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"Lending" a domestic supply to community CCTV project

NigelWard
A friend asked me what he should look out for if he agrees to allow a new communal CCTV system to be powered from his home supply.  I wonder if any of you more expert than I has any wisdom to pass on?


The CCTV system is to be installed on a shared piece of land owned by the surrounding residents and needs power.  One option that the installer says is frequently used is to take off a feed from the domestic ring of the nearest house, via a meter to measure how much power has been used so that the kind resident isn't out of pocket.  In principle, if properly installed, it sounds OK and a pragmatic solution.


However, I wonder if that might be storing up trouble because any earth leakage in this spur could trip the RCD of the main house circuit and be a pain to fix.  Outdoor cable length might be up to 50m depending on routing.  (How deep should it be buried by the way?)  The power requirement is not likely to be more that a couple of hundred Watts, so I don't think voltage drop is a concern.  A more difficult installation could take a feed from a separate MCB on the consumer unit, but the cable run would be longer and more disruptive than making a hole in the nearest wall as proposed.


I wondered about the merits of inserting a back to back isolating transformer as the supply leaves the house - any thoughts on that?
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    Does it need mains outdoors - if practical to do so it may be nicer is to export 24volts DC or Power over Ethernet, so all the mains voltage bits are in the dry.

    Also who is liable if the local pranksters damage the cable and someone gets a shock- is the house holder  RCD the only defence ?

    You could put a more sensitive RCD (10mA ones exist  but are not so common or cheap) and a very small fuse after the private meter.

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    As the "donor house" I would be more concerned of any implied consent or liability. Someone will need to sell the house at some time. If the arrangement is to save the landlord [ or who ever is the owner of the communal land ] some money, the donor house could be left with similar problems to "rent a roof" solar installs.

    Really this should be a new supply with its own little brick enclosure somewhere in the communal area.


    If the Donor is going to be so accommodating, something fairly robust is needed to be drawn up with respect to what "consent" is being given, how long for or when and how it can be terminated.
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    Presumably there will be some sort of video recorder somewhere too - where will that be? If at the same house then +1 for PoE (and an IP camera).


    Possibly consider a small UPS too - so the CCTV isn't lost during power cuts, or during electrical problems/maintenance at the house, ... or if the n'er'do'wells can spot where the power is coming from and decide to tamper with the meter box outside the house prior to doing whatever the CCTV is there to discourage them from doing.


       - Andy.
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    I`d really be looking idealy at a RCBO protected sep supply from the origin and a metered cheapo thingy (unofficial because it probably would be viewded as an uncalibated supply therefore not legal but informally between friends might be "OK"). Or better still make an assessment of likely supply and an informal agreement,
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    Good questions.  I think low voltage is unlikely to be viable because the system will need power for more than one camera, a mobile data connection and possibly a small amount of IR lighting, hence my estimate of a couple of hundred Watts.  A lot of current for low voltage or POE over the distances involved.  The proposal is to use recording in the cloud rather than a local box via mobile data, so there wouldn't be a wired LAN connection for POE anyway.


    Liability is also a question I thought about.  One solution would be to ask the communal landowner to make sure it's covered by their liability insurance, which I don't think would be unrealistic.  I think the best starting point though, is a safe and trouble-free installation from a technical point of view, then deal with the risks/ liability issues that may arise from that.  'Rent a roof' issues are a good point for the longer term.


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    Ideally, get the owner/operator of the  CCTV equipment to supply the electricity meter for you to fit, then they cant later say that they don't like it/wont accept the readings.

    A dedicated circuit on its own RCBO would be preferable, but an RCD fuse connection unit from an existing ring final is probably acceptable.


    If possible, use ELV for the camera equipment. I have seen extensive systems that operate at 12 volts DC from a central PSU. Purpose made PSUs are available for this purpose from CCTV suppliers. Some types incorporate a back up battery.

    A relatively expensive very low light camera may be cheaper in total cost than providing illumination for a standard camera.


    Another not strictly electrical point to consider, is will the "donor house" or the occupants thereof  become a target for those doing whatever the cameras are being installed to prevent.
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    This sounds like something being attempted for a cheap price.


    If the owner of the flat decides to have a prepayment meter fitted, what then? If the meter runs out of credit, the power goes off until more money is added.


    If the supply goes off, what is the liability for the flat owner the supply is taken from, if the CCTV misses something? 


    Regards,


    Alan.
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    It is not uncommon to go to an estate of former council houses where the was a communal TV aerial with a supply taken from the end of terrace house that had the mast and amplifier mounted on its gable wall.


    The electric was accounted for as a reduction on the rent, my mates sister lived in an end of terrace council houses back in the 70’s and without realising what she had done went off to get some paint having thrown the main switch just before the cup final started on the telly. There were irate neighbours waiting for her when she got back.


    When I was doing EICRs for a housing association over in Hereford I used to take a can of intumescent squirty foam with me to fill the holes in the internal gable walls where the co-ax went through, that were big enough to put your hand through, rather than write it on the report as they only wanted satisfactory EICRs as otherwise the house or flat could not be let out, so we repaired as we went along and added it to the bill.


    So yes you can probably do it, but not have total control over the supply.


    Andy Betteridge
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    In terms of the cost it will approximate to £1 per Watt per year so the homeowner is being rather generous if he allows 100W to be connected continuously.

    It seems more reasonable to take it from the communal stair supply.
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    A dedicated circuit on its own RCBO would be preferable, but an RCD fuse connection unit from an existing ring final is probably acceptable.



    No, the RCD fuse connection would have no discrimination from the RCD for the ring.



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