Can I safely touch a 5V 5A pcb trace?

Are PCB traces/copper fill areas insulated in some way? If not, will 5V 5A do any significant damage to me?

They may or may not, depending on the board design. Many boards have "solder mask" covering all the board surface, EXCEPT the spots that will be soldered. Cheaper boards will not have a solder mask. SO, the answer is a definite "maybe".


A 5A power supply should either have current limiting or some kind of fusing.
You must always respect high voltages and/or high current power supplies.

The solder mask on PCBs is just that, it is not meant as a power insulator !

5V will not hurt you if you touch it (with your hands**).

If the 5V was causing the traces to be over heated it might burn your finger.

Has your post been modified? I don't see the danger @LarryD and @Paul_KD7HB saw and I know both of them to be pretty good at this sort of thing.

** As opposed to connecting it to other parts of your body. An extreme situation but its been done. This note brought to you by the Lawyers Association.

The op was asking about an insulating layer on the copper?

Always wash your hands before and after handling PCB's. Your skin has natural acids that are corrosive, and the PCB may have contaminants that you don't want to consume the next time you pick up a sandwich.

If you put your fingers across the 5V track and gnd on the PCB, even though your power supply can output 5A, the current through you will be regulated by OHMS LAW.

V = I * R
Voltage across a resistor = Current through the Resistor * The value of the resistor.

If you rearrange the equation.
I = V / R
So the current that will flow through you is;

I = 5 / Body resistance.
The resistance between my adjacent fingers is 25 MOhms at the moment.

I = 5 / 25,000,000 = 0.0000002A or 0.2uA.
Using this table;
From here;
The level is well below the "Threshold of Sensation".

However if you short the 5V PCB track to gnd with a short circuit, you may not feel it but your PCB will probably physically suffer.

Tom... :smiley: :+1: :coffee: :australia:

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Regardless of the solder mask, board voltage will be "contactable" at the terminals of many of the components.

Remember those electric train sets you used as a kid? Those had a voltage of 12V on them, that makes them over twice as dangerous to you as your 5V system. They also carried both the + and - on the rails and so were even more likely to expose you to a shock. Remember you need two points of contact to get current to flow.

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This is all assuming that there is a galvanic separation with the mains voltage. For example by a transformer on a well designed board. I have seen instances on this forum where that was not the case.
So, normally it should be safe, but not always..
If in doubt send a picture of your setup to this forum.

I'm not so sure that the question has an actual answer on a public forum. Consider a conversation between OP and lawyer.

I put my fingers on 5V and ground. I got a shock.

Why would you do this, asks the lawyer?

The man on the forum said I could.

You may be interested in having a look at some of Big Clive's videos on Youtube where he takes apart some cheap usb power suplies and shows how little there can be between yourself and the mains with some of them.
e.g. Inside some dodgy Chinese USB power supplies from Greece. - YouTube
Nuff said

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It can hurt your feelings


Reminds me of a minicomputer maintenance course decades ago, were we were taught to never wear watches, jewelry, etc, while working on a computer. A 5 volt power supply capable of supplying in excess of 100 amps will try to melt a ring off your finger, and probably will temporarily weld it in place when you short something out.

I won't purchase a power supply that is not UL listed. A 5 mil polyester tape is not enough insulation between mains and local ground.

See also: Circuit for 5A from USB PD with ESP12-F

lowest lethal voltage

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