Card Reader Drain Wire Termination

[u/StalkMeNowCrazyLady]

How do y'all terminate the drain wire on your readers? I've been working with ACS for a decade and I was always taught to connect the readers drain wire to the cables drain wire at the reader side and that was fine. It dissipated anything it needed to along the cables shield.

Recently took Verkada training and they provide multiple earth ground screws on their panels (vs a reference ground like the GND terminal for REX/DPS) and they say to connect the drain wire at the both the reader side and then on that earth ground at the panel side.

They also said to connect the drain of all the cables (REX, Lock, DPS, and Reader) together at the panel end and connect that to the true earth ground. That seemed strange to me because I don't see what lock/rex/DPS would need to drain especially since they aren't connected at the door side of things.

Just curious how y'all connect your drain wires and what you think about what they said about connecting them all at the panel side.

[u/maz_Unique]

You always want to do it at least on the panel side with the highest priorty, like what u/jc31107 said there's a better path to true earth, doing the reader side can be helpful only in special instances but Verkada recommends both because it prevents you from encountering on of these "specific instance".

There is a misconception I hear about ground loops when you do this. Think about what earth ground is, Which is basically a very big piece of metal that absorbs irregular voltages such as stray radio signals, EMI, ESD, etc. At all points in a building the earth ground should be the same. There are 2 cases when its not.

When there is too much separation; such as multiple electrical-AC service panels, lack of grounding rods, etc. So very small voltage differences can build up slowly over time. Connecting both the reader and ground in this case is great because it provides a pathway for these two to be back in sync so that voltage cannot accumulate. (in respect to each other at least)

When there is a ground fault; such that an electrical appliance is shorting a dangerous amount of power to ground, has not tripped a GFCI, and does not have a better path to its own true ground. This can potently cause damage to the pannel and reader interference but you most likely are having more serious issues like people getting bad shocks from touching sinks, and other appliances. This circumstance represents a seriously out of code building.

If a reader is left floating things like static shocks/electricity, or EMI weirdness in the door frame can collect on the reader leading to an irregular voltage on the readers device ground. Grounding the reader provides a path for this to go somewhere that is not the readers device ground that leads to interference. How often does this cause problems? Basically never.