Bonding in greenhouse

I think the Building Act or other legal definition would be used?

This one?

121 - (1) The word "building", for the purposes of-
(a) Part I oft his Act, and
(b) any other enactment (whether or not contained in this
Act) that relates to building regulations, or that men-
tions "buildings" or "a building" in a context from
which it appears that those expressions are there in-
tended to have the same meaning as in Part I of this
Act,
means any permanent or temporary building, and, unless the
context otherwise requires, it includes any other structure or
erection of whatever kind or nature (whether permanent or tem-
porary).
(2) In subsection (1) above, "structure or erection " includes
a vehicle, vessel, hovercraft, aircraft or other movable object
of any kind in such circumstances as may be prescribed (being
circumstances that in the opinion of the Secretary of State justify
treating it for those purposes as a building).

(with the possible exemption of schools and buildings belonging to statutory undertakers under 4.(1)?)

Sounds to me like my bean poles would be included in that one.

   - Andy.

Whay size is this controversial green house?

Z.

So you may be kneeling on the earth floor and touching the greenhouse frame. No problem then, apart from falling over.

The stats for electrocution ref. metal greenhouse frames are what?

Z.

Surely a beanpole, like my antenna masts, would be an erection, not a building. 

Titter ye not ladies and gentlemen..

But this is pedanty. TT the supply and all talk of underfloor grids goes away - I've never seen one under an earth floored barn, but there is plenty of fairly shonky TT where the electrode is the building steel, or the taps, or indeed just missing. Luckily RCDs mean even these last are usually non-lethal. I'd expect a greenhouse to be similar.

Mike

mapj1 said:

Luckily RCDs mean even these last are usually non-lethal. I'd expect a greenhouse to be similar.

I suspect so. Depends whether voltages are imported from outside to exposed-conductive-parts though. Again, little different to Class I appliances outdoors ...

Interesting discussion though, and definitely good evidence that the deprecated term 'equipotential zone' from 16th Ed is often misleading.

Building or not?

If red houses are made of red bricks, and blue houses are made of blue bricks, what are green houses made of? Try it next time that you see a 5 year old!

So if a greenhouse is a type of house, and a house is a building, is a greenhouse not a building?

Whilst "house" is usually associated with a dwelling, it might refer to a church (house of God), part of a zoo (e.g. reptile house), part of a farm (e.g. cow house), parliament, etc.

So I think that a greenhouse is a building.

So we will bond it to the earth then Chris, blindly following an illogical mis-interpreted regulation.  That is in this case an earth rod used as a main Earthing terminal. Round and round in circles like a teddy bear......The possibly earthy greenhouse frame will be bonded to an TT earth terminal at an unsuitable metalclad socket, in a damp or humid greenhouse, that is connected to an earth rod.

And how does that actually improve safety?

Z.

And while I am still in angry mode....if equipotential bonding is designed to keep exposed-conductive-parts and extraneous-conductive-parts at SUBSTANTIALLY THE SAME POTENTIAL (page 35) how are those parts not already so. 

Greenhouse frame insulated from earth=safe.

Greenhouse frame earthy and TT earthed class one earthed appliances in greenhouse TT earthed then they are substantially at the same potential.

No bonding required.

Z.

Zoomup said:

So we will bond it to the earth then Chris, blindly following an illogical mis-interpreted regulation.  That is in this case an earth rod used as a main Earthing terminal. Round and round in circles like a teddy bear......The possibly earthy greenhouse frame will be bonded to an TT earth terminal at an unsuitable metalclad socket, in a damp or humid greenhouse, that is connected to an earth rod.

Only if the 'earth rod' (or other electrode) is in the range of influence of the frame (and vice-versa). If the TT earth electrode is remote (more than a few m separation below ground), the assumption they are at the same potential is not always true.

Zoomup said:

how are those parts not already so. 

Not just faults in the installation, but ground potential rise from conditions outside the installation.

Zoomup said:

No bonding required.

I would agree ... if and only if the earth electrode for the TT earthing arrangement is part of, or very close to the greenhouse extraneous-conductive-parts.

Otherwise, a potential can develop from things extraneous to the installation (such as PME or HV ground potential rise).

Even 3.5 m separation below ground can create a voltage potential that will give you "tingles", and more than that, shock risk increases.

I agree there are cases where it's less likely a ground potential rise will occur.

Graham. It is extremely rare for me to do a TT install (almost never) , however I have decided to put in two earth rods and verify each on its own then connect together (around my neck of the woods I would usually expect around 40 to 65 ohms on a single 4` rod).  The two rods to be about 8` apart therefore outside each others sphere of influence.

My reasons for two rods :-

1/ Redundancy can`t hurt.

2/ Lowers total Ra - not to half the value of one rod but quite a good difference though.

Is there some merit to my reasoning or am I barking mad?

I would welcome your comments on my reasoning (as an approx first thought then if say each rod were to be 100 ohms to the rest of the planet as measured at the antipodes then 80 ohms might be just local and the other 20 ohms to the rest of the earth. Therefore two 100 rods have 80 ohms/2 = 40 ohms total and the other 20 ohms takes it to around 60 ohms with two rods. Very rufly speaking of course