For reliable operation, overload relay must be located at same temperature environment as motor. The heating effect of bimetallic strip mechanism is supposed to represent heating of motor windings.

Melting alloy overload relays calibrated by manufacturer are considered most reliable of all thermal overload protective devices. However, more commonly used is bimetallic overload relays because tripping current setting can be adjusted.

All overload relays have one major limitation - because they operate on line current, they do not directly sense motor temperatures. For normal steady running conditions, this poses no problem at all.

However, when a motor starts and stops frequently, relay may not completely protect motor. Why is that so?

During motor running, relay temperature follows motor temperature closely. When motor is off, relay tends to cool off at a faster rate because of its lower mass. After a number of starts and stops, temperatures of relay and motor may drift further and further apart. Eventually motor becomes hot, and yet 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. http://www.free-marine.com/et.htm

As an Angeleno who lives with real threats like smog, gang warfare, earthquakes, wildfires, landslides and rush-hour traffic, I decided to fully embrace Wi-Fi movement. I wanted to be one of those happy people plucking away on laptops at Starbucks Latest News about Starbucks or Borders in between sips of cafe Americanos. So I called up Terry Halberg, telecommunications planner for city of Los Angeles, to get me started with a personal tour of Van Nuys community Wi-Fi zone. To prepare, I bought cheapest wireless modem card I could find for mylaptop Latest News about laptop - $20 at Fry's.

The city's free Wi-Fi network itself is not much to look at. It's as visual as radio. There's not much to see other than Wi-Fi routers placed strategically inside meeting rooms and out on utility polls on streets surrounding MBSFVCSC. The routers are no bigger than a hardback Jackie Collins novel, with two antennas on top and two on bottom.

"It looks like a little robot guy," Halberg said. They beam signal all around area and into computers of anyone who wants to access it.

Anyone with a laptop or PDA Latest News about PDAs with wireless capability (such as my $20 card) can plop down anywhere around Van Nuys Civic Center/ Courthouse complex and log on for free to community network. Because city is providing service, users must start at a registration page and agree not to use network to do illegal things such as download child porn or sell unregistered firearms to Third World countries, and not to sue if you get hacked while online.

Logging into Wi-Fi Community Network hooks users up not just to network but with anyone else using it. This brings up more disturbing questions such as, if my computer can pick up data from these Wi-Fi waves, can data be sucked out of it same way?

Yes, it can.

According to nonprofit Wi-Fi Alliance's Web site: "If your transmissions are not secure, you take risk of others intercepting your business e-mails, examining your corporate files and records, and using your network and Internet connection to distribute their own messages and communications."

In other words, people can peek on what you're looking at online as if they were looking over your shoulder. That might not bother Net surfers who limit their online travels to sites such as Howtoknit.com or Allaboutmarsupials.net, but most people want their Internet experiences to be private. If that's case, dial-up may still be way to go until there's improved security Latest News about Security for Wi-Fi networks. That probably won't be too long. This revolution is spreading in months, not years. And though it may not be televised, it is definitely coming to a screen near you.