| |
| |
|
Home Improvement |
|
|
|
The Motors Best Friend
The starting current of motor can become 3 to 6 times the normal running current! That's normal for motors. The motor can experience this high current for a period ranging from 20 to 50 seconds. A fuse will not be very useful in protecting a motor from this type of overload condition. A selected fuse large enough to permit passage of the necessary starting current would give little or no protection against overheating of the windings under normal running load conditions. The same case happens for the circuit breaker. Overload relays offer protection of motors that is both compatible with the starting current of the circuit, and the requirement of protection in the event of overload running condition. These conditions need to be adjustable. A particular motor requiring 56 seconds starting time under normal load will suffer serious damage if the rotor locks and the motor is not tripped in 20 seconds. Another motor may be able to withstand 25 percent overload for 30 minutes. A hermetically sealed compressor motor may burn in 3 minutes at 25 percent overload! Good protection against overheating of the motor windings can be obtained from temperature monitoring protector devices that are embedded into the motor windings. These do not protect the motor itself, but act as sensors to trigger a temperature control circuit to stop the motor. A thermal overload relay, however, uses a heating element to heat up a bimetallic strip so that it can trip a latch that will open the motor control circuit. This action will disconnect the motor from the line. For reliable operation, the overload relay must be located at the same temperature environment as the motor. The heating effect of the bimetallic strip mechanism is supposed to represent the heating of the motor windings. Melting alloy overload relays calibrated by the manufacturer are considered the most reliable of all the thermal overload protective devices. However, more commonly used is the bimetallic overload relays because the tripping current setting can be adjusted. All the overload relays have one major limitation - because they operate on line current, they do not directly sense the motor temperatures. For normal steady running conditions, this poses no problem at all. However, when a motor starts and stops frequently, the relay may not completely protect the motor. Why is that so? During the motor running, the relay temperature follows the motor temperature closely. When the motor is off, the relay tends to cool off at a faster rate because of its lower mass. After a number of starts and stops, the temperatures of the relay and the motor may drift further and further apart. Eventually the motor becomes hot, and yet the relay does not trip because it is still cool. The motor burns. Frequent starting and stopping of motors is no good both electrically and mechanically. Until next time... Are You Stumped by Complicated Electrical Calculations? Useful Electro-Technology Questions & Answers available for all electrical installations. Many years of working experience in Marine, Facilities, Construction has given the author material for writing e-books and articles related to engineering, and management. Subscribe to facworld ezine More information at Marine Engineer and M & E Engineer
MORE RESOURCES: Lowe's 2Q Net Up 9.6% But Sales Growth Light; View Cautious - Wall Street Journa.. Ladies rule: Free Martha Stewart home improvement workshop at Home Depot - Walle.. Majors Home Improvement Ranks 140th in Remodeling's Top 550 National List - PR W.. Avoiding home repair scams focus of Powder Springs seminar - Atlanta Journal Con.. 'Toy Story' & 'Home Improvement' star Tim Allen becomes Chevy pitchman - kypost... Silverthorne council OK's Lowe's - Summit Daily News Georgia Gulf to Present at Morgan Keegan 2010 Industrial/Transportation Conferen.. FALL HOME IMPROVEMENT: Ways to seed your lawn - Newton Kansan Woolworths open to acquisitions - Business Spectator Four Lowe's customers claim overcharging - abc11.com  |
|
|
|
RELATED ARTICLES
Choosing a Home Builder So you've decided to build a new home. Like many home buyers you realize that buying a new home offers a wide range of advantages over buying an existing home. Color Help: Color Imagery for Happy Homes Color researchers have estimated that up to 70% of our subconscious reactions to people and environments are based solely on our reactions to color. With that in mind, it's important that you give special attention to the effects you want to create when choosing the color schemes for the interior spaces in your home. The Best Time to Inspect Your Home! Home inspections conducted prior to a home being placed on the market is one of the wisest moves a seller can make. The initial response from sellers when approached with the idea of an inspection done as the home is about to be put up for sale is most always the same - "What?!"Let's review a few of the most common concerns about Pre-Listing Home Inspections. Where's the Care Label for my New Bedspread? I love bedspreads, don't you? A comforter can be used for the winter months but the bedspread is brought out of the linen closet in the spring when it's warming up and the whole world is freshening and renewing itself outside. A bedspread is available in most any color, pattern or fabric and it can be one of the most expensive items you put in your bedroom. How To Completely Rehab Your Home In 10 Days! This report is about taking a house and restoring it to an aesthetically pleasing dwelling that has reclaimed it's functional utility. In effect, it is the anti-aging medication for bricks and mortar. Hardwood Floor Refinishing - For The Faint of Heart Are your beautiful hardwood floors not so beautiful anymore? Maybe they just need a refinishing job. It can be a daunting task, but here are some ideas to make it a little easier. How to Install a Ceiling Fan - A Simple Guide A Complete manual on how to install a Ceiling Fan may take more than just an article; it may all even take up an entire booklet. Let me just give you a simple, no-nonsense essential guide in installing a ceiling fan. Log Wall Characteristics Looking at all the beautiful full-color glossy photos of log home in magazines gives us an idealized vision of the perfect wooden house. Like a supermodel, we can't imagine wrinkles and imperfections, but like any natural product, log walls are full of traits that are an integral part of their character. Laminate Flooring Is Attractive And Long Lasting Laminate flooring is perfect for people who want to install a floor covering that is easy to install and combines the rich look of hardwood with the easy care of a laminate counter top. Laminate floors that have been constantly gaining popularity since their creation a few years ago. Wall Oven - A Necessity For The Disabled Wall ovens, available in electric and gas forms, are best ovens for the people with disabilities. The ovens can be placed considering the required height of the user, and the controls can also be placed within the reach of the standing or sitting user. Ten Things You May Not Know About Selecting Hardwood Flooring 1) Red Oak is not the only choiceIf you want your home to look like everyone else's, this is a great choice. If you want your home to be unique try hickory, cherry, walnut, white oak, maple or many others. Color Help: Many Factors Affect Color Preference Understanding color psychology helps home makers choose colors for home decorating.Color affects human beings every day of their lives, even during their very earliest childhood. The Benifits of Home Ventilation The purpose of a home ventilation system is to maintain a healthy living environment by supplying fresh air to your home while at the same time removing stale and polluted air. Home ventilation also helps to maintain proper humidity levels of 30 to 50 percent. Scented Candles - Take Me AWAY! Remember the old Calgon commercial-"Take me away Calgon!" There's only one thing that can take you away faster than a Calgon bath, and that's a scented candle. Whether you want a breath of fresh spring air, or you want to transport yourself to a South Sea paradise minus the hassle of airport security, crowded, delayed flights and lost baggage, grab a scented candle, and travel wherever your imagination leads. With A Stylish Bathroom Vanity You Can Take Pride In Your Bathroom's Appearance! An easy way to instantly improve your bathroom's image is to buy a stylish new bathroom vanity set. Bathroom vanity sets come in a huge range styles and finishes. Easy Renovations for Your Home Renovating should be a fun and exciting process (really!). The key is to plan the project out in advance, hire the right people, allot the appropriate amount of time, and make provisions for delays. Router Bits Basics A router bit is a tool for woodworking giving a quality finish to woodwork. It cuts wood providing a way to give a clean and even a decorative edge to woodwork. The Right Bathroom Accessories Will Make Your Bathroom Unforgetable Bathrooms aren't just about the basics but are about the bathroom accessories! Bathrooms have become places to relax and unwind. They are not just for doing your business and leaving. The Best Way To Clean Carpet? What is the absolute best way to clean carpet? Carpet manufacturers are almost unanimous. The best way is to use hot-water extraction, also called steam cleaning. Hand Hooked Rugs Hand hooked rugs are a great way to add splendor to a bedroom, a kitchen, sun porch, or children's room. A number of designers like Jane Keltner, Suzanne Nicoll, Sally Dailey, Dena, and Tracy Porter focus exclusively on designing hand hooked rugs.
|
| home | site map |
| © 2006 |