The Unglorious task of Vermin Control

Warm, unmanned buildings in the wilderness are very attractive to all sorts of uninvited guests; mice, rats, snakes, insects, etc. Unfortunately, these can do damage to equipment, as evidenced here:

Mouse infested power panel, remote transmitter site
Mouse infested power panel, remote transmitter site

Thus, some steps need to be taken to secure transmitter sites, generators, outbuildings and even vehicles from mice in particular. Mice can squeeze into a hole that is .7 inch (17 mm) in diameter when they are full grown. In many transmitter buildings, this leaves lots of opportunities; coax feed through ports, ingress holes drilled for wires, electrical service entrances, cooling fans, gaps under doors, soffits, etc.

Many people simply call the pest control people who will come and put poison out. That does not solve the problem and can in fact make it worse. If the poisoned mice go outside to die, they are eaten by the snakes and birds that naturally control mice in the wild. Those animals then die from the poisoned mouse. Meanwhile new mice are being reproduced every 20 days or so. Fairly quickly, the bait is consumed, the mice no longer have any predators to naturally keep the population in check and there is a mouse explosion.

Hole in cinder block building covered with aluminum rack panel blank
Large hole, formerly a vent for propane heater, covered with aluminum rack panel black.

The best way to keep them in check is to seal up building as much as possible. For some reason, coax entry ports are often left open. This is very easy to fix and whenever tower crews are running new lines, ensure that they apply the correct boot for the port and line.

Replacement door jamb
Deteriorated door jamb replaced with pressure treated wood

Another thing that happens; door jambs deteriorate or the bottom of steel doors begin to rust away. This opening is very attractive to insects, snakes, mice and even plants.

Screen covering generator ventilation opening
Chicken wire screen covering generator ventilation opening
Generator radiator opening covered with chicken wire
Generator radiator covered with chicken wire

Generators need special attention. Radiator and ventilation openings should be covered with chicken wire. This can be attached to the metal housing with self taping screws and fender washers. Be careful and look inside of the housing to make sure that the area inside the housing where the screws are being applied is clear of wires and hoses.

Stainless steel pot scrubbers filling space around conduit and pipes
Stainless steel pot scrubbers filling gaps around conduit and fuel line

Ingress for fuel, control and electrical conductors need attention as well. I found stainless steel pot scrubbers to be effective for filling gaps around these conduits and pipes. They are available on Amazon or many other places.

New Power Panel, an expensive lesson in pest control

Other openings can be filled with a combination of pot scrubbers and spray foam. Using spray foam alone often does not work, as the mice will crew through it.

I also keep a can or two of bee spray at most sites. Bees, hornets and paper wasps love to make nests in propane tank fill covers, ATU’s, under air conditioning units or anyplace else that is sheltered from rain.

Transmitter trips main breaker

Received a call last night, after a particularly bad thunderstorm, that WGHQ in Kingston, NY was off the air.  Earlier in the day, the transmitter had tripped the main breaker after a thunderstorm.  I arrived at the transmitter site and found the breaker tripped again.  Once the breaker was reset, the transmitter came back on and ran without any overload indications.  The transmitter is a 10 year old Nautel ND-5.

WGHQ Nautel ND-5 transmitter
WGHQ Nautel ND-5 transmitter

I was thinking breaker fatigue as the breaker is the original 1960 breaker installed when the building was built.  I reset the breaker and turned the power output down to 3 KW, thinking the reduced load might not trip the breaker until we could get a replacement.  The transmitter was on the air running as I was about to lock up and go home when I heard, but more felt through the floor, a THUMP! There I stood and watched the transmitter go dark.

At least it happened when I was there looking at it.  Because of the lightning, I was thinking something in the output network.  I reset the breaker and once again, no faults and the transmitter came back on.  Strange.  Obviously some sort of power supply issue.  Here are the clues:

  1. The B- voltage was right where it should be at 72 volts.
  2. All other readings, reflected power, forward power, power supply current are normal before and after the breaker trip
  3. No fault lights
  4. The service panel breaker, which was tripping, is rated for 70 amps, the transmitter front panel breaker which did not trip, is 50 amps.

The Nautel factory rep was thinking either breaker fatigue or the big transformer in the base of the transmitter had gone bad.  According to him, no one had ever heard of a transformer going bad in these transmitters, which makes a certain amount of sense.  Unlike a tube transmitter, which steps the B+ voltage up several times, these transmitters reduce the B- voltage by about 2/3rds or so.  With a step up situation, a surge would be multiplied many times and could very easily punch a hole in the transformer’s secondary winding insulation.  I have, in fact, experienced this on at least two occasions.

That leaves the wiring between the transmitter and the service panel.  I double checked the panel breaker with my volt meter to ensure that the voltage was indeed off.  Then I removed each phase from the connection lugs in the transmitter and tested the wire to ground with my Fluke 77 DVM.  Sure enough, two of the phases showed resistance of 1.2 and 1.7 MΩ to ground were it should have been infinite.  Further, when I took the cover off of the service panel, I found a dead mouse.  Unfortunately, I didn’t have any #4 THHN and all the home improvement stores were closed by that time, so it had to wait until morning.

The thunderstorm seems to be a coincidence.

After we pulled the wire out of the conduit, we found this:

mouse chewed feces encrusted electrical cable
Mouse chewed feces encrusted electrical cable

It is a little hard to see, but that shiny spot is copper.  The cable jacket is chewed back quite a ways and the entire thing is encrusted in mouse feces and urine.  I love to work on stuff like this.  LOVE IT!  Hantavirus, here we come!  That reminds me, I need to get some of those blue latex exam gloves and throw them in the truck…  Anyway, far back in the conduit running through the concrete floor where it bends to go up to the service panel, the mice apparently had a nest.  They got into the conduit under the transmitter, where it transitioned from 3 inch rigid to 1 1/4 inch flexible metal without benefit of a junction box or proper fitting.

We pulled new copper conductors in and installed a proper junction/transition between the 3 inch and 1 1/4 inch conduit.  The service panel was also missing several knockouts of various sizes, which were sealed with knockout seals.  The transmitter was back on the air at full power about 16 hours after it went off.  Unfortunately, the station has no back up transmitter, so they were off for that period of time.  Perhaps now they will look into a backup transmitter or at least an exterminator, but probably not.