40kva Generator Earth to Neutral Link missing

[jack123455]

After a rather large generator of 40Kva with a 63A, 32A, 16A and 16A circuits landed on a building site. A test for the Earth fault loop brought up a result of 1440 ohms from the generator feed to the main board. Obviously as this was quite high some further investigation brought to light that the centre tap of the generator was not linked neutral to earth. There has been a bond attached to the external metal work of the generator and this leads to an earth spike and would provide an escape for an earth fault. The unit has a 63A RCD and breakers.

Question is what additional risks and benefits would adding a link between earth and neutral bring?

We are under the impression that this will make the rig safer due to the fact that there will be an escape path for a short circuit which at present we don't have. Is there anything we are overlooking?

Advice would be appreciated.

 

[Andy™]

larger generators like that usually have a N-E link and used an TNS with a rod for connection to earth. its possible its previous hire / use was for something that needed a different earthing system and it hadn't been put back

 

[jack123455]

larger generators like that usually have a N-E link and used an TNS with a rod for connection to earth. its possible its previous hire / use was for something that needed a different earthing system and it hadn't been put back

The unit can be hung from a crane not in contact with the floor, in this instance would a earth to neutral link be removed? This would make sense as its past use was hung and we need it on the ground?

 

[Andy™]

why would you want to use it hung from a crane? the lifting points are to move it, not keep it suspended whilst in use

 

[Phoenix]

I think sometimes its closed through a contactor and may just need some settings change, chances are it was run sync'ed with others and you'd only want one N-E bond in the system. Has this before on an event, got hold of the chaps doing the generators and got very quickly sorted.

Can't remember if it had anything to do with it being set wrong, but the enc client was a bit paranoid about loosing supply and was originally down for two sync'ed sets where each one could easily handle the loading. I eneded up convincing them that they'd be fine with them set up with a non running backup on auto start/failover, as even if it took a couple of minutes for the backup to come online, the EPOS systems would be held up by the UPSes and the refrigeration equipment would be fine with that sort of gap. The cause of the paranoia was a previous issue whih had nothing to do with genearators stopping, but the previous gnerator company providing a distro that was really a TPN DB on a frame, full of single pole RCBOs downstream of the generators earth leakage really, and then someone managed (unknowingly) to magale the flex on a piece of equipment

 

[jack123455]

The hung from a crane is to get the item closer to the roof and it;s designed to be used that way.

Issue we are having is the unit has a high earth fault loop is a stand alone system that is bonded to a rod in the ground. Obviously that's a good path for a earth fault but a short circuit without the N to E link is only protected with a 300ma RCD and there is no path to ground, so in theory if your the path it would cause a fatal shock.

 

[Andy™]

might have been setup as an IT earthing system then to limit how much current can flow through earth