Exported PME to steel floodlight columns, public tennis courts

Do we have any idea what went wrong?

Might it have been a fault which was not cleared by ADS? A faulty RCD?

Different ball park?

The guy in the news report linked to above died in a ball park with lights on high columns.

Yes, in that instance lack of maintenance appears to have been an issue and in the pub garden substandard installation was an issue, but the Wiring Regulations have been revised since these incidents, partly due to what happened.

True, but if the hundreds of amps was actually in the form of lots of floodlights each with a 20 ohm electrode,

Doesn't seem likely in the OP's case though - we're told it's a "local tennis club" - so I'm guessing there's a club house, changing rooms, showers, bar etc. and the floodlights have been tagged onto the main installation rather than receiving their own DNO supply. If that is thee case then while the floodlights might appear superficially to be similar to street lighting, in terms of sensible earthing precautions they're in a different ball park,

   -  Andy.

AJJewsbury said:

Where the lighting columns are supplied from a conventional installation that might have loads of tens or hundreds of amps (after the single N-PE bond) - a 20Ω electrode or two are going to provide negligible safety benefit.

True, but if the hundreds of amps was actually in the form of lots of floodlights each with a 20 ohm electrode, or indeed a street of houses each with an earth bond to many metres of water pipe serving as a horizontal electrode, whether or not those then meshed together to form a neutral "conductor of opportunity", then it starts to look less shaky. That is the whole PME premise, and works quite well in built up areas - and during a fault  the surface step voltages are limited by paving, and electrodes do not generally come to the surface. It is less suited to wet mud, overhead singles and small transformers whose own earth electrodes may approach that 20 ohms - it is possible in the small substation case to have a fault from live to true terra firma earth that is lower resistance than the official neutral to terra-firma electrode(s), so the neutral 'centre' of the 3 phases gets pulled significantly off earth - also not ideal but safer at the point of fault - but at the price of being more dangerous somewhere else...

There is a tendency for some to pooh-pooh TT, rather like the old ring final, as being a bit last century, and that is not really correct either.

M.

 AJJewsbury 

the extract reads as it is good practice to install the additional earth rods for a TN-S lighting circuit being supplied from a TN-C-S supply, if and how you write a recommendation into an EICR is a matter for debate as there’s a “should” and a “good practice” mentioned.

”2.5.3 Lighting authority/asset owner private cable distribution system
A lighting authority/asset owner may design and install their own cable networks but these usually consist of a separate neutral and earth (TN-S), which is connected to a PME point of supply.
An earth electrode SHOULD be installed and connected to the earth terminal at the point of supply. It is GOOD PRACTICE to install and connect an earth electrode at the last or penultimate lighting column on the circuit where there are three or more columns on that circuit.”

An earth electrode should be installed and connected to the earth terminal at the point of supply. It is good practice to install and connect an earth electrode at the last or penultimate lighting column on the circuit where there are three or more columns on that circuit.

I think that comes from BS 7430 and is a precaution against broken PEN faults - which is really only going to be effective where there's a separate PME supply to the street lighting system - i.e. i broken PEN conditions the current through the electrode(s) is limited by the loads so 20Ω can pull the system down to an acceptable voltage. Where the lighting columns are supplied from a conventional installation that might have loads of tens or hundreds of amps (after the single N-PE bond) - a 20Ω electrode or two are going to provide negligible safety benefit.

   - Andy.

www.mirror.co.uk/.../man-died-after-being-electrocuted-20159577

Doesn't mean that RCDs are a requirement of the regulations though.  In that particular case we don't know the cause or whether an RCD would have helped at all - it might have been the result of a grumbling PEN fault (like that school incident that make the school doors and fencing live), or if the installation had been properly maintained that ordinary ADS would have done the job anyway.

   - Andy,

chilling!

I've been on and off the forum since I trained in 2010 and you were, and still, are a really useful contributor to this forum Andy, always polite and give briliant, easy to understand input. Thanks

I should point out that the IET Guide to Highways Electrical Street Furniture was published in 2018, so predates the current edition of BS7671 and the amendments to the regulations need to be taken into consideration.

Also the additional earthing electrodes are “good practice” so may not be considered an absolute requirement.