Low voltage and phase failure alerts, 3 phase

Hi all

Apart from the load shedding, it seams we are getting a lot of voltage fluctuations and phase drop outs on the farm lines. I want to put protection on my main incoming 3 phase DB, but I also want to be alerted of this without having to walk out to the main power box.

I found this protection device 12-01035 Trip-Connect 3P-V2 | Clearline Store
It has all the protection I want, but no smarts, so no way to communicate over RS485 or the internet etc.

Any idea how I would be able to get communication out of it or maybe suggestions for a alternative product?

Meters like the Carlo Gavazzi’s have the coms side sorted, but they again lack the protection, they are only meters.

Have a look at the big gun’s offerings… Country Selector | Schneider Electric Global

That Trip-Connect only has a 5A relay…

This one is 65A @ R12k, but think carefully if you want to drop the entire supply due to a phase loss.

You might need to forgo the full incomer protection due to cost, and just put a Surge Protector in: 12-00418 for DB Boards (3-Phase) | Clearline Store ← This one has remote signalling contacts, presumably for “faulty”.

Add a fancier Carlo afterwards, which you could then use for phase loss detection, imbalance, etc. Or three Sonoffs, 1 per phase if you only care about loss.

Then put the smaller protection devices closer to your 3-phase appliances.

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Ja I don’t want something which will drop the entire supply because of a missing phase, I rather want to be notified of it and then decide for myself how to handle the situation, or automate it in future using HA.

I anyway plan to put a Carlo EM540 in that DB if stock becomes available one day, so I’ll do some further research to see what the best option will be, maybe surge protection with a Carlo for notifications will be the way to go.

I already have surge and over / under voltage protection on some of the downstream single phase DB’s and will do the others as well in the new year, so the single phase side is pretty much sorted.

Yesterday afternoon a buurman who is on a different power line from us for example had 276v coming in to his single phase DB in the house for at least a hour while his 3 phases was shooting up and down like a pinball machine.

Years ago, I started with a relay that was apparently specialized as a 3ph submersible borehole pump protection.
It had no settings barring that you initially pressed a button on it while the pump did a healthy start.
It then had a “fingerprint” of what a healthy start was and supposedly provided a huge range of pump protection based on this.
Including loss of phase, over/under-voltage and even borehole dry protection.

Long story short, I lost pumps using this relay, and I lost more pumps after replacing this relay several times.
I think the clever electronics themselves are sometimes not up to the circumstances they are supposed to protect against.
What did I do?
First, I use 1ph motors where possible now, and where not possible, I use my own loss of phase protection. (Non-electronic).
I have used this on a pump, two large air conditioning units and an industrial dishwasher for nearly a decade without issues.

A simple circuit:
2 X 220Vac din rail mount relays and a 3 ph contactor.
Relay 1 is pulled in by L1, Relay 2 is pulled in L2, L3 goes through Relay1 and Relay2 contacts in series and then pulls in the Contactor. The contactor switches all phases to the motor.
This ensures the loss of any phase and the contactor drops out.

It isn’t necessary, but the relays I use have a LED built-in which is a nice visual touch.
No smarts are involved, and it is a robust solution.

But, if a remote alarm really is your bag:

The relays and the contactor aux. contact pairs can the wired to operate an alarm using a variation of this circuit:
(S1 & S2, S3 & S4, S5 & S6 are NO & NC aux. contact pairs of the respective relays/contactor).

This will only alarm when necessary, not when all 3phs are OFF.

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Fair enough, but a regular phase failure relay will provide the same protection IMHO. Phase Failure Phase Reversal/Sequence Relay - YouTube

One of the relays referenced in your clip is an electro.
Which happens to be the same make as the relay I referenced that I don’t trust to work reliably.

Assuming these simple protection devices work they do make for a simpler board. When you do a fancy wiring job to do the same thing it gets complicated. And for those who come after you they also need to understand the circuit. (A schematic/wiring diagram would then be essential but I haven’t seen many of those recently)
On the same topic I have been unimpressed with the standard thermal overloads that are connected to motor starters. Instead of actually measuring the temperature of the motor windings one has the thermal equivalent installed. My gut tells me this is better than nothing but what does it take to actually have the temperature sensors installed in the motor windings when it’s manufactured?

I am trying to be as transparent as possible and state my default position was to trust the device was fit for purpose, and it wasn’t.

If my circuit baffles an electrician for longer than 3-5 min, get a real electrician.


I think one needs to identify if it’s one particular product that failed or that the company itself is suspect…
Having been in the automation business I learned to respect Siemens. Not all their products are great (and they have some real dogs IMHO) but they tick a lot of the boxes overall.

“I think one needs to identify if it’s one particular product that failed or that the company itself is suspect…”
I chose to identify a reliable alternative, me.