RSS

My Motor-Driven Big CB Resetter

Jun 20

Written by: Charles S. "Buc" Fitch
6/20/2012 12:01 PM

“Time and tide — and now technology — wait for no one.” Gazing back through the 20-20 rear-view mirror of life, our industry looks more and more like a prime example of this cliché.

A recent multi-party exchange amongst confreres about a pending 50 kW AM installation — in which the entire RF plant fits in a cell site-sized concrete manufactured building — spawned a flurry of comments about “the good olde days.”

Ah yes, back when dinosaurs ruled the earth, transmitters were BIG. You could walk through them, stand up while inspecting or maintaining, use wrenches and other hand-size tools to fix them, heat the building in deepest winter with just the waste heat … near tech nirvana.

These BIG rigs required 24/7 love and attention; and real buildings surrounded them … structures with comfortable furniture, nice bathrooms (occasionally with a shower), a kitchen and even an odd occasional bunkroom!

We all agreed that the good olde days are never coming back and none of us wants them to come back; yet there is something fuzzy and comforting in memories of a time when our immediate attention and knowledge were critical to staying on the air and keeping those BIG machines running.

Equipment reliability and cost pressures precipitated changes, many of which have been annotated in my Milestone columns. Remote control of transmitter sites was probably the first where engineers’ expertise was moved to the studio, and the remote control was the Waldo for those tech talents.

These early facility conversions generated interesting technical challenges. For one: How to remotely control transmitters never designed for this function?

My good friend Paul Gregg reminded me that many conversions used motor-driven circuit-breaker operators to motivate the circuit-breaker switches on some World War II-era gear. That is how major subsections were turned on and off.

Although motor-driven CB operators are seldom used today, the most ordinary motor drive attached to a CB now is a “re-setter.” I actually have a BIG CB re-setter on my shop shelf. If you spend 50 years in this business, you’re bound to pick up odd things.

Although the accompanying pictures may appear to show some sort of medieval torture device, this gismo actually is a motor-driven, BIG circuit-breaker re-setter.

Often, the main or a very BIG CB has a nuisance trip caused by line surges or back surges from an abrupt or bouncing power disconnect. Or maybe you just want to have really close protection on your very expensive system. Anyway you don’t want to drive all the way out there to re-set the circuit breaker, so you have this motor-driven BIG CB re-setter.

How does it work? To allow the CB free travel to trip, you place an attachment on the handle (first pic) such that there is no “drive” tension on the CB handle. When over current or a thermal trip occurs, it can move to the tripped position.

The motor is 120 volts, so obviously you would get this power from an UPS if the re-setter was on the building or system main.

The rotary motion of the device picks up the CB handle and moves it through its “off” and then “on” positions, resetting it (see the second pic).

A standard option (which can be field installed) is an aux switch on these big CBs. Those contacts stop the motor and drive system in the “trippable” position.

Not simple, not elegant, not beautiful (actually ugly). But it does the job well.

The last one of these re-setters I specified was on a rig in a miserable station located on an island. To reach it, the chief engineer had to drive for an hour, and then row out.

Later, the CE had the audacity or affection to call me in the middle of the night (forgetting the time change) to tell me how happy he was the first time he had to reset the CB. He was able to do so remotely, getting his station back on the air using his telephone on the night stand — rather than getting up, driving an hour, rowing in the dark and walking up the hill to reset the CB. So these units do have their place in broadcasting.