High Zs's on a Genny

[Kenny.]

Right Ladies and Gents I would appreciate your input on this one, I've been asked by a customer to repair some defect highlighted by a recent EICR carried out by a large industrial inspection company.
The plant in question is fed from a 200kVA Genny.
4 of the defects are related to high Zs reading on sub main CP's, All are protected by Merlin TP 32A type D's, the highest reading I recorded was 0.37 ohm, obviously above the requirement of the BGB but below 0.51 ohm stated on Schneider's web site.


The other contributing factor I noticed was when carrying out the loop tests the Genny main switch tripped, whipped the cover off and there's no noticeable RCD but there is control wiring going to the switch so there could be a UVR coil or a shunt release in there and a RCD somewhere else in the circuitry.
A ramp test showed the Genny tripping at 350mA and a time of 38.8 at 500 mA. Surely if it has an RCD table 41.5 applies What should I do next ?
Thanks Ken

 

[Engineer54]

Only talking from memory here, but as far as i know a 32A Type D breaker has a max of 0,37 ohm Zs. also remember that manufacturers requirement data is far more accurate than those given in the BGB, which are in essence, coverall guidance figures...

Not sure about the earth leakage side of things, maybe there is a protective relay in there somewhere. Don't you have any manufactures manual for this Gen-set??

As i say that 0.37 ohm is only from memory, i have no reference data with me to hand... lol!!

 

[Kenny.]

Thanks for the reply E54, we dont have any paper work for the Genny so Ive sent them an Email so should hear soon.

 

[Jimsparky]

I worked on a genny that had an extra ct around one phase and another on the neutral. This went back to a small module where you change the settings for mA and for time delay. This then activated the shunt trip coil in the main switch when it needed to.

 

[Kenny.]

Hi Jim, sounds like this one has somthing similar but just waiting on the manufacturer to confirm.