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Bonding in greenhouse

Alan B

On an eicr

I have a greenhouse connected to a sub DB in an outhouse, which is on a TT earth. Circuit is protected by upstream 30mA and 100mA RCD's.

I am debating in my mind if the frame of the greenhouse should be bonded to the single socket in the green house.

I would consider the frame as an extraneous part and therefore first reaction is to bond it.

But then thinking about it. bonding would reduce the risk of shock inside the greenhouse in the case of the socket became live but increase the risk of shock outside the greenhouse if the socket and greenhouse became live.

On balance I am tempted to go with not bonding, what are your thoughts?

  • 0

    First, I assume that it is a metal greenhouse. More importantly, what is the rest of the construction. A greenhouse could sit on paving slabs, a concrete base, or even on dwarf walls.

    If it is extraneous, how does it introduce a potential: or in other words, how well is the metalwork connected to the general mass of the earth?

  • 0 in reply to Zoomup

    Sorry not very clear. I am thinking worst case scenario is case of metal clad socket becomes live along with cpc connections. Could happen if there is a short to earth and RCD fails to operate.

    Then if the socket is bonded to the greenhouse there would be minimal Potential difference between the socket and green house frame but someone outside the greenhouse is at risk because there could be a significant potential difference between the green house frame and earth.

    If the greenhouse has a very low resistance to earth, lets say 20 ohms then bonding makes sense but much above that, if the RCD fails there is a real potential for a fault to create a dangerous voltage.

  • 0

    What do you mean by this statement please?

    "But then thinking about it. bonding would reduce the risk of shock inside the greenhouse in the case of the socket became live but increase the risk of shock outside the greenhouse if the socket and greenhouse became live."

    The socket became live???????? The socket is best being a plastic weatherproof type to keep water out.

    Z.

  • 0

    If the earth of the circuit is TT, and the electrode is not far away from the greenhouse, then they will idle at more or less the same voltage. In effect if you bond you are adding another electrode in the form of the greenhouse frame, unless it is more or less built on insulators.

    I'd not bother to bond if the green house is electrically floating, it can add neither to the safety nor to the danger if it is left alone. If it is actually a pretty good electrode then I'd probably bond to it rather than have two different TT grounds.

    If the socket is plastic bodied and the things that get plugged in are double insulated it makes very little odds.

    Less off the cuff answers will probably be along shortly.
    Mike

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