Safety of Conditioned Balance Supply without secondary protection


I have only been able to come up with two scenarios where equipment connected to a balanced power supply could become dangerous and in each case two faults would have to occur simultaneously:

  1. For an electric shock risk the following two faults would have to occur at the same time: (i) a short circuit occurring between either the mains live or the mains neutral to the case or earthed points of the equipment (a catastrophic event) and (ii) the earth connection would need to be disconnected
  2. with the equipment mains fuse blown and a short circuit occurring between the equipment live earth (a catastrophic event), current could still flow inside the faulty equipment

 In other words there would need to be a catastrophic failure of the audio/visual equipment for either scenario to occur. If any customers can come up with any other scenario we would be interested to hear from you. Please get in touch via our contact page

For both safety and the correct operation of the PSU a sound earth connection is required.

Always disconnect equipment from the mains when replacing mains fuses!

A recent question and answer which helps to address safety concerns regarding the use of balanced power supplies:


I have read much about the safety aspects of these sorts of devices, especially in respect of a fuse on the live line blowing which still leaves power on the neutral rail. Do your devices address this concern (linked fuse or circuit breaker for example)? Thank you.


Some of our balanced supplies incorporate RCBO’s on the output. (See the individual equipment specifications on our website for details). This addresses any over-current or earth leakage fault on both output legs of the balanced power supply. Having said that, all supplies have input protection which will trip in a fault condition turning the whole supply off. In a situation where just one item of equipment attached to the supply fails and takes out its own input fuse, it is the case that the neutral within that unit will still be powered to half of the mains voltage. Given the safety requirements for all consumer equipment it is highly unlikely that this neutral voltage would become hazardous as, if this were to somehow short to the equipment chassis, it would cause a neutral to earth current path which would then trip/blow the input breaker/fuse of the balanced supply.

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