I see that I can buy different types of lamps: industrial and
Thinking back to the dim past of college, I recall that they have a
power factor such that your meter doesn't measure the full
consumption. I assume that one has some form of correction built in.
Which sort do I need? (Which will be cheapest to run)
I assume Scottish Power can't measure the power factor at my house.
Power factors are generally low for ballast-ignited and run lights, but on an
average domestic load it has other stuff (ordinary lamps, cooker rings/lights)
that is resistive to even things up. The average pf of 0.8 is calculated from
'average' loads, but these days 'everything' has a switch-mode front end and
they now have to have pf correction to get through the approvals.
Resistive loads have a unity power factor (1) transformers have a low pf of
about 0.6, inverters with pf correction are quite high up, I have seen claims
for over 0.9 which is pretty good.
The board can't determine your pf at home unless they put a pf meter in which
involves metering the current and voltage, the electronics works out leading and
lagging power factors and displays it on screen. I have one somewhere in the
Peter & Rita Forbes
Engine pages for preservation info:
I would assume that the domestic type have a PF correction capacitor fitted,
whilst the industrial type does not. This allows an industrial user to use
a PFC unit further up the power distribution chain. The type with PFC will
be cheaper to run.
Domestic properties, AFAIK, do not have their power factor measured. Large
industrial consumers do, and are charged a premium for having a power factor
outside a certain range.
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Thanks for the replies.
I suppose I had better have a look in the loft for my old text books.
I assumed if I can get the current and voltage out of phase that the
meter would read less. You imply it would read more.
I don't suppose a 6' tube is going to cost much to run in comparison
to the heater anyway :-)
I wish I had had the sense to run a hot water spur off the house
central heating before we laid the patio :-(
Power factor is only measured on 3 phase systems. In a 3 phase supply, kW
consumed is (VOLTS x AMPS x 1.73 x Power Factor) / 1000. The Electricity
Company supply you VOLTS x AMPS and they have to supply extra to make up for
the loss caused by poor Power Factor. When the power factor falls below a
set figure, the electricity supply companies charge a premium on the kW
being consumed, or, charge for the whole supply as kVA.
You will get no cost reduction from fitting power factor capacitors to
single phase domestic units. Although fitting capacitors to fluorescent
units seems to halve the current it does not effect your domestic meter.
Have a word with Scottish power they will explain it.. I live in the south
west and run a Coral Farm. This involves a lot of fluorescent lights. I have
spoken to my local electricity board and that was their comments. I could
have 3 phase fitted to my house but the cost would never be recovered.
Not sure what that first sentence implied :-))
It is measured on both single and three-phase systems, perhaps you
meant that the supply boards only measured it on three-phase?
We have a single-phase pf meter as already posted, and they are freely
available from various suppliers.
Typically we were originally interested for the purposes of rating
generating sets that ran HMI/CSI discharge lighting which were a
ballast type of discharge light.
I am a marine biologist and know very little about this subject. I commented
because I got the info from my Electricity board
My electricity boards does not measure domestic power factor. I asked if
they would but told me there was no point. It will only save me money if I
have a three phase supply, which they were happy to look at. just not worth
it. If I expand I will rent an industrial unit which come with three phase
The original post asked "Which sort do I need? (Which will be cheapest to
run)" Basically I was trying to say that it would not save him any money to
have power factor capacitors fitted on a single phase domestic supply.
I hope I have not mislead him
Absolutely no apology required, I was just trying to make sure we
didn't confuse the issue :-))
I don't think there is any problem, between the various posts I think
we covered everything. It's always worth looking at other comments, I
find, as there is always something new to learn, especially from
people like yourself with different jobs and interests.
It's only because we are supposed to have pf correction on our
chargers, and we can't do it economically on the big stuff that I have
had an involvement, plus the job I had in the film & TV days when we
ran single phase gennies with the halide lights. The crews tried to
get 50kW out of a 50kW genny, but they couldn't unless they were
straight filament lamps. It caused no end of rows with the crews so we
ended up putting a pf meter on the generator panel, to show exactly
what they were doing and why the output available with ballasted
lights was only about 36kW.
Regarding three-phase supplies, it is only really a problem with
factories that have large amounts of motors and flourescents and peak
loads that tend to be hit by the boards. We have 100A per phase here
and at home, but rarely use that amount. The nearest was last summer
when we had 80A per phase on a big 60kW charger.