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DNO Tails on ladder

Apostolos
Good morning

I have a big student accomodation building with a dedicated DNO substation and a nearby LV switchroom where the DNO will place the cut-out ACB (1250A)

On the opposite wall we are putting our Main Distribution Panel.

Now, usually in previous cases the DNO cut out and the MDP panel are side by side and the tails go into a trunking.

In this case they will go on a ladder. From the DNO cut out box up to the ceiling, across the room and down to the MDP panel.

I know that ladder does not offer mechanical protection.

Can I still go with tails on the ladder? Or I need XLPE/SWA single cores in this case?

Is there something in BS7671 that prohibits the use of double insulated tails on a ladder?


Sorry for my ignorance

Kind Regards
  • 0
    Well two caveats to add first:


    1) I don't do HV

    2) I'm just a spark (Not a design engineer)


    We've just done something similar for a supply to a Railway station (West London) and had 900mm ladder rack suspended from a basement ceiling, 40 odd meters, onto which the HV lads have run in their HV cables (Big fat Red ones). Similar size of supply assuming you're talking of the LV size. 


    I have no idea if they are armoured or not (But the induced voltages in the ladder rack would be pretty bad if they weren't, so I suspect they are) but the whole ladder rack thing certainly works for all concerned in our situation.


    I suspect it will for your situation too.


    Another thought - Do Check with the HV chaps - The bonding of the ladder rack may be an HV requirement (no idea; I'm pretty sure the HV guys sorted out their earthing and bonding) and quite how the earthing divisions between LV and HV might integrate - or not - and work
  • 0
    I have never seen plain insulated and sheathed tails of any length on a cable ladder.  I don't see why you couldn't use them provided you take steps to protect them mechanically from damage during installation and from subsequent maintenance activities. They will need suitable support and restraint all the way.  Can you actually get the larger sizes in quantities you need.  You would also need to check the mechanical properties of the cable.  I suspect that they will sag a lot more than AWA etc and this will put extra pressure on the sheath/insulation at the support points. You might need extra rungs on the ladder to support them.  It might even be difficult to get a decent trefoil.  You would need to find cleats designed for the softer sheath.


    Why are you considering this sort of cable?  It is certainly an unconventional approach which may well raise questions that could be difficult to answer.  Have a look at the recent thread on theatre cabling.
  • 0
    You won't be getting a cut out on a supply from a transformer to a panel.


    UKPN and no doubt other DNOs will not accept insulated and sheathed conductors as they are finely stranded and they will not terminate them.


    AWA singles are the usual way of supplying a panel from a transformer with a separate earthing conductor. The DNO will not terminate the aluminium armour at the transformer end and you will have to gland the ends off with Ali glands and Ali back nuts into an Ali gland plate on the main panel.


    JP


  • 0
    ....  I have never seen it done on the larger sizes and not that I am recommending this method but couldn't you crimp on a suitable lugs one the DNO kit was in place.  All they would have to do would be to make the final bolted connection.
  • 0
    I have only seen a DNO MCCB cut out in the consumers premises in the form of a steel cabinet which is locked on and the consumer does not have access.


    In UKPN land you present the tails to them and they terminate in to their equipment usually in the sub station and they will not accept finely stranded HO7RNF type cables.



    Just use AWAs and everyone will be happy.
  • Former Community Member
    0 Former Community Member
    Apostolos Kasinalis:

    Good morning

    I have a big student accomodation building with a dedicated DNO substation and a nearby LV switchroom where the DNO will place the cut-out ACB (1250A)

    On the opposite wall we are putting our Main Distribution Panel.

    Now, usually in previous cases the DNO cut out and the MDP panel are side by side and the tails go into a trunking.

    In this case they will go on a ladder. From the DNO cut out box up to the ceiling, across the room and down to the MDP panel.

    I know that ladder does not offer mechanical protection.

    Can I still go with tails on the ladder? Or I need XLPE/SWA single cores in this case?

    Is there something in BS7671 that prohibits the use of double insulated tails on a ladder?


    Sorry for my ignorance

    Kind Regards


    Are they not coming straight from lv side of transformer into your lv panel, also have you looked at LV waveform cables from their equipment to yours, as for double insulated cables on ladder that isn’t an issue as the out sheath is classed as protection, you can also get covers for ladder system if you should require. 


  • 0
    No.

    The DNO will install single core Al AWA cables in a trench from the LV side of the Tx and terminate in a DNO owned ACB on the wall in the LV switchroom
  • 0
    Re "they will not accept finely stranded HO7RNF type cables." I dont think that this is what is proposed.  I thought we were talking about something like 6181Y.  I have seen this in 120mm2 but this application would need much larger cross section hence my original query on availability.


    I agree HO7RNF would not be suitable.


    Regards
  • 0
    I already changed the cables from the DNO ACB from double insulated tails to singles XLPE/AWA armoured on the ladder I mentioned

    Looks like all opinions converge to this

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