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Questions about grounding a cab

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DaOld Man:
I dont think adding a second transformer is necessary, unless the first one is bad.
you can check it if you have an ohm meter, disconnect the transformer from the monitor and read from each lead to the metal case or part of the transformer. it should read very high resistance, maybe in the megohms. If it reads low resistance from either secondary lead to the metal part of the transformer, then the secondary winding is shorted to the metal part of the transformer. The transformer is bad. You should get the same results on the primary side, if both of the primary wires are disconnected from the supply line.
primary on a transformer is power in (line) and secondary is power out to the monitor (load).
If the GFIC circuit breaker from the supply is tripping, you have either a direct short, or part of the circuit bleeding to ground. Most likely the insulation of the windings in the transformer have broken down, or a lead coming out could be rubbing against the transformers case, perhaps worn through the insulation and copper touching steel.
Side note: Neither lead of the secondary should touch either lead of the primary. this is why you use the isolation transformer, to remove the common connection between the primary and secondary circuits.

MonMotha:

--- Quote from: eerie on September 10, 2011, 10:42:40 am ---
--- Quote from: MonMotha on September 09, 2011, 06:05:48 pm ---It sounds like your monitor needs an isolation transformer on its AC power lines and you either don't have one or it's broken.

--- End quote ---

I have a 220/130v transformer which feeds the monitor, I think that should do the function... or maybe not? would adding a second transformer really do anything?


thanks

--- End quote ---

Many step-up/step-down transformers sold to consumers are autotransformers and do not provide the isolation needed.  You can check this by using a meter on resistance setting between one of the primary (input) taps and one of the secondary (output) taps.  It should be very high resistance (megohms) or totally open circuit to indicate an isolating transformer.  You can get isolating step-up and step-down transformers, but they're less common, so be sure to know what you buy.  Putting a separate isolation transformer between the autotransformer and monitor would also work.

eerie:
hi, I did the checkings and indeed I have one terminal of the primary "connected" to another pin in the secondary so it's just a common transformer and not an isolation one. I'll go look for one tomorrow and let you know if I got my problems solved. many thanks guys :)

BKahuna:

--- Quote from: MonMotha on August 15, 2011, 12:40:04 am ---To make this clear for the OP, the AC neutral (brown in Europe, white in North America) should NEVER be connected to the earth ground/safety ground (green, green/yellow, or bare) in an appliance nor should it EVER be connected to the DC common (black wire) on a new design or a design where a dedicated earth ground (green wire) is available.

--- End quote ---
This is incorrect. I realize you stated it correctly, elsewhere in your post, but since this is relatively important, I had to point it out. You might want to edit your post to help eliminate confusion. AC neutral in Europe is Blue, not Brown.

MonMotha:

--- Quote from: BKahuna on September 11, 2011, 12:18:50 pm ---
--- Quote from: MonMotha on August 15, 2011, 12:40:04 am ---To make this clear for the OP, the AC neutral (brown in Europe, white in North America) should NEVER be connected to the earth ground/safety ground (green, green/yellow, or bare) in an appliance nor should it EVER be connected to the DC common (black wire) on a new design or a design where a dedicated earth ground (green wire) is available.

--- End quote ---
This is incorrect. I realize you stated it correctly, elsewhere in your post, but since this is relatively important, I had to point it out. You might want to edit your post to help eliminate confusion. AC neutral in Europe is Blue, not Brown.

--- End quote ---

Hum, looks like I did swap those.  Corrected.  I should know those better: while I live in the US, appliance wiring often uses the IEC colors.

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