Tales of disaster – Page 11 – Engineering Radio

The 100 amp fuse

I found this fuse in an old electrical panel that we were removing from the WICC generator shed. This was the original service entrance for the site as it was built in 1932 or so. The generator shed had a manual three pole two position transfer switch, which was fine back when a licensed transmitter engineer was on site whenever the station was on the air. The generator, according to the old records I could find, was an upright 2-cylinder slow-speed engine with a belt-driven generator. They were mounted on concrete pads about 5 feet apart. The motor had a big flywheel that was hand-cranked with the compression off. Once a good head of speed was built up with the hand crank, the compression lever was thrown and the engine would start. Alternatively, the procedure was tried again.

That was all replaced in 1971 when the transmitter site underwent a major upgrade. The old electrical service was bypassed and abandoned in place when a new meter and panel were installed in the transmitter building. The old service seems to have been frozen in time, untouched for forty years.

This fuse is a Kirkman Engineering Company and has a manufacture date stamp of January 1945. It is a replaceable link AKA “renewable” fuse. It has “peak lag” links, which I think would be called “slow blow” today. Peak lag may also indicate a large inductive load, which would lower the power factor. What I find interesting is that someone, once upon a time, placed two 100 amp links in parallel, then crossed the 100 AMP label out and wrote “200” on the fuse body.

The problem with this setup is that the panel and wiring were all rated for 100 amps. The wiring is #4 copper, and the transfer panel and switch are clearly labeled “100 amp, 3 pole.” It would appear that the finger stock holding the upper blade in place was loose, causing the fuse body to overheat. In fact, it became so heated that the case and the wood fiber holder were charred and missing.

Fortunately, there was never a fire.

The reason why we use properly sized fuses and breakers.

I Got The Air Conditioner Blues

Back in the day, when tube transmitters ruled the broadcast world, the common practice was to have a big cooling fan moving outside air through the transmitter building connected to a thermostat. Temperature swings of 30 to 40 degrees were common, however, the tube rigs could handle almost any temperature that didn’t melt plastic or freeze water.

Today’s solid-state transmitters are not that rugged. They like to have their rooms around 70 degrees +/- 10 degrees or so. Not to mention the other computer-controlled equipment commonly found at a transmitter site. Things like air chain processors, STLs, remote controls, etc. So, lots of air conditioning is the norm, and with lots of air conditioning comes lots of maintenance.

Air handler air filters need to be checked and replaced often. Condenser coils seem to attract every type of flying debris on the planet and need to be cleaned once, possibly twice per year depending on tree and weed species near the site. Even with preventative maintenance, occasionally things like this happen:

Of course, the entire cooling coil inside is frozen solid.

This condenser is low on refrigerant, causing icing problems. It has a slow leak somewhere and is about to be replaced. Other reasons for this happening are malfunctioning or non-existent low ambient kit on the condenser fan. Sometimes less than knowledgeable persons will install a 5-ton unit designed to run throughout the year but not take into account the effect of moving below-freezing air at high speed across the coils. Insufficient air moving across the cooling coil will also cause this. Insufficient airflow can be due to plugged air filters or clogged fan/blower blades.

This one is even better (same condenser unit):

The fan blade is sheared off and jammed into the condenser coil. This happened during power transfer from generator power to commercial power. Naturally, it was at 1 a.m. in the morning after a pole-mounted transformer had been replaced. When the building transferred back to commercial power, I went outside to use the “bathroom” before my two-hour drive back home. I thought I smelled something hot, you know that cooked paint/plastic smell, but couldn’t really track it down… the winds were kicking up and another thunderstorm was on the way.

The next afternoon, however, when the sun was up and the site was working on one air conditioner, the temperature alarm went off. Upon arrival, I found the condenser breaker tripped, resetting it caused the building lights to dim. The fan motor was shorted to the case. I would theorize the aluminum fan blade suffered from metal fatigue, likely because the blades were not balanced causing a vibration. When the power transfer occurred, there was just the right combination of torque and centripetal force to cause the blade to rip, and then lodge in the condenser coil.

The fan motor has been replaced, but I think it is time to replace the whole condenser unit, which will be expensive.

I found having a set of gauges to check the head pressure and suction is a good diagnostic tool to quickly pinpoint problems with HVAC units. This way, when the HVAC tech shows up, you can quickly point him in the right direction.

The breaker keeps tripping…

This is yet another addition of the “Burned up Sh*t” collection:

It is a breaker from a 5-ton AC compressor. Back in the bad old days when I was the Director of Engineering for a 28-station group Headquartered in Harrisburg, PA, I received a phone call from one of the local engineers. He stated that the studio AC unit compressor had burned out again and the breaker kept tripping. What did I think, asked him. I thought perhaps he should dig a little deeper and determine why the breaker was tripping before throwing another AC compressor at it. When are you coming to town again, he cheerfully inquired.

Okay, I get it.

I started by calling the HVAC company to inquire what had gone wrong with the compressors. Winding shorted to the case for both units was the answer received. It being July and mighty hot out, the various worker bees in the studio were feeling inconvenienced by the sweat in their eyes and dripping on their work, etc. I called the local manager and asked for a hotel room, I’d be up tomorrow. Then I called the HVAC guy back and asked in to meet me at the studio tomorrow afternoon.

Upon arrival the next morning, I found the fifth-floor studios to be hot, as reported. I trip to the roof location proved to be hotter still. I tested the voltages at the compressor unit with a DVM and everything looked good. A trip down to the utility room found the electrical panel in reasonable shape. Then the local engineering guy chimed in, “Oh yeah, I forgot to tell you, the breaker hums and gets hot when the compressor is on.”

It’s always that little bit of missing information…

I took the breaker out and sure enough, the fingers were all arched and nasty-looking.

I replaced the breaker, the HVAC guy showed up, with a new compressor and the studios began to cool off around 3 p.m.

Since then, I have specified Square D QO bolt-on breakers for new installations, especially for heavy loads like AC units, transmitters, and so on. They are a little more expensive, but in light of two AC compressors, the unscheduled trip out of town, and the grumbling staff, it is better to pay upfront for better equipment than to put up with preventable outages.

Crown D75 monitor amp goes terminal

Happened the other day, took out the monitor speakers too. I am not sure how this happened, but the production director reported that the speakers began making very loud squeals. Somebody finally thought to turn off the amp using the conveniently located on/off switch on the front panel.

Crown D75 audio board burned open resistor

The two-watt resistor is burned open. Also, this got so hot it burned a hole in the circuit board below it. Truth be told, I think this amp was about 25 years old and due to be replaced when the new studios were built out.

I’ve seen these Crown amplifiers self-destruct in the past.