Two dimmers died yesterday

[RohitNz 7]

Two dimmers died yesterday.  

 

1. The one in the pantry stopped responding to the switch as well as the HC.  I have had many dimmers fail, so replaced it with a switch.  I havent checked if I can factory reset the dimmer and reuse it.
2. The following one was responding erratically, not turning off from the switch, but working from the HC.  On opening I found it had come apart and had a hole in it.  I assume its a varistor of some sort for over-voltage protection.  Just posting it in case someone is interested.

 

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Edited August 10, 2023 by RohitNz

[SmartHomeEddy 865]

wow, some kind of meltdown 😳

[Martin_N 146]

Heh, ... "Burnout syndrome".
Anyway, well that did not burn your house.
Just out of lifting. What was the load (bulbs, dimmable voltage source, ...) was used on the outputs?

eM.

 

[RohitNz 7]

4 hours ago, Martin_N said:

Heh, ... "Burnout syndrome".
Anyway, well that did not burn your house.
Just out of lifting. What was the load (bulbs, dimmable voltage source, ...) was used on the outputs?

eM.

 

This time I think it was over-voltage. It was powering two led pendants together with a Fibaro bypass.

• The solar install guys were here the day before to install a second set of panels and battery. 
• They were trying to minimise power down time. 
• They were tracing cables by wiggling them. 
• According to them, one came off and shorted the DIN rail. 
• In retrospect, the DIN rails are not wired to anything, so there should have been no short.
• Then they asked to turn the power off
• When they left at the end of the day, I discovered the kitchen rangehood was not working.  I was busy trying to get that working.  The wife makes it the most important item.  I failed.
• Then I noticed the pantry dimmer was not working, not responding to switch or HC.  Replaced it with a double switch (I have been doing that progressively- see problems later)
• This morning, took apart the range hood discovered that  a varistor on the control board had fried itself and made the fuse vaporise.  Bad design if the whole fuse just vanishes.
• Then I went to the the above device and found a hole.
• There is still one more that is damaged, tomorrows task. (Its a bit time consuming to figure out how many others are fried, with 137 devices in the system)
• And how many are walking wounded ? (Do they still use this term ?  I first heard it in a seminar on dangers of static electricity, in early 1980s)
• We have 3 phase, so I suspect that the one of the phases was shorted to another, potentially providing 400V to all or selected devices (I am unclear as to how)

Issue with Dimmers

• I have a solar power system for backup that backs up one phase.
• When the grid is down, the diesel generator starts automatically for the other two phases.
• When the solar battery is exhausted, it switches to the generator.
• All dimmers (25+, except one) start blinking rapidly when on solar or generator. It drives everyone nuts. I think they are raising an alarm or re-calibrating.
• The only thing I found was that the grid is 220V, and the solar and generator (both sine wave) are 240V. 
• And every thing else works fine, including LEDs on fibaro switches.
• So, I have been slowly replacing the dimmers with switches.  In retrospect, we didn't need the dimmers anywhere except the bedroom.  Still got 2 more to go.
• Also 18 of the led fixtures have died, all were on dimmers.  I suspect the blinking used up their limited switching life.  About 20,000 according to this article that I wrote for an eco website. 

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[Martin_N 146]

1 hour ago, RohitNz said:

We have 3 phase, so I suspect that the one of the phases was shorted to another, potentially providing 400V to all or selected devices (I am unclear as to how)

Yes,... that is one option, but I think some safeguards would work.
It is far more likely that the neutral wire N (center wire) interrupted.
It may then happen that the circuit closes through one device on one phase and continues through another device to the next phase, instead of both devices of each phase continuing to the neutral conductor N.
Burning varistors may have saved you other, more expensive appliances.
You really get 400V phase to phase (inter-phases)... I felt it on my hands too

Before that varistor worked, the triac must have enjoyed itself.
The varistor can non-destructively save short-term peaks (us/ms) of overvoltages and inrush currents. Unfortunately, in your case, it looks like this state was of longer duration (on the order of whole seconds).

 

 

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[Fabir 65]

On 8/10/2023 at 1:56 PM, RohitNz said:

 

• We have 3 phase, so I suspect that the one of the phases was shorted to another, potentially providing 400V to all or selected devices (I am unclear as to how)

 

@RohitNz

 

According to your description, you have a 3 Phase + Neutral system, this is called TN-S system, 3x400 volt between each of the three phases and 230 volt from every phase to the neutral N. 

If one of phases was shorted to another phase by your solar install guys, the MCB Breaker in front of this electrical circuit, would have detected that and shot down the voltage immediately. Nothing bad would have happened.

 

In this case, as @Martin_N explained, your Solar install guys have interrupted the N Neutral wire without turning off the MCB breaker, ahead of that.

 

In a perfect world, when every one of the 3 phases had exactly the same load, there's no current flowing trough the neutral wire, nothing bad would happen.

But in a real house, this is almost never the case. You will have different loads on every phase, therefore, current is flowing back trough the neutral wire to main breaker panel and than out to the utility transformer. In the main breaker panel, all neutral wires are connected together.

 

If the neutral N wire is disconnected from the utility line neutral wire, in an active 3 phase + N circuit and also 230 volt devices connected, this can be catastrophic.

This issue is well known among electricians.

For instance, current is flowing from phase 1 trough your fibaro dimmer trough the now floating neutral wire back to the neutral bus bar in the main breaker panel than trough another neutral wire to another fibaro dimmer. Assuming this second dimmer is connected to phase 2. Remember, the voltage between the two phases is 400 volt.

Depending on the impedance resulting of that, between the 3 phases and the now floating neutral wire. The following happens.

 

The voltage between phase 1 and the neutral wire can become up to 400 volt instead of 230 volt. In the same second the voltage between phase 2 and the neutral wire can become only 80 volt instead of 230 volt. The voltage between phase 3 and the neutral N wire can become 160 volt and so on.

This error can destroy a lot of 230 volt devices in a short time.

 

A circuit MCB Breaker can not detect this issue in the time needed, to protect the devices.

If you have an SPD over voltage surge arrester in the main MCB breaker box of the house, this wouldn't help either. This device can eliminate over voltage coming from the outside line into your house.

When you want to work on an 3 phase electrical circuit that has a neutral and connected 230 volt devices, it is mandatory to switch off the MCB Breaker ahead of disconnecting the neutral wire from the supply neutral N wire. When you want to activate this circuit again, it is mandatory, to connect the neutral N wire to the supply wire, ahead of switching on the MCB breaker.

 

RCD protective devices with 3 phase and N Neutral switching, do the same automatically, as it is mandatory for them to do so.

 

I recommend you to do the following:

Don't touch anything.

Call the solar company and tell them, you need a recall from their liability insurance representative.

When you have the goo from the insurance, call a certified electrician, to check all of your electrical circuits, connections and devices in the house about this issue.

This can become an expensive case. Some devices maybe still working, but will fail to early.

Replace the defective devices. Replace any device that looks suspicious.

Edited August 11, 2023 by Fabir

[Martin_N 146]

Well done @Fabir excellently explained. I didn't want to burden my colleagues with such an explanation, but it's great that you broke it down.

At least @RohitNz  can solve with the incident matter-of-factly.

 

 

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RCD protective devices with 3 phase and N Neutral switching, do the same automatically, as it is mandatory for them to do so.

Regarding the RCD, I would only say that I still encounter old type AC installations. This is the type that is only intended for AC residual currents. Due to the fact that in installations there are usually a lot of switched-mode sources, various dimmers, drivers, washing machines, dishwashers, etc., which also generate a residual pulsating DC component, it is necessary to use types A (or F, B).
And it is precisely photovoltaics that can generate higher harmonic, direct currents,.. protections of type B (all types of currents) are explicitly offered here.

Therefore, if there is an AC type RCD in the object, it is the direct current components in the network that can "turn off" the effective detection of residual currents in the circuit.

[Fabir 65]

@Martin_NThanks for the additional Infos about RCD Types. A Type B RCD 30mA device, is mandatory for PV Solar Systems in Switzerland.

 

For any type of RCD, in order to trip and shut down the connected electrical circuit, a part of the current must flow outside of the RCD device. Regarding the case of@RohitNz it is possible that the over voltage, or the under voltage, as described above, the flowing current in the cuircut had caused a device to become defective. After that, trough this defect, some current could flow outside of the RCD and so causing the RCD to trip. But in this case, the damage would already have occured.