DIN mounted electricity energy meters

[shackec]

I have read, with interest, some previous posts on this subject. This prompts me to ask if anyone could give me a brief description of how these units work? Does the current being drawn have to go through the unit or does it sense the quantity indirectly (maybe strength of field generated)? In either case how would the unit be wired into a standard consumer box. It would be interesting to see what the recorded value is compared to the supplier's main meter!
Although my interest is focused on measuring the power consumed through a consumer box in my barn. This controls power to workshop tools, floods, and external camper vans.
Any information would be appreciated.
regards. Chas

 

[ericmark]

A consumer unit is a type tester distribution unit, and to retain the type testing it can only be populated with items approved by its manufacturer.

There are loads of energy meters, some can even detect the direction of the power, I am unsure on the accuracy of the different types, I know I can bring up details of my own power use

which are great out on interest to see how much energy has gone where, but not used to work out payment.

These can be used, this one rated 5 mA to 32 A there are also smart versions, but it is not how they work, but if permitted in the consumer unit you have. This Wylex one has a £324 price ticket, and still states

Standard Meters - Non MID approved
If a meter is being used purely for a “check meter reading” and not being used to resell
or charge for electricity consumed, then a standard meter that is energy used at that point in time.

So no simple answer.

 

[SUNRAY]

How does this compare with the size of your existing MCBs

 

[JohnW2]

How does this compare with the size of your existing MCBs

Your diagram is of a "2-module-wide" one, which many of them are, but there are all plenty of "single module" ones (17.5-18mm wide) available.

Kind Regards, John

 

[SUNRAY]

It is, do the single module now fit in a cu, they didn't used to.

 

[JohnW2]

It is, do the single module now fit in a cu, they didn't used to.

I assumed that they did (fit in a CU). Indeed, I have always assumed that they did in the past, since I thought that was 'the whole point' of most of them - but perhaps I was wrong!

In what sense/manner did they "not fit". Many current ones look very similar (shape/size-wise) to MCBs, and some not as tall as an RCBO.

Kind Regards, John

 

[ericmark]

I assumed that they did (fit in a CU).

This is why I pointed out having to keep to same make of items within the CU, we have to consider heat and physical size of the units and will they fit in the window size of CU being used, DIN rail is a German standard but where the hole is required to operate items fitted on the DIN rail is not. The same applies to many DIN rail mount devices, bell transformers and the like.

I use to build control boxes with DIN rail mounted devices from PLC's to power supplies, and I would often fit a perspex sheet over the items so the box could be opened to inspect without exposing live parts, I still got told off by HSE for leaving the handles in the boxes, he pointed out the handles could be removed and used to open other boxes, so I had to remove them all and carry a key around with me.

The whole point of a CU is the type testing. But it is tempting to mix and match makes of items within the CU specially with things like SPD where the price between makes can vary so much. With domestic the heat is not normally a problem, it is rare a CU is loaded to the max of 125 amp, or less many rated at 100 amp, but as they are used for non domestic applications it is easy to find they are running near to capacity, so heat dissipation has to be taken into account.

 

[Why Not Indeed]

Does the current being drawn have to go through the unit or does it sense the quantity indirectly (maybe strength of field generated)?

It Depends. ericmark linked to one that uses current transformers [split cores that clamp around the conductors], other ones are "invasive":

SDM120 Modbus MID 45A

Open-source hardware tools for energy monitoring and visualisation

shop.openenergymonitor.com

 

[SUNRAY]

... Does the current being drawn have to go through the unit or does it sense the quantity indirectly (maybe strength of field generated)? ...

Generally these units up to a fairly minimal current (say 5-16A continuous but don't take that as a quote) will go through the meter, anything over that will have a current transformer added around the current carrying wire, as an example a 20:1 will make a 5A meter into a 100A.
Different arrangements exist (such as current to voltage) but that is the basic principle of current transformers.

Devices designed to mounted in a panel/enclosure such as these as an example:

Seem to standardise on 5A continuous (again gon't quote me) and will require current transformers to read anything higher, This one is 200/5A:

 

[SUNRAY]

I assumed that they did (fit in a CU). Indeed, I have always assumed that they did in the past, since I thought that was 'the whole point' of most of them - but perhaps I was wrong!

In what sense/manner did they "not fit". Many current ones look very similar (shape/size-wise) to MCBs, and some not as tall as an RCBO.

Kind Regards, John

I haven't handled a narrow unit for a number of years but they tended to not have the 45mm limit to fit the standard slot, excuse my crude buchery as explanation:

Any disply screen tended to be mounted sideways and extend beyond the 45mm whereas the 35mm wide didn't have the issue. I dare say there will now be a plethoral of 'what about this one?'

And of course not all MBC manufacturers lined up the din rail and the 45mm slot the same although I haven't encountered that issue recently.

 

[JohnW2]

I haven't handled a narrow unit for a number of years but they tended to not have the 45mm limit to fit the standard slot, excuse my crude buchery as explanation:

Fair enough. I obviously was not aware of that.

Kind Regards, John

 

[hllns]

Any scope to put anything at at the other end where it's fed from?

Current clamp metering round a live or neutral needs a voltage measurement to accurately measure the power consumption but an old Current Cost home energy monitor unit that assumes a fixed voltage value might give you a vague idea if you've somewhere to put it.

 

[SUNRAY]

Any scope to put anything at at the other end where it's fed from?

Current clamp metering round a live or neutral needs a voltage measurement to accurately measure the power consumption but an old Current Cost home energy monitor unit that assumes a fixed voltage value might give you a vague idea if you've somewhere to put it.

That's raised a point anyway, the meter should be as early in the circuit as possible to include the cable losses.

 

[SpecialK]

Depends what you want to measure and how accurately?
Something like the shelly EM will give you fairly accurate usage stats. If you have wifi you can get info in the app.

 

[JohnW2]

Current clamp metering round a live or neutral needs a voltage measurement to accurately measure the power consumption but an old Current Cost home energy monitor unit that assumes a fixed voltage value might give you a vague idea if you've somewhere to put it.

I would say that "a vague idea" is probably somewhat over-stating the potential issue. For almost 'domestic purposes', a device which assumes a fixed voltage will give adequate accuracy - particularly if (as if often the case), one can set the voltage to be used, since variation of supply voltage within a particular installation is not all that great.

The other thing which can't be taken into account in the absence of voltage information is obviously power factor but, again, I doubt that varies enough in a domestic setting for it to be a major problem.

Kind Regards, John