Bonding in greenhouse

the thing that makes a greenhouse unusual compared to a normal building, and more like outside, is the intimate connection of the floor to the terra-firma earth. A few other types of farm buildings, maybe stables, certainly barns, can be like this. As such the distinction between inside and out is lost, and all pretence of creating an equipotential zone at any other voltage than that of the bare earth of the greenhouse is also lost. So, ideally in the no expense spared world you would TT,and the electrode would be in the centre of the floor, or perhaps better a perimeter tape with rods at corners. At this point it would make sense to bond the thing to that TT earth as it would all go up and down together. The question has to be how closely does it approximate that ideal - because as soon as the local CPC is not at local ground potential you have an issue.

Mike.

mapj1 said:

the thing that makes a greenhouse unusual compared to a normal building, and more like outside, is the intimate connection of the floor to the terra-firma earth.

There are other situations like this also. Sports club showers is a good example. Grid in the floor is the usual remedy where the likelihood is increased (e.g. PME).

mapj1 said:

A few other types of farm buildings, maybe stables, certainly barns, can be like this.

Note 2 to Regulation 705.415.2.1 is a good practical example.

Zoom has a good point regarding RCDs, but that's not the only issue if the voltage arises from phenomena outside the installation.

"Note 2 to Regulation 705.415.2.1 is a good practical example."                                                                                              An earth grid in a farm building under the animals' feet may equalise any stray Voltages present. The biggest problems will involve acidic animal waste that will be conductive and corrosive to electrical connections and grid material, and mechanical damage by animals. Typically the grid may be useful in a milking parlour.

BUT, there will be a point where the four footed animals like cattle will have two feet on the grid area and two off as they approach or leave the area with the grid.

Will there be any potential problems there from the point of practical compliance with the regulation regarding installation and maintainability? (705.415.2.1)

I do not think that our greenhouse problem involves any animals.

Z.

"I do not think that our greenhouse problem involves any animals."  Humans ?

Yes I know, other animals might have a longer "wheelbase"

Good to see my question has created a healthy debate.

Actually from my experience at least most people that own greenhouses also have pets.

I could easily see a dog being in contact with the ground and the greenhouse at the same time. Less likely to have the same issues with corrosion, but presumably still with 4 legs more susceptible to electric shock? 

Pets. An even greater reason then just to leave the greenhouse "floating" and not connected in any way with the electrical installation.

This applies to humans as well.

And, if the internal greenhouse electrical installations is that dangerous, lock the door and stay outside.

Z.

THE DANGERS OF THE GREENHOUSE, AND NOT ALL OF THEM ARE ELECTRICAL. By Singed Moustache.

https://ggs-greenhouse.com/blog/top-10-causes-injuries-greenhouse

Z.

Would you bond my greenhouse here illustrated at the bottom of my garden?

I partly agree. The showers at the local Rugby club do seem to support plant life, at least in an algeal form. However the building has a damp course, (well a membrane really) and no body seems to dig the floor up to plant anything, I suspect the contact of bare feet is to an internal potential only loosely coupled to the over-site cement, and even more loosely to the ground beneath. In a green house you may well be on the earth, but unless its a hippy commune, less likely to be barefoot, let alone naked and wet.

Mike.

I partly agree. The showers at the local Rugby club do seem to support plant life, at least in an algeal form. However the building has a damp course, (well a membrane really) and no body seems to dig the floor up to plant anything, I suspect the contact of bare feet is to an internal potential only loosely coupled to the over-site cement, and even more loosely to the ground beneath. In a green house you may well be on the earth, but unless its a hippy commune, less likely to be barefoot, let alone naked and wet.

Mike.