Discuss no mixing of earths? in the Solar PV Forum | Solar Panels Forum area at ElectriciansForums.net

Welcome to ElectriciansForums.net - The American Electrical Advice Forum
Head straight to the main forums to chat by click here:   American Electrical Advice Forum

P

PeteC

Hi, any ideas please?

A modern barn structure, sudivided, has a common internal sub-supply from a TNS head.
At the end an adjoining switch room for external plant, with a TNCS sub-supply from a TNCS supply head.

The building has steel frame (set into concrete) steel purlins and roof. Metal clad, metal everywhere.!

An on-roof mounted array (framework earthed through direct contact to metal parts~ TNS side) SMA 17000TL's connected to The TNCS sub-supply.
Only theory I can come up with is turn both TNCS and TNS sub-supplies into TTs, but the building structure would remain a common grounding?
 
You have TNS and TNCS on the same site? That seems strange.

It's a good question. Is there any connection between the TNS earth and the TNCS earth currently?
 
No link currently. The TNCS supply is recent, installed to supply the external plant. Technical advice from accreditors advised if framework bonded to steelwork no bonding conductor needed to be brought off roof to TNCS MET (EMB) The inverters are mounted on lower concrete wall but within feet of exposed metalwork from both sides. Worse is the client has a liscence for another system he want's to connect to the TNS side (seperate buisiness/Mpan for fits) on the same roof?!
 
I would have thought TTing both incomers would be a good solution. The equipotential zone is relevant to both supplies so they will both need bonding together as far as I can see.
 
Yes, my thoughts~ bonding the TNS and TNCS earthing together (probably from the same local grid) I would think could create one system raising earth potential on the other in fault conditions through differring Ze's and why mixing earths is so dangerous.

I'm hoping someone from the IEE will come back on this to explain more fully.
 
I would have thought sticking a spike in was the way to go for a simple solution
 
If your turning it into TT then yes you need an RCD but it depends on the characteristics of the inverters wether you need a B type. I believe G83 Sunnyboys don't but not sure about these ones.
It may be the DNO comes back that they will turn the TNS into a TNCS supply,, have to wait and see!
 
What about this
The final connection into a distribution board that contains one or more circuits protected by an RCD, shall be made in such a way that the outgoing circuit for the PV system is not connected into the outgoing side of an RCD installed for the protection of other circuits (ie in a split board – connected into the part not protected by the RCD) .
 
alternative solution would be an isolating transformer inverter for the system that's run off the other supply, then there shouldn't be an issue as it's only the isolated DC circuit that's sharing the roof space )just remember not to bond the sheath of any SWA cable you might use for the DC side).

I think... but there may be a flaw to this I've not thought about.
 
What is the problem if you two types of earthin system in one building?
Which one would you use for any bonding of the metal in the barn? You have two possibly differing potentials. The situation could be made even worse if the supplies are on differing phases as well.

Safest option has to be to TT the barn.
 
Which one would you use for any bonding of the metal in the barn? You have two possibly differing potentials. The situation could be made even worse if the supplies are on differing phases as well.

Safest option has to be to TT the barn.

Going by the OP's description of the Barn build, it's probably is a TT system in it's own right!! The problem being, is isolating the two differing earthing/bonding supply types. This is a DNO's total cock up, and it's they, that should be sorting this problem out, especially if these two supplies come from separately derived TX's....
 
Going by the OP's description of the Barn build, it's probably is a TT system in it's own right!! The problem being, is isolating the two differing earthing/bonding supply types. This is a DNO's total cock up, and it's they, that should be sorting this problem out, especially if these two supplies come from separately derived TX's....
Good point mate, hadn't thought about the frame itself effectively TT'ing it.
 
it's the potential(?) for introducing different potentials in the same building.

I had this in my parents business when they expanded into a shop next door, one was TNS, one TCNS and the DNO put them both onto TNCS
 

Reply to no mixing of earths? in the Solar PV Forum | Solar Panels Forum area at ElectriciansForums.net

OFFICIAL SPONSORS

Electrical Goods - Electrical Tools - Brand Names Electrician Courses Green Electrical Goods PCB Way Electrical Goods - Electrical Tools - Brand Names Pushfit Wire Connectors Electric Underfloor Heating Electrician Courses
These Official Forum Sponsors May Provide Discounts to Regular Forum Members - If you would like to sponsor us then CLICK HERE and post a thread with who you are, and we'll send you some stats etc
This website was designed, optimised and is hosted by Untold Media. Operating under the name Untold Media since 2001.
Back
Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.

I've Disabled AdBlock