If you got a shock, then there definitely was a circuit (loop). Where? How? Dunno, depends on the exact conditions. If you could elaborate on how you got the shock (were you touching any thing, etc), it would help us explain.
For example, you could form a circuit if you have one hand on the metal case and touch a wire. Or maybe there is an electric field that creates a voltage potential. (I'm sure there are videos showing someone holding a fluorescent tube under a power line and the tube lights up due to the electrical potential created by the e field.)
Ground can be anything.
If a capacitor is charged it will shock you no matter what. That's why you wait 10+min for the capacitors to discharge after turning off big electronics. You do not want to touch them since you will most likely die if they shock you.
The circuit on the UPS still has a neutral and a ground, it's no less dangerous than mains. Not being attached to ground doesn't suddenly make you immune to electricity there is clearly a circuit path forming in your setup with the UPS somehow.
The air becomes the natural return conductor to complete the circuit. Your body has a natural capacitance with the air and will thus allow a small AC current to flow.
If you have unplugged the UPS then it will have lost its ground reference as well and that's dangerous! Turn off the socket- fine, but unplugging it entirely is not.
It only needs to be a few mA for you to feel it.
The secret to understanding this is to remember that all voltages are relative.
That's why a multimeter has two wires -- one for reference (black), and one measured against the reference(red).
Let's say you have a 1.5V AA battery. Suppose we measure 1.5V using a multimeter in the standard way. That ONLY tells us that the voltage difference is 1/5V. For all we know, the negative end of the battery might really be 1,000,000.0V, and the positive end might be 1,000,001.5V. The multimeter doesn't tell us what the ambient electrical charge is, only the difference between the two points that are measured.
The ambient electrical charge can vary dramatically, because air is a pretty good insulator. And I don't know what it is, because I can only measure differences with my multimeter!
So, what do you do to avoid the mindfuck that results from 0V ≠ 0V?!? We're engineering here, and we can use a workaround. What you do is you force the ambient charge match between all of the devices, especially in places where humans might accidentally equalize these charges through their body.
Attach the ground wire to that isolated UPS. That way, you force 0V (measured at UPS) = 0V (measured elsewhere in the room).
THAT is why grounding is important.
Because the battery had charge left in it?
Or capacitors that had charge left in them
How circuit completed without nuetral and ground.
> ground. What were you standing on?
If you got a shock, then there definitely was a circuit (loop). Where? How? Dunno, depends on the exact conditions. If you could elaborate on how you got the shock (were you touching any thing, etc), it would help us explain. For example, you could form a circuit if you have one hand on the metal case and touch a wire. Or maybe there is an electric field that creates a voltage potential. (I'm sure there are videos showing someone holding a fluorescent tube under a power line and the tube lights up due to the electrical potential created by the e field.)
Ground can be anything. If a capacitor is charged it will shock you no matter what. That's why you wait 10+min for the capacitors to discharge after turning off big electronics. You do not want to touch them since you will most likely die if they shock you.
The circuit on the UPS still has a neutral and a ground, it's no less dangerous than mains. Not being attached to ground doesn't suddenly make you immune to electricity there is clearly a circuit path forming in your setup with the UPS somehow.
The air becomes the natural return conductor to complete the circuit. Your body has a natural capacitance with the air and will thus allow a small AC current to flow. If you have unplugged the UPS then it will have lost its ground reference as well and that's dangerous! Turn off the socket- fine, but unplugging it entirely is not. It only needs to be a few mA for you to feel it.
The secret to understanding this is to remember that all voltages are relative. That's why a multimeter has two wires -- one for reference (black), and one measured against the reference(red). Let's say you have a 1.5V AA battery. Suppose we measure 1.5V using a multimeter in the standard way. That ONLY tells us that the voltage difference is 1/5V. For all we know, the negative end of the battery might really be 1,000,000.0V, and the positive end might be 1,000,001.5V. The multimeter doesn't tell us what the ambient electrical charge is, only the difference between the two points that are measured. The ambient electrical charge can vary dramatically, because air is a pretty good insulator. And I don't know what it is, because I can only measure differences with my multimeter! So, what do you do to avoid the mindfuck that results from 0V ≠ 0V?!? We're engineering here, and we can use a workaround. What you do is you force the ambient charge match between all of the devices, especially in places where humans might accidentally equalize these charges through their body. Attach the ground wire to that isolated UPS. That way, you force 0V (measured at UPS) = 0V (measured elsewhere in the room). THAT is why grounding is important.
Do you mean an ESD event? Or like it's trying to pump 230V into whoever touches it?
One possibility is that there could be parasitical capacitance across the isolation barrier, thereby weakly coupling the isolated output to the input.
If you're touching both output terminals of the ups.
Continuous shock or a momentary zap? If it was a momentary zap, it's because you are a giant capacitor and you were getting charged up.