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?

 

[Tom.G]

Since the wall plugs are not polarized you can just turn one of them over, effectively swapping which wire is the "Hot" one.

TL;DR Summary: Just installed electric mattress pad - now I get a tingling sensation when touching my partner

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).

Since both of you are living creatures with a high water content, each of you were a conducting capacitor plate to the wiring in the mattress; the dielectric was the covering over the heating elements.

To find which heater needs its plug reversed, you can use your meter with one wire connected to Ground (such a a water faucet) and the other wire connected to a large metal pan or sheet of Aluminum foil placed on one side of the bed.

The meter voltage reading will be quite low so start at a high range and switch to a lower range as needed to get a reading. Individually check both sides of the bed.

Any side that shows a voltage should have the wall plug reversed.

You may want to mark the plugs and wall outlets with some paint or a piece of tape to mark the preferred orientation.

A) Or better yet, mark the plug and outlet of ONE side;
B) Plug the heater from the other side into the marked outlet;
C) And whichever way gives the lowest voltage reading using the above

testing procedure, gets marked to match the wall outlet;​

D) Move the plug back to its default outlet and repeat the meter testing;
E) When you find the plug orientation that gives the lowest reading,

mark the outlet to match the plug.​

Let us know what you find, we like to learn too!

Cheers,

Tom

 

[Dullard]

A bed-wetter's nightmare...

 

[sophiecentaur]

Wait, you feel this when touching your MacBook too?

Me too,too. Many electrical devices give me a slight 'trembling' when I touch them very lightly. No effect when 'definitely' holding.

House wiring tested ok recently and an extra earthing rod connected in the garden. The supply is overhead and a long cable (1km ish) to the nearest sub-station. My low cost socket tester says Earth connection is higher than ok but no problem.

 

[Baluncore]

Many electrical devices give me a slight 'trembling' when I touch them very lightly. No effect when 'definitely' holding.

Likewise. I can sense the AC voltage on a device that has no protective earth connected. I guess I have a different electrostatic voltage due to stray capacitive coupling.

Making a better connection momentarily prevents the sensation.

For me, the sensation feels like 50 Hz, not 100 Hz, so it could be voltage polarity that is causing the nerve sensation.

To test for floating AC, I brush with the back of my middle finger, rather than my fingertip pads, which are more sensitive. It is also safer if muscles involuntarily retract, so I may avoid grabbing a live chassis.