On Wed, 24 Sep 2014 21:28:04 +0100, Jeremy Nicoll - news posts
wrote:

Johny B Good wrote:


The most practical way to get such readings, without intercepting the feed
to connect a watt meter, is to shut everything else off and monitor the
suppliers KWH meter for a sufficiently long sampling period (counting disk
revs or led blinks) to at least keep the error down to less than 10%. In
the case of the CH, this might take half an hour or so (circa 100 watt
load, mainly the pump).

Thinking about this, I think my last attempt might have been before quite a
lot of rewiring was done, and now there's probably more separate circuits
than before, so using the supplier's meter and selective turning off of some
circuits might actually be easier...

And, I can also work out how much power one unit on a circuit uses (even if
it's hard to get at) if I can use the plug-in thing to monitor some other
units on the same circuit (eg temporarily running them off an extension lead
connected to the plug-in thing).

So eg I could use the plug-in meter to measure the fridge freezer's use, but
make sure only the oven was also on the same ring main, turn off everything
except that ring main, then oven use = supplier's meter - plug-in meter.

You seem to be making it harder to test than is necessary. Assuming
you're talking about a small electric hob designed to be plugged into
a 13A socket on your kitchen ring main, just unplug/switch off the
fridge for the required time to get a useful reading off the
supplier's meter (or else use the plug in monitor).

The fridge will keep its cool for an hour or more provided you keep
the door closed and it shouldn't take more than 10 or 15 minutes of
rev/led blink counting on the meter to collect the data you're after
(assuming you just want to verify the manufacturer's data on element
wattage(s) - select maximum heat so the stats don't kick in too soon).

An electric oven is usually connected to a cooker point fed via a
dedicated spur from the CU, usually 6 or 10mm FT&E cable fused at 45A
(same applies for the immersion heater but fused at 15A using 2.5mm
FT&E). You'd need to make sure everything else was shut off to test
this by counting revs/blinks at the supplier's meter.

Again, you can set the oven stats to max to verify the manufacturer's
wattage figures for the various heater element combinations. Any
further analysis regarding real world consumption will be a matter of
stopwatch timings for the on/off cycling of the thermostats during a
typical cooking cycle and temperature setting. For heavy duty fixed
wired loads, the use of a plug in energy monitor is precluded so
you're really stuck with timed consumption registered by the electric
meter or a whole house energy consumption meter. You'll have to shut
off every other load in either case.

A clamp on whole house energy meter might have an option to measure
such loads by allowing you compensate for the effect on the conductor
and insulation thickness variations (possibly by using an optional
plug adapter to pick up the voltage from a handy 13A socket such as
the one commonly incorporated into most cooker points)


And, like the boiler, no simple way to intercept the mains supply
to measure it. I have wondered if anyone makes a plug that one
could use on a flying lead to insert into the spur's fuse holder
to break out a connection?

You might be able to make one up but the main problem will be accessing
the neutral connection

Good point...

(although you could get away with using a handy earth bonded point as a
substitute neutral - the meter draws only microamps from the neutral for
the voltage sensor). It'll be tricky enough making up a fuse cartridge
'plug' to divert the live via the meter's current sensor but doable with a
little ingenuity.

But for example for the alarm's spur, there's a 13A socket right next to it;
I could take a neutral wire from a 13A plug (with nothing connected to its L
or E pins).

Maybe I should take the faceplate off the fused spur unit and interecept the
supply much as I suggested for the PIR outside lights.


- halogen hob; it's connected via T&E to a kitchen oven supply; if
I bought the sort of energy monitor that's meant to be clipped
to meter tails could I get a reading by clipping that around the
T&E?

That may work ok if the voltage probe relies on a galvanic connection to
the live (or has that as an option. Some of these clamp on current sensors
designed to clamp around meter tails also use the clamp itself to sense
the live voltage via capacitive coupling which may be compromised when
clamped round a thinner cable (reduced coupling of the electric field
(voltage) which will give a lower reading than actual.

These things designed to go around a L meter tail; are they influenced by an
adjacent (very adjacent in T&E) neutral?

I'd expect the outer of the clamp to have an electric screen to
isolate it from such external influences. I haven't seen the spec on
any of these clamp on monitors but I could well imagine it might well
cater for an accessory 13A plug and cable to get a more reliable
access to the Live and neutral for sensing the voltage component. Such
an accessory would be most useful to allow testing of other fixed
wired kit where there's room to clamp onto the live wire to sense the
current component.



- ovens ... timer is on all the time; surely this uses hardly any
power, but it's quite old technology so maybe it wastes more
than I'd expect. ISTR the supply is from a 13A socket but it's
hidden behind kitchen units.

It's unlikely to be more than a watt or two when 'switched off'. If you
really need to 'know', you can always fumble around to gain access to the
13A socket.

Low wattage - I certainly hope so, but I remember a certain amount of
desperation when trying to work out what else was on in the house, to
account for more load..


- PIR-controlled outside light, permanently wired into a lighting
circuit... though there's an isolator switch... Can one use the
sort of plug-in energy monitor that's meant to be plugged into a
13 A socket to measure power used by a light - there must be a
L & N running through the isolator to the light so presumably I
could divert them to a 13A socket, plug in the monitor & connect
flex from a 13A plug to the outward part of the light's supply?

That's certainly a workable solution. It just needs a modicum of care and
common sense. Presumably the main aim here is to log the consumption over
a few days of use (you know what the lamp takes, you just don't know how
much run time it'll typically be clocking up - the rest of the circuit
standby consumption is unlikely to be more than a watt or two, but you'll
be able to verify this to remove such 'mystery' from your estimates)

Yes, I'd want to measure several nights' use.


- bell transformer, meant to be illuminating a bell-push, but I
think the bulb's blown... so presumably the transformer uses
nothing at all, or a negligible amount?

Some of the older ones could be using as much as 4 or 5 watts just
keeping themselves at nice and toasty 40 to 50 degrees. A good quality
bell transformer could well be wasting as little as half a watt or
less with the lamp in the illuminated bell push consuming a further
half watt or so with the bell itself perhaps taking no more than
another watt or two on each press of the bell push.

Before the rewise, the bell transformer was screwed into a brick subwall
well under the floor - so (in line with my other thread, unlikely to be much
of a fire risk!) - and just wired into the nearest 13A plug - so easy to
measure... if only I had done then. But during the rewire the sparks
mounted it on the wooden board that the CU is on, making its connection
nearly impossible to get at...

If the transformer is a modern one with built in thermal fuse
protection and mains terminals designed to accept 2.5mm FT&E cable,
he's probably wired it into one the ring main circuits using a short
length of 2.5mm FT&E.

I'm not sure whether the older designs of decades gone by were
designed to be so directly connected to a 30A fused circuit. Possibly
they required a mains connection via FC box with a 1 or 3 amp fuse
fitted. I'd check that your existing one has been safely connected to
the mains.

I tried searching for info on these little power vampires but the
suppliers/manufacturers seem just as coy about the running costs as
the manufacturers of UPSes are, i.e. no information whatsover on their
efficiency or idle consumption. However, one interesting point that
stood out was that the overheat protection was a one shot deal in that
once the thermal overload protection had operated, you would have to
toss it away and buy a new one. Fair enough in the case of a
transformer fault but a kick in the goolies if it were simply due to
an external wiring fault.


It's always irritated me that illuminated bell pushes have bulbs that burn
out reletively quickly, spare bulbs are/were hard to get and fiddly to
change over. When I came here the cable through the wall into the back of
the bell push was friable and really short... I put a surface mount box and
blank plate on the inside wall near it, into which the supply from the
transformer & the cable out to the bell sounder & the bell-push wires now
all come... so that I could change the through-wall cable easily AND have
some spare cable coiled up in the box so that there was a few inches of
spare to work with each time I took the bell push off the wall.

When we moved into the present house just over thirty years ago, I
decided to make good use of parts I already had in my possession
rather than spend money and make more work for myself, hence the
ex-GPO trembler bell screwed onto the door frame behind the bell push
with a couple of 8 cell AA battery holders stuck back to back with
double sided adhesive tape to provide an everlasting 24v to lend the
bell enough loudness (it could be adjusted to run off a DC voltage in
the range of 10 to 24 volt - it wasn't really loud enough off just
12v, hence the 24v battery pack (now 27 volts).

The alkaline cells lasted long enough, about 15 years or so. what
retired them was corrosion which had damaged my home made 16 cell
battery holder to the point where it seemed simpler to try a cheaper
(and far less bulky) alternative. Despite all the corrosion, the bell
still worked, albeit just a little bit queter than it once did.

Since the idea of using a large enough battery to, in theory, last
for decades was rather flawed by age induced corrosion, it finally
dawned on me that a cheaper, shorter lived battery option would be
much better. Since the local pound shops were selling zinc carbon
PP3's in packs of three, it was a no brainer to turn the whole pack
into a 27 volt battery instantly ready to hang off the screw head I'd
originally used to hang the first 'monster battery pack' off of.

All I had to do was solder a couple of straps and connect the
resulting 27 volt battery to the bell wiring. The result was a less
intrusive neater looking bell and battery installation which had only
used a couple of feet of bell wire from the bell push which also
activates the wireless bell push sender unit fitted on the inside of
the door frame so the wireless door chime in my upstairs office could
act as a repeater.

I added a a zenner dropper and reverse polarity protection diode so I
could power the sender from the 27v bell battery but I kept the 12v
internal battery which allows independent operation of the remote
office door chime for testing purposes.

However, it has also proved handy for when the XYL gets in late from
her nannying job to alert me of her return without having to shout to
be heard through the closed office door against the sound of a TV
program I would often be in the middle of watching at that time of the
evening.

The battery powered door bell has served me well these past three
decades with a running cost on a par with a mains powered bell but
without the faff of running yards of bellwire and the capital
investment of a bell transformer.

In this case, battery power trumps mains power despite the energy
cost using primary cells being several thousands of times greater than
what the electricity supplier charges. And, one more thing, it'll
still function during a power outage. :-)


Thanks for your thoughts!

You're welcome. Sorry I couldn't offer any experience based help in
regard of the bell transformer.
--
J B Good