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OPTIMIZING 24 VDC POWER INSTALLATION Jerry Wick, Advanced Energy Industries, Inc. Proper wiring of AE products to the master 24 VDC power supply can prevent a variety of problems. This guide recommends specific wiring practices required for consistent product performance. It assumes that the relevant application has a main 24 VDC power supply and the output voltage from this supply is distributed to various devices located on or adjacent to the main equipment. The tables on pages 9 and 10 provide recommended wire gauge for various wire-length runs. Table of Contents Questions and Answers 2 General Wiring Recommendations 2 Wire Gauge and Voltage Drop 3 Wire Gauge Recommendations 4 Stray Signals 5 System Troubleshooting 6 Environmental Conditions and Cooling 7 This is a guide to recommended practices. These recommendations are not intended as mandates or absolute requirements. Local and internal requirements must take precedence as appropriate. General System Recommendations8 Products Recommended Four-Wire Gauge for Various Wire Length Runs 9 Recommended Two-Wire Gauge for Various Wire Length Runs 10 • All AE power supplies Applications • Vacuum processing Questions and Answers The following section provides key questions and answers, assembled from numerous problem solving sessions and best-practice recommendations. Question Question How can electrical power problems impact production? Why should product/system wiring be designed for performance? Answer Some negative effects include: Answer • No production (system or site down) Multiple power surveys indicate that approximately 80% • Damaged output (product does not meet specification) of all electrical problems originate within the facility. Only 20% • Additional and unexpected maintenance costs of electrical problems originate external to the facility. General Wiring Recommendations Question Question What overall wiring method does AE recommend between Why does AE discourage the use of series-connected (daisy the main 24 VDC power supply and the AE product? chain) loads connected to the main power supply? Answer Answer Each AE product should be individually connected to the Series-connected equipment requires complex, detailed, 24 VDC power supply via dedicated wiring of appropriate and careful load calculations. It would also require the use gauge. Wiring in a “daisy chain” pattern can cause issues with of multiple wire gauges. For example, if the site requirement equipment performance. were for eight 7 A loads, then: Question We use a common set of wires between the main power supply and a distribution point. Individual wire sets then go to each product. What wire gauges should we use? Answer Carefully sum the peak currents from each product. Use a conservatively high current listing to determine an acceptable wire gauge between the supply and the distribution point. Use individual product peak currents to determine what wire gauges should be used between the distribution point and each specific load. a)The wiring between load one and load two is calculated for 7 A. b)The wiring between load two and load three is calculated for 14 A. c)The wiring between load three and load four is calculated for 21 A. d)The wiring between load four and load five is calculated for 28 A. e)The wiring between load five and load six is calculated for 35 A. f) The wiring between load six and load seven is calculated for 42 A. g)The wiring between load seven and load eight is calculated for 49 A. h)The wiring between load eight and the power supply is calculated for 56 A. Thus, the appropriate wire gauge grew from reasonable to very large. Finding a series of power connectors that can accommodate this range in wire gauge would be extremely difficult. 2 Wire Gauge and Voltage Drop Question Question Why is it important to use the recommended wire gauge? 3% of 24 V is only 0.72 V. Why does such small voltage drop matter? Answer Wiring without sufficient current-carrying capacity results in excessive voltage drop. This reduced voltage, if even for a few milliseconds, may cause the using device to report “low input Answer A 3% drop is 30% of the total 10% allowable drop, a significant reduction in operating margin. voltage” or not to operate as expected. Voltage drops can cause anomalous product behavior. Question Can I gain any actual input voltage data from equipment that Question is already on my site? What is the significance of the voltage lost between the power supply and the AE product? Answer Most AE products are designed to function with a nominal 24 VDC ±10% input voltage. If there is excessive voltage drop in the wiring, the product has insufficient voltage to Answer Possibly. Some AE products have an input voltage logging function already in their software. Where available, this monitor function can be accessed using AE Virtual Front Panel (VFP) software. correctly function. The lower voltage substantially decreases the product’s ability to ride through any externally caused 24 VDC voltage reductions. Energy storage in a capacitor Question is calculated as 0.5CV2. Thus, seemingly small changes in What maximum current is recommended for some common voltage cause dramatic changes in total energy storage. The wire gauges? product typically reports an input voltage failure and likely will not operate as desired when the voltage does drop below the allowable minimum. Answer Please refer to the following table. Table 1. Maximum current recommendations for common wire gauges [1]. Wire Gauge Max Recommended Current 24 6 22 8 20 10 3 Wire Gauge Recommendations Question Question What assumptions did AE make in providing the wire What product current (peak, instantaneous, nominal, gauge recommendation/run length distance tables inrush, other) rating do I need to use with the tables on pages 9 and 10? on pages 9 and 10? Answer Answer This guide assumes that the main supply output voltage Use the peak or maximum current rating. Do NOT use is 24.000 VDC measured at the output terminals of the nominal or steady state values. You do not have to use supply. The recommended wire gauge tables are based on maximum inrush current rating. an allowable 3% voltage drop. There are two sets of tables. One set of tables is for cases in which there are two wires in parallel for both the positive and negative conductors. The Question other set of tables is for cases in which there is just a single My equipment voltage specification is 24 VDC ±5%. Can I use wire for each polarity (positive and negative). No remote the tables? voltage sensing is assumed. Answer Yes. The tables are set up to provide a 3% voltage drop. Question Why do the wire gauge/run length distance tables, on pages 9 and 10, stop at approximately 30 m (100') length? Answer The 30 m distance accommodates the vast majority of actual use at most installations. Question How does the AWG wire gauge listed in the tables compare in area to either circular mills or millimeter squared dimensions? Answer The following information is identical to that in Table 8 in the NEC® Handbook. Table 2. Wire size equivalents [2] 4 Size in AWG MM Squared Circular Mills 18 0.823 1620 16 1.31 2580 14 2.08 4110 12 3.31 6530 10 5.261 10,380 8 8.367 16,510 6 13.30 26,240 4 21.15 41,740 3 26.67 52,620 2 33.62 66,360 1 42.41 83,690 Stray Signals Question Question Does AE have any recommendations for situations in which I observed excessive process-related signals on the 24 VDC the 24 VDC wiring must pass near RF cables and products power wiring. What solution does AE recommend? (stray signal pickup defect)? Answer Answer Do both pieces of equipment share either power or signal Small-amplitude RF can be eliminated or greatly reduced wiring? If moving power or signal wiring causes the observed through the use of ferrite beads or cores. The power wiring is signal to vary, the problem is caused by radiated emissions. run through the center of the bead/clamp. Use steel conduit Physically separating the wires is a low-cost aid to reduce to shield the power wiring if RF coupling to the 24 VDC wires the induced signal pickup. The following method to create is an issue. Use of flexible conduit is not recommended as a low-cost twisted-pair wire may help if the radiated noise has solution. Please note that a key assumption is that the power a frequency of less than 500 kHz. and RF wiring is already separated from the 24 VDC wiring as much as possible. Twist the wire approximately four to six turns per foot to create cables that can reduce stray AC or low-frequency magnetic pickup. The wire twisting causes the noise to Question How can I tell if the electrician installed the desired type of steel conduit? Answer Test with a small magnet. A magnet sticks to steel. become common mode. Common mode noise is reduced at the downstream transformer. Wire shielding or other EMI reduction techniques provide solutions if the two items share common I/O or power. Verify that you have correctly found the actual sources by turning equipment off. You do not have the correct source if the signal doesn't go away. Question What distance between products do you recommend, with RS-232 wiring? Question Answer Does AE recommend any wiring separation distance between The original RS-232 standard (1962) states a maximum wiring used for different functions? 15.2 m (50') distance. Today, longer distances are often used, with some data integrity issues. Low-capacitance wire and Answer wire shielding, as well as attention to wire routing, often A rule of thumb is that a separation of 2" (5.1 cm) or more results in good performance. Very long runs may also use often substantially reduces any signal cross coupling. This electronic boosters to amplify the signal. practice typically provides sufficient voltage reduction for most AC and RF cables. Question I see stray RF or process signals when I monitor the RS-232 Question wiring. What solutions do you recommend? How do I arrange two different types of wires that need to cross? Answer If wire separation hasn't reduced the signal pickup sufficiently, Answer use RS-232 cable equipped with an outer shield to reduce any All wiring that needs to cross should do so at a right angle. stray signal pickup. Connect the cable shield to earth ground This minimizes stray signal pickup. Always follow the at both ends if total cable is longer than 3 m (9.8'). 2" (5.1 cm) minimum separation rule. 5 Question We routinely place any extra cord or cable lengths behind a product. Is this a problem? Answer The cords/cables can couple energy simply due to being in close proximity. We suggest that you separate the cords/cables to reduce the coupling effect. Arranging the wire coils at right angles also reduces any signal coupling. The 2" (5.1 cm) separation recommendation generally reduces the coupled signal amplitude to less than a critical value. You can electrically reduce the wire/wire coupling by coiling the wire in a figure eight arrangement. This cord pattern is commonly used in product conducted interference testing. System Troubleshooting Question Question The system worked acceptably for a reasonable period of time. We recently experienced inconsistent performance. Suddenly, performance has been inconsistent. Any thoughts Any thoughts on possible causes? or suggestions? Answer Answer Check to see if any periodic maintenance or cleanup was Something has probably changed. What events happened scheduled. Verify that all switches are fully on/off in the at the date of the failure? A common problem is that an correct position and all cables are fastened. Keep a list of inadvertent change caused the failure. Has anything on the settings or create physical marks to show the desired switch tool, cables, or other nearby equipment been moved or positions. Always verify that all inner and outer covers are added? Did the system start running a different recipe? Were installed using the proper number of screws. any product or system covers removed or not installed using all hardware? Question Use only known (measured) facts when troubleshooting. This Several systems have what seem to be similar failures. approach quickly leads to the true root cause. This structured Any suggestions? approach to problem solving may go by such names as analytic trouble shooting or 8D, or another internal best- Answer practices term. Is this a new failure mode? If the systems used to work without defect, possibly some new or common factor is causing problems. If different but identical systems have near-simultaneous, identical issues, look for the common factors. Verify both the AC and DC local power quality at a point of concern. It's good practice to periodically measure the delivered power quality at the point of use. If an anomaly exists, it is important to know if this is a recent change or if this parameter has always existed at this location. 6 Question We measured large swings in DC voltage at the point of use. Suggestion? Answer Determine if the same voltage swing is present at the tool power supply. If it is, the supply either is defective or has excessive load. Check carefully for any short-term peak current load. Has any new or different equipment been added to the supply load? If the supply performed acceptably in the past, then a very common problem is that the cooling fan may be defective or turning slowly. Another common problem is a blocked air cooling path that causes the supply to overheat. If the tool power supply is connected to a “low” mains voltage, check to see if the voltage select switch (if present) was inadvertently set to the high-voltage position. Finally, check the supply electrolytic capacitors to see if they have an acceptable capacitance value, as they have a finite lifetime. Capacitors that are worn out cause excessive ripple on the output voltage or large swings as the supply regulation circuit attempts to create and hold a constant output. Question We measured large swings in AC voltage at the point of use. Suggestion? Answer Determine if the same voltage swing is present at the power panel. If it is, it’s likely that the supplying transformer is undersized or has excessive load. Check for both peak and RMS loads at the transformer output. Insufficient peak current capability typically manifests as waveform “flat topping.” Also check for new or unknown additional loads connected to the power panel. Environmental Conditions and Cooling Question Question The power supply will be located in a very warm environment. How much room do I need to allow for airflow at the fan The temperature might be close to the maximum ambient intake and exhaust? product temperature rating. Do you have any suggestions? Answer Answer The individual product manual should define the minimum Duct nearby cool air from an adjacent area to the air inlet space required for airflow. A rule of thumb is that the gap for of the product. Use a fan to force air to the product if the both intake and exhaust airflow should be the same size as product does not have a fan. If a product fan is present, it can the fan diameter, to avoid unnecessary restriction. pull the cool air via ducting. A necessary assumption is that the air intake has access to cool air. It also should not be located near the hot exhaust of another product. The hotter the air is, the shorter the product Question lifetime is before failure or need for service. My company doesn't want to add any air ducting to our equipment. The local area ambient temperature will be approximately 55°C (131°F). What are some possible effects from this planned usage? Answer We recommend operating AE products in accordance with their ambient temperature rating. 7 General System Recommendations Question Question Does AE have any general recommendations for the 24 VDC Why should the main power supply be plugged into main power supply? a “higher” voltage? Answer Answer AE strongly recommends that any 24 VDC main power supply The most common type of VAC power disturbance is a be selected with “universal” auto-voltage VAC input capability temporary voltage reduction. This lowered voltage condition (85 to 264 VAC). Any power supply of this type should be remains for a fraction of a second. The auto-voltage select plugged into a 240 VAC nominal outlet when possible. power supply automatically switches to the “lower” voltage range during this anomaly. The power supply automatically switches back to the “upper” voltage condition once the problem is not present. Result: The connected load(s) see Question Must I always consider using an uninterruptible power supply (UPS) for powering either critical equipment and/or processes? Answer No. Most installations can mitigate the majority of expected AC power problems with a properly sized line conditioner or constant voltage transformer along with thoughtful attention to on-site installation practices. A UPS should only be considered where absolute power quality is mandatory (for example, for a data center). 8 a constant steady state voltage and function without error during the external power defect. Recommended Four-Wire Gauge for Various Wire Length Runs These tables assume two wires in parallel for both positive and negative polarity. Run length refers to the one-way distance between the tool power supply terminals and the product use terminals along the path where the wires will be located (not line of sight). All wire lengths are rounded to the nearest whole number. 1 A Load 6 A Load Wire Gauge Wire Run Length Wire Gauge Wire Run Length 24 8 m (26') 22 2 m (7') 22 13 m (43') 20 3 m (11') 20 21 m (69') 18 6 m (18') 18 33 m (109') 16 9 m (29') 14 14 m (46') 12 22 m (71') 10 37 m (120') 2 A Load Wire Gauge Wire Run Length 24 4 m (13') 22 7 m (21') 7 A Load 20 10 m (34') Wire Gauge Wire Run Length 18 17 m (55') 20 3 m (10') 16 26 m (86') 18 5 m (16') 42 m (138') 16 7 m (24') 14 12 m (40') 12 18 m (61') 10 31 m (103') 14 3 A Load Wire Gauge Wire Run Length 24 3 m (9') 22 4 m (14') 8 A Load 20 7 m (23') Wire Gauge Wire Run Length 18 11 m (36') 20 3 m (9') 16 17 m (57') 18 4 m (14') 14 28 m (92') 16 7 m (21') 43 m (141') 14 11 m (35') 12 16 m (53') 10 27 m (90') 8 41 m (134') 12 4 A Load Wire Gauge Wire Run Length 24 2 m (7') 22 3 m (11') 9 A Load 20 5 m (17') Wire Gauge Wire Run Length 18 8 m (27') 18 4 m (12') 16 13 m (43') 16 6 m (16') 14 21 m (69') 14 9 m (31') 32 m (106') 12 14 m (47') 10 24 m (80') 8 36 m (119') 12 5 A Load Wire Gauge Wire Run Length 22 3 m (9') 10 A Load 20 4 m (14') Wire Gauge Wire Run Length 18 7 m (22') 18 2 m (7') 16 10 m (34') 16 5 m (17') 14 17 m (55') 14 8 m (28') 12 26 m (85') 12 13 m (42') 44 m (144') 10 22 m (72') 8 33 m (107') 10 9 Recommended Two-Wire Gauge for Various Wire Length Runs These tables assume a single wire for both positive and negative polarity. Run length refers to the one-way distance between the tool power supply terminals and the product use terminals along the path where the wires will be located (not line of sight). All wire lengths are rounded to the nearest whole number. 1 A Load 6 A Load Wire Gauge Wire Run Length Wire Gauge Wire Run Length 24 4 m (13') 22 1 m (4') 22 7 m (22') 20 2 m (6') 20 11 m (35') 18 3 m (9') 18 17 m (55') 16 5 m (15') 14 7 m (23') 12 11 m (36') 10 19 m (60') 2 A Load Wire Gauge Wire Run Length 24 2 m (7') 22 4 m (11') 7 A Load 20 5 m (17’) Wire Gauge Wire Run Length 18 9 m (28') 20 2 m (5') 16 13 m (43') 18 3 m (8') 14 21 m (69') 16 4 m (12') 14 6 m (20') 12 9 m (31') 10 16 m (52') 3 A Load Wire Gauge Wire Run Length 24 2 m (5') 22 2 m (7') 8 A Load 20 4 m (12') Wire Gauge Wire Run Length 18 6 m (18') 20 2 m (5') 16 9 m (29') 18 3 m (7') 14 14 m (46') 16 4 m (11') 12 22 m (72') 14 6 m (18') 12 8 m (27') 10 14 m (45') 8 21 m (67') 4 A Load Wire Gauge Wire Run Length 24 1 m (4') 22 2 m (6') 9 A Load 20 3 m (9') Wire Gauge Wire Run Length 18 4 m (14') 18 2 m (6') 16 7 m (22') 16 3 m (8') 14 14 m (35') 14 5 m (16') 12 16 m (53') 12 7 m (24') 10 12 m (40') 8 18 m (60') 5 A Load 10 Wire Gauge Wire Run Length 22 2 m (5') 10 A Load 20 3 m (7') Wire Gauge Wire Run Length 18 4 m (11') 18 2 m (4') 16 5 m (17') 16 3 m (9') 14 9 m (28') 14 4 m (14') 12 13 m (43') 12 7 m (21') 10 22 m (72') 10 11 m (36') 8 17 m (54') References [1] Alpha Wire, Alpha Wire Catalog, Master Catalog Version 3A , Elizabeth, NJ: Alpha Wire Company, 1997. [2] National Fire Protection Association, National Electrical Code® (NEC®) 2011 Handbook, Quincy, MA: NFPA, 2010. 11 To view AE’s complete product portfolio, visit: www.advanced-energy.com/en/Products.html Advanced Energy Industries, Inc. 1625 Sharp Point Drive Fort Collins, Colorado 80525 U.S.A. T: 800.446.9167 F: +1.970.221.4670 www.advanced-energy.com Specifications are subject to change without notice. ©2013 Advanced Energy Industries, Inc. All rights reserved. Advanced Energy®, and A Powerful Advantage™ are U.S. trademarks of Advanced Energy Industries, Inc. National Electrical Code® and NEC® are trademarks of National Fire Protection Association {NFPA). ENG-24VDCInstallation-260-01 0M 12.13