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Telephone box earthing

Discussion in 'Electrics UK' started by RF Lighting, 10 Aug 2017.

  1. ban-all-sheds

    ban-all-sheds

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    Last edited by a moderator: 12 Aug 2017
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  3. deadshort

    deadshort

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    I second that !

    DS
     
  4. chivers67

    chivers67

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    When I worked for BT back in the 80's Earth Hum was a common fault induced by water ingress, so I don't doubt Bernard's knowledge as to the "missing" Earthing arrangement. I'd have thought at the very least The Kiosk would need to be grounded for lightning protection at the very least now or even back then.
     
  5. This reminds me of a fault I had on my phone/broadband service at my old flat in Manchester city centre. The PCP (green cab) was ancient, and the link between the exchange-side and distribution side cables was a simple piece of wire (a pair of course!). Over time, and as more and more work was carried out at the cabinet, the twists in this jumper cable became untwisted, which resulted in the characteristic 50Hz hum on my phone service, and a very intermittent broadband (ADSL) sync.

    It showed up on the Openreach guy's tester as a poor AC balance, and was basically that untwisted bit letting in lots of external noise. He replaced this jumper, and everything went back to normal.

    The broadband on this line was always poor, even though it was only a mile or so from the exchange. Following the well-known BT tunnel/duct fire in Manchester, lines were rerouted, meaning this line goes on a couple of miles diversion through central Manchester, rather than going direct to the exchange. Saves digging up Deansgate, along with the associated disruption I suppose!
     
  6. Adam_151

    Adam_151

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    You might find you don't have any class 1 items:

    Class 2 maintained LED em bulkheads are not too uncommon, the JSB ones spring to mind https://www.fastlec.co.uk/zel3icel-...MI6Puw84LU1QIVhLDtCh1S4QMaEAYYASABEgLaPPD_BwE

    As to the defib unit, you'll be limited by what they supply, but I've seen both metal cabinets with standard door code locks on which are class one, and more modern looking plastic units which have a separate ELV power supply (which is class 2)

    But i'd be looking to go down the TT route I'd imagine, this is just thinking out loud and I've not looked into it, but I wonder if the framework of the phonebox could be used as an electrode, a quick loop test might be in order to see what you get, depends whether you can class it as "structural steelwork"....
     
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  8. bernardgreen

    bernardgreen

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    I asked the question on a telephone engineering forum, the consensus is that when a telephone kiosk it would be TT but the jury is out for non telephone use.

    "" Most if not all street furniture should be TT (rod) earthed rather than using the distributors facility, whether the rod is any good now is another matter!""

    ""We had a report of a rural kiosk near Tewkesbury with a 'hot floor' I went with the lineman and sure enough the concrete floor was so hot you couldn't stand on it for more than a few minutes. We measured the voltage between the frame of the kiosk and the ground a yard or so away... 240 Volts! The overhead mains feed to the box had gone faulty and the 'earth' wire was live heating up the soil around and under the kiosk. We had to place barriers around it, I wonder what would have happened to a dog if it had lifted it leg against the box"""" I understood most kiosks to be class 2 appliances with no earth, and relying on primary insulation only? Certainly I have been in several that have "this installation is not earth" stamped on them, and fused spurs embossed with this and plastic bits to hold them in. ""

    "" Certainly on the IET forums there is a few threads about people installing defibrillators in them which require an earth, and lots of debate about what to do""
     
  9. JohnW2

    JohnW2

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    Interesting. The labels and visible wiring in the photos in RF's initial post seem to indicate that (when used as a telephone kiosk), the kiosk in question deliberately had no earth at all.

    Kind Regards, John
     
  10. EFLImpudence

    EFLImpudence

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    Yes, I always think that on the IET site, there would be someone who KNOWS.

    Silly me.
     
  11. JohnW2

    JohnW2

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    I suppose that one of the problems is that there is no ideal answer, so it's a matter of opinion/a judgement call.

    For reasons I've mentioned, there could be a (very small) theoretical hazard to passers by (or those entering the kiosk) if one used a TN-C-S earth (if available). On the other hand, if one TT's the kiosk, one would presumably have to install an RCD, and should that trip (and not be reset), the defib's battery could presumably go flat - the only way I can think of to partially address that (if there is a telephone line) would be to have a (battery powered!) system which would alert someone if the supply failed.

    I suppose that, if available, a TN-S earth would avoid both of those problems.

    Kind Regards, John
     
  12. DIYnot Local

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