Bonding to External Stair case

[YoungBart]

Hi All.
A few months ago we installed a 3 story modular building, The building an external staircase made of steel. The staircase has not been bonded but the steel chassis of the building has, Do we need to bond the staircase. One of the office staff at work rang the niceic helpline and they said something about it depends if the staircase is 'earthy' and said it needed bonding if it is over '6k ohms'.
Two questions
Would you normally bond external staircases anyway?
and what does 'earthy' mean ?

Thanks
James

 

[telectrix]

is the staircase bolted to the steel of the building? if so, it is bonded already.

 

[Guest123]

One of the office staff at work rang the niceic helpline and they said something about it depends if the staircase is 'earthy' and said it needed bonding if it is over '6k ohms'.

I believe they mean that you should test to see if the staircase could be classed as an extraneous conductive part.

 

[Deleted member 9648]

If the staircase is external it will be outside the equipotential zone and should not require bonding.

 

[YoungBart]

Right, Thanks for the info.
It's bolted to the steel so yes it is bonded. I don't really know what there problem is.
Does anyone know what the term 'earthy' means (as used by niceic). I've never heard it used before proffesionally.

 

[Mark_Burgess]

Right, Thanks for the info.
It's bolted to the steel so yes it is bonded. I don't really know what there problem is.
Does anyone know what the term 'earthy' means (as used by niceic). I've never heard it used before proffesionally.

Ask them for their definition so you are absolutely clear of what they mean.

 

[Des 56]

Here is a dictionary definition

(Engineering / Electrical Engineering) Electrical engineering on the earthed side of an electrical circuit, but not necessarily with a direct connection to earth

There you are then,straight forward :whatchutalkingabout

 

[SimpleSimon]

With such a cruddy term can only assume they mean to check if it's an extrenous part so using a wonder lead do an IR test between the staircase and MET and if over 22K ohms than no need to bond.
But you don't need to do this anyway as it's bolted to the already bonded steel structure.

 

[Chr!s]

If the staircase is external it will be outside the equipotential zone and should not require bonding.

Spot on

If the stair case is outside the equipotential zone, what will bonding achieve.

What would happen if a voltage appears on the stair case and some one in contact with the general mass of earth touches the steps?



Chris

 

[pushrod]

Is the staircase outside the equipotential zone though? (tbh not a term that i'm particularly familiar with as not defined in the 17th 2008 - is it from the 16th?) I would have thought that there is a good chance that there is some external lighting attached and that there is a real chance of a voltage appearing on the staircase. My own thought would be to test if it is already earthed and if not, then is it an extraneous-conductive-part and then bond if needed.

edit: oops just noticed post 5!

 

[MarkieSparkie]

What not to do:
As others have mentioned bonding external steelwork INCREASES the potential danger to persons and livestock, because the potential on the MET and anything bonded to it will be at a different voltage level to that of the local earth on which the person or animal is stood.
What to do:
Carry out an insulation resistance test between the MET and the staircase. If the IR is below 20k ohms ('NICEIC earthy'), earthing the staircase to a local earth electrode to minimise the metalwork floating above true local earth potential would be the correct course of action in my opinion. I suspect this is the NICEIC view, but worth clarifying with them first.

 

[MarkieSparkie]

I would check that the designer/architect has considered the possible need for a full BS EN 62305 lightning protection system if the external structural steel work is approaching the roof line of the building. If a lightning protection system is necessary the staircase would become part of its earthing system and not require you to take additional safety measures. The lightning protection system may require bonding to the MET in certain circumstance, but that would be usually done by the specialists.
If in any doubt seek advise from the experts in the link below:
Furse Earthing and Lightning Protection and Electronic Systems Protection by Thomas & Betts

 

[Engineer54]

Right, Thanks for the info.
It's bolted to the steel so yes it is bonded. I don't really know what there problem is.
Does anyone know what the term 'earthy' means (as used by niceic). I've never heard it used before proffesionally.

Reading the first post of this thread, then a further post (#5), ....This staircase is effectively connected to the steel frame of the building, so is part of the installations equipotential zone!!!

Normally, like any other suspect metalwork, it will need to be checked to ascertain if the metallic staircase is under 22k ohm or not...

 

[Chr!s]

Reading the first post of this thread, then a further post (#5), ....This staircase is effectively connected to the steel frame of the building, so is part of the installations equipotential zone!!!

How do you intend on creating an equipotential zone out side!!!

Normally, like any other suspect metalwork, it will need to be checked to ascertain if the metallic staircase is under 22k ohm or not...

1, Applying all the various weighting factors, will this building require "Lightening Protection" if yes then this will be bonded to a down conductor which will at some point be connected to the MET.

If no.......

2, Will the stair case introduce earth potential into the installations "Equipotential Zone"

If no, then why would you bond it?

If yes, then you bond at the nearest point of entry.

Further consideration may be required be if the supply is TNC-S PME.

Chris

 

[Engineer54]

1, Applying all the various weighting factors, will this building require "Lightening Protection" if yes then this will be bonded to a down conductor which will at some point be connected to the MET.

If no.......
2, Will the stair case introduce earth potential into the installations "Equipotential Zone"

If no, then why would you bond it?

If yes, then you bond at the nearest point of entry.

Further consideration may be required be if the supply is TNC-S PME. Chris

The major consideration here, which literary negates your choices whether to bond this staircase or not, is that it is already structurally connected to the buildings steelwork, probably at several locations!!!

So in answer to your question, like it or not, it's already inherently part of the buildings equipotential zone!!

'' How do you intend on creating an equipotential zone out side!!! ''



If, ....this building met all the weighting requirements for a lightning protection system to be fitted, which to be honest, is unlikely. ...The steel frame of this building will effectively act as the down conductors, and an appropriate number of the steel columns, will be roded, if not themselves suitably grounded... The outside staircase is already bonded to the buildings steel framework by bolted structural connections. There is no need for further bonding connections, Once the structural steelwork of the building has been bonded/connected to the electrical MET.


The requirements are the same for TN-S, TNC-S, TT when connecting Lightning Protection systems to electrical MET. Obviously, lightning protection and TTsystem earth rod positions are going to have to be outside of each others area of influence...