Fuse on each AC wire of component when fed by Balanced Power Transformer?

[brucew268]

I've been feeding my HiFi with a balanced power transformer the last few months to good effect. But lately I've been considering internal fusing on the components. Since there is no Neutral & Live wire anymore, just two Live wires, if the internal fuse blows it only affects the wire that has always been Live. The formerly Neutral unfused wire is still Live in a balanced system, I think. So if I have the opportunity, especially on the amplifier, it seems good to fuse the second Live wire, right?

[Barry]

No - what you should have is a double-pole RCB in the output from the secondary winding, so if there is a leakage to earth by whatever means, the current imbalance will cause the RCB to trip.

If you use double-pole fusing, should one fuse blow, the mains will not be fully disconnected and there will be 120V on the line with the intact fuse.

[brucew268]

I already have a double pole rcb on the balanced transformer output. I'm talking about the additional internal fusing once we get just inside the amp.

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[Barry]

The same argument applies: if there is an overcurrent, owing to fuse tolerances, it is unlikely that both fuses will blow, so one leg or the other could still have 120V on it.

I would leave the single fuse in place. After all, if it were to blow you would of course unplug the amp from your BMU before investigating the fault.

[brucew268]

If I understand correctly, the internal fuse does two things: 1) it protects me if a fault puts voltage on the enclosure; 2) it protects the amp's circuitry in case of a fault. Right?

Unplugging the amp protects me. But if a fault was dangerous to the circuitry, the internal fuse only protected one leg, right?

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[Barry]

If the internal fuse blows, current is cut off from the amp's internal transformer and no harm will be done to the circuitry.

[brucew268]

Ah yes, that. Thank you

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