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  1. How is the strain relief supposed to be done on this replacement plug?

There is no way to tighten the clamp enough for it to actually securely hold onto the power cord. The threads on one of the clamp screws started stripping well before it even started gripping the power cord. The power cord is about 3/8" in diameter (update: turns out it's 1/4"), while the inside diameter of the strain relief "tunnel" is a good 1/2", so for it to make contact it seems like the rubber would have to be seriously crushed.

Alternatively, I thought about putting a knot in the cord, but as can be seen, the cord is not flexible enough with the outer sheathing, nor would the resulting bulky knot fit inside the plug. I suppose I could strip more sheathing and knot the insulated wires, but that doesn't seem like a good idea as the sheathing would not be taking any of the strain.

This seems like a common plug design so how is that strain relief supposed to work?

  1. Should the plug be wired as it was originally, or according to standards?

In the original plug, the black wire goes to the polarized, wide prong of the plug. In contrast, multiple resources affirm that the white should go to the polarized, wide prong.

This repair is for a polarized two-prong plug on a vacuum cleaner where the prongs came loose in the molded plug. I have no idea how it is wired internally (i.e. are the wire colors connected the wrong way inside the vacuum too?), but for now I wired it the same way as the original plug, even though it seems wrong. Is this a problem? I don't want to change something without being confident.

UPDATE for Q1: Strain relief "fixed" with small concentric sections (split horizontally to slip over the cord) of clear PVC tubing (1/4" ID, 3/8" OD) and another PVC fuel hose (3/8" ID, ~1/2" OD).

Also used a worm gear hose clamp that secures the whole assembly very tightly and evenly, as opposed to the oval-shaped clamps which crush unevenly, not to mention the weak screws whose threads strip when it gets tight.

Next time, I will buy a different plug for sure, but for now with these improvised fixes, it works better than the original design.

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UPDATE for Q2: I have wired the black/hot wire to the right/narrow prong, and the white/neutral wire to the left/wide prong, according to the standard. The prongs on the plug being replaced are broken, and I believe they may have come entirely detached from the plug and someone might have reinserted them the wrong way! Seems more plausible than the plug being wired incorrectly by a major manufacturer.

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    don't be changing the way the wires are connected ... connect the wires exactly same as with the original plug
    – jsotola
    Mar 13, 2022 at 3:20
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    A plug of that sort typically includes some filler pieces to take up the space between the cord and the clamping area. Sometimes several different ones to accommodate different cord sizes. Yours appears to be missing those parts (you have what seems to be a thin reducer at the very end of the plug - this would be more of a sleeve or block slightly longer than the clamped section.)
    – Ecnerwal
    Mar 13, 2022 at 3:20
  • It looks like the plug is for a heavier gauge of wire (unless @Ecnerwal is correct and there are missing filler pieces.) You could wrap the wire in black tape to make it thicker. Mar 13, 2022 at 5:54
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    I would spend a couple dollars more and get a better quality plug. Make sure you are getting a listed plug, some cheep imports are just that and have issues.
    – Ed Beal
    Mar 13, 2022 at 16:48
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    @adatum Yes, unswitched would be neutral and switched would be hot, if designed properly. Obviously you don't want always-hot on he shell of a light bulb socket. Sounds like a faulty plug/cord assembly, and that is surprising for a UL listed assembly. Mar 14, 2022 at 22:36

3 Answers 3

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'Power cord is 3/8" diameter'. So find an inch or two of tubing that's about 3/8 " ID. Slide it over the cord, and into the clamp. It may be easier to cut the tube longitudinally, rather than take the fitting off. Clear plastic tube would look better, although it shouldn't protrude from the end of the plug anyway.

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  • Thanks, this is exactly what I did (updated my post with pictures), with two concentric PVC tube sections. Combined with a worm gear hose clamp, the strain relief is now held very securely.
    – adatum
    Mar 14, 2022 at 2:40
  • If it's AC it won't make any difference which way round the wires go, as long as they go to the original pins - not the earth. It may make sense to say where in the world this is.
    – Tim
    Mar 14, 2022 at 7:37
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If the original filler pieces are missing then I would be going to my spares box.

I would be looking for the small plates that can be clamped to the cable - they have two screws and are, or were, fairly common in some types of plug.

Any sticky tape will move over time, been there, done that...

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  • Good tip about avoiding tape, sparing a mess and frustration.
    – adatum
    Mar 14, 2022 at 2:44
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It's the wrong type of plug for that cord (or it's broken).

I agree with a comment that it probably is the type that uses one of several inserts or spacers, and the spacers are missing.

When I have trouble matching a cord to a plug or strain-relief, I bring the cord into an electrical supply house. They know what to give you.

I would advise not converting it from a 2-prong plug to a 3-prong plug. 3-prong cables are larger, and that will make it difficult to find a match.

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  • Unfortunately the 2-prong plugs I saw looked really flimsy. I think the main issue was, as you and others point out, missing spacers. I updated my post with pictures of an improvised fix with concentric tubing which now results in a well-secured strain relief.
    – adatum
    Mar 14, 2022 at 2:43
  • @adatum try a real electrical supply house. They will tend to have better selection, but most importantly, a clerk who knows the product and knows the inventory. Mar 14, 2022 at 22:42
  • If only I knew of a real electrical supply house. It is notoriously difficult searching for such shops, and the ones I find tend to be geared towards commercial professionals and not the general public. Even a local electronics shop told me they had drafted their own list of suppliers for different types of components because finding this information online is next to impossible. The search continues.
    – adatum
    Mar 15, 2022 at 2:27
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    @adatum Yes, they are geared for professionals. But most will cheerfully deal with you, and even give you good pricing if you make an effort to not be the customer from hell and not expect them to teach you (that's our job lol). Mention that you're sick of overpaying at Home Depot, that helps. Mar 15, 2022 at 5:48

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