This video covers everything you need to know about working with EMT (electrical metallic tubing) as an electrician. I cover the topics discussed in the national electric code article 358 on uses permitted, securing and supporting, and much more. This video is more of a code-overview of EMT, so let’s begin at the beginning of article 358 of the NEC with the uses permitted and not-permitted.
WHAT IS EMT?
EMT stands for electrical metallic tubing, and is a thin-walled raceway that electricians use to pass conductors through. It is often called a conduit in layman’s terms, however it is more specifically a type of tubing. EMT is used indoors and outdoors, and there are several types like Aluminum, Galvanized, and Stainless that can be used in different situations and at different price-points.
358.10 - USES PERMITTED
EMT is allowed to be used in dry, damp, and wet locations as well as in concrete or direct contact with the earth as long as you follow 358.10(B)
There are different types of EMT that have different properties as well, so make sure that you're using the correct type in the correct environment before making assumptions that everything is ok for general use. For example Aluminum EMT is not approved to be direct buried unless there's a supplimentary coating or protection around it - whereas stainless steel and galvanized steel EMT are allowed.
358.12 - USES NOT-PERMITTED
You cannot install EMT where it is subject to physical damage, or where it is used as a support for a luminaire or other equipment. For both of these RMC (rigid metal conduit) would be acceptable. So if you're working in parking garages near vehicle traffic, or in corrosive environments where the EMT may get damaged, you need to use a better method like Rigid to protect your conductors.
358.14 - DISSIMILAR METALS
Galvanic action is a serious issue to look into when dealing with dissimilar metals touching each other. A lot of people don't think about this when installing conduit, but the nature of two different metals is that one of them is more active and the other is more passive. The more passive metal will begin to weaken/corrode the more active metal and over time may destroy the active metal. This is especially dangerous when using EMT as an equipment grounding conductor. Over a long enough time, that one complete conduit system may turn into several disjointed segments due to corrosion, leaving you with no equipment ground.
358.20 - SIZE
There are minimum and maximum trade sizes that are allowed to be used as EMT. They must be no smaller than 1/2" and no larger than 4." You can't just take a piece of 6" pipe, slap some conductors in it, and call it EMT.
358.24 AND .26 - BENDS
348.24 specifically talks about ensuring that when bending conduit, your bends are not damaging the internal diameter of the tubing, and not reducing the diameter of the tubing. This makes damaging the conductors inside more likely, as well as more difficult to pull in or out.
358.26 Talks about how many bends you can have in one complete run of EMT - from box to box, or pull point to pull point. The max for most conduits/tubing is 360 degrees of bends. So that means no more than 4 90-degree bends from one box to another. The more you do this you'll see why this is - it's difficult as hell to get conductors pulled through, and more often than not you damage the insulation of the conductors when pulling both in and out - if more than 360 degrees of bends exist in the run.
358.28 - REAMING
This section requires you to ream, or clean, the inside of any newly cut conduit before installing it. When cutting EMT you will often times have an extremely sharp inner edge that conductors can be damaged by pulling across these edges. It’s on you to clean the cut end of the conduit in whatever way you see fit, and the NEC doesn’t say you have to ream with any specific tool. Most people carry with them a reaming-screw-driver to make this job easier, but I’ve seen others use channel-locks, pliers, needle-nose, other pipe, and a whole host of other methods. The end result should be a clean inner and outer edge at that newly cut edge.
358.30 SECURING & SUPPORTING
With most other rigid conduits and tubing the 10-foot rule still applies to EMT. This means that you must securely support EMT no more than every 10-feet. This means you can strap it every 3 feet if you want, just not more than 10 feet between straps/supports.
This section also requires you to strap within 3-feet of any box, panel, or termination point for that conduit run. That’s not difficult to remember. From your panel or box, run your conduit up, strap it within 3 feet of the panel, then every 10 feet after that. Now I will say THIS IS THE MINIMUM STANDARD - meaning I personally prefer doubling up on straps so a lot of times I’ll strap within 3 feet of the panel, then every 5 feet after. This is WITHIN the standard, and EXCEEDS the standard. Inspectors appreciate when you exceed standards, but they hate when you fall short of them.
358.42 - COUPLINGS & CONNECTORS
Couplings and connectors must be made up tight, and when installed in concrete or wet locations must be approved for the use. This is extremely important because EMT is considered an equipment grounding conductor in 358.60. If any part of the EMT system is not tight, you lose the effective ground-fault path and could potentially lose your ground if employing this method. This is very rare nowadays but you do see it in older systems that you come across.
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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.**