Main article: Magnetic coupling A magnetic coupling uses magnetic forces to transmit the power from one shaft to another without any contact. This allows for full medium separation. Therefore can provide the ability to hermetically separate two areas whilst continuing to transmit mechanical power from one to the other making these couplings ideal for applications where prevention of cross contamination is essential. Oldham[ edit ] Animated Oldham coupler An Oldham coupling has three discs, one coupled to the input, one coupled to the output, and a middle disc that is joined to the first two by tongue and groove.
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Since the coefficient of steel conduit is between 2—3 times less than that of PVC conduit you would need more expansion fittings for PVC conduit for a given temperature and length than for steel conduit. We have used the coefficient of expansion of steel, rather than the 0. NOTE: Listed fittings are tested under prescribed torque, which represents normal, not excessive force. Set-screw type The length of screws provided with set-screw type fittings varies.
The appropriate torque for some designs is reached when the head of the screw touches a screw boss on the fitting. This cannot be universally relied upon, however. Screws on certain fitting designs, particularly larger trade sizes, can offer more than one tightening option including screwdriver Slot, Phillips, or Robertson-square drive and bolt head for wrench application hex or square.
Greater mechanical advantage and torque can generally be achieved with a wrench. Where tightening options for both screwdriver and wrench application are offered, torque should be limited to that which can be applied by the screwdriver.
Compression gland type Generally, most compression gland nuts achieve maximum securement after hand tightening and then wrench tightening one or two additional turns. Tape shall be applied after the fitting is assembled and secured to the conduit.
Threaded fittings Threaded joints, both fitting to conduit and fitting to threaded integral box entries, shall be made up wrench tight. NOTE: Avoid excessive force. Generally a force equivalent to hand tight plus one full turn with an appropriate tool is recommended. This should ensure engagement of at least three full threads. Conduit bodies generally have an integral bushing to provide a smooth surface for conductors when pulled. This bushing is often mistaken for a conduit end stop. It is not necessary that the conduit be inserted flush against this bushing to assure a secure joint.
Attachment to boxes and support Prior to attachment to a box, enclosure or a threadless coupling, RMC, IMC and EMT shall be supported at intervals required by the NEC, using raceway supports intended for the purpose and secured by hardware acceptable to the local jurisdiction. NOTE: The variability of mounting surfaces, expected loads, and application environments will determine the appropriate support options and securement hardware.
Project specifications normally calculate support requirements based on the minimum spacing intervals given in the NEC. Properly align the raceway, fittings and knockouts to provide secure mechanical and electrical connections. Allow sufficient conduit length to complete engagement of the conduit and fittings at joints and entries.
A locknut shall always be assembled between a conduit bushing and the inside of the box or enclosure. EMT connectors are permitted to be assembled into threaded entries of boxes, conduit bodies or internally threaded fittings having tapered threads NPT. Threaded openings where these fittings are intended to be used are permitted to have either tapered NPT or straight NPS threads.
NOTE: While securing the locknut, take care to avoid excessive pressure when gripping the body of the fitting is necessary. Do not rely upon locknuts to penetrate nonconductive coatings on enclosures. Coatings shall be removed in the locknut contact area prior to raceway assembly to ensure that a continuous ground path is achieved. Touch up bare area as needed after installation.
Verification of installation After the raceway is fully installed and supported, and prior to installing conductors in the raceway, all fittings and locknuts shall be re-examined for secureness see 5. Stay in Touch — Subscribe to our blog, The Conduit Connection, to receive insights and industry news: Subscribe to our blog.
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