Earthing of metal fire escape stairs

alphonse mephisto

Hi guys. Thanks for the help in the past, just hoping for some insight and discussion today.

A building has three floors, each electrically separate with their own single phase supply, meter, earth electrode etc.
A metal staircase connects all three floors and as extraneous metalwork should be bonded.

I am wondering what is the best practice for bonding in a situation like this?

2011

In my opinion:
Bonding is all about ensuring that simultaneously accessible extraneous conductive parts are at the same potential under normal and fault conditions.

In a case such as this it may mean connecting the stairs to an earth bar at each floor. Depending on the building it may be possible to cross bond the staircase to other large conductive parts which all already bonded, such as an RSJ.

Once bonding is completed an ohm meter should be used to measure the resistance between the stairs and pretty much anything else that is metal. Ideally all readings should be less than 1 ohm.

Risteard81

alphonse mephisto wrote: »

as extraneous metalwork should be earthed.

Exposed conductive parts are earthed but extraneous conductive parts are bonded. These serve very different functions.

alphonse mephisto

2011 wrote: »

In a case such as this it may mean connecting the stairs to an earth bar at each floor. Depending on the building it may be possible to cross bond the staircase to other large conductive parts which all already bonded, such as an RSJ.

I appreciate your reply,
So it's acceptable able to bond to existing building metalwork provided it is already bonded but would it be permissible in such an instance to bond the staircase to the buildings central heating pipes or services? Or is a separate bonding conductor required by the regs or just for best practice? If so what is the thinking behind it?

Thanks again for all help!