odd problem with heating

wexfordman2

Hi,

This is going to be a strange one, I'm throwing it out with the hope that someone can help narrow it down.

Basically, I live in east cork and have a system in my house which controls the lighting and heating. It is done via a system of smart relays mounted in the fuse board, and the relays have a communications bus wired to each other to send commands to and from different devices and a main controller.

My problem is that, over the last few weeks I've had an unusual problem in that the operation of the oil heating knocks out the smart system. It only happens during certain times of day, to be specific, between approx 5pm and 9am, and works perfectly outside of these hours.

My first thoughts were a bug in the controller and have spent a few weeks trying to identify it, but I can pretty much rule this out now. I have alsa replaced the relay controlling the heating and this has made no difference.

I have now got to the point where I have the heating working in complete isolation front eh overall smart system, in that the relay is simply a manuaky operated relay and all comms and wiring from it to the smart system have been unplugged. The odd thing is, it still knocks out the smart system when it is powered up during the problem hours.

The only link between the hesting relay and the entire system is a 12v power supply which powered the relay.

When doing some testing On the 12v supply to see was it being interrupted or reduced, all looked fine.

So, the only possible conclusion I can come to now, is that the load of the heater (a simple oil burner) is some how interfering with the communications channel of the smart system. I can't explain the near regularity of the problem, which only occurs between 5pm and 9am, as hard as I try.

One thing i did notice, and aplogies for the long winded post, this is the main thing I wanted to clear up, is that when checking a few things yesterday, I went to measure the voltage between the relay and neutral bus bar (was meaning to measure to the earth too check for mains presence but went to neutral by mistake) and when I did so, the mcb tripped.

Now I also noticed that I had mistakenly had my meter measuring resistance instead of voltage, but I thought The mcb tripping was unusual ?

I checked to see if the same thing happened in other relays and it did not, it just seemed to happen on the heating relay.


Can anyone explain the last bit from an electrical perspective ?

Would really appreciate an opinion on this, I'm quite competent on the smart control aspect of this system, installed it myself with the assistance of an electrician, and it's been working fine for fifteen years nearly, but this has me flunoxed !!

frankmul

Do you have outside lights on one of the relays, 5pm to 9am sounds like the running time of the outside light? Could it be that one of the lighting relays is causing the problem?

wexfordman2

frankmul wrote: »

Do you have outside lights on one of the relays, 5pm to 9am sounds like the running time of the outside light? Could it be that one of the lighting relays is causing the problem?

Hi,

There are absolutely no timers on my system outside of the controller. It's very weird that the timing is so regular though, but as much as I can prove, there is no timer or schedule doing this.

swampgas

That's weird! Does the smart system get knocked out simply by having power to the heater, or is it when the burner kicks in, or when the water pump starts?

wexfordman2

swampgas wrote: »

That's weird! Does the smart system get knocked out simply by having power to the heater, or is it when the burner kicks in, or when the water pump starts?

That's something I'm struggling to understand. It appears that even when there is no ac going into the relay, it still knocks the system out when it is activated

The Nutty M

My thoughts would be along the same lines as Frankmuls, outside lighting. An inherited fault from street lighting maybe, some outside influence anyways seeing as you have ruled out everything within the house. The time the fault appears and disappears is too concise to be coincidence.

Is the 12v supply earthed? You may be getting a voltage spike breaking the coil (inductor) that sends transients down the earth tripping the MCB. You could try a double insulated 12v supply or a battery.
It's possible that if you are running other transformers on the same MCB that you are overshooting your allocated 30mA.
Better passive filtering can help if this is the issue.

whizbang

I suspect the heating system wiring is the longest run of wiring, probably double that, if the house thermostats are included, and it basically the most (electrically) noisy. Maybe this is why its the heating thats causing the fault.

Is the 12v supply earthed? You may be getting a voltage spike breaking the coil (inductor) that sends transients

Protection diodes on all the relays ? - I would fit suppressors to the AC side of the relays also.

Earth one side of the 12v Output. -Is it a switchmode power supply? What power supply runs the smart system, or is it the same one?

Are there temperature sensors connected to the smart system, -make sure they are electrically isolated from the pipework.

KK4SAM

I would suspect the the heating control relay, has someone inserted a relay with the wrong coil voltage thus bringing down the intelligent controller 12 Volt rail when its called.