3-phase 208 V system in Saudi Arabia

Taking all 3 recent posts together…

@Abhishek_Singh said in the other thread that his system voltage was 127 V line-neutral, 220 V line-line, so I was originally answering that question. If you say your supply is 120 V line-neutral, 208 V line-line, then clearly you have a different system voltage and you need to design your set-up for that.

No. I’m in the UK, so I can’t check! I can only go by published information and what you on the ground tell me.


Yes, with the attendant caveats (see the comments in the sketch). As you’ve potentially got 150 A per phase, it would be a good idea to check (a) the maximum realistic load on each phase and (b) the cable diameter, to make sure you get the right CTs. (The shop CT can only accept a 25 mm2 cable - look at the “EmonTx in N.America” page for a whole list of larger current and aperture CTs.)
The default calibration in the sketch will clearly be wrong.

Ye Gods! That means that a “neutral”-earth fault in the appliance hasn’t got a fuse to blow in the plug!

It is a normal household with the main load being the HVAC with 60A 3 phase circuit breakers (CB) for the heating and 50A 3 phase for the condensing unit. The rest of the circuits are 20A CBs with the main load being washing machine and fridge. So the CTs should work. I measured the diameter of the feeder to be 13mm, so hope that the manufacturing tolerances allow it to be installed. If the CTs fit physically at their limit are there other precautions required to handle a higher current than 100A? I am trying to save the expensive shipping costs to Saudi Arabia.

You must not force the CT onto the cable. The core material is ferrite and it is very brittle, so any pressure is likely to fracture it. I’ve just measured one at 12.8 mm, so if your 13 mm is exact, it’s a no-go. I cannot advise shaving the cable sheath down, even by 0.15 mm each side.

I see you’ve listed the sub-circuit ratings, but my question was “the maximum realistic load on each phase”. That will (should) be significantly lower than the total rated current.
Above 100 A, the core will saturate and accuracy will suffer - see the report in Resources > Building Blocks. And the ADC input might well be stressed unless you add a parallel burden resistor to lower the voltage.

Have just installed the CTs. They just fit and can be moved slightly up and down the cables. Without modifications to the cable or CTs :smile: Thanks to the OpenEnergyMonitioring Team.

As the load within the house is not really balanced as on a three phase machine, just distributed over the three phases, do I actually require the 3 phase sketch or just the single phase sketch and measure the power over each of the phases?

You can have real or apparent power on phase 1, but you can have only apparent power on phases 2 & 3 if you use the standard (single-phase) sketch. Real power will be correct for phase 1, but wrong by a factor of -0.5 for phases 2 & 3.

The 3-phase sketch assumes the phase voltages are reasonably well balanced, which will be the case if your supply has a sufficiently high fault level. The loads need not be balanced. If the voltages are not balanced, then there will inevitably be errors in the power calculations for lines 2 & 3.

If everything was always accurately balanced, you would only need to measure one phase, then multiply by three!

I have changed the config to reflect 110V
calibration = 110V # (UK/EU: 230V, US: 110V)

but still see a Vrms of around 250V in the inputs.
I have the 3 phase sketch set-up.
Why isn’t the Vrms showing approx. 110V?

[This comment and the following 6 were originally posted under “emonPi Use in USA” - hence the confusion.]

Are you using a USA plug AC-AC adapter plugged into the emonPi?

Are you running the three-phase sketch on the emonPi or an emonTx?

Are you sure you have the 3-phase sketch? You cannot sensibly use the 3-phase sketch in an emonPi, as it has only 2 current inputs. In any case, that line does not appear in the 3-phase sketch. The nominal calibration coefficient for the emonTx with the ‘shop’ a.c. adapter (Ideal Power 77DA-10-09 (US Plug type)) is 130 here.

Yes this is what I was eluding to! I think there could be an emonTx involved, is this correct @Soren? The line calibration = 110V is from emonhub.conf and is used to set the emonPi USA calibration

Note he’s in Saudi Arabia, so misleading to hang onto this thread. They do have 3-Φ there, which is why I’m reasonably sure he’s going to have an emonTx somewhere. But it looks as if he doesn’t realise that emonHub can’t calibrate his emonTx.

Yes it is for me in Saudi Arabia where we have a 3 Phase 110V system, based on the US system, but moving towards a 230V system.
I am running 3 Phase sketch on the emonTx (setup when ordered) connected wirelessly to the EmonPi running the Emoncms. The US Plug AC-AC adapter is plugged into the emonTX. The socket that the AC-AC adapter is plugged into has a voltage of 122V phase to neutral. To add confusion the EmonPi is running on 208V (as mentioned in the Saudi forum entry) as the country is converting to 230V.
Which forum should I continue to post in? As this solution would also apply to the US system?

“But it looks as if he doesn’t realise that emonHub can’t calibrate his emonTx.”
That seems to be the problem. How can it change the emonTX setting?
Or should the Emoncms be adjusted?

You might be able to get away with using “scales = …” in emonHub to change the voltage, but you will need to apply the same (or slightly different if the currents are not calibrated accurately) factor to the powers also. The voltage from the emonTx needs to be multiplied by 122/230 (or whatever the actual numbers are when you measure them).
But the 3-phase sketch is very sensitive to errors in your CTs as well as errors in your a.c. adapter, so for best accuracy it would be best to calibrate the sketch according to the specific instructions in the comments. The general warnings and procedure is on the Calibration page under Resources > Building Blocks.

(It’s confusing referring to this as a U.S. system because the U.S. uses a split (2-phase) system rather than 3.)

Actually a single phase, split into two legs that are, as you said on the old forum, mirror images of each other

Yes, exactly, but there are those who consider it to be 2-phase with the phases 180° apart. Hence (2-phase) in brackets.

like a balanced feeder.

Tossing this into the mix, should raise the confusion factor a bit.

and this, even more…

Trust you Usians to come up with something weird like that. What happens if somebody on a supply like that asks for a smart meter? :smiling_imp:

Since it’s only a few buildings in each of the two cities, we’re probably not talking about a large number of electrical utility customers. I’d say the chances of any of them wnting a smart meter is quite low. Even if they did, uness their energy supplier can accomodate them, they’re simply out of luck.

Here is the background info on the voltage conversion, which will take place over the next 25 or so years. Smart meters will be installed here with 12 million forecasted by 2030.

A big job. For your emon system, it will probably mean only replacing the a.c. adapters and checking the calibration. Of course, the UK has traditionally had a 240 V supply whereas the European standard is 230 V. That’s been dealt with by changing the tolerance in the specification!