Bonding to External Stair case

[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.