I recently found a job and saw what looked like an apprentice electrician who was really struggling to get his band of fish through an EMT race. It caught my attention, so I hung out to see what was going on. After seeing him fight a little, I went inside to investigate, and his line stroke had curves of 630 degrees (6 – 90s and 2 – 45). He was able to push it through the first 4 to 90 corners, but almost ironically, he couldn`t get the group through the 5th. A box offset is the small degree that folds back to back in opposite directions to move the pipe to an electric box. The rule of thumb is no, box offsets do not count towards the total number of offsets if the offset is less than the diameter of the line. In this case, there is always a straight path through the line where the wires can be pulled without additional friction. For example, if you have a line of 1″, then if the offset curves are less than 1″, there is always a straight path through. This means that you will still be able to see through the line in the curve. Curves 358.26 — number in one go. “There must be no more than the equivalent of four quarters of curves (a total of 360 degrees) between the points of traction, for example, pipe bodies and boxes.” Today we are entering the 360-degree bending rule for bending pipes.
We cover 358.26 of the National Electrical Code, which deals with curvatures in EMT (electrical metal pipes). The NEC codebook does not differentiate between bending radii, nor does it make exceptions to the total of turns allowed for long sweeps. As a rule, a long sweep is always an elbow and adds friction to the ladders during traction, and therefore should always be counted as a fold when adding the sum. The obvious follow-up question is: “How many degrees in the direction of a line course does a quarter-angle turn offer?” A quarter turn to the NEC is what the rest of us call a 90-degree turn or just a “90.” In simple terms, it simply means which combination of turns (90s, 45s, 30s, etc.) should not exceed the total number between train points. As you can imagine, the pipe creates another point of friction on the wire during traction, making it increasingly difficult to pull it as it passes through additional turns. The purpose behind the curve boundary is to solve such problems and ensure that the conductors can be pulled through the track without damaging the insulation on the wires. However, nowhere do I find that the NEC specifically defines a “point of attraction”, with the exception of the examples of “Bodies and boxes of ducts”. It makes sense to me that “pipe body” means that two separate pipes are connected with a single plug (depending on the connectors up to 90 degree curvature in the image above), since the pipe bodies can be separated to allow pulling without overloading the wire, but I want to confirm if this is the correct interpretation. For a Tool-Box Quick-Card field guide, read this 4-page waterproof guide that contains essential information about bending electrical wires used in architectural plans and technical drawings. Get it on Amazon in just a day or two for less than the price of lunch.
However, if your offset is to be greater than the diameter of the line, the curvatures must be added to the total number. This is usually a 20-degree addition (two 10-degree curves). When bending the pipes, we must be careful not to bend our strokes between the points of traction. I`ve seen too many times and made the mistake myself very early, where people do a great job of piping but forget to put pull points between their curves. There is a certain point where we can get where you will NOT be able to pull the ladder across the line. Background: I have to make six 90-degree turns in a 2″ EMT channel to lay wire for a new sub-panel, which means my 2011 NEC run is subject to clause 358.26: in fact, you should buy the wires last. We so often see beginners learning more about their situation and realizing that they are better off with a different thread than the one they have chosen. But it`s too late! You have already purchased it.
So don`t do it – buy the thread for the complicated work after everything else is done. A great video and resource that I found if you want to learn the basics of duct bending can be found here. LinkedIn – www.linkedin.com/in/dustinste. Instagram – www.instagram.com/electrician_u To not lie, it took me a bit of Google research until I finally realized that the NEC is actually published by the NFPA (National Fire Protection Association) and is actually called NFPA 70 “National Electrical Code”. The reason for this is that you can damage the insulation around the ladder if you pull too much from it or try to remove it again. There are other factors to consider, such as heat aggregation and dissipation, but most importantly, physical damage to drivers is a major concern. However, it`s fun. Looking at this apprentice hanging from the ceiling and on a ribbon of fish (she. B.
not yours), who tried to pull wire through a pipe, just screwed them. Then you can teach without saying anything. EDIT: Thank you all for your answers. I kind of overlooked the definition of conduction bodies in the standard: there`s a good reason for the old phrase I`ve heard more than one electrician say. “You whistle it, you pull it.” NFPA allows free access to book online when you sign up for a free subscription on the site, but its viewer is clumsy and so painful to navigate. It seems that with the 2020 version, they have removed the option to buy PDF, so you can only get a 1-year subscription service for about $1400.