When to install an earth rod to an outbuiling

[Sparky83]

Hi,

Just had a friend tell me his electrician (who messed up his DB change at his house recently as detailed in another thread) as now told him he needs to install an earth spake next to his garage that has a small 2way DB in it.

What are the requirments for adding an additional earth stake, im assuming the Zs reading would need to be too high at the garage for this to be required?

Garage is only about 20ft from the house.

thanks

Sparky83

 

[Engineer54]

The guy is obviously a Duffer, the very last thing you want to do is Rod an outbuilding, when there is no need for it. At 20ft there is absolutly no need for it, even if the main house supply is PME. Though with PME you will need to take a 10mm bonding cable to the building IF it has, say a water supply fed by a copper/lead/steel pipe, otherwise you will need nothing special.

 

[Sparky83]

This is the kind of response i was expecting to get...

There is no water supply, or anything else come to think of it. Just the 2.5 or 4mm (My mates not sure without looking) cable that feeds the little DB for 2 lights and 2 DSSO's.

Am i right in thinking that to establish the need for an earth spike you would do a Ze test at the outbuilding DB and if it wasnt right then you would require it??

 

[Engineer54]

Your Zdb and Zs is totally dependant on the size of cable and distance from the house supply CU. So calculate first and see what size cable you need to comply with min Zs requirements. Personally i would always go for a bigger CSA cable than needed ...you never know what the future may bring...lol!!!

And don't forget all the other calculations and observations to comply with the Reg's!!