(pardon if this question is a little elementary for this site...)

I have done a variety of Google searches trying to get to the 'right' answer(s) here, part of the problem is I'm not even sure of the terminology involved.

I have several strands of Christmas lights. Some sets came with what are actually two strands of different types (C7 bulbs and Icicles) wire tied together.

Both strands have two-prong male and female connectors at each end. The female connectors are designed in such a way that a male three prong connector will not fit into the plug, the physical design blocks the grounding prong.

One strand has "like sized" prongs/slots (I'll call this Type A) and the other size has unlike sized prongs/slots (Type B). I have attempted to lay out my lights so that I have a couple of 'those strands' together, then connected to a couple of single strands, then I want to add in a couple more of the doubled strands...but alas I only have a single 'Type A' female end, and can not presently find (at Home Despot or Blowe's) an adapter that suits the situation.

Should I be able to find such an adapter? ( I would also like to know...) 1. If there is a 'better way' I should like to hear it. 2. If not will creating one (grinding the oversize prong to fit) pose a safety risk? 3. What are the 'correct names' for the various adapters described?

  • This could probably use a photo or diagram.
    – Bort
    Dec 6 '17 at 18:40

Type A

enter image description here - used typ. for 100~140Vac 60Hz 10A, e.g. North/Central America, Japan. - Neutral is the wider (7.3mm) spade pin, Line (hot) is the narrow 6.3mm spade pin - requires double insulated loads.

Type B

  • both pins narrow 6.3mm enter image description here

enter image description here

The Neutral plug is polarized so that the the risk to access is reduced with Neutral being 0 to 5% of line V such as the Edison socket=N and center = Line= "hot" which corresponds the the narrower spade pin.

To prevent polarized lamp plugs from being connected to non-polarized string light extension sockets, they use the narrow blade socket to block these.

Best bet may be a long indoor extension cord compatible with all U.S. 2 pin plugs to reach extra loads. Note the non-polarized plugs without a hole in the spade pin are horrible for mating contact force ( perhaps due to lack of CN quality design choices or awareness) and often do not wipe the contacts clean or even make contact!!. So I tend bend apart slightly to create contact tension and plug retention forces without the spring contact friction of the hole. (usually found on low quality Asian products)

p.s. *You almost guessed the correct UL/CSA Types A & B but not quite. I'm not sure of the type letter for non-polarized 2 pronged plugs. ... old joke when they introduced the change in plugs ... "two plinked plongs"

  • 1
    Thanks for the pics. I can tell you I was referring to the Type A Non-Polarized 2 pin (what I called Type A) and Type A Polarized 2-pin (which I called Type B)... it was indeed a random guess. I might well have said Type 1 or Type 2. :) Thanks
    – Cos Callis
    Dec 6 '17 at 21:20

One strand has "like sized" prongs/slots (I'll call this Type A) and the other size has unlike sized prongs/slots (Type B).

Your 'Type B' is properly known as a polarized plug.

It is unsafe to connect an unpolarized plug to a polarized outlet. This is because the purpose of polarization is to reduce the chance of your touching dangerous line voltage such as on the threads of an empty bulb socket; North American power has a “hot” and “neutral” wire, and the “neutral” is generally closer (but not necessarily equal) to earth potential (voltage) than the “hot”, so it is less dangerous (but still unwise to touch).

You should not grind down a pin to make it fit. Would it work, electrically? Yes. But it is removing the designed safety features.

(From a strictly technical perspective, it would be safe to plug in such an altered plug to a GFCI outlet or portable GFCI — GFCIs provide better protection against the same hazard than polarized plugs. But then you would still have an unsafe plug configuration around in the future.)

Use extension cords (of the type designed for outdoor lights) instead. This also has the advantage of ensuring you are not overloading the pass-through outlets with more strings than intended.


Your "Type A" is a NEMA 1-15 non-polarized connector. The blades are 1/4" tall.

Your "Type B" is a NEMA 1-15 polarized connector. The blades are 1/4" and 5/16", with the taller blade being neutral.

The polarization is for your protection, as the hot wire requires better insulation than the neutral. Non-polarized one are either rather old, or double insulated.

While our friends in east Asia will make anything, such an adapter (which basically exists to defeat a safety feature) would be as illegal as such a thing can get. There is no Big Brother chasing down these shady vendors, the consequences are mainly that your fire/liability insurance will not pay out.

For an old non-polarized set, throw it out and buy LED. For a new non-polarized set, I don't see any problem polarizing it by changing plug and socket. Make sure the wide blade is the same on both ends.

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