2
\$\begingroup\$

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?)

\$\endgroup\$
3
\$\begingroup\$

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

\$\endgroup\$
  • \$\begingroup\$ Thanks. For a 5 year old LED TV, does the plug orientation matter at all? Or do you agree with Bimpelrekkkie that it does not? \$\endgroup\$ – RockPaperLizard May 22 '18 at 17:40
  • \$\begingroup\$ If you understand my answer , it answers that. \$\endgroup\$ – Sunnyskyguy EE75 May 22 '18 at 17:44
  • \$\begingroup\$ I guess I don't fully understand your answer! Can you answer my question? \$\endgroup\$ – RockPaperLizard May 22 '18 at 17:46
  • \$\begingroup\$ There may be a situation where functional interference is influenced by polarity. If none , it does not matter. There may be other reasons for using a polarized plug that improve margin above required limits, but are not critical. \$\endgroup\$ – Sunnyskyguy EE75 May 22 '18 at 17:55
1
\$\begingroup\$

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.

\$\endgroup\$
  • \$\begingroup\$ 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. \$\endgroup\$ – RockPaperLizard May 22 '18 at 7:45
  • 1
    \$\begingroup\$ 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. \$\endgroup\$ – Bimpelrekkie May 22 '18 at 7:52

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.