I studies the posts on this blog regarding isolation transformer and its working. But I don't understand that when there is no ground reference in the secondary winding of the isolation transformer, then how is the current able to circulate in it. I mean as per my knowledge, we need some reference with respect to which the current can flow, like ground in general cases. If there is no reference in isolation transformer secondary, how is the current able to flow through any load that I connect to its secondary side ?

Could someone tell me some detailed explanations regarding my doubts?

  • 2
    \$\begingroup\$ You reference 'this blog' but there is no hyperlink we can follow. \$\endgroup\$ – Li-aung Yip Sep 13 '13 at 7:25
  • \$\begingroup\$ Doesn't seem to be a question that should be closed. It focuses right on the question why a safety transformer is safe, maybe just thinking the problem backwards (compared to the usual explanation). \$\endgroup\$ – zebonaut Sep 13 '13 at 10:43
  • \$\begingroup\$ Current requires Closed Path and voltage drive to flow. Voltage value is quantitatively expressed w.r.t some reference. As such current doesn't require any reference. electrons will move from Low voltage point to High voltage point, Current direction will be reverse of electron movement direction. \$\endgroup\$ – user19579 Sep 13 '13 at 11:16
  • \$\begingroup\$ @Li-aungYip ... and still, the question runs just fine - just like an electrical circuit that doesn't have a reference assigned to one of its nodes ;-) \$\endgroup\$ – zebonaut Sep 13 '13 at 13:32

It's really arbitraty where you put a reference in a circuit, and if you desire to need one at all. You pick the reference, if you like, and put it where it works best for you when thinking about the circuit. The circuit itself will not even know you did this, and it will not even give a holy firetruck care about the question if it has a reference or not.

Think of a battery powered device: It works when there is no connection to any other object, i.e. when it is not grounded or referenced. And it's up to you how you measure or think about the voltages in the battery powered device. Most times, it is practical to consider the (-) end of your battery the reference, which gives you (mostly) positive voltages in relation (reference...) to this reference. But you can also consider the (+) end of the battery the reference, and you end up having negative voltages. Note that the circuit works no matter how (and if) you define your reference.

With a safety transformer, the whole point is having no reference to earth ground. This way, if you accidently touch the circuit powered by your safety transformer (using one hand only!!!), you can't get too much of a shock (aside from bridging something with just one finger), because current coming from the transformer can only go back to the one same winding where it came from, and not close a path via ground (through your body).


A battery powered transistor radio works without ground.

A flashlight (torch for UK) also works without a ground connection.

Solar panels don't rely on some form of electrical connection to the sun in order to produce a few volts.

My multi-meter works when I don't have the leads connected to anything.

My electric shaver does.

RFID tags receive magnetic "power" with no connection to the "system".

Contactless phone chargers do the same.

Deep space probes can emit signals that are still detectable on earth - there is no wire between the probe and earth (not ground).

There are plenty of battery powered electrical devices that work without a ground connection. At this point should anyone feel like providing a list, keep it clean!!


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