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.