I'm curious about something here, how do many technicians imagine that an ESD mat is used or required ?
It's not supposed to be connected to live or grounded things to remove household electricity, it's to discharge the built-up static from ourselves as we move around.
As we move, we make up a static charge, any kind of movement where there is friction creates this effect. Rubber and other non-conductive chemicals don't allow this to happen, or to be more accurate they just reduce the flow of atoms to so few it become next to nothing.
A neat test as I use to show students, is to buy one of them $1 screwdriver/mains testers, looks like a flat blade screwdriver but has a red LED - this lights when it senses power, and especially when it picks up static - I have students walk over different surfaces, wearing different shoes, clothing etc. Try bare feet and a nice woolly sweatshirt lol.
Anyway, the idea is this, as far as I see it to be (like electricity, there are many ideas of just what it is). . . .
You, and your circuit will/may have current in them - certainly you 'will' create current as you move while working. This is a danger to any complex circuit using degradable low power components, so you want that spare current to all go away.
This is impossible completely because you add more as you touch the circuit, your tools, the floor etc. Friction = power :-(
Your ESD mat is a convenient way to 'slowly' take away unwanted power - nothing more than that. Your ESD strap on your wrist is the same, but just a personal version of the same thing.
You use both (mat and strap), because the circuit will have your static slowly wandering thru it, and if you touch one end of a long circuit to the ESD mat and the other has your fingers on it (as an example) you will flow power thru it (in theory) as you will work like a battery power cell until all your personal static is drained away.
The ESD mat slows the flow right down, thereby making the rush of electrons nowhere near so harmful. Keep in mind what electricity is - it's only dangerous/electrified if its atoms are moving fast enough - if you slow it down, it becomes low power and harmless (again, in theory).
The ESD strap instead, drains power from you, more efficiently/quickly onto whatever 'grounded' object that you are connected to, than a mat will do - obviously a mat will only be of use if bare parts of the board are in contact with the mat itself.
It doesn't necessarily need to be to a house etc. that you are strapped onto, as static only zaps when it jumps suddenly, but if in constant contact thru a strap/mat, it flows instead, again slowly because of the straps/mats resistance.
Try this one - do you get a zap when you touch a car door? or a kitchen sink? Why? because of that sudden zap - power looking for an escape. Now, go to your car door after rubbing your feet all over a carpet, rubbing a curtain etc. Make sure you cover your hand in a towel (dry), put the towel in contact with the door first, press it against it, now slide your hand along the towel onto the cars metal door surface, and.....no zap. The towel takes it away by working exactly the same as a strap would - slows that initial zap/shock.
Any strap or mat just needs to ground to something that will logically be big enough to have enough atoms to take the shock, regardless of it actually going to the earths surface - although that's obviously quite big lol. The reason for using the planet as a ground, is its size - nobody ever sees sparks as they walk across the floor, because the earth gives too much resistance for the foot/floor circuit to work.
Here in the UK, we have the ground wire too, which makes it all soooo much easier, but the reality is, you dont need it to be going to actual ground, just something big enough to take it.
Sorry for ranting !! I gotta stop drinking so much cola on hot days lol :-)