surprised at the numbers through - 0.03MΩ for 6 RCBOs would imply a resistance of around 180kΩ each (or 1.3mA each) - which feels a bit poor to me. I wonder if there's some capacitance involved that's not being fully charged by the IR meter and so fooling it into thinking it's a lower resistance than it would appear to be to 50Hz supply, or at that extreme end of the scale the IR meter isn't entirely accurate.

   - Andy.

Andy,

Thought it could trip at 12kohm (at 240v) since 20ma is over half the rcd rating.

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Well a 30mA trip could pop out at 15mA and just meet spec. Having tested a few 20mA to 25mA is more common.  In any case losing 10mA of the headroom you need makes for an unreliable system. (Put another way if the clamp meter on L&N reads 10mA or more on a 30mA RCD, then in my head I mark the circuit as possibly trippy, take extra care and do not add to it.)
Mike

AJJewsbury said:

or at that extreme end of the scale the IR meter isn't entirely accurate.

I very much doubt that it is - the manual should give an indication. If "full scale deflection" is >999 MΩ, 30 kΩ is only 0.003%. The ohms setting may give a more reliable estimate, or even a good old-fashioned multimeter.

Thought it could trip at 12kohm (at 240v) since 20ma is over half the rcd rating.

True - you'd need 30mA for a "would trip", but anything over 15mA for a "might trip"  - so anything below about 15.3kΩ carries a risk.

    - Andy.

I recognise that figure of 0.03Mohms. Strangely, with these RCBO units with loss of neutral I have recorded the same reading whether one or more are in circuit, hardly obeying parallel laws. 

The connection to the earth bar remains irrespective of the position of the dolly meaning that with a neutral to earth connection in place, any legitimate line to neutral connection will cause a tumble in the line to earth insulation resistance test.