Some, but not all, three-way light switches are marked with a "Top". Why?

Here are some examples. These pics are all taken from ordinary three-way Decora light switches.

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It's easy enough to search for photos of ones that do not have the marking.

The first one I saw was the Cooper one and I thought maybe it's so the UL marking will be prominent and right-side-up for inspection. But the others don't have the UL marking in the same place.

Perhaps it is because regular on/off switches must be marked with a top, and these manufacturers want to accustom installers to looking for the marking and getting it right? So marking three-way switches reenforces a good habit? Just a theory, not very likely.

The Legrand one has "Legrand" marked on the paddle (visible to users) so if it's mounted upside down that writing is upside down. But the others don't have exposed writing. And as far as that goes, if it were the only reason, if some fool is going to install the obvious "Legrand" mark upside down, I don't think a much more subtle and hidden "top" will change anything!


One possibility is that the manufacturers simply maintain a single die for stamping all their yokes of a given size, rather than one with the "top" mark and one without. It doesn't hurt anything to mark 3-way switches with a "top", and it simplifies the manufacturing line a tiny bit.

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    UL/CSA/ETL can be a bit persnickety, if submitted for testing with the stamp or instructions they are obligated to include stamp unless resubmitted without the stamp. Dec 4 '21 at 15:58
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    If correct, and if additionally these standard yokes are consistently mounted the same way on all devices from the same manufacturer, then the ground terminals will all line up along the top or bottom of the box making installation of mixed devices a little easier.
    – jay613
    Dec 4 '21 at 15:59
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    @jay613 No they won't lol, on 3-way switches the positions of screws are completely randomized. If you presume "ground down" there are 12 possibilities, and I've seen 6 in the same building! Dec 4 '21 at 20:40
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    This is almost certainly it, as there are also dozens of models with internal lights, dimmers, etc. Dec 4 '21 at 23:05
  • @jay613, installation and inspection easier. The latter far more important to UL/CSA/ETL
    – bsd
    Dec 5 '21 at 9:11

In addition to the very likely answer already posted of simplifies manufacturing, it may be so that screw positions can be defined for that particular model. There is no standardization across the industry, or even necessarily within a particular product line. But every device comes with instructions and for those instructions to make sense, screw position and device orientation matter.

In this Leviton from Home Depot, the screw configuration (pictures on Home Depot web page and instructions) are:

  • Green = Ground = Upper left
  • Black = Common = Lower Right
  • Travelers = Brass = Lower Left and Upper Right

That is actually an interesting combination. It might seem more logical to have the travelers be one of:

  • Top Left/Right
  • Bottom Left/Right
  • Top/Bottom Left
  • Top/Bottom Right

but this particular configuration has the neat side-effect that if you do rotate 180 degrees (a.k.a., install upside down), the travelers are still Lower Left and Upper Right. Of course, then you need to look at the screw colors to determine where to connect the common (Hot or Switched Hot) wire, but all you need to remember for that is "Green = Ground", which is the one thing guaranteed everywhere.

  • I agree that if they are manufactured and installed in a consistent orientation, it may make installation, inspection and maintenance easier in a facility if all the switches are from the same Manufacturer/line and the electricians are required to follow the correct orientation. But ... this all seems rather far fetched.
    – jay613
    Dec 6 '21 at 3:50
  • I'm not saying that the installers actually have to install them "Top side up". I've certainly seen plenty of receptacles installed with ground at the top (I have one in my house) and ordinary toggle switches (which do have a normal "top") installed sideways, etc. But in order to be able to follow instruction manuals there has to be a way to identify "top". Doesn't have to be, because the screws are color-coded, but it helps. Dec 6 '21 at 3:53

Simply - its an aid at re-assembly time. Presuming the switch was assembled with "TOP" at the top originally, subsequent reassembling doesn't require the wiring to be traced, or the switch to be tested live to make sure it is going back in the right way around.

It can be quite annoying to re-do work you just finished reassembling because of something simple like assembling it upside down.

  • Except that a 3-way switch with nothing extra (dimmer or smarts) really can go in either way with no functional difference and prefectly save. Dec 5 '21 at 12:46
  • @manassehkatz-Moving2Codidact Sure - there are some cases that don't need this. Doesn't mean that it is pointless.
    – Criggie
    Dec 5 '21 at 18:23
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    If there is something "extra" then the "TOP" can make sense (e.g., an unlabeled slider for a dimmer might not be obvious which way is "up"). But that doesn't explain all the other switches. Dec 5 '21 at 19:08
  • I don't understand this answer. If you're saying you can remove the switch, for some reason, then put it back without checking that you've got the traveler on the correct screw, just make sure to put it back the same way ... I suppose that would work. But another way would be just just make sure you put the traveller on the right screw. I doubt "Top" is a facilitator of carelessness.
    – jay613
    Dec 6 '21 at 3:50
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    @manassehkatz-Moving2Codidact The three switches in my pictures are all vanilla three-ways. Nothing directional about them. Agreed re dimmers etc., but this possibly reenforces the answer with all the votes .. .They just stamp this on everything for all kinds of consistency reasons.
    – jay613
    Dec 6 '21 at 3:50

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