Select Committee on Northern Ireland Affairs Minutes of Evidence


Further Memorandum submitted by Northern Ireland Electricity plc

  Our letter of 4 June 1999 (Appendix 31) explains that the NAFIRS system, which is our main fault recording system is not an ideal data source for analysing the frequency with which specific customers are affected by faults. The proper analysis requires a significant effort in researching the circumstances surrounding individual faults and for that reason we have limited Table 1 to circumstances in which fuses have operated five or more times. The figures in the columns headed 11 kV circuit breakers" in Table 1 are still an appropriate estimate of the number of customers affected by faults cleared by circuit breaker operations.

  We consider that the data on faults cleared by circuit breakers taken together with the revised data on faults cleared by fuses is sufficiently accurate to draw broad conclusions along the following lines:

    —  Of those customers who were subject to one or more faults, around 90 per cent experienced no more than two interruptions per annum, and

    —  in respect of a worst case" situation less than 100 customers experience in excess of 10 faults per annum. (Our previous letter suggested several hundred customers are affected to this degree).

21 June 1999

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