CPR Method for a Boat Anchor

Discussion in '"Boat Anchor" & Classic Equipment' started by KA5SDC, May 18, 2019.

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  1. K6BSU

    K6BSU Ham Member QRZ Page

    A "U" ground type connector has 3 contacts. The "U" is the one with that shape. It is connected directly to earth at the AC service panel. Intended for safety only in case of a fault. The U ground never carries current (or should not).
  2. K1APJ

    K1APJ XML Subscriber QRZ Page

    A seldom mentioned benefit of an isolation transformer (or any small power transformer) is the limited fault current it can pass. That limits the size of the BANG (and the amount of damage) should the probe slip or a power supply capacitor fail or a rectifier arc over.

    Always use an isolation transformer when troubleshooting AC/DC sets.
  3. W2VW

    W2VW Ham Member QRZ Page

    I have the round transformer up on the pole for that.
  4. AD5HR

    AD5HR Ham Member QRZ Page

    Limits current to only one or two hundred Amps??
  5. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    Exactly! sheesh.
  6. W2WDX

    W2WDX Subscriber QRZ Page

    Ah ok ... I understand. I thought we were talking about ham gear. I've restored a couple of old RCA BC receivers from the 20's that where like that. Like this Model 18 I restored ...

    I still use isolation transformers regardless, just to keep that noise that can creep into the neutral from the earth ground minimized. As well as, its tendency to smooth transients a bit.

    And yes ... a variac is not an isolation transformer.
  7. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page


    So you like living dangerously!

    The typical "pole pig" is normally limited to something like 5000 amperes before the voltage starts to drop! Also, the voltage is NOT isolated from ground so if you get between a "hot" leg and ground, you are going to be the conductor. With an isolation transformer, there is no "hot" or "ground". You have to get across both of the transformer secondary wires to become the conductor. Otherwise, no current flow through you or into test equipment, etc., which has one terminal connected directly to ground if you come in contact with the voltage from just 1-wire.

    Glen, K9STH
  8. K6BSU

    K6BSU Ham Member QRZ Page

    K1APJ was talking about a SMALL isolation transformer to limit the available fault current, which it will do. Pole transformers never a consideration in this thread. No matter what you are working on, a pole transformer is involved.
  9. W2VW

    W2VW Ham Member QRZ Page

    We went from using a variac to unknowingly strip electrons from an old rectifier cathode to touching a pole pig secondary minus service drop, mains panel/wiring and circus breakers.


    My last position had an electric bill of 60K every month.

    Nothing wrong with a low source impedance when one is competent.

    I save isolation transformers for useful applications like the 30S-1 screen voltage modification.

    There's also one on my outside lighting which delivers 62.5 volts under load. looks a lot better than the blue colored LED accent lighting the neighbors use.

    Not even close to living dangerously but thanks for the concern.


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