Portacabins and Earthing

[bernardgreen]

So if we go for TT and not only knock in an earth rod for each unit but also link the units together. However we then produce rather a good earth mat between all the units. Now we have a different problem. The earth is too good. So a fault on the DNO supply can cause huge currents to run. I have seen 4mm earth cable melted as a result of a really good earth.

If the "earth" from the DNO is isolated from the earth supplied by the rods then a floating neutral and hence floating DNO "earth" will not create currents into the rods.

There is really no one size fits all answer. One must look at the installation and decide what is the most appropriate method for that installation.

More and more I am seeing TT as the better way to go as first choice for supplying an earth. That is provided the earth rods are properly designed, installed and maintained and tested regularly. It is that last requirement that precludes using them in the average domestic supply.

 

[viewer]

Non-spark, so sticking my neck out here - and these are more confounding factors than electrical science. There are good guides to providing power to external buildings and caravans etc and lots of old posts referring to the guide and practicalities. My queries would be "Are these really portacabins?" ; in other words will they be picked up and moved at some time in the future? If so then the whole system needs to take into account the disconnection system/procedure. It wouldn't be the first time a crane has lifted a cabin still fastened to an earth rod that people forgot. Expensive and dangerous. The other question is about earthing and animals. With separate, but relatively close TT rods could there be a problem?