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Maintenance intervals & requirements for PFC units in schools (SFG20 / GN3 / BS 7671)

Auryn Morgan

This query is in relation to power factor correction (PFC) units.

The PFC unit was installed as part of a new build in 2016 for a secondary school. There has recently been an incident connected to the ongoing maintenance of this asset, and I’m now reviewing what the actual drivers and requirements are for its inspection and maintenance regime.

I’ve identified SFG20 ref. 40-03, which sets out 12-monthly tasks for PFC units. I’m also looking at how the requirements for routine inspections under Guidance Note 3 would extend to the PFC unit itself, and whether a 6-monthly check (as per Table 3.2) would be appropriate or expected.

The panel builder is Kane and EPCPS were the PFC manufacturer, but their documentation isn’t particularly clear on what maintenance is required or at what intervals.

I wanted to reach out to see if anyone has experience with this and can advise:

  • What drivers under BS 7671 (and related guidance such as GN3) you use to justify inspection and maintenance intervals for PFC units, particularly in an education environment.

  • How you set appropriate maintenance thresholds/frequencies to demonstrate good industry practice when manufacturer guidance is limited or vague.

Any practical examples, references or approaches you’ve used would be very helpful.

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  • 0

    Why was a PFC put in there in the first place?  Sales and marketing is my guess.

    If the PFC goes after the meter the consumption will already be metered as such.  PFC tend to just lower the voltage lets say from 230v ac to to 216v AC but if we think about the humble kettle to boil water at 216v AC it will take longer than at 230v AC therefore is there really an energy/cost saving at all?

    In the mid 80's there was a council that put smaller versions in to all the housing stock.  The premise was to save money.  They spent thousands on the kit and installs.  Years later they were proved to be useless snake oil.  

    If the school want to save money they would be better looking at their light bulbs yes light bulbs and see about replacing the fluorescent and halogen/outdoor flood lights for LED.  They could also look at using PIR or Microwave occupancy sensors for the classroom/corridors and such.  The most efficient lamp is the one that is turned off when not needed.  

    A standard 4-foot fluorescent lamp (T8/T12) uses roughly 30 to 40 watts (W) of power per hour, but the total fixture power can be higher (around 60-100W total) due to the ballast, with an 8-foot lamp using about 96W; this translates to a consumption of about 0.03 to 0.04 kilowatt-hours (kWh) per hour

    Thus

    As an example 10.5W LED can replace a 36W fluorescent tube

    Some people put PFC into enviroments where they have large inductive loads.  BUT is that still the case now, sometime probably not.

    It is certainly food for thought.

  • 0 in reply to Sergio Fernandez

    If the PFC goes after the meter the consumption will already be metered as such.  PFC tend to just lower the voltage lets say from 230v ac to to 216v AC

    That sounds more like a "voltage optimiser" (VO) rather than power factor corrections (which typically switch in/out capacitors to improves the power factor, rather than altering the voltage as such). For "small" installations, the tariff meters do indeed register only true power (kWh) so there's little financial advantage to correcting the power factor, but larger installations can be financially penalised for poor PF (and sometimes even poor balancing across phases). There are also potential losses within in the installation (from conductors having to carry the extra "Wattless current" in addition to the normal current - but to help that you'd need the correction as close to the load as practical, rather than say close to the origin.

    I agree though, a schools (from my memory at least) weren't that full of large motors or other inductors, lighting (esp. fluorescent) tended to have their own PFC built in) so if does seem a sightly curious place for PFC.

       - Andy.

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  • 0 in reply to Sergio Fernandez

    If the PFC goes after the meter the consumption will already be metered as such.  PFC tend to just lower the voltage lets say from 230v ac to to 216v AC

    That sounds more like a "voltage optimiser" (VO) rather than power factor corrections (which typically switch in/out capacitors to improves the power factor, rather than altering the voltage as such). For "small" installations, the tariff meters do indeed register only true power (kWh) so there's little financial advantage to correcting the power factor, but larger installations can be financially penalised for poor PF (and sometimes even poor balancing across phases). There are also potential losses within in the installation (from conductors having to carry the extra "Wattless current" in addition to the normal current - but to help that you'd need the correction as close to the load as practical, rather than say close to the origin.

    I agree though, a schools (from my memory at least) weren't that full of large motors or other inductors, lighting (esp. fluorescent) tended to have their own PFC built in) so if does seem a sightly curious place for PFC.

       - Andy.

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