Is it acceptable to use a handrail to interconnect a lightening protection system

It is normal to bond  roof edge rails like that to a lightning system. Less wise to use them as the primary current path!! There should be a no-one on the roof policy in a thunderstorm on a roof like this.
I'm not too sure what is in the pics, are we seeing the copper ribbons that are interlinks between stuff on the roof or going down to electrodes, or is that section of hand rail the only thing in series between a higher roof top element  and the earth below ? The latter would have me tutting and wondering about the joints in the rails. Chimney, like any antennas and masts, I'd expect to be solidly connected- even if it was via the hand rails.

Folk like Dehn and Furse do good tutorial application notes ,but without knowing what you do or don't already know it is not easy to recommend. There is the BS of course, but the standards are not written in a tutorial way.
https://new.abb.com/low-voltage/products/earthing-lightning-protection/furse/literature

https://www.dehn-international.com/sites/default/files/media/files/lpg-2015-e-complete.pdf

Mike.

Hi Mike 

Thank you for your response, there was another section of building on the roof you can see which was the lift and ventilation rooms. 

So they are using the rail to interconnect the drop from the aerial to the rail then from the rail down to the rod. Each connection at the rail drops down to the rod. So they have used the rail to interconnect all the rods to form a sort of mesh format.

Appreciate its hard to give a yes or no if its ok or not. I think it warrants further investigation, do you agree?

Thank you for the links I have seen the first one but not the second one.

It does not sound ideal, but as you say we cannot see it from here. Personally I don't think it is especially dangerous, so long as all the connections are solid, and no-one goes on the roof in thunderstorms and the rail is not connected to other things -or if it is, then  to ensure it cannot pass high a high voltage into the building by some other metallic connection such as to building steel.

It is also worth asking what the antennas connect to, and what would happen if those coax cables shot up by a few hundred kV for a little while...

I presume the system is inspected periodically for insurance reasons.  I suggest, that the next time this occurs, you ask the person doing the inspection for a professional opinion  when it is in front of him/her.

Mike.

In many ways it's like the Hyatt Regency walkway collapse where a single direct connection was converted to a separated connection .. Continuos; Protective; Conductor ?

Hello Daniel,

Handrail can be used as long as it meets the minimum thickness requirements - likely it will.  

The metal flue should be bonded if it can be confirmed it can carry the expected lightning current, if not it should be included within the protection system.  

BS 62305-3 gives the minimum material thicknesses, but as Mike has said, Furse do some good guides to BS 62305 for free.

Handrail can be used as long as it meets the minimum thickness requirements

Would those requirements also apply to the joints? The pictures aren't entirely clear, but they look a bit like "tube clamp" connectors to me - i.e. just a loose socket fitting with a (large) grub screw to hold them together. Mechanically I'm sure they're fine, but I'm not sure how much reliable c.s.a. they give electrically.

   - Andy..

I recall from some training I had on lightning protection, albeit many years ago, that one of the concepts to remember is that lightning and the path the current takes, is different from regular AC and DC power circuits. Regular power current will of course happily flow around bends, loops, long circuitous paths flowing along the route of the conductor. Whereas lightning being a travelling surge of current, thousands of amps at millions of volts, wants to follow the most direct, straight path down to earth, irrespective of where that takes it. 90 degree bends, loops, or other long and winding paths appear as high impedances to the lightning surge, so when it encounters these it takes the shortest path, arcing across them, and even punching its way through building materials such as walls, floors, jumping over to more convenient metallic routes down to earth.

The role of the lightning protection is to provide the most straight, direct, low impedance path down to earth so the lightning flows down that route rather than taking alternative routes which results in damage to the building.

Looking at your hand-rail, my concern would be with the path for the lightning. It needs to come down from the aerial, at which point I'd wonder what metallic structures and cables run down the lift room to earth (metal rails for the lift, cables and tray, plumbing etc) and how they are interconnected to the lightning protection system, whether it might arc through the roof or walls and follow that direct path.

But assuming it follows the LPS across the roof, I'd wonder if it will follow the dog-leg route from the roof, vertically upwards onto the hand rail, then back down again, a total of 4 sharp, 90 degree bends. I wonder whether in reality, the lightning surge would head along the conductor, then take the shortest route, arcing across to the metallic cable tray and possibly the cables on the tray, along the tray, then arc across to the down conductor near the edge of the roof.

Yes, that's a good point - it applies to the complete system and so the joints would also need to be checked.

"whereas lightning being a travelling surge of current, thousands of amps at millions of volts, wants to follow the most direct, straight path down to earth, irrespective of where that takes it."

I think this is almost correct - It wants to follow the most electrically direct path to earth.  If it can extend on to a piece of earthed metal within its strikezone, but at a 90 degree - or larger angle, then it would prefer to do this than to ionise the air in a stepwise fashion and create it's own conducting path to ground.

In terms of route for current after the strike, Ithink the lightning current would follow all available routes to earth along any conducting material that is bonded to the LPS, dividing based on the relative impedances to earth. The quantity that would flow through the handrail would depend on the location of the strike in relation to down conductors.  

The cable tray, like the flue, should be bonded if it can be confirmed it can carry the expected lightning current, if not it should be included within the protection system to prevent dangerour arcing.  I.e. bond what ever can safely carry lightning current and protect whatever cannot.

So quick update, I have highlighted my concerns to the contractor, just waiting for reply back. I'm thinking they didn't even go on the roof. Just tested the earth rods and didn't enter the building.