agricultural tt earth

[Simon-0116]

Just been to look at a job subing to grain drying firm to help then installing cables, lighting etc. The mains is 3ph in house, across newly tarmac to a small out house were it goes to db, then off to variouse sub dbs. The main swa from house is 16mm 4 core, swa as earth. ( No 300 / 500ma main switch in house.) From here it will run to the main board to the new grain shed. There electrican says put 300ma main switch on db in grain store and make it to tt, (as they havent priced to altet anything) But I thought it should be a source. So I proposed making main swa in to tt system / eart rod / 300 ma, then all of farm protected and wont trip the current farm house. Ah this is a arable farm, no livestock ever present, am I right or totally wrong and should keep my thoughts to my self

 

[Rockingit]

What is the original earthing arrangement anyway? You don't say!

 

[Engineer54]

Why would you make a grain house TT?? I can understand where livestock is involved.

 

[Simon-0116]

Tnc, just ever one goes on about every farm should be tt, and with there not been a dedicated earth core

 

[Rockingit]

Without knowing an overall design it's impossible to be sure, but from what you've described I would keep the TNS throughout (double check your earth conductor requirements using the adiabatic, but I'd have thought a 16mm SWA would be sufficient csa eq.) and just look at fitting RCD protection at 300 or 500mA only to locations where they may be risk of fire (think about dust etc). If the design has been done properly and discrimination taken into account then there shouldn't be any tripping issues anyway.

However........I suspect that it's probably like any other farm I've ever been on and is a real spider-web mess of DIY electrics and broken kit!!

 

[davesparks]

Tnc, just ever one goes on about every farm should be tt, and with there not been a dedicated earth core

Read the regs book and guidance note, don't just go by what you have heard or think everyone else does.

 

[GLENNSPARK]

Why would you make a grain house TT?? I can understand where livestock is involved.

here...some livestock:



keep the mice down....

you`l need to construct a faraday cage for it...

 

[JD6400]

You do not have to go TT as no livestock will ever be about ( As long as you are absolutely positive of this ! ) , but you will need to protect everything with a RCD of no greater than 300mA ( Used to be 500mA for he 17th , but has now changed to this for the 16th ) , you could even drop this to 100mA , but as most grain handling systems are now starting to go inverter drive you may have issues with just 100mA of fault protection , and don't forget it wants to be an s-type .
As for placing it at source , in the house , or at the first shed , only you know the site conditions .

 

[Engineer54]

The main swa from house is 16mm 4 core, swa as earth.

Nope, using the SWA for your main earth to this grain shed is a non starter, the Armouring will not comply where main bonding is also required, it's only suitable for purposes of providing the cables CPC.... You're going to need to provide a separate earth conductor, 10mm minimum.

 

[atm84]

What's the equivalent csa of armouring on a 16mm2 4 core??

 

[Richard Burns]

What's the equivalent csa of armouring on a 16mm2 4 core??

16mm² 4 core SWA would have a csa of 50mm² steel but you would need 80mm² steel to comply with bonding requirements.

 

[Engineer54]

What's the equivalent csa of armouring on a 16mm2 4 core??

In terms of copper equivalent, nowhere near what is required!! Steel needs to be approx 8.5 X that of copper....

 

[GLENNSPARK]

here:

View attachment pvc_xlpe.pdf

 

[Engineer54]

here:

View attachment 24721

For gods sake Glenn, dump that bloody old table where it belongs, in the bloody BIN!! lol!!

 

[GLENNSPARK]

For gods sake Glenn, dump that bloody old table where it belongs, in the bloody BIN!! lol!!

hmm...

sorry about that..lol..:sad_smile: