photocells and rcds

[reidla88]

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]

Thought the whole point of the street lights was to shed light?
How are the photocell and the contractor wire?
Do they share a neutral, do they have separate neutrals, or is the contractor wired live in and live out?

 

[Plonker 3]

Why have you removed the TN-C-S and installed a TT?

Did ths fault occur before you did the above?

 

[uksparks]

The TN-C-S supply, is this at the main intake you have this reading of greater than 0.35? If it is, have you tried contacting the DNO?

Are you sure that it is TN-C-S and not TNS?

 

[Farmelectrics]

Couldn't you have left it as it was installed earth rod to bring reading down

 

[gnselectricals]

Wouldn't you also get a cracking zs with all the coloums connected via the swa's

 

[Darkwood]

I would suggest the combined LED inrush is creating the tripping as the spike is field saturating the sensitive rcd components. Try adding a 2nd contactor or even 3rd and off-set them with a time delay, it seems a poor design concept to have 20 fittings on one rcd unless we are not talking 30mA. What is the rcd rating?

What is your background leakage while the lamps are on, noting there maybe a significant designed earth leakage if many fittings are in the circuit? Its sounding more like a poor design issue rather than a genuine fault, is this a new set-up or have the posts been upgraded to LED.

 

[jackhammerJIM]

what was the ZE reading ???

 

[reidla88]

Hi again. Thanks dark wood your explanation has helped. To clarify a few points. I have made no changes to this system or alterations. This has all been done by a rail network contractor. We were simply sent to have a look at what they had done. Just needed help understanding the possible fault

 

[Guest125]

Would a time delayed RCD help? Is the main head in the Lucy cabinet? If not you are not allowed to export a PME earth to a steel container / cabinet which may explain the TT set up.

 

[Plonker 3]

Would a time delayed RCD help? Is the main head in the Lucy cabinet? If not you are not allowed to export a PME earth to a steel container / cabinet which may explain the TT set up.

Why not just leave the TN-C-S in place and no RCD/RCBO protection was needed, the OP has altered a installation and created a problem that never needed to be there.

 

[Guest125]

Why not just leave the TN-C-S in place and no RCD/RCBO protection was needed, the OP has altered a installation and created a problem that never needed to be there.

I was a little confused myself hence I thought maybe the main head was elsewhere in which case you cannot export a PME earth to a steel housing so a TT at the load point (Lucy cabinet) would have to be installed. Some DNOs will not provide an earth to any head housed in a steel cabinet either which is why most cabinets are jow GRP.

 

[Guest125]

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

Also is the RCD within 20 meters of a DC conductor rail?

 

[Darkwood]

Regulation, protection and install methods for the rail network will not fall under the BS7671 to what this forum is based around, UKESrail may be able to help if this is his area of competence but mine and others advice may not be permissable and thus should be comfirmed before implementing any of it, you will need to liase directly with the installers, if this is a regular set up that in past has had no issue then its possible you may have a fault somewhere.

 

[Guest125]

Regulation, protection and install methods for the rail network will not fall under the BS7671 to what this forum is based around, UKESrail may be able to help if this is his area of competence but mine and others advice may not be permissable and thus should be comfirmed before implementing any of it, you will need to liase directly with the installers, if this is a regular set up that in past has had no issue then its possible you may have a fault somewhere.

Unless it is signals, telecoms, conductor rail, points heating or OH 25Kv lines then it will be required to follow BS7671. It sounds like it is just lighting columns so should be within BS7671. These could be platform lighting or maybe a walking route to a depot or signal box. Thanks for the vote of confidence.

 

[Deleted member 26818]

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]

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]

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]

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]

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]

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]

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.

 

[Farmelectrics]

Not that that long ago when we were bonding metal window frames in site cabins that's when bonding went a bit silly in my eyes anyway