FAQ
TL;DR: Up to 4 A short-circuit current was logged on damp plaster [Elektroda, wada, post #11543753]; "The better it is, the wetter it is" [Elektroda, Plumpi, post #11524582] Stray or “wandering” currents follow any conductive path, including wet walls, damaged cables, rebar and plumbing.
Why it matters: Hidden voltage on building fabric can injure people and destroy equipment.
Quick Facts
• Safe touch voltage (dry skin): 50 V AC [IEC 60479-1]
• Dry brick resistivity: ~10^6–10^9 Ω·m; saturated brick: ~10^2–10^4 Ω·m [Building Science Digest 163]
• 30 mA RCD disconnects within 40 ms [IEC 61008]
• Insulation test pass mark: ≥1 MΩ at 500 V DC [IEC 60364-6]
• Measured wall fault current on forum: up to 4 A [Elektroda, wada, post #11543753]
1. Can electrical current really travel through walls or floors?
Yes. Moist masonry, embedded metal, or leaked phase conductors create a low-resistance path. Forum users measured tingling and up to 4 A fault current on plaster surfaces [Elektroda, wada, post #11543753]
2. What conditions increase wall conductivity?
High moisture, dissolved salts, metal rebar, and contact with live wiring lower resistance by six orders of magnitude compared with dry brick [Building Science Digest 163]. "The better it is, the wetter it is" captures the effect [Elektroda, Plumpi, post #11524582]
3. How do stray currents differ from simple leakage currents?
Leakage leaves an intended conductor via insulation defects. Stray current completes its circuit through unintended structural paths—rails, rebar, pipes—and then returns to the source [Elektroda, Anonymous, post #11525866]
4. Why do wet walls sometimes tingle but not deliver a full shock?
The internal resistance of the fault plus footwear resistance often limits current below the pain threshold (≈1 mA). When the wall saturates or skin contact grows, current rises and a shock occurs [IEC 60479-1].
5. Could an appliance in another flat electrify my faucet or wall?
Yes. A punctured TV filter capacitor once placed phase on the antenna shield; the ungrounded bracket spread voltage through walls and floors, shocking users at faucets [Elektroda, Anonymous, post #11524622]
6. How can I measure voltage on a wall safely?
Use a high-impedance voltmeter with one probe on the suspect spot and the other on a verified PE conductor. Keep one hand behind your back and wear insulating shoes. Record both open-circuit voltage and short-circuit current through a 1 kΩ resistor [IEC 60364-6].
7. Quick 3-step diagnosis procedure
- Verify RCD operation with a tester.
- Measure wall-to-PE voltage; if >25 V AC, continue.
- Isolate circuits, re-energise one at a time to locate the faulty branch [Elektroda, Akrzy74, post #11524509]
8. What standards define acceptable touch voltage?
IEC 60479-1 sets 50 V AC and 120 V DC for dry skin; wet contact limits drop to 25 V AC. National wiring rules adopt these numbers for living areas [IEC 60479-1].
9. Are RCDs effective against wandering wall currents?
A 30 mA RCD trips before dangerous current passes through a person, provided the fault current returns via the protective conductor. However, if the return path is masonry only, imbalance may be small and the RCD may not trip [IEC 61008].
10. Do lightning strikes produce wall stray currents?
Indirect strikes induce kilovolt surges on nearby lines; transient wall voltages last microseconds, unlike continuous stray currents from faulty wiring [Elektroda, Jacek Rutkowski, #11530674].
11. Edge case: footwear masking danger
Slippers act as one plate of a capacitor; at 50 Hz they allow microampere currents, making a neon tester read zero yet shocks still occur when resistance paths change [Elektroda, lukiiiii, post #11535056]
12. Can stray currents start fires?
Yes. A wall outlet spontaneously burned after electrochemical corrosion created a 16 V DC source that drew sustained current; the 16 A breaker never tripped [Elektroda, wada, post #11542252]
13. How do I eliminate stray currents in my apartment?
- Repair damaged conductors and replace cotton-insulated wiring.
- Install 30 mA RCDs on all socket circuits.
- Bond metallic plumbing and ensure the main equipotential bar is <1 Ω to earth [IEC 60364-5-54].
14. Do HV line lightning conductors carry railway stray currents?
No. High-voltage shield wires normally stay near earth potential; most problematic stray currents originate from DC traction systems sharing soil return paths [Elektroda, Anonymous, post #11530715]
15. What additional statistic illustrates the risk?
A 30 V fault on a wall with only 300 Ω skin-hand-foot impedance delivers 100 mA—double the ventricular-fibrillation threshold (50 mA) [IEC 60479-1].
16. Expert tip on moisture control
"Dry the walls first—minimise electrolytes before hunting electrics" [Elektroda, Wirnick, post #11528891]
