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...

 

[Chr!s]

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...

If the outside stair case is fortuitously connected or even bonded to the MET of the installation, this does not mean its within the equipotential zone of the installation. The problem with oustside is its very difficult to create an equipotential zone.

Chris

 

[Deleted member 9648]

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...

The very fact that the staircase is external mean it cant be part of an equipotential zone. Being outside it will be completely surrounded by the general mass of earth,thus it will not be possible to ensure there can be no potential difference between it and it's surroundings,therefore bonding it is pointless.

 

[Engineer54]

The very fact that the staircase is external mean it cant be part of an equipotential zone. Being outside it will be completely surrounded by the general mass of earth,thus it willnot be possible to ensure there can be no potential difference between it and it's surroundings,therefore bonding it is pointless.

Sure it's pointless bonding the staircase, as it's solidly connected to the main frame of the building. So no matter what you do, or don't do, it will always remain at the same potential as the structrual steel frame of the building ....That will be connected to the MET, ... or are you seriously saying, that this buildings structural steel frame shouldn't be connected to the electrical MET??

 

[Engineer54]

If the outside stair case is fortuitously connected or even bonded to the MET of the installation, this does not mean its within the equipotential zone of the installation. The problem with oustside is its very difficult to create an equipotential zone.

Chris

I know what your saying here, but as the staircase is always going to remain at the same potential as the equipotential zone of the installation, what would you call it???

 

[Deleted member 9648]

Sure it's pointless bonding the staircase, as it's solidly connected to the main frame of the building. So no matter what you do, or don't do, it will always remain at the same potential as the structrual steel frame of the building ....That will be connected to the MET, ... or are you seriously saying, that this buildings structural steel frame shouldn't be connected to the electrical MET??

Er....no,the OP was asking whether a separate bond should be connected to the external stairs,there was no question regarding the steel structure of the building.

 

[Engineer54]

Err, .... That was answered within the first page on this thread!!! Then others went on about because the stairs were external to the building, the staircase shouldn't and /or can't
be part of the equipotential zone, even though it was extraneous ....when obviously it already was, and will always remain so...

But to clear matters up, ...If an external metal staircase was bolted/fixed to the non metallic structure of a building, then on checking it's resistance, is above 22k ohm, it is deemed not extraneous and need not be bonded to the electrical MET....

 

[Deleted member 9648]

Err, .... That was answered within the first page on this thread!!! Then others went on about because the stairs were external to the building, the staircase shouldn't and /or can't
be part of the equipotential zone, even though it was extraneous ....when obviously it already was, and will always remain so...

But to clear matters up, ...If an external metal staircase was bolted/fixed to the non metallic structure of a building, then on checking it's resistance, is above 22k ohm, it is deemed not extraneous and need not be bonded to the electrical MET....

Tosh.....it is external,it is totally surrounded by earth potentials,you cannot create an equipotential zone,therefore there is no requirement to bond it regardless of the 22k ohm stuff......If you go down that road you would also have to test and possibly main bond metallic downpipes etc bolted to the outside of the building..If part of the said stairs structure enters the building,(or metallic downpipes for that matter)....then that would be a different matter,they would have to be treated/tested as extraneous conductive parts and main bonded at the point of entry.

 

[Engineer54]

Tosh.....it is external,it is totally surrounded by earth potentials,you cannot create an equipotential zone,therefore there is no requirement to bond it regardless of the 22k ohm stuff......If you go down that road you would also have to test and possibly main bond metallic downpipes etc bolted to the outside of the building..If part of the said stairs structure enters the building,(or metallic downpipes for that matter)....then that would be a different matter,they would have to be treated/tested as extraneous conductive parts and main bonded at the point of entry.

Not so Tosh, in the real world there are always variables as you clearly point out above, Which is why i always check/test what i'm dealing with, ...before making any decisions!!!

 

[YoungBart]

Thanks for all the help guys, It's certainly an interesting one, I think the cliient seems happy with the bonding from the steel frame of the building providing an eath path for the staircase.