Fixing my kitchen oven. The panel fuse keeps opening.

Thread Starter

babaliaris

Joined Nov 19, 2019
172
Hello!

I have an old siemens kitchen (don't know the model but it's very similar to siemens hb12320gb). It has four stoves (not glass, solid ones) and each one of them has 4 cables connected to it (I believe that since each switch has 3 positions, the 3 cables are the phase carriers that are connected to 3 different resistors and the 4th one is neutral).

The problem seems to be random since it does not occur at every attempt (sometimes the fuse opens some times it just works normally).
I'm sure though, that the small stove always triggers the panel fuse to open and cut the current when I'm switching it on.

Also, the grounding system is two large pieces of metal, connected directly below the stoves (One piece of metal for the 2 big stoves in the back and another one for the stoves in the front).

What I tried so far:
1) I disconnected the grounding cable from the grounding system (because it was very short in length and I couldn't open the chassis without over-stretching the wire) and I noticed that switching on the small stove was not triggering the fuse panel to open anymore (I also tried all the other switches as well and everything worked normally). Though later it started triggering again, so this observation was not helpful.

Anyway, I thought that maybe one of the stove cables was shorted with the chassis, and this was why it was triggering the fuse to open. So, I used my multimeter to check for shorts between each stove cable (4 cables * 4 stoves = 16 total) and the ground but I didn't find any shorts!!!

2) Then I tried to find shorts between each cable that is connected to the small stove switching mechanism, and still I did not find any shorts, except the ones that are supposed to be shorted (you can see the connections in the switching mechanism are differentiated by rectangles, so cables that are on the same rectangle are supposed to be shorted, I'm not sure I'm just assuming it but its probably correct).

So what else can I try? Do you want me to send you pictures as well?

I mean, it's just 16 cables connected to 4 different switches that lead to 4 different stoves (resistors), so how hard could it be to fix it?
I'm an Electrical & Computer Engineer for gods shake, and I can't fix my damn kitchen...

Could it also be that nothing is shorted, but maybe some of the resistors are damaged so that the stoves sometimes draw more current than they ar supposed to draw and this current happens to be big enough to open the panel fuse?

Thank you!
 

LesJones

Joined Jan 8, 2017
4,214
The first thing to establish is if the fault only occurs when one of the four elements is in use. I originally thought your device was just 4 hotplates but when I looked at the link to the Siemens device I see it is a combined oven and 4 hotplates. Cab yo clarify this point.
Disconnecting the grounding cable is VERY DANGEROUS. The whole casing of the device can become live.
The fact that it does not blow the fuse when the ground is disconnected suggests that the fault is between live and ground.
I suggest testing each element for leakage to ground using a high voltage insulation tester.

Les.
 

Thread Starter

babaliaris

Joined Nov 19, 2019
172
I suggest testing each element for leakage to ground using a high voltage insulation tester.
Isn't that the same as using this functionality:
TLS.130153.jpg

and checking if one of the cables is shorted with the ground (By ground, I mean the area that is connected with the chassis and the yellow-green cable).

I checked every single cable under each of the 4 stoves, and none of them is shorted with the ground.


The first thing to establish is if the fault only occurs when one of the four elements is in use.
It seems that it only occurs when the small stove is on. I also tried to turn on the rest of them simultaneously (but with the small stove off) and everything seems to work just fine.
 
Last edited:

LesJones

Joined Jan 8, 2017
4,214
The insulation may only be breaking down with a high voltage which is why a specified an insulation tester.
You have not clarified if it is just a hob (The top of a cooker with a number of hot plates (Which I think you are calling stoves.) on which you place pans.) or a hob combined with an oven.)
Edit I have just noticed that you have circled the continuity range on your meter. If this is the range you are using it will only show continuity for a resistance of less than a few hundred ohms. The 20 megohm range MAY be good enough to show up the leakage.

Les.
 
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Thread Starter

babaliaris

Joined Nov 19, 2019
172
You have not clarified if it is just a hob (The top of a cooker with a number of hot plates (Which I think you are calling stoves.)
Sorry, I thought they were called stoves. I'm talking about the top where you place pans.


The insulation may only be breaking down with a high voltage which is why a specified an insulation tester.
Too bad I don't have an insulation tester... At least, I think so. This is my multimeter:
https://meters.uni-trend.com/product/ut89x-series/ (My model does not have that live (with the lighting strike symbol) function or the temperature functions.)
 

SamR

Joined Mar 19, 2019
5,060
Looks like you've given it a pretty good look-see. It could be a loosened or oxidized connection in the supply from the panel. Open the main breaker in the panel and check the connections at the unit breaker and buss. It could even be a bad breaker. You did say fuse though which would mean just the wiring connections. Clean bright, maybe use some anti corrosion protection on the connection and retighten. That's the easy part. Then it's the wiring at the plug box and any splices between it and the panel (shouldn't be any).
 

LesJones

Joined Jan 8, 2017
4,214
From what you say in post #3 it is almost certain that what you call the small stove is the faulty one.
See my edit of post #4 about the range on your meter that you are using to check insulation. Note you also need to disconnect all 4 wires from the "stove" before doing the insulation test on it.
You will need to find the model number of your cooker so you order the correct "stove" for it. There will probably be a plate on the back of your cooker that will give you the model number.

Les.
 

Externet

Joined Nov 29, 2005
2,236
Can be any hot plate, can be the fuse box heating a bad fuse joint and not withstanding the current. Can be the oven. Do not make it work without a connected ground as now is a hazard in the true failing mode.
Visual inspection for sparked signs of its guts and wiring is mandatory inch by inch. A broken 'turn on control' is also a suspect if nothing is visually detected. Disabling one 'burner hot plate' at a time to rule it out of the problem takes longer to diagnose, but effective.
 

Thread Starter

babaliaris

Joined Nov 19, 2019
172
From what you say in post #3 it is almost certain that what you call the small stove is the faulty one.
See my edit of post #4 about the range on your meter that you are using to check insulation. Note you also need to disconnect all 4 wires from the "stove" before doing the insulation test on it.
You will need to find the model number of your cooker so you order the correct "stove" for it. There will probably be a plate on the back of your cooker that will give you the model number.
Les.
So I need to check the insulation of the actual plate?
1-ska-blitz-hot-plates-1.jpg


Question 1: So you are telling me that the insulation of this plate might be breaking under the right voltage, which means it shorts the circuit and causes it to draw a big current, and this is why the fuse is triggered?

Question 2: In order to do that, I can use the 20MΩ range of the multimeter and see a value? If the multimeter displays zero or out of range, it means the insulation is broken?
 

Externet

Joined Nov 29, 2005
2,236
If that is the stove in trouble, the picture should be from upside down with no bottom cover.
First do a visual inspection of its guts inch by inch everywhere.
Take a photo of all wiring where it connects, so you can go back as original.
Unplug one plate,
Retest.
If fuse blows, return the connections to original as in your photo.
Disconnect another plate
Retest.
....
....
It is matter of isolating the trouble.
 

LesJones

Joined Jan 8, 2017
4,214
Re question 1. The suspicion is that the insulation between the heating elements within the plate and the plates metal casing is breaking down when supplied with it's normal rated voltage. (From your profile giving your location this voltage will be about 230 volts RMS which has a peak value of about 325 volts. You would normally use an insulation tester which applied 500 volts DC to test the insulation. As you do not have an insulation tester the best you can do is to use your meter set to the 20 megohm range. This MAY show up the fault but it will only be applying a test voltage of less than 1 volt. I would say that if you get a reading of less than 1 megohm then the plate needs replacing. If you get a higher reading it does not confirm that it is NOT faulty.
Re question 2. You do not seem to understand taking resistance measurements with your meter. If your meter reads zero it means that the resistance is less than the value of the least significant digit on the display. So with your meter set to the 20 megohm range any resistance less than 1000 ohms will be displayed as zero. An out of range display indicates a resistance value of greater than 20 megohms.
The tests you did with the meter set to the continuity / buzzer range would probably display out range for any resistance reading of greater than about 200 ohms. So that test would only show up almost a dead short between the element and the casing.
Take a picture of the connections as Externet has suggested.
Remove the 4 connections to the plate. With your meter set to the 20 megohm range connect one test lead to the metal top of the plate. Then touch the other test lead on each of the connections on the plate and note each reading.

Les.
 
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