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I live in an old house and I painted my kitchen light blue. After several years I noticed that there are strange white line-like patterns on the wall. They always run in right angles and seem to align with electrical wires behind the wall.

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I am wondering, is it possible that somehow the electrical wires have caused the wall paint to pale? If so, what is the underlying mechanism? The only thing I am aware of is heat, since each imperfect conductor emits heat with passing current.

One other possibility would be an electro-magnetic field generated by the current interacting with iron particles in the paint, but I am not competent enough to tell if this is plausible.

EDIT

The walls are made of brick and the wires are covered by plaster. I am not sure what kind of wiring is inside.

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    Are these lines along the joints between sheets of drywall? What kind of wiring you have? Really whatever kind you have, there cannot be any electromagnetic effect on paint. Ordinary wiring has the coming and the going conductors in the same cable so the magnetic fields cancel out. I also think that heating would be negligible. The only thing I could imagine would be water leaking into the wall at the top, running along the wires and wetting the wall. There are moisture probes with sharp points that stick into drywall for determination of water content. Be careful you don't damage the wall. – Jim Stewart Aug 20 '18 at 21:01
  • @JimStewart Thank you, I edited my question to answer your questions. I was also thinking about moisture, but I dismissed it because it is a brick wall and I think moisture coming from the top would manifest itself sooner. – Martin Drozdik Aug 20 '18 at 21:14
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    What is the type of wiring (knob-n-tube, romex, conduit)? What is the wire gauge of the wiring (14AWG, 12AWG, 1,5mm, 2,5mm), what is the circuit breaker size on that circuit (15A, 16A, 20A, 32A), and which electrical loads are placed on that circuit? – Harper Aug 20 '18 at 21:19
  • Are the wires in conduit embedded in plaster on a brick wall? Or are the wires deep in the brick or block wall? – Jim Stewart Aug 20 '18 at 21:20
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    Fair chance the Soviet masters of collectivism did not find a way to make a fridge inefficient, so the fridge draw is probably minimal. The oven and cooker are both very heavy draw appliances, however, and stand to make a lot of heat especially if the wire is undersized. Feel the area of the wall when the oven and cooker are going full tilt. Good news is with conduit, you can change the wires to bigger or more, and Soviets were into grounding and overbuilding -- stout metal conduit is a usable ground path, which saves you a wire. – Harper Aug 20 '18 at 21:50
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Most probably from temperature. Electromagnetic fields usually do not change plaster or color in that way.

If your installation is old and plastered in, and undersized, the wires would beat up and the wall material would e.g. loose some Cristal water over time and thus change color.

If you can verify your hypothesis with some metal or wire detector. If you think it is best, try to find the consumers for the wires and turn them on. After some time you should be able to notice a difference. The ideal way would be a thermal camera, but they are quite expensive and you probably cannot easily get one.

If it is temperature induced, you should consider replacing them with an up to date Installation and make sure you are not overloading them.

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    I believe the English word for "unterdimensioniert" is "undersized" – Johnny Aug 20 '18 at 22:13
  • So we think they would not have hot and neutral in separate paths. Inductive heating is not likely, but you should be able to count the wires in each conduit and note color of insulation to verify you have modern accepted wiring. – Jim Stewart Aug 21 '18 at 12:17

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