Never trust breakers or disconnects!

Discussion in 'Amplitude Modulation' started by W8KHK, Sep 9, 2019.

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  1. W8KHK

    W8KHK Ham Member QRZ Page

    This is not directly related to AM per se, but it applies to QRO, whether it is a ham rig, A/C system, etc.

    When I returned home on Sunday, things were quite warm, both inside and outside. I expected around 78f inside, not 94f!

    At first, I thought I had a problem with the A/C thermostat. Previously I have had trouble with the five-minute short-cycle safety that is built in. A weak battery makes this feature erratic. I was troubleshooting an intermittent problem, as the outside compressor/condenser/fan operation was erratic. But monitoring the relay voltage indicated the problem was outside.

    Opened it up, and found severely burned contacts in the main contactor. Replaced that, and thought all is well, it worked for a while. Then cooling discontinued, but it appeared everything was getting power. The condenser fan still running, but no compressor. Suspecting the capacitor (2 section, one for fan, one for compressor) I decided to disconnect the wires and test it.

    After switching off the disconnect, I still had 120 volts from ground to each leg. But no 240 between the legs. It turns out the disconnect, an old bread-slicer switch, failed mechanically, in that one of the swinging switch poles disconnected from the shut-off lever assembly, so one side of the 240 volt line was still connected. I attached a couple photos at slightly different angles to illustrate the failure mode. You can see the switch blade on the left is still connected at the top. while the right blade is properly disconnected. The fibre link on the left has failed, and no longer moves with the switch lever.

    20190909_161129.jpg 20190909_161129.jpg

    I ALWAYS check with a meter before touching anything, I NEVER trust a breaker or disconnect. It only takes a few seconds!

    I must go off and get a safe disconnect switch and install it before I can proceed. I really like the version where you actually remove a plug instead of a knife switch or a breaker, but those are hard to find.

    It is 97f and the mosquitos are predominant. No fun in river city today.

    Attached Files:

    AI3V, AG5CK, W2VW and 1 other person like this.
  2. K4KYV

    K4KYV Subscriber QRZ Page

    Or use one of these. This is the main power switch to my station equipment. Foolproof.

    Main radio power switch.JPG
    W8KHK likes this.
  3. W8KHK

    W8KHK Ham Member QRZ Page

    Yes, it is nice when you can visually verify the disconnect. "Old School" is cool! No pun intended.
  4. W7TFO

    W7TFO Premium Subscriber QRZ Page

    Pilot lights save lives...

    WQ4G, AG5DB and W8KHK like this.
  5. W8KHK

    W8KHK Ham Member QRZ Page

    I seriously considered putting a pilot light on each side of the line, as well as a "contactor energized" indicator.

    This disconnect should be much safer. $9.95 well spent! It will be wired much more neatly than the box which was installed in 1968. I hope I need just a capacitor and not a compressor to finish the job.
    20190909_182045.jpg 20190909_182053.jpg

    I can hide the plug where Murphy cannot find it.
  6. W7TFO

    W7TFO Premium Subscriber QRZ Page

    Most of those have it so you can put the plug in one way for on, the other for off.

    Or put it in yer pocket.

    NE4EB, WQ4G and W8KHK like this.
  7. K4KYV

    K4KYV Subscriber QRZ Page

    Just be careful not to come in contact with the knife switch blades with your fingers while opening or closing. But when disconnected, very little likelihood of a voltage spike from a nearby lightning discharge jumping the contacts.

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