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I have a handful of power cables like this:

polarized example of power cable

Some have polarized male plugs, while others are not polarized.

Given that the female end appears to be reversible, why are some of them polarized?

I have an LED television that came with a polarized version of one of these cables. But I have a longer non-polarized version. Would it harm either myself or the TV to use a non-polarized version of the cable?

(Bonus: Do these cables have a name?)

RockPaperLz- Mask it or Casket
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  • Possible duplicate of [Aren't non-polarized plugs a little dangerous? Why still use them?](https://electronics.stackexchange.com/questions/124215/arent-non-polarized-plugs-a-little-dangerous-why-still-use-them) – winny May 22 '18 at 06:42
  • Updated question to make sure not a duplicate. – RockPaperLz- Mask it or Casket May 22 '18 at 06:53
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    Figure 8 C7 to US Plug 2 pin AC Power Cable – jsotola May 22 '18 at 06:53
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    more official name .... NEMA 1-15 male plug to a IEC 60320 C7 female connector ...... fond at this site https://www.stayonline.com/reference-iec320.aspx – jsotola May 22 '18 at 07:10
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    For the record, NEMA is an acronym for National Electrical Manufacturers Association NOT the North American Equipment Manufacturing Association as stated above. – Kevin Tucker Feb 19 '21 at 07:34

2 Answers2

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Your photo is the polarized NEMA 1-15 P (Plug) to the non-polarized IEC 60320 C7.

It is safe for consumer goods that are double-insulated that do not require grounded polarized plugs for 120Vac line, Neutral nor earth ground.

However, the alternative non-polarized Receptacle NEMA 1-15 P is available but it's corresponding receptacle the NEMA 1-15 R has been prohibited in new construction in the United States and Canada since 1962, but is still allowed for repairs to older homes.

The non-polarized plug allows the user to swap orientation in case of a difference in high frequency noise (buzz) that can sometimes be unbalanced or have inputs that are unbalanced such that swapping leads of the unintended conductor or receiver can reduce interference in audio systems. However this is a poor man's solution to audio EMC and not often needed or explored.

NEMA is the North American Equipment Manufacturing Association that provides guidelines but not laws nor enforcement.

What may be curious to some is your cable has a polarized male plug but a non-polarized the C7 adapter, so the above tweaks to EM compatibility can still be tried reversing line and neutral. Although line and neutral return noise tends to cancel out, in some situations where it is not uniform noise might not cancel yet still be below unintended radiation thresholds or may be above on grandfathered equipment not qualified.

This is the polarized version of the C7 female plug.enter image description here

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Tony Stewart EE75
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Since mains voltage is AC, the "polarization" can only refer to the difference between the live and neutral wires. Depending on how your mains is wired (which depends on your country) the neutral wire isn't supposed to have a voltage relative to ground.

However, this cannot be relied upon so it is unsafe to assume the neutral is "safe to touch". That in turn makes it rather pointless to make a difference between live and neutral so obeying a certain "polarity" is also pointless.

In addition to that, any modern device with a "figure 8" mains input (the female end of that cable you're showing) needs to have "double insulation" meaning it does not need an earth/ground connection. You can recognize "double insulation" from the symbol consisting of two squares:

enter image description here

Your new TV should have this symbol!

Note that there are also mains devices like toasters and computers which have 3-pin mains inputs. These devices do require the ground connection to make sure that the metal case is safe to touch.

Modern power supplies like the one in your TV do not care or even notice how you connect live and neutral so it does not matter how you connect them.

So you can safely use a non-polarized lead, the TV doesn't care at all assuming it is designed properly according to modern safety standards.

Bimpelrekkie
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  • Fantastic answer. Thank you. Additional information follows... just let me know if it changes anything: TV is about 5 years old and is installed in the USA. – RockPaperLz- Mask it or Casket May 22 '18 at 07:45
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    5 Years old is still "modern" enough for my answer to apply. Only very old equipment (1980's and before) might not meet the modern safety standards. When in doubt, check for the logo, if it is there then "mains polarity" should not matter. – Bimpelrekkie May 22 '18 at 07:52