Shocking: are Surface laptop cases really dangerous?

The Microsoft Surface Laptop 4’s magnesium-aluminium case absorbs a small amount of power when connected to the mains. The voltage, at least in my two test models, depends on how I insert the power supply plug into the socket.

In my Surface Laptop 4 double review, I felt a distinct tingling sensation in my finger without being aware of the cause. Thankfully, our community soon enlightened me. An anonymous user posted the following comment:

Thanks a bunch, oh mysterious user! As you predicted, a test has now shown: the laptop doesn’t tingle in battery mode. The fact that this is electricity flowing through my body via the housing is something I should’ve been aware of thanks to years of experience. I’ve encountered this pleasant tingling sensation in quite a few devices. Be it Surface Books, MacBooks with Magsafe ports or a company iPad that tried in vain to vanquish me more than half a decade ago.

How to turn your laptop into a stun gun

Three distinct factors allow the Surface Laptop 4 to convey a current. First up, a lack of any grounding whatsoever. The power supply unit lacks a protective conductor. Secondly, you’ve got the proprietary, magnetically adhering Surface Connect connector that supplies the power. It isn’t isolated like your usual USB port. And thirdly, there’s the conductive housing material.

The tingling sensation, which this Reddit user also refers to as a painful tingling needle-like sensation, is known as touch voltage/touch current. In basic terms, it’s the voltage between conductive parts on a device – in this case the housing – and a human or (other) animal.

Naturally, there are standards for electricity flowing through the body. According to DIN VDE 0701-0702, the touch current for safe operation of a device must not exceed 0.5 mA. If the value is above this, a device won’t receive a CE mark and therefore can’t go on sale.

By the way, much lower voltage values are more than enough for a device to emit a perceptible touch current. Thus, a MacBook Air from 2012 can trigger a tingling sensation, even though this measurement by c’t magazine only comes to 0.06 mA.

What Microsoft has to say

Microsoft’s support page has an article called «How to charge Surface» with an FAQ attached. In it, the company describes what touch current is and how it comes about. In summary, Microsoft further states the following:

• The tingling is triggered by a harmless amount of residual electric current.
• The sensation caused by the touch current can be felt as a vibration, slight tingling or small pinpricks.
• Good equipment design and testing for protection against electrical hazards ensure that touch currents flowing through a person are insignificant and harmless.
• Microsoft’s internal standards for touch current, which are more stringent than current regulatory standards, are intended to minimise the perception of touch current.

I doubt that a good device design will ever fully ensure that touch voltage remains harmless. In my eyes, a truly solid design would completely eliminate touch current. Otherwise, I get Microsoft’s point.

As a user, I don’t have to worry. All limits are complied with, and there’s no danger to myself or others whatsoever.

I still wouldn’t hold my tongue to it ;).

How to circumvent the «problem»

If you’re not trusting enough or if touch current makes you uncomfortable, the problem can always be fixed. On the one hand, you can rotate the power adapter plug or the Surface Connect port by 180 degrees. With my test devices, the issue is resolved if I plug the power supply into the socket backwards. Now the tingling sensation can only be felt if you’ve got particularly sweaty hands. Well insulated shoes go a long way as well. Still, this isn’t a long-term solution either.

Your best move might just be to switch to a USB-C charger or a -notebook power adapter. A USB-C connector goes further into the case and won’t cause any contact voltage. This should eliminate any problems with newer Surface devices if they possess the corresponding port. When purchasing, I recommend getting a power supply with the same electricity values as the original.