Did you know…
“Drag chains/cables have been known to be unreliable for grounding mobile equipment. Due to the variability that may be encountered with resistance measurements on mobile equipment, it is recommended that the mobile equipment be moved slightly and the test procedure be repeated.”
From ESDA documents TR20.20 and TR53
Carts and Mobile equipment presents the ESD Control Coordinator with several challenges.
- If the cart fails the test to ground < 10^9 ohms Rtg and can not be brought into compliance, product riding on the cart should be in enclosed ESD shielding containers and the control program documenting this. Cart should be label to this fact as well.
- Drag chains alone are known to be an unreliable connection
- The connection measurement to ground will vary as the floor varies
- Conductive casters help but the system still relies on the cleanliness of the floor and floor readings.
Think about it, your operators that wear footwear for gorunding are required to test a minimum of once a day, should the carts also be tested?
It is highly recommended that carts when stationary be hard connected to ground with a ground wire. A great solution to this is the Desco “magsnap” coil cord as it is a magnetic attachment and will connect to metal carts without any additional hardware. Then the banana plug end of the coil cord simply connects to an extra banana jack that is frequently found at work stations.
I will continue to share these little tid-bits of information as I encounter them or remember them from past ESD Audits/Surveys I have preformed for customers. If you would like to schedule an ESD Audit / Survey send me a request and lets “check-out” how effective your ESD control program really is.