A standard 3-prong surge protector is plugged into a US 15 amp 3-prong wall outlet. I want to protect a Christmas light string with a "computer" controller box. The light string only has a 2-prong plug to plug to the surge protector. Will the light string controller be protected? Bottom line - is it useless to expect surge protection for a device with only a 2-prong plug?


The surge protector will dump high voltage spikes from hot to the ground and many will drop from hot to neutral, so it would depend on the model, if internally the mov’s or metal oxide varistors are wired hot to neutral you would still have spike protection. If only wired got to ground it will do no good as their is no connection.

  • AIUI, the surge being protected from is coming from outside the house (lightning strike, heavy load cut-off, etc.). The surge protection is between the surge protector's plug and its outlets. Therefore the SP's outlets are protected whether there is a 3-prong, 2-prong or no-prong device plugged in. Is that an incorrect understanding?
    – FreeMan
    Oct 23 '19 at 15:00
  • The op was talking out a local device at the outlet, not a whole house suppressor. All the whole house systems I have installed tie each pole to ground through a MOV BANK. Some have pole to pole but if you look at a schematic you can see this is a gimmic in most cases because each pole is already protected. I hope this helps, at the plug a 2 wire with no ground may not work at all depending on how it is wired some will some will not.
    – Ed Beal
    Oct 23 '19 at 23:11
  • I too was talking about a plug in surge protector "power strip" type device. My understanding of how they work, however, is based purely on how I think they should work with no real basis in fact, so I'll wander off now and leave your otherwise fine answer alone.
    – FreeMan
    Oct 24 '19 at 1:13

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