I'm looking for a reasonably simple way to measure consumption of
one circuit on a consumer unit. I installed the CU myself so
I'm not afraid of doing a bit of poking around.

It's a circuit on a 20 amp MCB. There are two spare MCBs in the CU.
Can one get DIN rail 'meters' that will measure total kWh. The two
spare MCB slots are side by side so a double width space is available.

--
Chris Green
·

Chris Green wrote:

> I'm looking for a reasonably simple way to measure consumption of
> one circuit on a consumer unit. I installed the CU myself so
> I'm not afraid of doing a bit of poking around.
>
> It's a circuit on a 20 amp MCB. There are two spare MCBs in the CU.
> Can one get DIN rail 'meters' that will measure total kWh.

Yes, analogue or digital versions available, e.g.

<https://www.jwsmartmeters.co.uk/product-category/din-rail-mounted-meters/>

> The two spare MCB slots are side by side so a double width space is
> available.
Only needs a single width module for single phase

On Monday, 31 October 2022 at 09:48:07 UTC, Chris Green wrote:
> I'm looking for a reasonably simple way to measure consumption of
> one circuit on a consumer unit. I installed the CU myself so
> I'm not afraid of doing a bit of poking around.
>
> It's a circuit on a 20 amp MCB. There are two spare MCBs in the CU.
> Can one get DIN rail 'meters' that will measure total kWh. The two
> spare MCB slots are side by side so a double width space is available.

Yes; if you are recharging for electricity you will need a MID-approved one

https://www.jwsmartmeters.co.uk/product-category/din-rail-mounted-meters/

You can also get with Modbus and pulse output if you want

https://www.jwsmartmeters.co.uk/shop/din-rail-mounted-meters/single-phase-din/sdm120-modbus-mid/

https://uk.farnell.com/c/automation-process-control/panel-displays-instrumentation/panel-instrumentation/energy-meters?energy-meter-mounting=din-rail

Owain

Chris Green <cl@isbd.net> wrote:
> I'm looking for a reasonably simple way to measure consumption of
> one circuit on a consumer unit. I installed the CU myself so
> I'm not afraid of doing a bit of poking around.
>
> It's a circuit on a 20 amp MCB. There are two spare MCBs in the CU.
> Can one get DIN rail 'meters' that will measure total kWh. The two
> spare MCB slots are side by side so a double width space is available.
>
.... and a quick search shows me there are such things! E.g. :-

https://www.cef.co.uk/catalogue/products/1781553-45a-single-phase-kwh-meter-din-rail-mounting-with-lcd-display-single-module

However I now have another question, how are these wired vis-a-vis the
CU's bus? Obviously I need to connect the meter in series with the
existing MCB supplying the circuit I want to measure. To do this
easily without major modifications to the bus-bar or other things in
the CU I'd need one of these meters to have both in and out
connections at the top rather than connecting to the bus-bar at the
bottom.

--
Chris Green
·

On 31/10/2022 09:46, Chris Green wrote:

> I'm looking for a reasonably simple way to measure consumption of
> one circuit on a consumer unit. I installed the CU myself so
> I'm not afraid of doing a bit of poking around.
>
> It's a circuit on a 20 amp MCB. There are two spare MCBs in the CU.
> Can one get DIN rail 'meters' that will measure total kWh. The two
> spare MCB slots are side by side so a double width space is available.

Depends a bit on how "elegant" the solution needs to be really...

A rough and ready option is using a normal clamp meter - clip it round
the live conductors on the top of the MCB and you will get a direct
reading.

If you want a slightly more "closed" but rough and ready option, then
run a loop of T&E out of the CU and back in. Using just the live
conductor wago/crimp the circuit wires to the T&E, and connect the other
end to the MCB. You now have a place to stick a clamp meter externally
and take a reading, but the whole thing is now "safe" with no accessible
live parts and the external measurement loop cable is double insulated.

The next option might be a variation on some of the power monitor
projects you can find here:

https://openenergymonitor.org/

I have a plan to build a posher "multi channel" that can instrument all
of the CU circuits, and then log real time readings into a database
along with real time voltage. (lots of small "clip round" current
transformers, and an Arduino Mega clone with wifi- I have the parts, but
have not yet mustered the enthusiasm!)

--
Cheers,

John.

/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/

On 31/10/2022 10:00, Chris Green wrote:
> Chris Green <cl@isbd.net> wrote:
>> I'm looking for a reasonably simple way to measure consumption of
>> one circuit on a consumer unit. I installed the CU myself so
>> I'm not afraid of doing a bit of poking around.
>>
>> It's a circuit on a 20 amp MCB. There are two spare MCBs in the CU.
>> Can one get DIN rail 'meters' that will measure total kWh. The two
>> spare MCB slots are side by side so a double width space is available.
>>
> ... and a quick search shows me there are such things! E.g. :-
>
> https://www.cef.co.uk/catalogue/products/1781553-45a-single-phase-kwh-meter-din-rail-mounting-with-lcd-display-single-module
>
> However I now have another question, how are these wired vis-a-vis the
> CU's bus? Obviously I need to connect the meter in series with the
> existing MCB supplying the circuit I want to measure. To do this
> easily without major modifications to the bus-bar or other things in
> the CU I'd need one of these meters to have both in and out
> connections at the top rather than connecting to the bus-bar at the
> bottom.

I've just looked at a different make and it seems to have two neutral
connections at one end and a live in and live out at the other. I
presume that it does not connect to the busbar, you connect your
load-side live and neutral to top and bottom, add a link from the other
neutral to the neutral rail, where your load neutral was previously
connected and add a link from the MCBs live output to the meter's live
input.

Owain Lastname <spuorgelgoog@gowanhill.com> wrote:
> You can also get with Modbus and pulse output if you want
>
> https://www.jwsmartmeters.co.uk/shop/din-rail-mounted-meters/single-phase-din/sdm120-modbus-mid/
>
> https://uk.farnell.com/c/automation-process-control/panel-displays-instrumentation/panel-instrumentation/energy-meters?energy-meter-mounting=din-rail

I have a DDM18SD (ebay, Amazon, Aliexpress) - it's Chinese but seems to work
ok. A 3kW immersion heater came out at 2997W which was pretty good. It does
Modbus and pulse output for about £20. Probably not MID approved.

The main thing is it flicks between various displays - voltage, current,
frequency, power factor, power, energy consumption. That is handy for
testing (and for Modbus recording) but might make it more annoying to read
as you have to wait for the kWh figure to go past.

(It may be this behaviour can be changed via Modbus - I haven't tried that)

Theo

Chris Green <cl@isbd.net> wrote:
> https://www.cef.co.uk/catalogue/products/1781553-45a-single-phase-kwh-meter-din-rail-mounting-with-lcd-display-single-module
>
> However I now have another question, how are these wired vis-a-vis the
> CU's bus? Obviously I need to connect the meter in series with the
> existing MCB supplying the circuit I want to measure. To do this
> easily without major modifications to the bus-bar or other things in
> the CU I'd need one of these meters to have both in and out
> connections at the top rather than connecting to the bus-bar at the
> bottom.

On the above (a DDS353) the live in and live out are on the top, and neutral
at the bottom. On my DDM18SD it's live in at the top, live out at the
bottom, neutral in (and pulse/modbus) via a second level terminal. Either
way would suit, as long as you have a busbar-free space at the bottom.

However you might want to consider whether the meter is before the MCB or
after it. After the MCB means the MCB protects in case of a fault in the
meter, but before means the meter stays powered when the MCB is turned off.
In my case I go MCB -> meter -> contactor, so the load is controlled by the
contactor but the meter stays powered if the load is off (which it will be,
most of the time).

Theo

On 31/10/2022 09:46, Chris Green wrote:
> I'm looking for a reasonably simple way to measure consumption of
> one circuit on a consumer unit. I installed the CU myself so
> I'm not afraid of doing a bit of poking around.
>
> It's a circuit on a 20 amp MCB. There are two spare MCBs in the CU.
> Can one get DIN rail 'meters' that will measure total kWh. The two
> spare MCB slots are side by side so a double width space is available.

Clip on ammeter or watt meter would be my first choice - assuming you
can find somewhere with that circuit's live or neutral on its own.

--
Regards,
Martin Brown

Theo <theom+news@chiark.greenend.org.uk> wrote:
> Owain Lastname <spuorgelgoog@gowanhill.com> wrote:
> > You can also get with Modbus and pulse output if you want
> >
> > https://www.jwsmartmeters.co.uk/shop/din-rail-mounted-meters/single-phase-din/sdm120-modbus-mid/
> >
> > https://uk.farnell.com/c/automation-process-control/panel-displays-instrumentation/panel-instrumentation/energy-meters?energy-meter-mounting=din-rail
>
>
> I have a DDM18SD (ebay, Amazon, Aliexpress) - it's Chinese but seems to work
> ok. A 3kW immersion heater came out at 2997W which was pretty good. It does
> Modbus and pulse output for about £20. Probably not MID approved.
>
> The main thing is it flicks between various displays - voltage, current,
> frequency, power factor, power, energy consumption. That is handy for
> testing (and for Modbus recording) but might make it more annoying to read
> as you have to wait for the kWh figure to go past.
>
> (It may be this behaviour can be changed via Modbus - I haven't tried that)
>
How is it wired though? Does it need connection(s) where the busbar
is on a CU? From the pictures I can find it looks as if it does have
its connections where the bus-bar normally goes so would be difficult
for me to install.

--
Chris Green
·

Theo <theom+news@chiark.greenend.org.uk> wrote:
> Chris Green <cl@isbd.net> wrote:
> > https://www.cef.co.uk/catalogue/products/1781553-45a-single-phase-kwh-meter-din-rail-mounting-with-lcd-display-single-module
>
> >
> > However I now have another question, how are these wired vis-a-vis the
> > CU's bus? Obviously I need to connect the meter in series with the
> > existing MCB supplying the circuit I want to measure. To do this
> > easily without major modifications to the bus-bar or other things in
> > the CU I'd need one of these meters to have both in and out
> > connections at the top rather than connecting to the bus-bar at the
> > bottom.
>
> On the above (a DDS353) the live in and live out are on the top, and neutral
> at the bottom. On my DDM18SD it's live in at the top, live out at the
> bottom, neutral in (and pulse/modbus) via a second level terminal. Either
> way would suit, as long as you have a busbar-free space at the bottom.
>
But I don't have a busbar-free space, that's the whole point. The MCB
whose power I want to monitor is in the middle of a 20-way CU with no
spaces at either end. The spare spaces are in the middle.

> However you might want to consider whether the meter is before the MCB or
> after it. After the MCB means the MCB protects in case of a fault in the
> meter, but before means the meter stays powered when the MCB is turned off.
> In my case I go MCB -> meter -> contactor, so the load is controlled by the
> contactor but the meter stays powered if the load is off (which it will be,
> most of the time).
>
Does it lose its readings if it's powered off then?

--
Chris Green
·

Chris Green <cl@isbd.net> wrote:
> Theo <theom+news@chiark.greenend.org.uk> wrote:
> > Chris Green <cl@isbd.net> wrote:
> > > https://www.cef.co.uk/catalogue/products/1781553-45a-single-phase-kwh-meter-din-rail-mounting-with-lcd-display-single-module
> >
> > >
> > > However I now have another question, how are these wired vis-a-vis the
> > > CU's bus? Obviously I need to connect the meter in series with the
> > > existing MCB supplying the circuit I want to measure. To do this
> > > easily without major modifications to the bus-bar or other things in
> > > the CU I'd need one of these meters to have both in and out
> > > connections at the top rather than connecting to the bus-bar at the
> > > bottom.
> >
> > On the above (a DDS353) the live in and live out are on the top, and neutral
> > at the bottom. On my DDM18SD it's live in at the top, live out at the
> > bottom, neutral in (and pulse/modbus) via a second level terminal. Either
> > way would suit, as long as you have a busbar-free space at the bottom.
> >
> But I don't have a busbar-free space, that's the whole point. The MCB
> whose power I want to monitor is in the middle of a 20-way CU with no
> spaces at either end. The spare spaces are in the middle.

I don't see how this will work then. Any DIN-rail device is likely to have
contacts where the busbar goes - that's the standard high-current location.
The extra wiring for neutrals etc may go to a second 'top deck' of contacts,
but typically the live goes through the lower deck.

You want a chain: busbar-live -> MCB -> meter -> load

but busbar-live -> MCB means the live emerges at the top of rail. If the
meter took in live at the top position of the lower deck (like the DDM18SD)
the output would be where the busbar finger goes. If the meter takes in
live at the bottom position on the lower deck then it'll be wired directly
into the busbar and will miss the MCB.

Either way the busbar is going to block doing what you want.
The only recourse is to find a device where the lower deck bottom position
isn't used, but that seems unlikely.

> > However you might want to consider whether the meter is before the MCB or
> > after it. After the MCB means the MCB protects in case of a fault in the
> > meter, but before means the meter stays powered when the MCB is turned off.
> > In my case I go MCB -> meter -> contactor, so the load is controlled by the
> > contactor but the meter stays powered if the load is off (which it will be,
> > most of the time).
> >
> Does it lose its readings if it's powered off then?

No, but it's an electronic display so you can't take readings if it has no
power as the display is blank. Since my contactor is remotely controlled,
it is awkward to power the load just to take readings.

Theo

On 31/10/2022 14:33, Chris Green wrote:
> Theo <theom+news@chiark.greenend.org.uk> wrote:
>> Chris Green <cl@isbd.net> wrote:
>>> https://www.cef.co.uk/catalogue/products/1781553-45a-single-phase-kwh-meter-din-rail-mounting-with-lcd-display-single-module
>>
>>>
>>> However I now have another question, how are these wired vis-a-vis the
>>> CU's bus? Obviously I need to connect the meter in series with the
>>> existing MCB supplying the circuit I want to measure. To do this
>>> easily without major modifications to the bus-bar or other things in
>>> the CU I'd need one of these meters to have both in and out
>>> connections at the top rather than connecting to the bus-bar at the
>>> bottom.
>>
>> On the above (a DDS353) the live in and live out are on the top, and neutral
>> at the bottom. On my DDM18SD it's live in at the top, live out at the
>> bottom, neutral in (and pulse/modbus) via a second level terminal. Either
>> way would suit, as long as you have a busbar-free space at the bottom.
>>
> But I don't have a busbar-free space, that's the whole point. The MCB
> whose power I want to monitor is in the middle of a 20-way CU with no
> spaces at either end. The spare spaces are in the middle.

Can you not unclip each MCB to one side of the spares, in turn, and move
them over two spaces, so that you end up with two spaces at the end?

>> However you might want to consider whether the meter is before the MCB or
>> after it. After the MCB means the MCB protects in case of a fault in the
>> meter, but before means the meter stays powered when the MCB is turned off.
>> In my case I go MCB -> meter -> contactor, so the load is controlled by the
>> contactor but the meter stays powered if the load is off (which it will be,
>> most of the time).
>>
> Does it lose its readings if it's powered off then?

I would expect that they either have internal power backup or (more
likely) write to EEPROM to retain information on power loss - indeed
they cannot lose the information or they'd not be MID certified - and it
is unlikely that non-certified ones lose readings either.

SteveW <steve@walker-family.me.uk> wrote:
> On 31/10/2022 14:33, Chris Green wrote:
> > Theo <theom+news@chiark.greenend.org.uk> wrote:
> >> Chris Green <cl@isbd.net> wrote:
> >>> https://www.cef.co.uk/catalogue/products/1781553-45a-single-phase-kwh-meter-din-rail-mounting-with-lcd-display-single-module
>
> >>
> >>>
> >>> However I now have another question, how are these wired vis-a-vis the
> >>> CU's bus? Obviously I need to connect the meter in series with the
> >>> existing MCB supplying the circuit I want to measure. To do this
> >>> easily without major modifications to the bus-bar or other things in
> >>> the CU I'd need one of these meters to have both in and out
> >>> connections at the top rather than connecting to the bus-bar at the
> >>> bottom.
> >>
> >> On the above (a DDS353) the live in and live out are on the top, and neutral
> >> at the bottom. On my DDM18SD it's live in at the top, live out at the
> >> bottom, neutral in (and pulse/modbus) via a second level terminal. Either
> >> way would suit, as long as you have a busbar-free space at the bottom.
> >>
> > But I don't have a busbar-free space, that's the whole point. The MCB
> > whose power I want to monitor is in the middle of a 20-way CU with no
> > spaces at either end. The spare spaces are in the middle.
>
> Can you not unclip each MCB to one side of the spares, in turn, and move
> them over two spaces, so that you end up with two spaces at the end?
>
Possibly, but it does rather spoil the nice, consistent set-up of the
CU. Maybe I should simply get a small (2,3,4 position) CU and install
the meter there. That wouldn't be too difficult and would leave the
main CU undisturbed.

> >> However you might want to consider whether the meter is before the MCB or
> >> after it. After the MCB means the MCB protects in case of a fault in the
> >> meter, but before means the meter stays powered when the MCB is turned off.
> >> In my case I go MCB -> meter -> contactor, so the load is controlled by the
> >> contactor but the meter stays powered if the load is off (which it will be,
> >> most of the time).
> >>
> > Does it lose its readings if it's powered off then?
>
> I would expect that they either have internal power backup or (more
> likely) write to EEPROM to retain information on power loss - indeed
> they cannot lose the information or they'd not be MID certified - and it
> is unlikely that non-certified ones lose readings either.
>
Yes, OK, that would appear to be the case so it's not an issue.

--
Chris Green
·