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What safety measures can be taken when using a 1:1 isolation transformer in order to avoid electric shock even if someone touches both ends of the secondary? Would an insulation monitoring device be a safety measure in this case or does it only detect a leakage between primary and secondary?

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  • \$\begingroup\$ What is the reason for using isolation in the first place? What are you powering? Is a grounded centre-tap on the secondary an option? \$\endgroup\$ – Transistor Aug 24 at 19:45
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What safety measures can be taken when using a 1:1 isolation transformer in order to avoid electric shock even if someone touches both ends of the secondary?

There's very little you can do if someone might touch both ends of the secondary.

  • Keep the secondary voltage below about 50 V.

  • Ensure there's not enough energy present at the secondary to harm a person. For example, by not having any capacitive load on the secondary, and by feeding the primary through a high resistance, so that the secondary voltage will drop when a "low" resistance load is attached.

The challenge is that a person touching the terminals doesn't look particularly different to the circuit than whatever load you are powering from the secondary. If there's something special about the usual load (for example, it's purely capacitive, or it never draws more than a few nanoamps) then perhaps you could design a useful safety circuit.

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You can't take any effective countermeasure for touching both secondary wires. The isolation transformer is not a device designed to prevent this action, rather it isolates a circuit from mains.

If the device isolation breaks, it makes a short circuit to the earth. In case you have a portable device, the supply wire can be live or neutral it depends how the plug is wired/twisted. So an isolation transformer prevents that in case of device break you get a live wire on chassis.

This kind of isolation is depicted on device with double square- double insulated appliance, Class II.

enter image description here

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  • \$\begingroup\$ The use case is powering up devices in the service department. \$\endgroup\$ – tonal_123 Aug 25 at 16:21
  • \$\begingroup\$ I need something fool-proof... \$\endgroup\$ – tonal_123 Aug 25 at 16:32
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1:1 isolation transformer isolates the ground(Earth) line from the secondary. Hence accidental connection between isolated line and earth won't be a problem. Main safety precaution to be taken:

Do not touch both line and neutral of secondary. It will still kill(or harm) the person.

Is there any safety precaution?

For primary side, There are current monitoring safety devices which can detect the current leakage (current taking other path than neutral) and trips the circuit with in 10s of ms but it is also enough to make a heart stop or skip a beat.

Other than that:

  1. Precaution
  2. Keeping high voltage stuff inside a plastic housing,
  3. Making opening in only the low voltage section of devices and
  4. Good safety practices and education
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  • 1
    \$\begingroup\$ "... current monitoring safety devices which can detect the current leakage (current taking other path than neutral) ..." The problem is that there is no neutral and no earth return so there will be no imbalance to trip the breaker. \$\endgroup\$ – Transistor Aug 24 at 17:39
  • \$\begingroup\$ @Transistor sorry for wrong info. I corrected it \$\endgroup\$ – Umar Aug 24 at 17:57

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