Generator earth

[Sparkystu79]

Hi all, first post for some time! Currently installing power and lighting into a small cabin. Supply will be from a permanently connected generator and using a rod for earthing purposes. Carrying out testing today and only getting 197v between live and rod. Guessing I may need another rod which I didn't have with me but there was a couple of old steel beams concreted into the ground so I connected to them to see if it would help but no diffence. Is installing a few more rods going to help, if not I don't know what else to do!

 

[Wilko]

Hey SS - perhaps check one pole of the gen output is solidly connected to your earth rod, as it might be floating ?

 

[Sparkystu79]

Getting 115 l-e and 121 n-e and generator outlet. I'm not too familiar with generators to be honest.

 

[Wilko]

Sounds like gen has an isolating transformer type output and might be intended to power a double insulated power tool? Gen details? (I can try to look it up on line)

 

[Sparkystu79]

Off site now so not sure if model. I know it was purchased second hand. I will see if I can find something similar online.

 

[Lucien Nunes]

Yes sounds like generator output is floating so you have an IT system not TN. You will need to investigate the N-E link options if you want TN.

 

[Sparkystu79]

Yes sounds like generator output is floating so you have an IT system not TN. You will need to investigate the N-E link options if you want TN.

What would you suggest as the best solution to this? As I said I'm not too familiar with generators and I'm struggling to find a definitive answer anywhere.

 

[Lucien Nunes]

There is no definitive answer. There are pros and cons for separated systems, although the larger the installation and the greater likelihood of undetected first earth faults the greater the argument in favour of earthed TN-S. BS7430 might have some useful info, see also points 11 & 12 here: OC 482/2: Electrical safety of independent low-voltage ac - http://www.hse.gov.uk/foi/internalops/ocs/400-499/oc482_2.htm

As to where to make an N-E link, maybe in the genny terminal box, maybe at the CU, the genny maker might have made specific provisions.

Don't forget that when you are testing the rod, it's not like an earth rod on TT where you're picking up an earth from the supplier's substation via the ground. Here you are the supplier and you are referencing your system to it.

 

[Sparkystu79]

I had connected my rod directly to the consumer unit, do I need to install one at the generator too and connect it to the casing?