Energy monitor clamp behavior!? (Looping live thru clamp)

[eveares]

Ok, sorry it's taken so long to post here; but here goes.

I disconnected the earth from the loop section, but I still got a reading roughley half of that when it is passed straight through the clamp. I also bought a plug in energy monitor.

1Kw fan heater:

Plug in meter: 1035w
Straight through clamp: 1030w
Looped through clamp: 370w

See video below for me testing it.

 

[JohnW2]

Ok, sorry it's taken so long to post here; but here goes.

I disconnected the earth from the loop section, but I still got a reading roughley half of that when it is passed straight through the clamp. I also bought a plug in energy monitor. 1Kw fan heater: Plug in meter: 1035w ... Straight through clamp: 1030w ... Looped through clamp: 370w

Interesting - and seemingly odd. Do I take it that you're sure that neither the neutral or earth in the loop cable had their ends joined together (even though not connected to anything else)?

As a matter of interest, have you, when using the 'passed straight through' method, examined what happens to the reading if you also pass a 'shorted turn' through the sensor (i.e. a loop of insulated wire with ends joined together). If you try that, make sure there is no current flowing through the system when you install the 'shorted turn'!

Kind Regards, John

 

[eveares]

Do I take it that you're sure that neither the neutral or earth in the loop cable had their ends joined together (even though not connected to anything else)?

Absolutely John; the earth wires can be seen hanging outside the junction box, and the neutrals are trimmed down to the outer sheath at both ends of the loop.

As a matter of interest, have you, when using the 'passed straight through' method, examined what happens to the reading if you also pass a 'shorted turn' through the sensor (i.e. a loop of insulated wire with ends joined together). If you try that, make sure there is no current flowing through the system when you install the 'shorted turn'!

No, but I will tomorrow.

If you try that, make sure there is no current flowing through the system when you install the 'shorted turn'!

Why?,will a single shorted turn really induce a dangerous voltage and potential current draw?

 

[JohnW2]

No, but I will tomorrow.

I look forward to hearing the result!

If you try that, make sure there is no current flowing through the system when you install the 'shorted turn'!

Why?,will a single shorted turn really induce a dangerous voltage and potential current draw?

Probably not, and certainly not whilst it is shorted!

Kind Regards, John

 

[EFLImpudence]

I still got a reading roughley half of that when it is passed straight through the clamp. I also bought a plug in energy monitor.

Just a point:
370 isn't really roughly half of 1030; it's nearer a third - 1/2.78.

However, it's about a sixth of what would be expected - 1/5.57.

Does that ring any bells?


Try a smaller cable. The device looks a bit tight - as has been said, it may not be closing properly.
May have been asked already - Do you not have a clamp meter to check the amps?

 

[JohnW2]

However, it's about a sixth of what would be expected - 1/5.57. ... Does that ring any bells?

Not any immediate bells - should it?!

Try a smaller cable. The device looks a bit tight - as has been said, it may not be closing properly.

Indeed - that seems quite a likely issue.

May have been asked already - Do you not have a clamp meter to check the amps?

As you've seen, he's reported that he's just bought a plug-in meter, and it gives essentially the same reading as his ah-hoc system with a single pass through it. Doesn't that tell you as much as a clamp meter would?

Kind Regards, John

 

[EFLImpudence]

Not any immediate bells - should it?!

Probably not.

As you've seen, he's reported that he's just bought a plug-in meter, and it gives essentially the same reading as his ah-hoc system with a single pass through it. Doesn't that tell you as much as a clamp meter would?

As no one knows why the reading is as it is, I just thought that if a clamp meter read 8-ish amps with two pass-throughs then it is obviously the monitor at fault.
I'm not sure how it converts amps to watts.
If it just multiplies by 240 then no reason for the error.

Does the monitor read zero with two passes in opposite directions?

Clutching at straws.

 

[JohnW2]

As you've seen, he's reported that he's just bought a plug-in meter, and it gives essentially the same reading as his ah-hoc system with a single pass through it. Doesn't that tell you as much as a clamp meter would?

As no one knows why the reading is as it is, I just thought that if a clamp meter read 8-ish amps with two pass-throughs then it is obviously the monitor at fault.

Sure, but if both the plug-in monitor and the OP's set-up (with single pass through sensor) are giving the same (watts) answers, that does seem to be a straw you are clutching at!

I'm not sure how it converts amps to watts. If it just multiplies by 240 then no reason for the error.

The OP's 'clip-on' setup necessarily multiplies current by some assumed voltage (240V or whatever) to get watts. The plug-in one could, theoretically, actually measure voltage. I would imagine that both would assume a unity PF, so are actually displaying VA, rather than watts, whatever they might claim.

Kind Regards, John

 

[eveares]

I am really stumped now!

As a matter of interest, have you, when using the 'passed straight through' method, examined what happens to the reading if you also pass a 'shorted turn' through the sensor

I tried but no difference John; and to cut a long story short, if I have anything but a single piece of cable passing straight through, I get a substantially lower reading.
​

i.e. When I replace the loop for a piece of outer sheath from a 0.75mm flex; 1kW still reads around 0.37kW!?

All I can guess is whatever is in the way such as the sheath, is partially blocking some of the magnetic fields given off, but find it hard to believe that a bit of pvc sheath would do that. Also does not matter whether the bit of sheath is on top or underneath the cable carrying the current, nor does it matter if i substitute the piece of sheath for a bit of rope, etc...

Anyone got any ideas what is going on?

 

[JohnW2]

I am really stumped now! ... to cut a long story short, if I have anything but a single piece of cable passing straight through, I get a substantially lower reading. ... i.e. When I replace the loop for a piece of outer sheath from a 0.75mm flex; 1kW still reads around 0.37kW!? ... All I can guess is whatever is in the way such as the sheath, is partially blocking some of the magnetic fields given off, but find it hard to believe that a bit of pvc sheath would do that. Also does not matter whether the bit of sheath is on top or underneath the cable carrying the current, nor does it matter if i substitute the piece of sheath for a bit of rope, etc... Anyone got any ideas what is going on?

In that case, is not by far the most likely explanation the one that was given right at the start - namely that putting additional things through the sensor is stopping in 'closing' (and hence completing the magnetic circuit) properly? I don't believe that 'inert' materials like PVC (or rope!!) would make any (electrical or magnetic) difference, per se.

As recently suggested by EFLI, the test of this is surely to try with much smaller cable, so there is no question of the sensor aperture being 'too full'. You could also try some sort of ('gentle') clamp across the sensor, to make sure that it really is 'properly closed'.

Kind Regards, John

 

[Lectrician]

I know for sure my clamp meter will read DC current, and will double the value if you loop the cable. I tried on a forklift charger once for absolutely no reason. I wonder if I can try mine on AC somewhere......

 

[ban-all-sheds]

You must surely be able to lay hands on at least one Lucy and one long length of 16/25mm² DI cable?

 

[eveares]

In that case, is not by far the most likely explanation the one that was given right at the start

But I insist the clamp closes properly; with 1.25mm flex and 0.75mm sheath it closes fine.

 

[JohnW2]

In that case, is not by far the most likely explanation the one that was given right at the start

But I insist the clamp closes properly; with 1.25mm flex and 0.75mm sheath it closes fine.

I was afraid that you were going to say that, since it really makes no sense that inserting an 'inert' non-conductor should make any difference! If you feed a bit of PVC sheathing (or 'rope', or whatever) through the sensor whilst it is measuring your heater's current, do you actually see the reading fall as you do the inserting??

Kind Regards, John

 

[eveares]

In that case, is not by far the most likely explanation the one that was given right at the start - namely that putting additional things through the sensor is stopping in 'closing' (and hence completing the magnetic circuit) properly?

That was it John, even a fraction of a mm causes a massive drop in the reading! The extra bit of sheath, rope, etc... in the sensor must of pushed open the clamp, only by 10th or so of a mm, but that's all it took.