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Power Cuts and Reduced Voltage

December 6th, 2008 Leave a comment Go to comments

If you live in Horwich or Blackrod, no doubt you know that we had a power cut on Thursday at 6:25. Although the power came back on half an hour later (with another outage five minutes later and one more at 14:251), one of my neighbours called round in the evening to ask if we were having trouble with our boiler as his (and another neighbour’s) was not lighting. The low pressure sodium (SOX) street lights were also struggling to strike up. I checked the voltage and found it was only 190V.

Although most people will refer to UK mains voltage as 240V, the voltage that your local supply company must supply has a tolerance band. This used to be 240V +/- 6% (226-254V2) but following European harmonisation in 1995, this changed to 230V +10% -6% (216-253V2) until 2008 when it became 230V +/- 10% (207-253V). This meant that nothing really changed as the voltage you were supplied before more than likely fell within the new range. Continental Europe changed too as their nominal voltage moved up from 220V to 230V. In reality, these changes had little effect on supply companies but it meant that manufacturers had to ensure that domestic appliances would work within the revised tolerances.

Most appliances will work quite happily above 200V but not when it drops below 200V, as was clearly indicated by the problems with boilers and street lights, so if you were wondering why some of your appliances were behaving oddly or not working at all, this is the most likely problem. Apart from the lights being dimmer, other appliances which appear to have been affected:

  • Microwave. The microwave didn’t sound quite right (it normally makes a ‘thump’ when it kicks in). This was confirmed by the fact that it took longer to heat milk than normal. Since the effective wattage was reduced, the microwave times for a given wattage will have been short;
  • BT Vision. A neighbour complained that his BT Vision box was acting strangely and refusing to record programmes;
  • Compact Fluorescents. In this age of energy conservation, it is interesting to note that fluorescent lamps are more sensitive to reduced voltage. Whereas a conventional lamp will simply get dimmer as the voltage drops, we had a couple of CFLs that simply refused to work at all when the voltage was low.

Late on Friday afternoon, our boiler also failed to light up, showing a fault lamp. The voltage at this time had dropped to 183V (over 20% below nominal).

The fault was apparently on the HV network, so United Utilities will no doubt have back-fed affected properties via another circuit, however I would not have expected such a large variation in voltage over short periods and such low voltages on the LV network as a result. It would appear that United Utilities found it necessary to bring in large portable generators to supply customers while the fault was isolated and repaired. This would explain the large variation in voltages and the reduced voltages experienced as the load increases and the generator struggles to maintain voltage.

As of Saturday afternoon, we have returned to a healthy and stable 242V.

United Utilities have recently been spending a lot of time (and money) upgrading the local HV network in Horwich, however although the cabling has been laid, the final connections are not yet complete. Hopefully these upgrades will mean any future faults can be handled without the need for generators.

1 – My ISP sends a text when my broadband line goes offline
2 – rounded figures, actually 225.6-254.4V and 216.2-253V

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