Every type of conduit has a listed approved series of connectors and couplings that are designed to be used as fittings for those specific raceways. Today we look at EMT couplings and connectors.
Let’s start out with couplings. A coupling is literally used to “couple” two pieces of conduit together. There are various styles of couplings, each with it’s own unique purpose that we’ll get into in this article. A coupling is the same on both sides, so there’s no right way to put it on. There are, however, some considerations that should be made when using set screw connectors for aesthetics and workability in the future.
Connectors look very similar to couplings but have a distinct difference. Connectors are meant to slide over the end of a piece of conduit on one side, and tighten down to the inside of a box or enclosure on the other end. You use connectors at the ends of conduit runs to land into a box. You will almost always use both couplings and connectors in every conduit run together.
Set-screw connectors are used indoors only. They’re not designed to withstand wet conditions, so we only use them in buildings. They work by tightening a set-screw down on the conduit once it is slid in place to keep a firm connection to the conduit. Larger sizes of couplings and connectors will have multiple set-screws that you have to use to properly secure the fitting to the conduit.
Using set-screw style connectors and couplings is often times much quicker than using compression fittings, as all you need to do is tighten the screw down and move on.
Compression connectors were typically used outdoors until a few years back. UL reviewed the listing of these connectors to be listed as “rain-tight” and found that they do allow water into the conduit so there needed to be some added efforts to be truly “rain-tight.”
Compression fittings can be used indoors as well. They actual bite down on the conduit a lot better than a standard set-screw connector or coupling. This is especially important when using EMT as an equipment grounding conductor. Set-screw will do the trick most of the time, but especially environments where vibration is an issue, it may be a better idea to use compression fittings since they secure 360 degrees around a piece of conduit.
These do take slightly longer to install, as you need to use two pairs of channel-locks to tighten them. Also they can be a pain to get over the conduit when installing them and many times you need to completely disassemble them to get them to fit correctly. A set-screw fitting just slides on, tightens with a screw-driver, and you’re done.
The last thing to mention is that some couplings and connectors are specifically designed to be use outdoors. They will always be the compression type, never the set-screw type.
In the image above you can see two styles of compression connectors. The top is a listed rain-tight fitting, the bottom is a standard compression connector - non rain-tight. For years compression fittings have been used outdoors to keep water out of the raceway, however Underwriters Laboratories has tested this and found standard compression alone does not do its job satisfactorily.
The recent changes to the UL listing for rain-fittings made the manufacturer have to add some pieces to their fittings to ensure they get their listing. The fitting at the bottom of the image can no-longer be used out doors as it is likely to allow moisture into the conduit.
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**Disclaimer - These videos are for training purposes alone, all work done on electrical systems should be done by a licensed and insured electrical contractor. If you are not an electrician, do not attempt any of the work you are seeing in these videos.**