photocells and rcds

reidla88 · Dec 30, 2014

Hi all. Have a single phase cne tnc-s intake inside a lucy cabnet supplying 20 LED sreet lighting columns. Ze @ intake was greater than 0.35 so intake was earthspiked and a RCD installed changing earthing system to TT. @ lucy I have a contactor being controlled/switched by a photocell (located @ nearest column aprox 4m). RCD is tripping sometimes. My question surrounds my bosses statement made yesterday. " The photocell is causing an imballance when switching the load between on and off at dusk before it stays as a constant on signal". Im unconvinced so can anyone shed light

Deleted member 26818 · Dec 30, 2014

As far as I am aware, BS7671 does apply to electrical installations within the rail network.
At least I've always worked to BS7671 whenever I've worked within the Rail network.
As far as I'm aware, it is only the traction side where BS7671 does not apply.
I'm wondering how the set up has been wired?
Dose the RCD cover both the Photo cell and the contactor?
Do the Photo cell and the contactor share the same neutral?
Really need a little more information.
As for the DNO allowing a connection to their PME earthing point for metallic street furniture, it all depends on which DNO area you are in.
Where I used to work with street furniture, both the LEB and South Eastern required that an earth electrode was installed. The LEB had the added proviso, that the Ra of the electrode had to be below 10ohms.

Marvo · Dec 30, 2014

Standing leakage through 20 integral surge arrestors in the 20 LED drivers? Clamp L+N simultaneously at the contactor as a live test, if global leakage is high then establish if it's evenly distributed throughout the fittings. If so then poor design and back to the drawing board.

Guest125 · Dec 30, 2014

We never export a PME earth to any metalic container or cabinet. We always TT in this case. lighting columns are normally ok due to their root. My understanding is that if there was an earth fault at the load end whilst the DNOs neutral went down this would potentially liven up the steel work and go to earth through you when you attempt to open the cabinet to search for why your columns are not working.

If the RCD is within 20 meters of the conductor rail then it should be a DC immune RCD. This could be the issue. We install FDB11 DC immune RCDs. It is cold now and if the points heating is turning on it could be this that is causing the intermitten tripping if a DC immune RCD is not installed.

Deleted member 26818 · Dec 30, 2014

Well from my experience at Temple Mills, Victoria Station and Kings X, just about anything Metalic was earthed/bonded and connectected to the PME Earth connection. Even track side furniture.

Guest125 · Dec 30, 2014

spinlondon said:
Well from my experience at Temple Mills, Victoria Station and Kings X, just about anything Metalic was earthed/bonded and connectected to the PME Earth connection. Even track side furniture.

I know and we get so much work because of it.

Deleted member 26818 · Dec 30, 2014

At Temple Mills, one of my tasks was to bond all track side furniture to an already installed earth conductor.
We had to crimp new conductors using a Tee crimp to the installed conductor wich ran parallel to the track.
Of course as per usual the work was done in January, and to allow us to work longer hours, we were provided with torches.

Guest125 · Dec 31, 2014

spinlondon said:
At Temple Mills, one of my tasks was to bond all track side furniture to an already installed earth conductor.
We had to crimp new conductors using a Tee crimp to the installed conductor wich ran parallel to the track.
Of course as per usual the work was done in January, and to allow us to work longer hours, we were provided with torches.

Yep. We have just been awarded the lighting replacement scheme on Barnes Bridge over the Thames. A perfect job for Winter.