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Chris Meadows |
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Product Line Manager
Panduit Corp.
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Chris has a B.S. in Industrial Technology from Illinois State University and an MBA from Lewis University. Chris has been with Panduit for the past 17 years - more than half of which was spent in manufacturing engineering functions before moving into product line management for wiring duct. In his current role, he is responsible for the design, development, product management and manufacturing of the wiring duct product line. Chris is fielding questions in the area of wiring duct usage in electrical control panels. Categories include material selection and characteristics, wirefill calculation, and installation methods.
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| Q. |
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I want to know if there is a standard for construction of electrical panels for industrial machines (ex. Digital Prining Machine) or not?
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The primary standards used for the construction of electrical control panels for industrial equipment are:
1. NFPA 79-2002 Electrical Standard for Industrial Machinery
2. UL 508 Industrial Control Equipment
3. NFPA 70-2005 National Electrical Code, Article 409 Industrial Control Panels
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i would like to design panel acccording to I/O counts and wires .can u suggest the sizing & selection of ducts ,and how amny condoctors it can carry for different conductor sizes.
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Thank you for an excellent question. Sizing the wiring duct to be used can be difficult to determine. Most wiring duct manufacturers do typically publish the wire fill of each channel for common wire types in their catalog for basic reference. However below are some additional calculations you may employ to help you get close to the optimal size(s) faster.
Please also note that if you are not looking forward to doing these calculations yourself a pre-configured spreadsheet is available for download from the Panduit website at the following link.
As specified in NFPA79-2002 section 14.5.2, Percentage Fills of Raceways (Ducts), a wire fill may not exceed 50% of the available internal cross sectional area of the channel.
To determine suitable duct sizes based on the wires you have, use the following formula to compare to the nominal area of (for example) a Panduit wiring duct channel: Comparison Area = 2.23 x Wire Area . (Wire Area = PIr2 x total # of wires.)
For multiple wire types and sizes you will need to sum the comparison area from each wire type or determine the average wire O.D. with the following formula: Sum of (# of wire1 x wire1 O.D.) + (# of wire2 x wire2 O.D.)/total # of wires
Choose wiring duct sizes with a nominal cross sectional area that is greater than the comparison area you calculated above. Duct width x duct height = nominal cross sectional area.
To do the opposite and determine the wire fill of an already known duct size use the following formula for Panduit’s Flush Cover Duct: Duct Width x Duct Height / 1.75 x D2 (D = Wire O.D. and 2 = squared)
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| Q. |
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In hospitals we frequently use surface mounted network jacks on plaster, tile, concrete walls where fishing is too difficult. However, we are always re-mounting these because the equipment users are taking off with the portable ECG, Ultrasound or mobile computer carts while still plugged in. With an in-wall box the jack pulls out and we can push it back in (after we verify integrity) but the surface mount boxes are pulling off (leaving adhesive strips behind on the wall). What products or techniques do you have to make these installations more robust?
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| A. |
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Thank you for your question. Panduit is a manufacturer of surface raceway and networking products which are often used in the application you describe. I have consulted my colleagues with more expertise in surface mount raceways and outlet boxes to answer your question.
Most surface mount outlet boxes have provisions for mounting with either screws, or adhesive tape. In those applications where there is a need for a more robust application, screw mounting the box, with a washer (to prevent the screw head from being pulled through the box base) under the screw head, and an anchor appropriate for the wall material would provide a more robust application.
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In certain circumstances, UL 508 requires separation/spacing between low and medium voltage conductors running in the same channel (duct). Can I use divider wall to separate these conductors?
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Per UL 508 Section 15, separation is required when the conductors are not insulated for the maximum voltage for either circuit. In an installation where separation by air spacing is not appropriate, an insulating barrier, such as a divider wall, is allowed. The divider wall must be manufactured from an insulating material, such as PVC, exhibiting minimum properties described in UL 508 Section 15. These properties include High Current Arc Resistance to Ignition (HAI), Hot Wire Ignition (HWI), Comparative Tracking Index (CTI), electrical Relative Thermal Index (RTI) and UL 94 flame class. Check with your supplier to make sure the divider wall is compliant with these requirements.
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What is the maximum use temperature and humidity for wiring duct?
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Most PVC wiring duct is UL recognized up to a maximum use temperature of 50 C/122 F. Since PVC material is not hygroscopic, it should perform as intended at a humidity up to 80 percent. If the inside of the enclosure is going to have prolonged exposure to temperatures above 50 C/122 F, than it is recommended to use a wiring duct made from a Polyphenylene Oxide (PPO) material that is typically UL recognized for 95 C/203 F
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