tt earthing on farm

[Simon-0116]

Been to look at agiving a qoute to install new bd in horse barn. Tested ze at existing socket 21 ohms. Soil floors. Concrete buildings. All done in plastic conduit, swa, rcd sockets etc. Looked at mains coming in over head. Rcd 30ma 4 pole main isolator. Tails in out to metal switched fuse, swa out of that. BUT no earth rod. So if i put in one rod to the met in the metal switched fuse and got a acceptable reading do i need to put a rod for my new board.

 

[Farmelectrics]

i would say yes you do need to install earth rods

 

[Simon-0116]

Will put a 300ma s type main 4 pole rcd in

 

[Knobhead]

??^^^??

What the hell is that going to do?

 

[telectrix]

Trip???

 

[stevey1983]

Look nice

 

[Farmelectrics]

its all i had lol

 

[Simon-0116]

Because it keeps tripping main switch when another rcd board trips. S type up front for discrimination, 300ma as agriculture.

 

[Engineer54]

You'll need to provide a hell of a lot more information before anyone can advise you. Just a couple of questions you need to address for starters...

What's the supply (TT/PME) at the DNO service head to this farm??
You CAN'T test Ze at a circuits socket, whatever you are recording there, it sure ain't Ze!!
So where is this 21 ohm Zs/Zdb coming from, as you say there is no main earth conductor at the incoming S/fuse to this out building and there isn't any sign of a TT earth rod??

Basically you need to get your test equipment out and start investigating and testing...., then come back here with the results. Simply banging in an earth rod isn't necessarily going to sort your problem, if indeed you have one!!

 

[Simon-0116]

Zs = 21 ohms at a socket on db.( my mistake before calling it ze) 3 phase tt supply. No earth rod. Supply goes from rcd main switch to metal clase switched fuse. Swa then across yard to db in a shed. Did notice where db was that the steel work of building was bonded, so i think this would be giving a low reading. So if i put rod at mains and get a low reading do i need to put one at every board even if i get a low reading. Thanks

 

[Marvo]

Zs = 21 ohms at a socket on db.( my mistake before calling it ze) 3 phase tt supply. No earth rod. Supply goes from rcd main switch to metal clase switched fuse. Swa then across yard to db in a shed. Did notice where db was that the steel work of building was bonded, so i think this would be giving a low reading. So if i put rod at mains and get a low reading do i need to put one at every board even if i get a low reading. Thanks

You can't work from a Zs, you need to take a Ze reading at the MET!!

 

[richy3333]

??^^^??

What the hell is that going to do?

Release the customer of a few hundred quid more than they expected?

 

[davesparks]

Is the steelwork just bonded or is it intentionally being used as the earth electrode for the installation?

 

[Farmelectrics]

A lot more info required here for people to offer any help

 

[davesparks]

So if i put rod at mains and get a low reading do i need to put one at every board even if i get a low reading. Thanks

What are the soil conditions like? What are you expecting one rod to achieve? What do you consider to be a low reading? Some daft people would consider the 21ohms you have already to be a low reading! What sort of fault currents are you expecting the rods to have to handle?