Refrigerator Circuit Anomaly

Bill.Thomson · 2019-12-20T02:45:07.795Z

moojuiceuk:

There is one other possibility - a second resistance heater within the appliance

I think you’ve hit it, MJ.

Even though it ran for 14 hours, the OP said the compressor cycled normally. That would have kept
the inside temp near normal, yet explain the resistive load as well as the flaky “shutoff.” (bad stat)

Hmm, weirder yet…

The defrost heater, having a typical power rating of 350 W to 600 W,
Ref: Auto-defrost - Wikipedia

Typical power rating… Maybe he’s got one that has a defrost heater “on steroids.”

moojuiceuk · 2019-12-20T03:02:30.676Z

Resistance heater + compressor running together?

Bill.Thomson · 2019-12-20T03:11:21.238Z

The graph shows changes of 200-300 watts during the period in question. Looks quite plausible!

Robert.Wall · 2019-12-20T12:53:36.889Z

I’d go with that too. Seeing the cycling behind the “heater” load is what worried me about the locked-rotor theory. And the second heater also explains why the protection didn’t work - the load was expected (by the manufacturer if not by us) so it shouldn’t have worked.

benergie · 2019-12-20T14:22:53.710Z

Robert.Wall:

The extra energy is about 20 kWh, that’s several bathtubs of hot water, so if that went in heat, I reckon you’d know about it. But does the heat pump show a commensurate change in consumption?

Exactly, that is a lot of energy and, if it is real, then it ended up as heat somewhere. If it ended up inside the refrigerator then I think we would have lost all our food because there is no way that 100 watt compressor would have been able to remove the 1500 watts of heat as it was being delivered.

Robert.Wall:

Being really cynical, does “no other outlet inside or outside the house is fed from that circuit” mean exactly that, or could it mean “no other outlet inside or outside the house that I know of is fed from that circuit”

You are correct… there is no other outlet that I know of.

Robert.Wall:

I’ve been studying that last graph for a while and I’ve just noticed - it doesn’t add up. Either the separate inputs are drawn to different scales, or your inputs aren’t calibrated, because the heights of the individual lines (yellow, red & green) add up to more than the blue.

You are right again… I have a CT on each of the Mains (A & B) but I am only showing phase B because that’s the phase where the mystery load showed up. Since the heat pump is a balanced 240v load, I capture that with a single CT and double the value. If you take half of the Heat Pump Total, then it starts to add up. Let me know if there is a more straightforward way to configure my IoTaWatt to avoid confusion like that.

Bill.Thomson:

It sounds like the compressor was close to being in a locked rotor state, if not actually locked.

I wondered this myself but then I saw the power profile of the compressor sitting on top of the 1500 watt load. That leads me to believe that the compressor was behaving normally before, during, and after the 14-hour period.

Robert.Wall:

I think I’ve got to say that something like 15× the normal running current, sustained for 14 hours, means that there’s something desperately wrong with the protection on that fridge. Fortunately, for the sake of the contents If that’s really what might have happened - and it sounds as plausible as anything - I hope there’s nothing combustible near that compressor.

But it cured itself and has run for another 4+ months?

An electrical fault of some sort is my biggest concern. If the energy is going somewhere useful, that’s fine. If not, then there is potential for a fire and I want to know how and where.

moojuiceuk:

There is one other possibility - a second resistance heater within the appliance?

I think you are on to something. The one thing I keep coming back to is where did all that heat go? If it went inside the fridge, wouldn’t the compressor have had to run non-stop for a much longer time to remove that much heat?

Here is a screenshot showing the full week surrounding the event:

Refrigerator circuit full week1964×1108 247 KB

It just seems like the compressor cycling is relatively unaffected by the mystery load.

Robert.Wall · 2019-12-20T15:10:13.226Z

benergie:

Exactly, that is a lot of energy and, if it is real,

I think the chances that it’s not real are slim. If it isn’t real, explain how it got onto the main c.t and no other circuit? If it affected one circuit or all, then I’d say it is feasible that it’s a fault in the hardware or software, but not as it affected two with a physical link between them.

benergie:

then it ended up as heat somewhere.

Is there any evidence of the heat going into the house, is what I meant when referring to the heat pump - assuming it was cooling given the outside ambient? That still fits with a second heater - just that the heat was going outside the fridge rather than inside. That then raises the question: for what purpose? To evaporate condensation run-off? 20 kWh? ! ! ! No.

benergie:

If you take half of the Heat Pump Total, then it starts to add up.

Ah, I did wonder that. But given the nature of the anomaly, it was worth checking.

benergie:

Let me know if there is a more straightforward way to configure my IoTaWatt to avoid confusion like that.

There are very few of us here who know anything about that. Lemaire has his own forum.

Gwil · 2019-12-20T15:25:06.381Z

Robert.Wall:

the load was expected (by the manufacturer if not by us) so it shouldn’t have worked.

From the owners manual, which I think is for the correct product:

owners-manual.pdf (2.8 MB)

Source:

whirlpool.ca

Whirlpool® 30" Wide Top-Freezer Refrigerator with Flexi-Slide™ Bin...

Whirlpool Whirlpool® 30" Wide Top-Freezer Refrigerator with Flexi-Slide™ Bin - Monochromatic Stainless Steel (WRT318FZDM). Shop now.

It recommends a “15 or 20 A fused” supply. Wouldn’t 15A have been insufficient?

benergie · 2019-12-20T22:11:20.477Z

The plot thickens…

Gwil:

It recommends a “15 or 20 A fused” supply. Wouldn’t 15A have been insufficient?

15A breaker might not be sufficient if the fridge was designed to draw over 1500 watts. However, it would be sufficient if it only has a “normal” defrost heater.

I downloaded the wiring diagram which describes the two types of defrost cycle controllers. Mine behaves like the Electronic Timer defrost with ~400 watt defrosts showing up every day or two.
WRT318FZD Wiring Diagram.pdf (702.8 KB)

Robert.Wall:

Is there any evidence of the heat going into the house, is what I meant when referring to the heat pump - assuming it was cooling given the outside ambient? That still fits with a second heater - just that the heat was going outside the fridge rather than inside. That then raises the question: for what purpose? To evaporate condensation run-off? 20 kWh? ! ! ! No.

I understand now. And after looking further into my data, it doesn’t appear that the heat was even generated inside the house.

The week before this incident, I happened to measure the real-world efficiency of my AC with some new enthalpy probes I got for work. I measured my AC at a COP of 2.7 with an outdoor temperature of 93°F. That means my AC would have to use an additional 7.4 kWh of energy to remove the 20 kWh of heat added by the mystery load (20 kWh / 2.7). However, that extra energy does not show up on my AC system that day. My heat pump used 18.5 kWh for the whole day which is actually less than the summer average when normalized for outdoor temperature.

I took daily heat pump energy use for all of July and August and divided it by daily Cooling Degree Days (CDD - base 65°F). For those two months, my worst day was 2.63 kWh/CDD, my best day was 1.08 kWh/CDD, and my average was 1.47 kWh/CDD. August 4th was 1.22 kWh/CDD which is below average. Keep in mind that no one was home most of the day so internal gains were marginally less and the thermostat was set at 75°F rather than 74°F, but these are small differences. If I subtract the 7.4 kWh, that I would expect to see, from the 18.5 kWh used that day, I’m left with 11.1 kWh. When I divide that by the 15.2 CDD, I get 0.73 kWh/CDD, which is unrealistically lower than any other day that summer.

This leads me to believe that the mystery load must have been outside the house. It also makes me question again if it is real or not.

Robert.Wall:

I think the chances that it’s not real are slim. If it isn’t real, explain how it got onto the main c.t and no other circuit? If it affected one circuit or all, then I’d say it is feasible that it’s a fault in the hardware or software, but not as it affected two with a physical link between them.

I agree that the chances of measurement hardware or software fault are slim but the chances of a real load that large for that long are becoming increasingly slim as well! What gives?

Robert.Wall · 2019-12-20T23:25:27.660Z

Do you feel it’s worth heading over to The IoTaWatt forum and asking about the likelihood of a hardware or software fault there? I think I know what the response will be - it’s your call.

Am I correct to assume that all the c.t’s are in your load centre and the Iotawartt is also close by? How far apart are the two c.t’s in question (the B leg feeder and the fridge circuit)?

There’s nothing on the A leg that corresponds with the mystery load?

benergie:

This leads me to believe that the mystery load must have been outside the house.

Coming back to my wild theory about mystery wires: Do you know the actual route the cable takes from your load centre to the socket? and is it possible it’s been “interfered” with? I’m now trying to think of what sort of signal could be injected into that circuit, that would look like a 1.5 kW load to the iotawatt and not appear on any other c.t.

stephen · 2019-12-21T15:26:14.395Z

just a thought for you as to mysterious load-- do any of your wires exist in damp or wet location… I had a mysterious load issue a few years back. turns out it was trickle charge of 300w across a 120 volt wire in a damp location. when the area dried it disappeared and when it got damp it came back.( strung a new underground wire and it stopped) … you live in the UK so your wires voltage ~230V so you can carry a significant higher trickle load then what I would at 120V which might account for the unaccountable usage … and that long duration was just the length of time it took for that area to dry from heat dissipation of the trickle charge to stop – curious does UK electrical code not require individual fuse/breaker just for a the fridge

Robert.Wall · 2019-12-21T16:18:58.911Z

Stephen, it’s a 120 V US circuit. Benjamin has his Country of Residence as “United States”, and in the top post he specifically states it’s on the “B” leg of a 240 V split-phase supply, which I believe is your standard.

So in that case, you’re looking at a leakage current of around 11.6 A, representing a shunt resistance of about 10 Ω. It was a good thought, but I don’t think the numbers stack up.

stephen:

curious does UK electrical code not require individual fuse/breaker just for a the fridge

In the UK, for domestic premises and offices, it’s normal to have a “final ring sub-circuit” where an unlimited number of socket outlets are connected in a ring (serving not more than 100 m² of floor area), the ring starting and ending at the “consumer unit”, where it’s protected by a 32 A MCB. Each plug contains a fuse rated at not more than 13 A. It’s usual for the whole house to be protected by a 30 mA RCD, so more than 30 mA leakage to earth (but not Line - Neutral) would result in an RCD trip.

So, excepting cookers and the like, every UK domestic appliance will be fed in that way.

stephen · 2019-12-21T18:20:54.968Z

oops my mistake I must of assumed a it was UK-- or I pick it up from another poster and transposed the location…
where I live the standard is outlet is every 8 - 10 feet for 100 feet of length to a max of 120 feet wire length - and no more then 3 light sockets per fuse if you have maximum number of outlets on that string – it probably increased now with the advent of energy efficient lights and the banning of sale of incandescent lights . fridges, microwaves have to have dedicated outlet. and kitchen outlet no more the 4 halves of an outlet ( using 14/3 wire and 2 15 amp breakers

Robert.Wall · 2019-12-21T19:24:49.939Z

stephen:

or I pick it up from another poster and transposed the location…

That is my favourite trick.

We use 2.5 mm² cable, rated at around 23 A (depending on how it’s installed) but of course each socket is fed from both sides of the loop, so a socket roughly in the middle will have two feeds in parallel, each capable of 23 A, and the current will share roughly equally.

I was wondering if I could do the maths to see just how much water 20 kWh of energy would raise from (say) 28 °C and turn into steam. From here it’s about 0.3 MJ/kg to raise it to 100 °C, and then 2.5 MJ/kg to evaporate it. So 0.77 kWh per kg. I reckon that our 20 kWh of energy that’s gone missing would boil away to nothing 25 kg (litres) of water - neglecting losses, so in real life somewhat less.

borpin · 2019-12-21T19:50:07.712Z

Robert.Wall:

We use 2.5 mm² cable,

When I built my house, the Leccy and I had a serious conversation about doing star layout using 4mm² cable for the sockets. In some places that was what we ended up doing.

Robert.Wall · 2019-12-21T20:03:30.560Z

Yes, that’s allowed too - up to 50 m² of floor area served per radial.

But we’re going OT.

benergie · 2019-12-23T21:29:45.517Z

Robert.Wall:

Am I correct to assume that all the c.t’s are in your load centre and the Iotawartt is also close by? How far apart are the two c.t’s in question (the B leg feeder and the fridge circuit)?

There’s nothing on the A leg that corresponds with the mystery load?

Yes, my IoTaWatt and all CTs are located inside my load center. The two CTs in question are about 1 foot apart.

Correct, the A leg does not show any part of the mystery load. It just shows the AC cycling on and off and a standby load of about 15 watts.

Robert.Wall:

Coming back to my wild theory about mystery wires: Do you know the actual route the cable takes from your load centre to the socket? and is it possible it’s been “interfered” with? I’m now trying to think of what sort of signal could be injected into that circuit, that would look like a 1.5 kW load to the iotawatt and not appear on any other c.t.

My load center is on an exterior wall, facing inward. I believe the wire goes down into the crawlspace, across for about 15 feet, and up an interior wall behind the refrigerator. As much as I would like to avoid it, I believe it is time for me to put the tone generator back on that circuit and trace the wire across the crawlspace to make sure it does not branch off anywhere and that the wire is undamaged.

stephen:

just a thought for you as to mysterious load-- do any of your wires exist in damp or wet location… I had a mysterious load issue a few years back. turns out it was trickle charge of 300w across a 120 volt wire in a damp location. when the area dried it disappeared and when it got damp it came back.

The crawlspace was definitely a damp location before I bought the house a year and a half ago and put a dehumidifier down there. I will admit that the dehumidifier has not run consistently since then. The plug would occasionally fall out of its socket on the crawlspace ceiling until I installed a new outlet a few months ago.

I am guessing there would be physical signs of a 1500 watt discharge sustained over 14 hours. I will meticulously inspect all visible parts of the wire from the load center to the refrigerator for anything unusual.

Robert.Wall:

Do you feel it’s worth heading over to The IoTaWatt forum and asking about the likelihood of a hardware or software fault there? I think I know what the response will be - it’s your call.

If I don’t turn up any evidence of a problem with the circuit wiring then I will head over to the IoTaWatt forum to explore the possibility of hardware or software faults.

Robert.Wall · 2019-12-23T22:29:22.769Z

benergie:

The two CTs in question are about 1 foot apart.

I think that more or less rules out anything external influencing both c.t’s/both inputs except for a common current in the cables they’re sitting on.

Hopefully a very stupid question:

benergie:

I will admit that the dehumidifier has not run consistently since then.

And which circuit is that on? (Not that one of those is likely to account for 1.5 kW.)

benergie:

I bought the house a year and a half ago …
I am guessing there would be physical signs of a 1500 watt discharge sustained over 14 hours.

So there’s a real possibility then that the wires do go somewhere else that you don’t know about. If a discharge is confined to a small area, then surely you will see it. If it’s distributed (don’t ask me how that could be), then it’s going to be a lot harder to see something.

dmajwool · 2019-12-24T23:00:31.530Z

Hi, sorry to be late to this discussion, but in the beginning you say the 14hr trace ends in a strange pattern. I quite often see that pattern of 3 short bursts at the end of long periods of consumption - when my Nissan Leaf battery reaches fully charged.
My Leaf here in the UK normally would draw 2500 watts from a low-spec house circuit, but it is possible to dial the car down further so that it charges at about 1500 watts.
So looking at your scenario from the other end of the telescope, is there any chance that an EV was being charged on that circuit at that time? 20kWh is an unremarkable amount of energy to be dumped into an EV.
Cheers,

image1136×640 157 KB

Robert.Wall · 2019-12-25T01:27:15.574Z

dmajwool:

I quite often see that pattern of 3 short bursts at the end of long periods of consumption - when my Nissan Leaf battery reaches fully charged.

Now that’s a very useful piece of information. Thank you.

benergie · 2019-12-26T21:38:32.196Z

dmajwool:

Hi, sorry to be late to this discussion, but in the beginning you say the 14hr trace ends in a strange pattern. I quite often see that pattern of 3 short bursts at the end of long periods of consumption - when my Nissan Leaf battery reaches fully charged.
My Leaf here in the UK normally would draw 2500 watts from a low-spec house circuit, but it is possible to dial the car down further so that it charges at about 1500 watts.
So looking at your scenario from the other end of the telescope, is there any chance that an EV was being charged on that circuit at that time? 20kWh is an unremarkable amount of energy to be dumped into an EV.

That’s it! Not only was there an EV charging but it was a Nissan Leaf! Well done, recognizing that termination pattern! It never crossed my mind that an EV could be charging on the refrigerator circuit.

I went out of town that day with my colleague who parked his Leaf at my house. We plugged it in to an outdoor outlet using a portable level-1 (120v) charger to keep the level-2 (240v) charger open for my wife’s car. That outlet happens to be fed off the refrigerator circuit. I must have had the sensitivity set too low on my tone generator when I checked that outlet last week. I just double-checked it today and confirmed that it is indeed fed from the refrigerator circuit.

Thank you you all for your help in determining that:

The mystery load was almost certainly a real load
It must have been outside the thermal envelope of the house
My refrigerator is not on a dedicated circuit as required by the electrical code
The mystery load was a Nissan Leaf charging up!

I can relax knowing that the mysterious 20kWh of energy was not a random and dangerous discharge but intentionally went somewhere useful. Again, thank you all.