Equestrian lighting possible issues under fault condition.

[Surlingham rob]

Hi all.
I’ve been asked to light a menagerie.
I will have to take a sub main from a nearby chicken shed to a point near the entrance where I will distribute from. It will be tt’d at this point and I am able to get the rod a good 8 m from where any horsey traffic may pass.
My problem is the owner wants to use metal poles around the ring to elevate the lights. (Telegraph poles being very heavy and expensive) I plan to use armoured cable up them to a weatherproof joint well out of reach, mounted on uni strut with the 100w led floods. I’ll have rcd protection and tt but I’m concerned about (under fault condition) earth issues around the base of the poles which cannot be seperated by any great distance from the livestock. Thought about insulating the fitting from the post somehow. Am I over thinking this or is it a real concern??
Any advice greatly appreciated if it avoids dead animals!!
Thanks in advance,
Rob.

 

[Surlingham rob]

Hi all.
I’ve been asked to light a menagerie.
I will have to take a sub main from a nearby chicken shed to a point near the entrance where I will distribute from. It will be tt’d at this point and I am able to get the rod a good 8 m from where any horsey traffic may pass.
My problem is the owner wants to use metal poles around the ring to elevate the lights. (Telegraph poles being very heavy and expensive) I plan to use armoured cable up them to a weatherproof joint well out of reach, mounted on uni strut with the 100w led floods. I’ll have rcd protection and tt but I’m concerned about (under fault condition) earth issues around the base of the poles which cannot be seperated by any great distance from the livestock. Thought about insulating the fitting from the post somehow. Am I over thinking this or is it a real concern??
Any advice greatly appreciated if it avoids dead animals!!
Thanks in advance,
Rob.

Edit
Ménage (horse riding area) !!

 

[SparkySy]

How will the poles be installed are they going in the ground? If so and it's a TT system and has suitability low Ra, all the swa and cpc's connected suitable RCD protection then it should be fine as they will all be at the same potential.
On another note I have seen this same thing with Scaffold poles and all sorts of lash ups on farms. I would think very carefully before using tube as to how the cables will enter and exit the tube and be suitably joined.
With no access panel at the base there is nowhere to terminate the cables and fit a at least isolator or cut out just in case there is a fault with one pole. At least it could be isolated and the rest still used until Repairs can be made.
Sy

 

[Surlingham rob]

How will the poles be installed are they going in the ground? If so and it's a TT system and has suitability low Ra, all the swa and cpc's connected suitable RCD protection then it should be fine as they will all be at the same potential.
On another note I have seen this same thing with Scaffold poles and all sorts of lash ups on farms. I would think very carefully before using tube as to how the cables will enter and exit the tube and be suitably joined.
With no access panel at the base there is nowhere to terminate the cables and fit a at least isolator or cut out just in case there is a fault with one pole. At least it could be isolated and the rest still used until Repairs can be made.
Sy

Thanks for your reply Sy,
The installation will all be done as you said.
The posts will be concreted into the ground and unfortunately I think they want to use scaffold poles as they are cheaper. Wait till they get my bill for all the high level armoured glands I’ve got to do! ?
I don’t have a worry about direct contact between livestock and the poles.
My concern was that although my rod will be out of the way and rcd should operate should a fault occur, if one of the lights develops an earth fault and the rcd was to fail is it feasible that the metal pole would become the path of least resistance thus creating potential in the ground surrounding the pole which will be in the vicinity of the horses.
Pretty sure I read somewhere at lease 3x the depth of the pole is safe distance which I won’t be able to achieve.
A lot has to go wrong for this scenario but it seems to me a possibility.
Saying this, what’s the difference between this and a metal framed barn with lights attached??
Again I think I might be over thinking it but want to be sure.
Rob.

 

[pc1966]

If this is a farm area there is a chance the supply already has a 300mA delay RCD and (hopefully!) an earthing arrangement that is low enough to reliably disconnect on that. While today it is the same 50V / 300mA = 166 ohms limit as other areas, it used to be 25V (i.e. 83 ohms) in 16th edition for agriculture areas.

You lights should have their own 30mA RCD but in the event of that RCD failing they would be able to trip the incommer. Not ideal, as you get a high voltage for 200ms or so which is bad news, but at least you won't get any sustained voltage beyond that time-scale.

If that is still worrying then you could look at cascading two 30mA RCD in the same DIN box. Yes, that is going directly against the concept of selectivity but in this case they both isolate just the one circuit (not taking out parallel branches off the upstream one, as there are none) and the effort of resetting one or both on a trip does not extent to finding them in different DB in different buildings, etc, etc. You can test the down-stream one independently by connecting your MFT earth lead to the neutral of the supply to it (i.e. N out of upstream RCD) so the forced current imbalance for test only is seen by that one.

 

[SparkySy]

Totaly what @pc1966 says above! I am also not a fan of relying on RCD's as a single point of failure on a TT system and would always go with an time delay upfront RCD just to be sure especially when livestock is involved! It doesn't take many mA to kill them!!

 

[Surlingham rob]

If this is a farm area there is a chance the supply already has a 300mA delay RCD and (hopefully!) an earthing arrangement that is low enough to reliably disconnect on that. While today it is the same 50V / 300mA = 166 ohms limit as other areas, it used to be 25V (i.e. 83 ohms) in 16th edition for agriculture areas.

You lights should have their own 30mA RCD but in the event of that RCD failing they would be able to trip the incommer. Not ideal, as you get a high voltage for 200ms or so which is bad news, but at least you won't get any sustained voltage beyond that time-scale.

If that is still worrying then you could look at cascading two 30mA RCD in the same DIN box. Yes, that is going directly against the concept of selectivity but in this case they both isolate just the one circuit (not taking out parallel branches off the upstream one, as there are none) and the effort of resetting one or both on a trip does not extent to finding them in different DB in different buildings, etc, etc. You can test the down-stream one independently by connecting your MFT earth lead to the neutral of the supply to it (i.e. N out of upstream RCD) so the forced current imbalance for test only is seen by that one.

Thanks pc1966,
Really like this idea and wouldn’t have ever thought of it!
There is a 300 ma upfront already and the chances of all 3 failing on top a fitting developing an earth fault Is, in my eyes a reasonable risk. At least I can’t be held responsible for not doing everything possible to negate the risk!
Thanks again for some peace of mind.
Rob.