I have a air humidifier connected to a timer, and every time it turns off there is a huge spike going through the lines; lamps and computer monitors flicker.

I'm thinking about buying a surge protector to put in front of the perpetrator, will this prevent it from sending out spikes? Or do they only protect again incoming spikes?

  • This sounds like imbalanced phases/improper circuit loading....
    – Tyeler
    Nov 8, 2016 at 20:53
  • @Tyeler Sorry for my ignorance, but what does that mean?
    – Alex
    Nov 8, 2016 at 21:13
  • 1
    @Alex Basically, what that means is that the surge is not coming from the device, but from the sudden lack of demand of current. Nov 8, 2016 at 21:23
  • @BrownRedHawk That sounds awfully lot like something I'm going to have problems with fixing myself.
    – Alex
    Nov 8, 2016 at 21:47

1 Answer 1


Most ordinary surge protectors are designed to protect against large incoming surges only. That is surges large enough to cause permanent damage to equipment. They are not intended to prevent mere flickering of lights.

Many (maybe most) of them provide only one-time protection against large surges (e.g. lightning strikes nearby)

It is very unlikely that a typical home/office surge protector will provide the benefit you seek.

The relevant Wikipedia article says:

A surge protector attempts to limit the voltage supplied to an electric device by either blocking or shorting to ground any unwanted voltages above a safe threshold.

The standard let-through voltage for 120 V AC devices is 330 volts

MOVs have finite life expectancy and "degrade" when exposed to a few large transients, or many more smaller transients.

Other types of protective device can be more durable, but they still might not prevent lights from flickering.

  • 1
    There is no "sense of direction" in a surge suppressor - it simply starts conducting when the voltage at its terminals is too high.
    – Ecnerwal
    Jun 23, 2017 at 22:58
  • 1
    I bought a cheap surge protector that you put between the device and the outlet, this solved my problem.
    – Alex
    Jul 11, 2017 at 13:00

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