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BANGKOK 20 June 2019 06:54
Arjen

Earth connecting needed?

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We have two small guest houses. Together behind a RCBO, from 10A, 10mA. One of these houses is bad affected by termites. I changed now the floor construction to steel, with Conwood on top, no food for the termites.

 

I am wondering, do I need to hit a earth rod in the soil, and ground the steel? The guest house is protected by a RCBO, and my thinking is a bit, when you do ground the floor (the steel beams are not easy to touch for guests in the house), and someone touches live (or neutral) wire, when being grounded the effect is more noticeable then when the floor is not grounded at all.

 

Earth or no earth, that is the question? (Shakespeare could have said this) 

 

Arjen.

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If someone touches live while standing on something that is not insulated from ground will get knocked on his ass whether there is ground or not.  RCBO will trip in any case.

 

You want ground (connected to a ground rod at some point) at the outlets.  

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Interesting, I may have to consult the oracle. Normally the steel will be "earthy" anyway, but an extra rod won't hurt.

 

What's the supporting structure holding up the floor, wood, concrete, steel?

 

Are the electrics grounded? Any wet rooms on the steel floor?

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Just now, Crossy said:

Interesting, I may have to consult the oracle. Normally the steel will be "earthy" anyway, but an extra rod won't hurt.

 

What's the supporting structure holding up the floor, wood, concrete, steel?

 

Are the electrics grounded? Any wet rooms on the steel floor?

The poles to what the steel is connected are concrete. No wet rooms, although this floor is the balcony (with a roof) On the steel is 25mm thick conwood. When heavy rain and strong wind the floor can get wet.

 

The floor itself is no steel, only the construction is steel (floor is conwood) 

 

There is not much electric, there is a fridge (not grounded) there are two flurorescent light, with a metal housing, both grounded to a ground rod.

 

No grounded wall outlets. As far as I know the guests use the outlets to charge telephones and laptops, tablets.

 

Arjen.

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The steel will be pretty earthy anyway due to concrete not being a perfect insulator. I would run a 10mm2 cable down to the existing electrics rod mainly to stop the steel bounding around if there's local lightning activity.

 

Possible update when the oracle responds.

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Posted (edited)

As it wont cost much I would ground it.

 

A set of regulations might say if its not part of an electrical installation it does not require grounding. Kitchen sink for example. Then there's the case where a protruding bolt touched a faulty refrigerator and put a steel frame up at 220V.

Edited by Fruit Trader
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There is no reason to earth the steel on the application you described unless you mount something electrical like a light or PowerPoint on the steel beam. Should you attach something electrical you only need your ground wire same size as your live conductor. If your ground wire goes back to a MEN that’s great as you will have both over current and RCD protection and if it goes to its own ground rod you have RCD protection also great. The long and the short of it is if it’s not part of an electrical installation there is no need to add it to the mix.


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3 hours ago, Fruit Trader said:

As it wont cost much I would ground it.

 

A set of regulations might say if its not part of an electrical installation it does not require grounding. Kitchen sink for example. Then there's the case where a protruding bolt touched a faulty refrigerator and put a steel frame up at 220V.

It is not about costs, (compared to the new floor, costs are close to nothing) it is not about the job (compared to the job, labour time is close to nothing) it is about safety. Is it wise to ground the floor where you are standing on?

 

A bird can sit safe on a high voltage line. Untill you ground the bird...... But it is metal, and to remove potential differences it should be grounded? Same reason as metal taps in a bathroom need to be grounded. (what I also do not complete understand)

 

It is not about the job, it is not about the costs, it is about what is wise to do.....

 

Arjen.

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4 hours ago, Arjen said:

I am wondering, do I need to hit a earth rod in the soil, and ground the steel? The guest house is protected by a RCBO, and my thinking is a bit, when you do ground the floor (the steel beams are not easy to touch for guests in the house), and someone touches live (or neutral) wire, when being grounded the effect is more noticeable then when the floor is not grounded at all.

If the steel frame is attached to the rebar in the concrete supports it will already be grounded. For detail lookup Ufer Ground.

 

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16 minutes ago, sometimewoodworker said:

If the steel frame is attached to the rebar in the concrete supports it will already be grounded. For detail lookup Ufer Ground.

 

Thanks for reply. 

 

No, there is no connection with rebar, I also never said this. 

 

The concrete poles are maximum 500mm buried in dry sandy soil. 

 

Again, it is not about material costs, it is not about labour time, it is about what is safe to do. 

 

Arjen

 

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2 hours ago, Arjen said:

Is it wise to ground the floor where you are standing on?

The answer is yes if the floor is exposed steel isolated from ground and likely to come into contact with equipment carrying dangerous voltages.

 

This is all guesswork here because we cannot survey your installation and assess the risk. I suggest a new grounding arrangement to stay on the safe side because I have no way of knowing if any existing ground connection is adequate.

 

2 hours ago, Arjen said:

Same reason as metal taps in a bathroom need to be grounded. (what I also do not complete understand)

I suggest you lookup the British earth bonding regulations as they offer some of the best explanations as to why some plumbing and other exposed metalwork must be grounded. 

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The oracles at the IET suggest bonding the steel to the existing ground rod assuming it is of decent length (> 1m). If the existing rod is too short or unknown, bash in a new one and link the two then bond the steelwork.

 

Of course all the usual disclaimers apply as we cannot see the actual installation.

 

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