Trouble with park home

[nrg]

Hi All

i really hope someone can help, I went to replace a CU at a park home and found the earth spike that was In place wasn't even attached to the old board. When I took a Zs at the board I got a reading of 17 ohms with no earth spike. After lots of investigation it became apparent that the oil line into the property was acting as the earth. Not good!

so as part of the work I installed a new earth rod, and a 100mA type S RCD at the head of the installation before swapping the board. The reading for the new earth rod was 28ohms without the bonding connected and 18.4 with.

All seemed to be fine until the customers turned on their A/C units. Although the A/C circuits were connected to a split way CU with the 30mA RCDs the main type s RCD tripped.

They work fine with the bonding removed but obviously it can't be left like that? The installation also works fine if the A/C units are not turned on.

Any ideas would be appreciated thanks

 

[ajelec10]

The main rcd is seeing an imbalance, so the current is is flowing some where other than the rcd you need to check all connections, and check insulation resistance, my gut feeling is lose neutral/high resistance neutral when the bonding is connected the current flows down the parallel path. But with out looking at the complete system it's hard to tell hope this helps?

 

[nrg]

Thanks for the reply, all IRs were fine when I tested but will test them again. Shouldn't the 30mA rcd trip if that was the case? Thanks again

 

[ajelec10]

Can you describe the set up please, is it a split board with a 100mA main switch then dual 30mA rcds?

 

[Guest55]

possibly an accumalative effect of individual earth leakages
eg not enough to trip the local 30ma rcd , but when combined all the Air cons switched on , enough to trip the 100ma rcd.

 

[nrg]

Setup

main supplier fuse
100mA time delayed RCD
50amp MCB swa 2 core to parkhome earth spike connected to armoured
10 way split 30mA rcd board

Thanks

 

[Engineer54]

Well for a start the earth rod should be connected to the MET of the installation, not to the SWA cables armour. The armour should also be connected to the MET (maybe...).

How is the supply take-off position for this park home earthed?? Is that a TT system as well, or a PME system that's been isolated from your supply cable??

 

[nrg]

Well for a start the earth rod should be connected to the MET of the installation, not to the SWA cables armour. The armour should also be connected to the MET (maybe...).

How is the supply take-off position for this park home earthed?? Is that a TT system as well, or a PME system that's been isolated from your supply cable??

I think there is some confusion here. No earth is supplied by the distributor. The service comes into a box on the outside of the park home and then runs through the 100mA S RCD & 50mcb. It then goes on a piece of 2 core SWA into an adaptable box inside the park home. The earth rod is next to the outside box with goes into the earth block on the small consumer unit and is then connected to the armour on the swa which goes to the park home. The armour in the park home is then glanded and supplies an earthblock in the park home. What's wrong with that?

 

[Engineer54]

I think there is some confusion here. No earth is supplied by the distributor. The service comes into a box on the outside of the park home and then runs through the 100mA S RCD & 50mcb. It then goes on a piece of 2 core SWA into an adaptable box inside the park home. The earth rod is next to the outside box with goes into the earth block on the small consumer unit and is then connected to the armour on the swa which goes to the park home. The armour in the park home is then glanded and supplies an earthblock in the park home. What's wrong with that?

Post up some photo's on here please. I'm just not grasping fully what your saying here!! Are we talking about a static caravan type park home or what?? If this is a static caravan park and the supply to yours and other homes outside supply boxes is via a distributed SWA network cable, then the armour needs to be earthed at it's supply end, be it by means of the sites TT system or TN-S system or by TNC-S, that has it's site earthing system isolated from connection to end users....

I'm assuming for now that this site is all TT, and there is an earth rod located at every external supply box. If that is the case, then you should in reality be seeing a far better Ra value than your seeing now. Unless of course, all the rods are of the short thin twig variety, then it's pot luck what you'll see, from one season to the next!!

Anyway post some photo's up, so that we can all see exactly what were talking about!!