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

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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Please do NOT cross post / duplicate as it wastes peoples time and efforts to have more than one post for a single topic.

Continued cross posting could result in a time out from the forum.

Could you also take a few moments to Learn How To Use The Forum.

Other general help and troubleshooting advice can be found here.
It will help you get the best out of the forum in the future.

But how could that ever happen?

Possibly the effect of ESD was mistakenly assumed to be from 5V.

Maybe OP was simply shocked that nothing happened

Forum members have previously posted projects where the PCB ground was connected the live mains.

Exactly. Some seem to willing to leave this planet early. Some might at least realize this can be as dangerous as touching the metal framework of old black and white televisions when plugged into mains...

It seems the OP is new at Arduino and does not have a electrical background. Is the goal of this forum to provide some useful help or recount old issues?

Touching 5V is not inherently dangerous.

However it is a good thing to verify the source of the 5V is via a power supply that has some safety approval like CE or UL etc. This will verify the power supply is not connecting you to the mains voltage.

Unsafe power supplies are not unheard of but are not that common.

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Great advice, I’ve experienced USB 5V power supply leads connected to
AC mains power.

Treat all power supplies and electronic components with respect.

As a side note, even AA batteries can cause a fire or cause a capacitor to explode.

The OP has vanished after touching 5 volts :cyclone:

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Care to elaborate?

Nah, he's just off down another rabbit hole!

Due to poor factor soldering, a solder splash connected 5v to AC mains terminal.

Something similar to these:

Chines unbranded of course.