mezzanine floor bonding

[mattysupra]

Hi, new unit we have took on has a mezzanine floor. The construction is steel.

There are wires running along some of the steel sections. (lying inside the void) but i cant see any earth wire directly connected to the mezzanine. It is bolted to the concrete floor tho so would this act as a earth? (concrete is direct to earth/soil with no dpm)


Question - should the mezzanine floor be earthed? If so does it just need one earth at some point as all bolted together? or does each metal joist need bonding separate like the pipe work below a boiler? (each metal joist is bolted to a RSJ so all metal is connected together)

 

[Lectrician]

What type of cabling is laying in the purlins?

Strictly speaking, steelwork which does not form part of the foundations is not glassed as extraneous, and does not require any bonding, although most will bond it anyway.

 

[mattysupra]

twin and earth cable.

 

[EFLImpudence]

should the mezzanine floor be earthed?

No - but it may need bonding.

does each metal joist need bonding separate like the pipe work below a boiler? (each metal joist is bolted to a RSJ so all metal is connected together)

Can't tell by looking at it or from here. You will need to test it.

 

[mattysupra]

should the mezzanine floor be earthed?

No - but it may need bonding.

does each metal joist need bonding separate like the pipe work below a boiler? (each metal joist is bolted to a RSJ so all metal is connected together)

Can't tell by looking at it or from here. You will need to test it.

When you say test it, do you mean test to see if it is earthed some where because maybe i cant see where it has been earthed? or do you mean test it to see if it requires to be earthed? as in if its bolted to a concrete subfloor that is direct to earth so might not need a earth?

I would presume if it has to be bonded some where then it would have maybe a 10mm earth cable running to it from the board or would a attached earth from one of eh 2.5mm cables be o.k? i say 10mm earth as that is what i think is regs to bond gas and water ? also there is a 10mm twin and earth running through the metals so guess the earth should be as large if not bigger than the maximum cable size that is touching it?

Should the electrician when he comes to check the wiring point this out? i ask as the place has been signed off, i had a problem with setting the new alarm and the cable was damaged and shorting out on the metal joists. This is what got me thinking that the same could happen to a 240volt cable and possible send the whole lot live?

 

[Adam_151]

should the mezzanine floor be earthed?

No - but it may need bonding.

Perhaps if its not an ECP and doesn't need bonding, it might still be a good idea to earth it

If it was a bit tray containing twin and earth you'd earth it...

 

[EFLImpudence]

When you say test it, do you mean test to see if it is earthed

It should not be earthed. It is not part of the electrtical installation - but

the cable was damaged and shorting out on the metal joists. This is what got me thinking that the same could happen to a 240volt cable and possible send the whole lot live?

If you consider this to be a possibility - which it should not be - then perhaps, after all, the metalwork should indeed be earthed.



The purpose of bonding is to equalise potential difference between the metalwork and the electrical installation earth in the event of a fault - not to connect it to THE earth (the ground).

Measure for continuity between the metal work and the Main Earth Terminal.

If the reading is greater than 23kΩ then it is considered to be isolated and does not require bonding.

If less than 23kΩ then bonding is required with 10mm².

Also make sure that there is continuity between all of the separate metal parts.

 

[mattysupra]

should the mezzanine floor be earthed?

No - but it may need bonding.

Perhaps if its not an ECP and doesn't need bonding, it might still be a good idea to earth it

If it was a bit tray containing twin and earth you'd earth it...

glad you mentioned that. There is tray running up to the mez and the twin + earth is cable tied to it.

This is defo not earthed. So the tray should earthed then? i take it each new section of tray should have a earth loop ?

whats ECP mean ?

 

[mattysupra]

When you say test it, do you mean test to see if it is earthed

It should not be earthed. It is not part of the electrtical installation - but

the cable was damaged and shorting out on the metal joists. This is what got me thinking that the same could happen to a 240volt cable and possible send the whole lot live?

If you consider this to be a possibility - which it should not be - then perhaps, after all, the metalwork should indeed be earthed.



The purpose of bonding is to equalise potential difference between the metalwork and the electrical installation earth in the event of a fault - not to connect it to THE earth (the ground).

Measure for continuity between the metal work and the Main Earth Terminal.

If the reading is greater than 23kΩ then it is considered to be isolated and does not require bonding.

If less than 23kΩ then bonding is required with 10mm².

Also make sure that there is continuity between all of the separate metal parts.

Thanks for the reply.

I would have no idea of how to test myself. Just trying to get information so when i get a spark out for a retest i know what i should be asking and if they are speaking rubbish. Im getting it re-tested as im not sure im happy (hence asking the questions) . As the public will be in this building i want to make 100% sure we are safe . We have to have a very rigorous H+S check soon and if we fail it for some reason it will destroy the business. I need every thing to be 100%.

 

[EFLImpudence]

Extraneous Conductive Part -

like a water pipe which is in the ground and may be at a different potential than the installation earth and so, should be bonded.

 

[mattysupra]

Extraneous Conductive Part -

like a water pipe which is in the ground and may be at a different potential than the installation earth and so, should be bonded.

that pretty much answers my question then. So it needs to be earthed.

So next question, does it need just one earth point in 10mm?

or does each and every metal joist need a 10mm loop? (the whole frame is metal and all bolted together)

 

[EFLImpudence]

So next question, does it need just one earth point in 10mm?

Probably but...

or does each and every metal joist need a 10mm loop? (the whole frame is metal and all bolted together)

...the only way to tell is to test for continuity between the Main Earth Terminal and each piece of the frame.

 

[RF Lighting]

The first thing to do is test it. Chances are if it's just bolted to dry concrete it's not going to be an ECP, so will not need bonding.

If however there are long studs or the concrete is damp then it might need bonding.

It sounds to me like the mezz is effectively being used as part of the wiring containment system with cables dropped into the purlin lips, so I would think it's probably wise to earth the structure.

As has already been mentioned, you do not need to loop earth wires here there and every where. Just carry out a continuity test between each joist and the point of earthing of the structure. If there is no continuity, clean up / remove paint etc from where the joist bolts on to the girder and recheck for continuity.

 

[SimonH2]

Or, to avoid the need to consider all the bolted joints and whether they are adequately conductive or not ... consider running a short bead of weld along each one so they are indisputably connected to each other (if you are allowed to, that is).

At my last place, when they expanded the office, the steelwork was both bolted and fully welded - a bit belt and braces as the bolts were enough. The magnetic fields from the welding current (they just stuck the welder earth on one point and used the structure to pipe the current to where they were welding) did "interesting" things to the CRT monitors

 

[mattysupra]

O.k,

Thanks for all the replies.


Im going to ask the spark to simply bond the mez. I will spot weld all metal bits together.