Electric mattress pad tingles when turned off

[Lennard]

TL;DR Summary

Just installed electric mattress pad - now I get a tingling sensation when touching my partner

I've recently bought an electric mattress pad for my girlfriend. It has 4 separate heating zones (body and feet) and 2 controllers with a 2 plugs (not grounded - standard 2 prong EU plug). We turned it on and finally enjoyed a already warm bed when going to bed.
Only problem: once we turned both sides off, we felt a tingling/vibrating sensation when touching each other (similar to that when touching a plugged-in macbook). I knew that it probably was some harmless capacitive effect, but still felt a bit scared. I unplugged one side and the feeling went away. I decided to sleep and investigate later.

After some research this is my hypothesis:

I guess the mattress cover only switches one wire, so that the heating element is still connected to the outlet. I guess that by chance my partners side of the blanked was plugged in the other way around, so that the sides of the bed act like capacitive plates going from line (L) to neutral (N). In this case we were the dielectric material, so when we touched there was a small discharge 50 times per second (or 100 to be precise).

When I get home I want to do some investigation and see what really is going on here. I would appreciate any tips on how to go about this. All I have is a very basic multimeter.

 

[Quantum Call]

Steps to Investigate:​

1. Understand the Setup:​

• You mentioned that the mattress pad has 4 separate heating zones with 2 controllers and 2 plugs (non-grounded 2-prong EU plug).
• It seems like there’s no proper grounding (which is risky for electric appliances).

2. Safety First:​

• Turn off and unplug the mattress pad before you perform any measurements. Be cautious and don’t operate the multimeter on a live circuit.
• Use insulated gloves if necessary to avoid accidental contact with any conductive parts.

3. Check for Grounding:​

• Do not measure directly with the multimeter on yourself or your partner when plugged in. Focus only on measuring the system, not live people.
• Use your multimeter to check if grounding is present. Since it's a non-grounded (2-prong) EU plug, it could cause floating potential, leading to the effects you're experiencing.

4. Measuring Voltage:​

• Set your multimeter to AC voltage mode (preferably on a low voltage range, such as 200V).
• Measure voltage between the plug’s live wire (L) and neutral (N) separately (if you can access the wires).
• Also check voltage across different heating zones to see if any parts of the heating element are leaking voltage.

5. Check for Capacitive Leakage:​

• With the mattress pad unplugged, measure the resistancebetween different parts of the mattress pad, such as:
  • Between heating zones (across zones that should not conduct electricity).
  • Between conductive parts and any conductive parts of the bed frame (or anything else in contact with the ground).
• Use the continuity function on the multimeter to see if there's a direct short between conductive parts and any other surfaces.

6. Testing the Heating Elements:​

• Use your multimeter in resistance measurement modeto check each heating zone (turn off the device first!):
  • Measure resistance of the heating wires to ensure there’s no break or damage in the circuits.
  • Compare readings between different zones to ensure the resistance is consistent and safe.
• Be cautious with any readings, especially since it sounds like the mattress cover might not be fully isolated.

7. Inspect the Controllers:​

• Check the controllers (the part where you plug in the power). Measure any voltage or current fluctuations when the controls are in use.
• Look for proper insulation between different wires or conductive parts. Faulty wiring or poor insulation could be causing unwanted electrical interactions.

8. Check for Any Faulty Connections:​

• Inspect each connection (especially where the heating elements meet the plug or controller). Sometimes, loose or improperly wired connections can cause leakage.

9. Contact the Manufacturer:​

• If the problem persists or if you're unsure about what you’re measuring, it might be wise to contact the manufacturer and explain what you’re experiencing.
• They might have specific guidelines for safely using the mattress pad and can provide further insight.

Important Safety Tips:​

• Avoid direct contact with any exposed wires or conductive surfaces while testing.
• Don’t rely solely on the tingling sensation—it could be harmless, but it could also indicate leakage that might escalate.
• Take precautions when dealing with electricity and electrical devices, especially those without grounding.

By carefully following these steps and being cautious during testing, you should be able to pinpoint what’s causing the tingling sensation.

 

[russ_watters]

once we turned both sides off, we felt a tingling/vibrating sensation when touching each other (similar to that when touching a plugged-in macbook).

Wait, you feel this when touching your MacBook too?