Change meter with no power loss?

[rjm2k]

I suspect I know the answer but could be wrong, at work we've got a 3 phase supply, the MOP (SE) has insisted they need to change the meter and has told us they can do it without downtime because the electricity doesn't go directly through the meter! Is this a call center fib or is it true?

I've saved my work just in case!

 

[ericmark]

Likely true as likely it uses current transformers to the meter not direct through meter as with a domestic.

 

[Iggifer]

It's probably true yes. You likely have what's called CT metering. I can't find a good link to explain it

 

[rjm2k]

Thanks, looks like it works by induction so makes sense. Out of interest, doesn't it make it quite easy to interfere with the meter (eg place a magnet over the sensor?)

 

[Iggifer]

thats why the magnets are locked in a big cabinet!

 

[ericmark]

It would need to be an AC magnet. As with any meter you can fiddle them but it would be just as hard to do it without detection.

 

[rjm2k]

thats why the magnets are locked in a big cabinet!

Ah, only saw this on wikipedia, minus the cabinet I guess - haven't seen our setup.

 

[Iggifer]

Untitled

• Iggifer
• 12 Nov 2012
• 2

that's the kind of cabinet that holds them

 

[Lectrician]

Yep, meters fed by CT's can be swapped with ease without any downtime, and with no risk to the operative (assuming all precautions taken). The setup is designed to allow this to be done.

 

[bernardgreen]

It would need to be an AC magnet. As with any meter you can fiddle them but it would be just as hard to do it without detection.

There is a very simple way to reduce the reading if you can get access to the current transformers. No magnets or complicated components needed, But I am not saying how on a public forum.

 

[JohnW2]

There is a very simple way to reduce the reading if you can get access to the current transformers. No magnets or complicated components needed, But I am not saying how on a public forum.

There is, indeed, and (assuming we're thinking of the same thing), it's not rocket science for anyone who understands about inductance/ transformers, yet I'm not sure what they could do (other than denying access to the CTs) to prevent people doing it.

Kind Regards, John

 

[ban-all-sheds]

Would an earthed screen around the cable be of use?

 

[JohnW2]

Would an earthed screen around the cable be of use?

You mean to 'fiddle' it? If so, I doubt that an earthed screen would have much impact on the CT functionality. The earthing would certainly be irrelevant, and the 'screen' itself unlikely to have much electromagnetic impact, I would have thought. However, we're not really meant to be discussing such things, are we?!

Kind Regards, John

 

[rjm2k]

I was thinking it was more about angles, or possibly bridging the magnet terminals

anyway, the law prohibits it and wouldn't reducing the hole in the magnet to the size of the cable remove the possibility of such interference, or would that impact on the inductance? can't be a big issue as we are talking generally about business and the companies keep it all tucked away in a locked cabinet which belongs to them, preventing physical access anyway

I suspect growers of certain "exotic" plants are more of an issue, bypassing the whole lot anyway!

 

[JohnW2]

I was thinking it was more about angles, or possibly bridging the magnet terminals...

There are obviously possibilities which involve interfering with the wires connected to the CTs, but that would probably leave 'evidence'. I believe that there is an easier way (can't say that I've tried it ), which doesn't require such interference, which I imagine is what Bernard had in mind.

I can't be a big issue as we are talking generally about business and the companies keep it all tucked away in a locked cabinet which belongs to them, preventing physical access anyway

That's probably all very true, but 'corporate crime' does exist! Interestingly, in the pic posted by Iggifer, there are no obvious seals on the CT enclosure/cabinet.

Kind Regards, John