Hi
We're doing an EICR at a local tennis club. It has a number of 3 phase floodlights mounted on galavanised columns illuminatimg outdoor tennis courts.
They are earthed via an exported PME TNCS system which was surprising because we'd imagined they would have sunk an earth rod at each column and not exported the PME.
The location is open to the public. Circuits not 30mA RCD protected foir additional protection.
I'm no
Many Thanks for your help
It is not quite fair to say that the regs do not allow us to consider the possibility of an NE offset voltage and to do so is in someway wrong. It is only true that we are not obliged to consider it, but that is not the same at all - there may be local conditions that push toward TT islanding.
And as an aside if you are building a milking parlour or an outdoor swimming pool then in many ways the advice in the regs does oblige us to consider touch voltages and the conclusion to that deliberation is that farms in general that are not private transformer and pure TNS, are instead TT, but almost never TNC-s.
So if the lamp post was in the middle of a the yard of a dairy farm, even if the supply is a sub-main from a PME supplied living area you may well decide it should be TT.
If however it is more like the city street light and in the middle of a tarmac pavement of nebulous contact with the terra-firma below, then it may as well be PME and the faster fuses only ADS time is an advantage.
The question is not stupid, and the regs are not the last word in thinking.
We do not all live in urban town and city centres, and one rule does not fit all. (and in my local south English market town we have rows of houses that are all TT as well, fed from bare overhead singles - you'd certainly not want to PME from that - a tree branch bringing down the lower wire only is a very credible fault indeed.)
Mike
When looking for justification for adding earth electrodes should this document be considered?
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.
www.theiet.org/.../guide-to-highway-electrical-street-furniture.pdf
Because of this, on a new installations we would not usually export the PME outside the equipotential zone
"export"! Why export? If, as is often the case nowadays, there are no extraneous conductive parts, there is no equipotential zone.
TT-ing the lamp posts is not without risk. It depends upon satisfactory long-term operation of an RCD, which is probably less likely than a lost neutral.
There is nothing to say that the RCD requirement depends on the height of the light source
But it is dependent on the light being "accessible to the public" - my point is that if it's umpteen metres up in the air, it's not accessible to the public.
- Andy.
AJJewsbury said “Presumably intended to be interpreted as the light fitting itself is accessible, as distinct from the column that's supporting it. So perhaps doesn't apply in this particular case (unless the column is unusually short). The would keep it consistent with the listed exclusions - which includes street lighting.”.
714.411.2.201 is a height specific requirement, light sources less than 2.800 metres have to be enclosed.
714.1 Scope specifically states that sporting areas and flood lights are within scope.
There is nothing to say that the RCD requirement depends on the height of the light source and the tennis court flood lights are within scope, so as an absolute minimum the lack of 30 mA RCD protection is a C3 and definitely cannot be ignored.
Lighting that is accessible to the public shall have additional protection by an RCD having the characteristics specified in Regulation 415.1.1.
Presumably intended to be interpreted as the light fitting itself is accessible, as distinct from the column that's supporting it. So perhaps doesn't apply in this particular case (unless the column is unusually short). The would keep it consistent with the listed exclusions - which includes street lighting.
I am not trying to be rude
I'm sure you don't, but please be aware that it can come across that way. None of us, however well privileged in training and experience, know everything and life will always push us beyond our comfort zones if we're to improve. Being willing to ask is perhaps the most valuable attribute, and we should take care not to discourage that in any way, however unintentionally.
- Andy.
There is nothing to suggest that were going to give it a code or that we go around trying to find problems where there aren't any. God know we're busy enough as it is and don't need to go around finding problems where there aren't any. I was wondering if I should make a comment on the EICR. I'm aware that there's no regulation with exporting PME in this situation but as we both know there are plenty of special locations where folk could be simultanously touching earthed metal work with a lost neutral and be in contact with true earth and that PME is not permitted. Because of this, on a new installations we would not usually export the PME outside the equipotential zone say to metal shed or a summer house with extraneous conducting parts and would put the system on a TT and very little extra cost ie an earth rod and a terminated unconnected PME earth. This is normal and have had numerous discussions with my NICEIC inspector about this over the years.
In this case we were doing a standard EICR on a commercial building and they asked us to include the floodlights. And I'm simply asking for people's thoughts on this because although we'rev aware of the regulations we were interested in the opinions of those professionals who install floodlights. We do this because we're aware that we don't know it all and take an interest in growing and developing professionlly by engaing.
Been on and off this forum for years even back in my rookie days when I'm sure I asked some dumb questions and was always answered professionally, supportively and courteously by all users. Are you a regular Twitter poster?
Section 714
Outdoor lighting installations
714.411.3.4 Additional protection
Lighting that is accessible to the public shall have additional protection by an RCD having the characteristics specified in Regulation 415.1.1.
My understanding is the impetus behind the introduction of this regulation, in amongst others, was the incident in a pub garden resulting in the death of a child.
But you are "trying" to do an EICR! If you don't know the regulations very well or industry practice, you should be nowhere near an EICR of a public building. That is what is ridiculous. Ok, Which regulation bans feeding outdoor lighting with any supply type? Simple question, not a simple answer? Which regulation in BS7671 says anything about exporting PME to street furniture? I imagine you find the OSG sufficiently specific?
I am not trying to be rude, I am simply protecting your customer and the Public in general. As you see Lyle makes exactly the same points as I have, but I question your ability because that is a risk to everyone. According to the HSE, the safety of PME is not in question, but you see a risk? I take it that you would happily charge to make this circuit TT, as you admit to having done before for lighting outdoors? Was this fair in view of what you now know?
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