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Hi all
I am working at a golf driving range installing some new circuits for a Trackman golf radar system.
The structure around the driving range bays is all exposed steelwork.
There are already lighting circuits installed in the roof area with cables clipped to the steelwork.
I have tested the steel work to the MET, which is within the same structure and there is no connection.
I think the structure (Exposed Conductive Parts) should be earthed to the MET.
The Installation has been Test and Inspected in 2017, but no report of Exposed Structural Steel not being earthed?
Am I missing something here?? Or should the structure be earthed??
The structure is 50m long, if I bond, should I take a reading at the furthest point from the MET?
What readings should I be looking at?
There are other items of metalwork, galvanised struts and tin cladding, I guess I need to bond all these together?
The old lighting circuits are on mcb's only. The new circuits will be on rcbo's

Any advice.
Thanks
GT
 
From what you describe, there are no exposed conductive parts. The structural parts of the units that are made of metal may or may not be extraneous conductive parts, and may or may not need main bonding back to the earthing terminal.
You can test for this with a wander lead back to the main earthing terminal. A reading greater than 22 kOhm would indicate no main bonding is necessary.
 
It’s always a do or don’t situation here…it seems the lights have no connection to the framework via their cpc.
Because it’s actually external then I suppose it’s not extraneous & like above check for the KOhm reading to confirm whether or not it need bonding.
 
I think you need to be very careful with this one

Things that need to be considered with metal buildings in open areas are the risk of a lightning strike so does this building have a lightning protection system
If there is no lightning protection by bonding the building to the MET you may be creating more problems than you are trying to solve and increase the risk of a strike

I had a similar one many years ago with a metal shelter on a golf course and because of the advanced stage of the build (the concrete base had been cast so an earth mat could not be installed under it) the advice was not to install lightning protection because of the possibility of dangerously high step potential issues in the event of a strike
 
The thing with a lightning strike is the building is already wired for lights, etc, and I doubt that the sheath of T&E or whatever is going to stop however many 100kV that appears when hit.

Same with the risk of a high step potential from poor LPS ground. It might get the installer, etc, out of trouble for not meeting those specific requirements if someone was killed or injured due to the step, but if they are adjacent to the same building without LPS that is hit I can't imagine their immediate future is going to be a whole lot better.
 
The thing with a lightning strike is the building is already wired for lights, etc, and I doubt that the sheath of T&E or whatever is going to stop however many 100kV that appears when hit.
I doubt the cable would take a direct hit as it is under the roof structure so would possibly only be subjected to a much degraded voltage
Same with the risk of a high step potential from poor LPS ground. It might get the installer, etc, out of trouble for not meeting those specific requirements if someone was killed or injured due to the step, but if they are adjacent to the same building without LPS that is hit I can't imagine their immediate future is going to be a whole lot better.
I'm not understanding the point you are trying make here
 
I doubt the cable would take a direct hit as it is under the roof structure so would possibly only be subjected to a much degraded voltage
No, I meant if the metal building is hit it will go to a high voltage, while the internal cable's CPC are all back to the MET. If you had a 20kA strike and a simple model of Ra = 5 ohms then you reach 100kV!

Real results would be much more complicated of course, there are companies who sell software to model this sort of thing (never used it but seen pretty pictures of step potential, etc, computed).
I'm not understanding the point you are trying make here
Situation #1 is there is a LPS with a small rod, it get hit you get a high step potential between your legs. Not a good day.

Situation #2 is the building has no LPS due to the only option being a small rod, and still gets hit. The lighting will go somewhere and it might well be down the outside and flash over to you. Or in the brickwork and you get exploding masonry in your face in to the bargain. Not clear your day is going better than #1 case...
 
No, I meant if the metal building is hit it will go to a high voltage, while the internal cable's CPC are all back to the MET. If you had a 20kA strike and a simple model of Ra = 5 ohms then you reach 100kV!

Real results would be much more complicated of course, there are companies who sell software to model this sort of thing (never used it but seen pretty pictures of step potential, etc, computed).
Predicting what lightning will do is not an exact science with so many variables while the voltage may peak at 100kV as the strike spreads across the structure the voltage will start to degrade

Having used the strike modelling software 20 odd years ago it can give some widely variable strike risk levels, but you are using some very variable inputs, how do you know what the ground / soil resistivity will be at the time of the strike to gauge voltage dissipation

Situation #1 is there is a LPS with a small rod, it get hit you get a high step potential between your legs. Not a good day.
So looking at you example you have a bad LPS design or no design at all and it's a case of winging it which probably means the LPS should never have been installed. Consideration has to be given to minimising the likelihood of high step potentials with any LPS design
A poorly designed LPS can be worse than none at all
Situation #2 is the building has no LPS due to the only option being a small rod, and still gets hit. The lighting will go somewhere and it might well be down the outside and flash over to you. Or in the brickwork and you get exploding masonry in your face in to the bargain. Not clear your day is going better than #1 case...
You keep on using a single rod scenario when it may be more prudent to use multiple rods if ground conditions allow. For one installation I had to bore a dozen 2.5m deep holes into solid sandstone to install enough rods to achieve a low enough resistance on other jobs if you were lucky you could get a 3 - 4m rod in and that was enough
I have had a situation where because the building work was so far advanced that it was not viable to install an LPS because it would have created more problems than it would have solved in the event of a lightning strike and that advice was confirmed by two of the big lightning protection companies, the customer didn't want to rip up a concrete base to allow an earth mat to be installed so there was a high risk of step potentials existing within the structure if an LPS was installed
Your scenario may have such a low strike occurrence risk that it is more prudent to not install, when it all comes down to it it is all about risk, how often do you hear of a house being struck by lightning in the area where you live, a few months ago a few miles up the road from me a young lad was struck and killed at football training he wasn't the only person on the field and there were a number of tall structures surrounding it so was he just unlucky
 
Predicting what lightning will do is not an exact science with so many variables while the voltage may peak at 100kV as the strike spreads across the structure the voltage will start to degrade

Having used the strike modelling software 20 odd years ago it can give some widely variable strike risk levels, but you are using some very variable inputs, how do you know what the ground / soil resistivity will be at the time of the strike to gauge voltage dissipation
I agree completely, predicting the likelihood of a strike, and probably consequences is very hard indeed.

You might get hit by something from a few kA to a couple of hundred kA if very unlucky, and usually it is inductance that dominates the impedance to any strike. So while soil resistance will have a big effect, the physical layout can be far greater.

However, sometimes inductance is you friend, as what normally matters is voltage difference. It might be that the nearby buildings/MET are raised to some extent by inductive coupling, so the peak voltage difference is much less than the peak to true Earth.

So looking at you example you have a bad LPS design or no design at all and it's a case of winging it which probably means the LPS should never have been installed. Consideration has to be given to minimising the likelihood of high step potentials with any LPS design
A poorly designed LPS can be worse than none at all
This is really my point. Is a poorly designed LPS worse than none?

From the point of the installer and their liability, yes it is.

But without any LPS I suspect the probability of a strike is no different, but the consequences could be very variable and it is hard to see how it could be less than a poor LPS.
You keep on using a single rod scenario when it may be more prudent to use multiple rods if ground conditions allow. For one installation I had to bore a dozen 2.5m deep holes into solid sandstone to install enough rods to
The single rod is just an example argument, really you always want multiple rods and/or distributed wires to spread the current around and reduce the potential gradients.

My original post really was about the previous point, is a poor LPA really worse than none for a person standing by the buildng that is hit?
 

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