Energy metering of small restaurant with / without Elster A1140 meter


a friend of min runs a small restaurant and asked me to monitor his energy consumption in detail. 

The restaurant has an Elster A1140 3phase electricity meters. (Attached you can find a picture of the meter and the distribution board)

What do you think is the easiest / most accurate / cheapest method of monitoring the energy consumption?

Those are the options that I came up with:

1)  emonTx Arduino Shield V2 SMT and 3 x CT

- Though the meter is 3phase, there are no 3phase appliances and each phase is used separately. I would connect the CTs to the standart 230V wires that leave the distribution board. However the live and neutral are in insulated together (see attached image). Can you put the CT around both live and neutral to work? 

2) Pulse counting from Elster A1140 and photodiode / TSL261R 

- The electricity meter emits a pulse for every Wh consumed. However as it is a restaurant it can consume up to 12kW. That would mean ca. 3 pulses per second. 

3) Optical communication via IEC 62056-21

- Apparently the protocol that Elster uses is open source. And the optical sensor that fit onto the optical port are expensive. 


3) seems expensive, so I will probably chosse between 1) and 2). Question is now which one is more accurate?

Thanks a lot in advance,




Lionel's picture

Re: Energy metering of small restaurant with / without Elster A1140 meter


I think the answer will depend on what you are trying to achieve. If you wish to double check the accuracy of the existing meter, then reading its pulses will be a waste of time.

Option 1 will give you the most flexibility. It may be more expensive than 2, but it will give you the ability to graph and log the individual phase currents.  Don't forget you have to still add the cost of an Arduino and Raspberry Pi.

I don't know anything about what available for the Elster, but given what I've learnt off this site, my recommendation is bite the bullet and go with 1. There is plenty of help and assistance available if you get stuck.

ONLY ONE wire must pass through the CT. If you have both, the current going to and fro will cancel each other out and you wont read anything.

Regards, Lionel

Robert Wall's picture

Re: Energy metering of small restaurant with / without Elster A1140 meter

If you want to measure the total consumption (only - not distinguish between different loads) then by definition the supplier's meter is accurate! Pulse counting or reading the optical port will (only) do automatically what could be done by reading the meter manually.

What do you want to do with the data? You have not mentioned recording or analysing it. You could send the data to web-based of course), or you could run the same software on a Raspberry Pi (or any other web server) locally. The recommended method is to use a RPi for both these options. For, it needs an Internet connection. Normally, the RPi gets its data by radio from your Arduino Shield or an emonTx V3. That means the RPi doesn't have to be next to the meter, but the Arduino or emonTx does, and needs a mains supply to run. The emonTx V3 can get its power from the AC adapter. The Arduino needs a separate 5 V supply as well as the ac adapter, which is in this case only for voltage measurement.

If you go for the emonTx/Shield with CTs, and you're measuring total consumption, you could put the 3 cts either on the incomers (3 browns probably labelled L1, L2, L3) or on the left-most 3 greys going in to the top of the consumer unit.

(BTW, that length of twin&earth is illegal - it should be clipped back! - so that I can't be accidentally caught and damaged.)

lorenz_g's picture

Re: Energy metering of small restaurant with / without Elster A1140 meter

Hi Lionel,

thanks a lot for that answer. 

I don't want to double check the accuracy of the meter. I would just like to record the consumption profile of the restaurant throughout one week. 

For Option 1, my problem is that I do not have any single wires that I could clip the CT around. Unless I use the ones that connect the meter and the distribution box. Do you think the CT (from open energy monitor) would fit around them?



lorenz_g's picture

Re: Energy metering of small restaurant with / without Elster A1140 meter

Hi Robert, 

thanks for that. 

Ideally I would like to track the consumption of individual devices, but as a start it would be enough to create a load profile for one week. And from knowing which devices are running when I can manually determine how much each device is using. 

I want to record and plot the data. I will use a 3G dongle to connect to the raspberry pi and then we might run the the data storage and the plotting on Heroku. 

Do you think the 3 cts (that openenergy monitor sells) would fit around the 3 greys going to the top of the consumer unit? In the datasheet is says that the max diameter is 15mm. 

Thank for the advice with the twin&earth cable. I will let my friend know. 




calypso_rae's picture

Re: Energy metering of small restaurant with / without Elster A1140 meter

Lorenz, if you want to measure the power consumption on each phase accurately, you will need to monitor the voltage and the current on each one.  To monitor the currents, a CT can go around each of the incomers.   To monitor the voltages, some means of accessing each of the phases will need to be provided.

I've just developed a 3-phase PCB which could do this for you.  It has its own power supply on board and can transmit the resulting power and voltage data by RF.   This data could then be received by a standard emonBase unit and the data processed within emonCMS - all of which could become expensive. 

As far as I'm aware, there aren't any other Arduino-type platforms which are equipped to measure voltage and current on three phases.  For your needs, however, it may be that a simpler approach will suffice which could provide you with a more cost-effective solution.

For monitoring only, my 3-phase PCB could be supplied in a smaller box (approx 190 x 160 mm) as shown here.  If you are interested in this option, please send me a PM. 


Robert Wall's picture

Re: Energy metering of small restaurant with / without Elster A1140 meter

The YHDC ct will fit on a 25 mm2 meter tail. You need to check the ct data sheet and measure your cables to be certain. You might struggle to get them all on the load side of the meter, but there's no reason why you cannot split them with one or two on the supply side. OK the purists will say you're then measuring the energy consumed by the meter as well, but at around 2 VA I defy anyone to prove it when measuring 100 A.

Robin's 3-phase board will need a low power protected feed of the three phase voltages to work properly (that can be 3 spare 5 A MCB's if available). This will give the most accurate power readings. If you use the emonTx V3 (or a Shield), both can measure only one phase voltage, but you can fudge it in software and by assuming the three phase voltages are identical, get a reasonably good approximation for the three phase powers. You'll need a standard socket for the ac adapter.
Or if you're not really interested in accuracy at this stage, you can measure current only, assume the voltage and estimate apparent power based on that assumption. In which case, your emonTx can be battery-powered for the week and you won't need mains power to it.

However, if you want long-term to measure individual feeds, you need to think of that now and count up how many channels you will need. It may be that you end up with 3 emonTx's, giving you 4 channels per phase (all feeding into the one RPi), and then you'd need 3 sockets, one per phase.

EnergyRnR's picture

Re: Energy metering of small restaurant with / without Elster A1140 meter

Robin;  that genuinely is a great piece of work! Really nice. I'm going to read through a bit more - I haven't been keeping up to date with it lately, but I'm sure you'll be busy shipping units.

Lorenz : There are 2 main ways to kill the costs for the restaurant (i) spend less and (ii) use less. Ask them whether they've critically reviewed their tariff structure and costs for ALL utilities (forgive me if this is obvious, but many people forget this part) and then start off with an emontx installation so you can help the owner to get some quick wins.  The Carbon Trust says that "In some kitchens, as little as 40% of the energy consumed is used for the preparation and storage of food"

So, the designs here will help you ask the questions [ e.g. why is our base load 'x' kW?, and why is that chiller 'kicking in' every 'y' minutes?] ; you need to help the restaurant owner answer these q's asap. Don't forget to use the events module to help the restaurant own 'keep' the savings. No point in cutting the demand only to see it go back up next year.

There are lots of actions that can be taken-Feel free to pm me. I've no agenda here but it's useful to talk with people and share what we learn. I have an urgency about reducing waste energy ( just ask my family :-) and running a restaurant isn't easy! 


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