Is it possible to use these meters to measure power usage without a contract?
I have collected a couple of these meters in my time and would like to use them in a stand alone application.
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The short answer is probably no.
STS uses symmetric crypto, that is, a secret key is shared between the vendor, and the meter. If you know this key (and this key is known by your supplier, indexed by the meter serial number), you can vend tokens.
You don’t know this key, and it is extremely unlikely anyone is going to tell you what it is.
What you can do, technically, but probably not practically, is rekey the meter with your own keys, and then you can vend for it. But to do that, the current vendor has to give you tokens for loading the new key.
Criminal syndicates have, through inside access, managed to do such things in the past, but I suspect it’s going to be highly suspicious and nigh impossible to do.
It’s going to be cheaper to chuck them in the trash. Or use the case and make your own thing.
City Of Johannesburg are pretty sure that this is going on right now.
The last year or so they have done a lot of conversions to pre-paid. Now they say that they are detecting a significant number of “non-vending” meters. Where “non-vending” means “not buying tokens from the City”.
So they suspect that bogus tokens are being sold. The number of non-vending meters is high, many are recent conversions, so either those folks by-passed their meters PDQ and/or somebody is selling bogus tokens.
Currently COJ are not accepting applications for conversion to pre-paid, and have suspended conversions until end November. All the technicians who would be doing installations are now doing follow ups and checking meters and the credit balance on the meter.
If it is as they suspect then the vendor key is compromised. They’ll crack down, but in the meantime the villains have made a bit of money.
They also think it is possible that some householders may not know that they are buying dodgy tokens.
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To combat this fraud one needs a simple procedure. I noticed that when CoCT installed the new pre-paid meter at my property it consisted of the unit inside the house with keypad but another smart unit was mounted in the distribution DB in the street.
These are accessed remotely over the power cables so no need to send a meter reader to site. This must be for fraud detection…
Yes, it’s possible but it depends on the type of meters you’ve got. Older or basic meters will usually work fine as standalone kWh meters; you can just wire them in and they’ll measure power flow.
If they’re smart meters, most need a supplier connection or activation, so they won’t record properly on their own.
Check the model numbers and voltage/current ratings before connecting. Post them here if you’re not sure someone can confirm if they’ll work standalone.
It is more for meter tampering. Can’t tamper with the thing if it is outside your reach. It’s a prepaid meter, so you already don’t have to send a meter reader.
I suspect they do have meters up in the box on the street that measures the total for a group of houses, and when the totals don’t tally with your prepaid sales (within some acceptable calibration difference), you can spend the manpower hunting down the culprit. Technically very doable.
When CoCT replaced my meter, they (or rather Elex Khanyisa) installed it in my home next to the distribution board. In fact the original feed cable is still accessible in the DB, and they simply extended it, and routed it out to the meter, and back into the DB. Not the most secure way, but then I am also not a criminal 
In new installs, you ideally place the meter such that the feed enters through the wall right into the meter enclosure, so that you cannot access it without removing the face of the meter (and activating the tamper condition).
The meters COJ install now work in this way. The interface unit inside the home requires a direct connection to the actual meter, via the power cables. The older one that I had used an RF connection.
But if you’ve bought a token from shady operator then the interface unit will quite happily send that token over the cable to the meter, and the meter will accept it.
With this new type of meter, the interface unit didn’t work if it was backed up by any sort of inverter, because that broke the direct connection it requires. I had a non-backed up socket installed to make life simple.
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Yes. In many parts of Johannesburg meters are actually inside the property. COJ proposed moving them to the top of the street poles, but there was lots of resistance. Not all of it knee jerk. In my street the meters are on the property, but there are additional breakers at the top of the pole so that COJ can cut supply to a non-paying house (or if they need to work on your meter). But these boxes are poor quality and the lid can usually be seen flapping around in the weather, if it hasn’t fallen off by now. So now they want to put meters in there?
It didn’t help that we had ward councillors telling us that now you would have to stand out in the street to reload your pre-paid meter.
I expect the proposal to relocate meters is going to be back on the agenda soon with the non-vending problems that COJ are reporting. This will rule out bridging of meters (unless you have a rather long ladder).
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That’s no different to your all-in-one meters. The “protocol” they use, namely STS, is the same. If you have an inside man that allows you to get a token to rekey the meter, or to vend tokens for it, having half of the meter outside in the street adds no extra security at all. It is really just to prevent meter tampering. And… probably… it is a tiny bit easier to install than having to make a space inside the cramped cupboard in the customer’s home…
I believe that was just because the inverter introduces filtering, or perhaps a bit of noise, causing the PLC (power line communications) to not reliably reach the other side. There are people without inverters who also struggle with this.
A bit more about all this STS stuff. In the crypto world we use these things called a hardware security module. It’s essentially a bit of memory inside a secure case, with tamper measures so that opening it destroys that memory, and enough bits and pieces so that the key never leaves the box: You send stuff in to get signed/encrypted/decrypted/verified, and the result comes out.
Usually the way you do this, is the master key, the one that controls the whole system, that is locked up in an HSM. Often also in a way that multiple people are needed to get access to it, it cannot be compromised by just one person. You use this, to sign other keys (which are considered a bit less critical), and these in turn signs/encrypts the stuff going to customers.
Usually, when someone’s SSL key is compromised on the internet (SSL is assymetric… but some stuff still applies), it is one of those lesser keys. The key gets revoked, and people stop using it.
So, in the South African context, where we suspect inside help in order to obtain such a key… we are talking about fairly advanced, fairly high level fraud. It is not your run of the mill stealing of a million by sending in a fake invoice kind of fraud.
COJ have been concerned about such goings on for a while now, but have recently got a lot more concerned as they supplying a lot but only getting paid a little. This follows an increase in conversions to prepaid, so they strongly suspect dodgy tokens.
But that they suspect means that there are multiple vendors of said tokens.
This is not unique to COJ either. For some years Gautrain have been warning riders to reload their cards only via the Gautrain app or at a station. They have had somebody or some gang selling bogus credits. They have a way to detect these, but it requires physically scanning your card.
Or they are just trying to scare folks, because if they could scan you card and determine that you loaded credits you didn’t buy from them, why isn’t that just built into the card readers at entrance points?
Where I live all the free standing homes have an enclosure built into an external wall that holds the meter and the main breaker. At my previous home we had an external box per block that held all the meters.
One is a pain for the City who want to read an inspect meters and protect against tampering. The other is a pain for the likes of me who like to monitor their meter and thus check that they are billed accurately.
Now I think about it, that box in the street was never locked.
In Cape Town, it is not uncommon to have the meter in broom closet under the stairs…
Given the complexity of the PAYG meters I’ll give it a miss. What inspired this question is the situation my trusty labourer has where he lives. Their shacks are supplied with power from a pre-paid meter. However there is only one meter for 4 shacks so they need to apportion the usage. Currently they simply divide the bill by the number of shacks.
So in the interest of fair cost of usage I’m volunteering to fit meters in each of the feeds. The consumers will have to agree on the recording date and calculation of units used but I think this will be a better system that the rough and ready system that they have currently.
unsolicited opinion from me. Admirable intention but if the people are so far happily co-existing with the costs/4 leave it be.
Also, I would be weary of touching any wiring in this setup for various legal/liability reasons.
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