Question about clamp meters

[Ray Pooley]

Well, I say that because I don't think there is a problem other than perhaps my meter reading.

Then again, it might not be a problem at all.

So I had an oil heater that was tripping the RCD. Element was leaking so replaced it.

Also did a complete check of all switches, terminal blocks and cables looking for grounding and all is fine.

Put it all back together, switched it on max and checked the draw on the line with the clamp meter
and it is what I would expect a spot on 10 amps.

So I then clamp the earth cable and it reads 46mA. The RCD is rated 30 mA but it doesn't trip.

Is my meter telling lies or is the clamp picking up the flux from the neighbouring line even though
the line is outside the clamp?

Any thoughts?

Thanks

Ray Pooley

 

[Pete999]

What clamp metre do you own ? is it a bog standard one or one capable of Read mA accurately?

 

[Ray Pooley]

What clamp metre do you own ? is it a bog standard one or one capable of Read mA accurately?

This one. I only wanted one for reading AC. That's the only thing I do with it.

I have three other meters for other purposes.

No mA option.

LAP AC Digital Clamp Meter 600A - Screwfix

Order online at Screwfix.com. High accuracy and performance. Non-contact detector for voltage, current and resistance. Includes work light. FREE next day delivery available, free collection in 1 minute.

www.screwfix.com

 

[snowhead]

You won't read Milliamps accurately with a £24 clamp meter

 

[Ray Pooley]

You won't read Milliamps accurately with a £24 clamp meter

I'm not trying to read mA with it.

 

[Pete999]

This one. I only wanted one for reading AC. That's the only thing I do with it.

I have three other meters for other purposes.

No mA option.

LAP AC Digital Clamp Meter 600A - Screwfix

Order online at Screwfix.com. High accuracy and performance. Non-contact detector for voltage, current and resistance. Includes work light. FREE next day delivery available, free collection in 1 minute.

www.screwfix.com

This one. I only wanted one for reading AC. That's the only thing I do with it.

I have three other meters for other purposes.

No mA option.

LAP AC Digital Clamp Meter 600A - Screwfix

Order online at Screwfix.com. High accuracy and performance. Non-contact detector for voltage, current and resistance. Includes work light. FREE next day delivery available, free collection in 1 minute.

www.screwfix.com

Hi Ray, if you intend to measure a lot of earth leakage problems then you could invest in a metre capable reading mA or get a Spark to measure it for you. I have a LAP clamp OK for measuring Amps but for mA I would go for something more suitable, try the Di Log range, that would be my choice.
[automerge]1576686176[/automerge]

I'm not trying to read mA with it.

What are you trying to read then Mate?

 

[Ray Pooley]

Hi Ray, if you intend to measure a lot of earth leakage problems then you could invest in a metre capable reading mA or get a Spark to measure it for you. I have a LAP clamp OK for measuring Amps but for mA I would go for something more suitable, try the Di Log range, that would be my choice.

No. I don't actually. This was just out of curiosity. Never done it before. I am satisfied with the line current reading. It was a spontaneous Hmmm moment. I was expecting to see 0.00 amps. So I am just wondering why I didn't. Is it the meter or is it a genuine leak. I shoud mention that I tested the switches and terminals using a different meter. Not this one.

 

[Bradneil]

Any other recommendations on clamp meters?

 

[MJPD29]

No. I don't actually. This was just out of curiosity. Never done it before. I am satisfied with the line current reading. It was a spontaneous Hmmm moment. I was expecting to see 0.00 amps. So I am just wondering why I didn't. Is it the meter or is it a genuine leak. I shoud mention that I tested the switches and terminals using a different meter. Not this one.

Most likely the reading you are getting is due to the inaccuracy of your meter Ray. Probably nowhere near that.

 

[Ray Pooley]

Hi Ray, if you intend to measure a lot of earth leakage problems then you could invest in a metre capable reading mA or get a Spark to measure it for you. I have a LAP clamp OK for measuring Amps but for mA I would go for something more suitable, try the Di Log range, that would be my choice.
[automerge]1576686176[/automerge]

What are you trying to read then Mate?

My question isn't about reading. It's about interpreting the results in the display. Although the meter does not have a specific mA range option it does display readings to 3 decimal places when the 20A range is selected. Therefore when it displays 0.046A I presume there is current detected and the meter is not making it up. But since it is not tripping the 30mA RCD I am wondering if it is a ghost current ie not originating from the original source. Induced perhaps by the juxtaposition of the earth cable to the line and neutral in the outer sheath for example? An induced current in the earth cable would not affect the RCD. See what I mean? Or do I perhaps need to calibrate this meter. I am reaching out to others who may or may not detect small currents on earth cables and have some idea of what causes them. So its not about reading.

 

[DPG]

Showing 3 decimal places on a display does not mean it is accurate to 3 decimal places. As Pete says, a meter like that one is certainly not going to be.

 

[Lucien Nunes]

I then clamp the earth cable and it reads 46mA

Is this the element elephant in the room?

It's not clear what kind of heater this is (an oil tank heater? Or an oil-filled space heater?) My question is; is the elephant element completely isolated from earth other than via the CPC that you are measuring? If not, (for example if it is bolted to the steel of the building) there can be all sorts of circulating currents that are nothing to do with leakage. What was the measurement with the heater disconnected from the supply?

TBH measuring leakage by clamping the CPC is unreliable at best. It's better to clamp the line and neutral and hence measure the difference, the way an RCD does.

 

[Julie.]

Looking at the link you provided shows the meter is accurate to +/-3% on the 20A range, so if you have 10A it could actually display +/- 0.6A to this - so 9.4 to 10.6A

With 0.0A flowing it could also read up to 0.6A out

Your measurements are well within the published error

If you need or want to measure much lower values, the you need a meter with a much lower range - something with a 200ma range with the same 3% error - is still +/- 6mA

 

[westward10]

I have cleaned this thread up. Can people remember this is a new member so helpful advice only. Maybe he will return, hopefully.

 

[James]

I am imagining an oil filled radiator here.

I have known them when unused for a long period of time to absorb a little moisture to the oil.
this gives a little earth leakage.
rightly or wrongly, in the past, I have been known to put them on a supply that is not rcd protected and leave them hot for 24h

leakage problem is normally gone when you come and re test.