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Service cable and cut out too hot.

broadgage
I was called by a local hospice to investigate "overheating" and found the DNO service cable and cut out to be alarmingly hot, I would estimate the surface temperature of the service cable to be at least 60 degrees. Definite smell of hot PVC.

Enquires suggested that the supply was originally 60 amps, single phase and was upgraded to 100 amps by fitting a larger fuse.


Measured load was just just under 100 amps, it probably exceeded 100 amps if anyone used a kettle.Service cable looks like only about 10mm. Voltage is rather low at 221 volts, but just within tolerance.


Is it worth calling the DNO, or will they simply say "supply working, do not worry" I suspect that the service cable is very undersized, but am aware that DNOs work to different rules.


I have moved combustibles away from the cable and advised reducing the load a bit,


  • 0
    This might sound like an odd question, but what colour is the cut-out?


    I came across a similar problem (office, 3-phase supply, one phase taking 80-odd amps most of the day, possibly a bit more when the kettle was in use) - 100A fuses in modern-ish black plastic cut-out - terminal had burned out. DNO's explanation was that the black cut-outs, although marked 100A, are only rated for 100A intermittently and are only really good for 60A continuous. They changed to a grey (100A) cut-out and all then seemed well.


    So the presence of a 100A isn't really grounds for assuming that the supply is capable of providing 100A continuously. Personally, I'd call the DNO - but they might be of a mind to treat it as a request for a supply reinforcement and want to charge accordingly.


      - Andy.
  • 0
    Well it sounds like the supply is in need of reinforcement, and if the DNO want to charge or not, it needs putting on everyone's radar, as it were. Unless there is a lot of temporary load because of the weather, it is unlikely to go away, loads tend to creep up, not down...

    " Hospice" sounds like the sort of place that might be more upset than normal if it all goes dark.

    Unless there is obvious scope for load reduction, it will be a DNO call, and its a less stressful one to make if an initial query is made now, rather than waiting until  power goes off  on a bank holiday at lunch time.
  • Former Community Member
    0 Former Community Member
    DNO's explanation was that the black cut-outs, although marked 100A, are only rated for 100A intermittently and are only really good for 60A continuous. They changed to a grey (100A) cut-out and all then seemed well.


    The grey ones are what WPD refer to as "dough moulded clay" and are the replacement for the previous black type.

    In the "old forum" I replied to a similar concern but if you look at section 3.1 in the link below, there is a good explanation of what cut-outs can do and WPD's policy.


    Not sure if the OP is in WPD area but if not, I'd like to think the OP's DNO would publish something similar.


    Regards


    BOD



    www.westernpower.co.uk/downloads/3347
  • 0
    Thanks for the replies,.

    The cut out is off white, Bakelite or similar material, made by AEI.

    The cable was hotter than the cut out.

    The premises were originally a large private bungalow, but was given to a charity some years ago and converted to a hospice. It was re-wired then to a good standard.

    I suspect that the service cable and cut out date from the 1960s. Green main earth, not green/yellow.


    There should be 100 amps available continually, as the supply capacity is stated as 23KVA.

    Fair amount of extra load, several large portable air conditioners.


    Meanwhile, events have overtaken me.

    The supply failed shortly after I posted. DNO investigating, I suspect that the pole mounted transformer  has died of heat/overload. One of the 11Kv fuses has blown.

    The standby generator at the hospice started and worked perfectly, and actually has a slightly greater capacity than the DNO supply.(94 amps prime power, 108 amps standby, 112 amps for 1 hour)
  • Former Community Member
    0 Former Community Member

    broadgage:

    I was called by a local hospice to investigate "overheating" and found the DNO service cable and cut out to be alarmingly hot, I would estimate the surface temperature of the service cable to be at least 60 degrees. Definite smell of hot PVC.



     



    Playing devils advocate here, but 60C isn't that hot - after all we design cables with PVC insulation to run to 70C. Many DNO service cables will have summertime design limits of about 90C (as they don't expect anyone other than DNO Personnel to be touching them.)


    Regards


    OMS

     
     

  • Former Community Member
    0 Former Community Member
    There should be 100 amps available continually, as the supply capacity is stated as 23KVA


    Odd that this is stated on a bill for single-phase.


    Regards


    BOD
  • 0
    I have not seen the electricity bill.

    The figure of 23Kva is from a letter confirming the supply upgrade which was done about 2 years ago, after the then 60 amp service blew in hot weather.
  • Former Community Member
    0 Former Community Member

    This might apply:

    Standby power rated generators are the most commonly rated generator sets. Their primary application is to supply emergency power for a limited duration during a power outage. With standby rated generators there is no overload capability built into the units. It is important to note that standby rated generators, under no circumstances, should run in conjunction with a public utility source.


    Standby power rating should be applied to the unit where public utility power is available. The typical rating for a standby engine should be sized for a maximum of 80% average load factor and roughly 200 hours per year. This includes less than 25 hours per year of running time at the standby rating. Standby power ratings should never be applied except in true emergency outage situations. Predetermined outages with the utility company, under UL guidelines, are not considered emergency outages. Manual load shifts for testing purposes can be performed with most automatic transfer switches.


    Regards


    BOD


  • 0
    The generator should be fine run at the standby rating. I doubt that it will be called upon for more than a dozen hours a year at the full standby rating. Most failures are in winter when the load is less as space heating and water heating are oil, with LPG for cooking.

    Unless someone has done a load bank test (UNLIKELY) then today was probably the first time that the generator has ever run on full load.

    There is no question of the generator running in parallel with the mains, interlocked changeover contactors.
  • 0

    OMS:

    Playing devils advocate here, but 60C isn't that hot - after all we design cables with PVC insulation to run to 70C. 




    That was precisely my thought.


    Referring back to the other thread on BS1363 bits and bobs: has anybody ever tried to pull out a plug and dropped it because it was at 70 deg C? They are allowed to reach 72 deg C with an ambient temperature of 20 deg C.


    We are not used to feeling hot cables (at least domestically) which rather suggests that many instalations are over-engineered.

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