How accurate are these? Just bought one - it's one with a magnetic clip
which goes around the live load cable coming out of the meter. It seems to
read about 20-30% under at low usage (500W) compared to the meter, but more
accurate at higher usage (2-9kW). I've tried another one which gives the
same results. Could I have a faulty meter? Or do these things usually read
under at low usage?

TIA

--
Andy

In article ,
Andy Pandy wrote:
How accurate are these? Just bought one - it's one with a magnetic clip
which goes around the live load cable coming out of the meter. It seems
to read about 20-30% under at low usage (500W) compared to the meter,
but more accurate at higher usage (2-9kW). I've tried another one which
gives the same results. Could I have a faulty meter? Or do these things
usually read under at low usage?

I'd guess so - most of these inductive or whatever coupling things tend to
not be accurate at smaller currents.

--
*The average person falls asleep in seven minutes *

Dave Plowman London SW
To e-mail, change noise into sound.

Andy Pandy formulated the question :
How accurate are these? Just bought one - it's one with a magnetic clip
which goes around the live load cable coming out of the meter. It seems to
read about 20-30% under at low usage (500W) compared to the meter, but more
accurate at higher usage (2-9kW).

They are basically just a clamp meter, as used for measuring current.
Clamp meters are not the best accuracy and they can depend upon the
type of load, but I would expect much better accuracy than 20 to 30%.
Have you tried it with a resistive load like a small heater or tungsten
lamps?

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

"Harry Bloomfield" wrote in message
k...
Andy Pandy formulated the question :
How accurate are these? Just bought one - it's one with a magnetic clip
which goes around the live load cable coming out of the meter. It seems
to
read about 20-30% under at low usage (500W) compared to the meter, but
more
accurate at higher usage (2-9kW).

They are basically just a clamp meter, as used for measuring current.
Clamp meters are not the best accuracy and they can depend upon the
type of load, but I would expect much better accuracy than 20 to 30%.
Have you tried it with a resistive load like a small heater or tungsten
lamps?

With lights as the main load (about 1.5kW) it reads about 20% under, with a
fan heater as the main load (about the same, 1.5kW) it reads about 15%
under. With the kettle or shower as the main load it seems pretty accurate,
although the usage is obviously much higher.

--
Andy

Andy Pandy wrote:
How accurate are these? Just bought one - it's one with a magnetic clip
which goes around the live load cable coming out of the meter. It seems to
read about 20-30% under at low usage (500W) compared to the meter, but more
accurate at higher usage (2-9kW). I've tried another one which gives the
same results. Could I have a faulty meter? Or do these things usually read
under at low usage?

TIA

--
Andy




The problem is that these devices all use split core CT's (Current
Transformers). The splitting of the core will produce inaccuracies. No
matter how good the joining of the core, there will always be small gaps
between the two surfaces which will affect the flow of magnetic flux
within the core. The reason for using them is that they are very easy to
fit around existing installations.

The best solution is to have a non split CT. You would have to isolate
your mains supply, disconnect the live tail, poke it through the CT and
then reconnect the live tail.

It could also be a phase difference issue. Are you using the same type
of load to produce the readings at 500W and 2KW-9KW?

"Rob Horton" wrote in message
...
Andy Pandy wrote:
How accurate are these? Just bought one - it's one with a magnetic clip
which goes around the live load cable coming out of the meter. It seems
to
read about 20-30% under at low usage (500W) compared to the meter, but
more
accurate at higher usage (2-9kW). I've tried another one which gives the
same results. Could I have a faulty meter? Or do these things usually
read
under at low usage?

TIA


The problem is that these devices all use split core CT's (Current
Transformers). The splitting of the core will produce inaccuracies. No
matter how good the joining of the core, there will always be small gaps
between the two surfaces which will affect the flow of magnetic flux
within the core. The reason for using them is that they are very easy to
fit around existing installations.

The best solution is to have a non split CT. You would have to isolate
your mains supply, disconnect the live tail, poke it through the CT and
then reconnect the live tail.

It could also be a phase difference issue. Are you using the same type
of load to produce the readings at 500W and 2KW-9KW?

No - 500W was mainly lights, telly, fridge, freezer etc.

2-9kW was kettle, shower.

--
Andy

Andy Pandy wrote:
"Rob Horton" wrote in message
...
Andy Pandy wrote:
How accurate are these? Just bought one - it's one with a magnetic clip
which goes around the live load cable coming out of the meter. It seems
to
read about 20-30% under at low usage (500W) compared to the meter, but
more
accurate at higher usage (2-9kW). I've tried another one which gives the
same results. Could I have a faulty meter? Or do these things usually
read
under at low usage?

TIA


The problem is that these devices all use split core CT's (Current
Transformers). The splitting of the core will produce inaccuracies. No
matter how good the joining of the core, there will always be small gaps
between the two surfaces which will affect the flow of magnetic flux
within the core. The reason for using them is that they are very easy to
fit around existing installations.

The best solution is to have a non split CT. You would have to isolate
your mains supply, disconnect the live tail, poke it through the CT and
then reconnect the live tail.

It could also be a phase difference issue. Are you using the same type
of load to produce the readings at 500W and 2KW-9KW?

No - 500W was mainly lights, telly, fridge, freezer etc.

2-9kW was kettle, shower.

--
Andy


Sooo, making some assumptions here, lights could be CFL? TV - maybe has
a switch mode power supply? Were the fridge & freezer actually running
at the time?

Kettle - simple heating element & shower - electrical heating with no motor?

I'm not saying that this is definately the cause just pointing out the
differences.

I would like to get a remote monitor and have wondered how accurate they
are.

How do you know it's the monitor and not the supply meter that is wrong?

"Rob Horton" wrote in message
...
Andy Pandy wrote:
"Rob Horton" wrote in message
...
Andy Pandy wrote:
How accurate are these? Just bought one - it's one with a magnetic
clip
which goes around the live load cable coming out of the meter. It
seems
to
read about 20-30% under at low usage (500W) compared to the meter, but
more
accurate at higher usage (2-9kW). I've tried another one which gives
the
same results. Could I have a faulty meter? Or do these things usually
read
under at low usage?

TIA


The problem is that these devices all use split core CT's (Current
Transformers). The splitting of the core will produce inaccuracies. No
matter how good the joining of the core, there will always be small
gaps
between the two surfaces which will affect the flow of magnetic flux
within the core. The reason for using them is that they are very easy
to
fit around existing installations.

The best solution is to have a non split CT. You would have to isolate
your mains supply, disconnect the live tail, poke it through the CT and
then reconnect the live tail.

It could also be a phase difference issue. Are you using the same type
of load to produce the readings at 500W and 2KW-9KW?

No - 500W was mainly lights, telly, fridge, freezer etc.

2-9kW was kettle, shower.

Sooo, making some assumptions here, lights could be CFL?

Mostly.

TV - maybe has
a switch mode power supply?

Not sure. How do I tell? It's a fairly new flat screen (probably about 2
years old). It takes a few seconds to respond when switching on.

Were the fridge & freezer actually running
at the time?

I think so but not sure.

Kettle - simple heating element & shower - electrical heating with no
motor?

Yup - no motor.

I'm not saying that this is definately the cause just pointing out the
differences.

OK thanks.

I would like to get a remote monitor and have wondered how accurate they
are.

How do you know it's the monitor and not the supply meter that is wrong?

I don't - that's my main concern! I may have been overcharged for 10
years...but before taking it up with the electric company and having them
laugh at me I thought I'd check whether it's usual for these monitors to be
so far out.

As it happens they've just written to me saying the meter needs changing...

--
Andy

on 28/08/2009, Andy Pandy supposed :
Not sure. How do I tell? It's a fairly new flat screen (probably about 2
years old). It takes a few seconds to respond when switching on.

All modern TV's use a a SMPSU, anything made in probably the last 15
years.


Were the fridge & freezer actually running
at the time?

I think so but not sure.

Kettle - simple heating element & shower - electrical heating with no
motor?

Yup - no motor.

I'm not saying that this is definately the cause just pointing out the
differences.

I would agree with that.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk

On Thu, 27 Aug 2009 16:29:55 +0100, Andy Pandy wrote:

How accurate are these? Just bought one - it's one with a magnetic clip
which goes around the live load cable coming out of the meter. It seems
to read about 20-30% under at low usage (500W) compared to the meter,

I have a CurrentCost CC128 (the newer model) this has TTL level
serial data dribbling out of the back that I've only recently
connected to a PC to log/plot the data.

Not really checked the accuracy, but our "rapid boil" 3kW plated
kettle only adds 2kW to the useage when it's on, I'll have to find my
plugin power meter and see how that compares... Having said that the
overall daily use is pretty close to what the bill works out at,
certainly not the gross error of 2kW v 3kW.

--
Cheers
Dave.