[LYN BYRD]

I Have 4 Cnc's And Was Just Wondering If They Each Need A Separate Earth Ground ( Copper Bar Driven Through The Concrete Floor Into The Ground) We Have Been Having Many Lightning Storms Lately And I Was Just Concerned. Normally I Do Not Run Them When A Storm Is Happening. My Electrical Service Is Grounded With An Earth Ground, But Is That Enough?
Thanks

[bborb]

Depends on several things. Is there a phase converter involved? Step up/down transformers for main power? State Electrical Codes apply, for example Ohio's is different than Kentucky's. Is there hard (metal) conduit mounted?

[moldcore]

My Electrical Service Is Grounded With An Earth Ground, But Is That Enough?
Thanks

Yes, that is all that’s needed and from what I have read and heard having a second ground can be dangerous. Do a search on this site or practicalmachinist.com for more information, it gets argued a lot.

[pminmo]

The objective of a safety ground (tied to earth) is to give a true 0V reference. That in turn should provide a non current carrying path throughout your electrical subsystem for safety-fault conditions. If you have not installed isolation transformers or power subsytems, then one should be enough. If there are isolation transformers, or power subsystems, there needs to be a ground rod for each. Safety ground should never carry current except in a fault condition. The metal frame on each of your machines should be tied to the safety ground.

[LYN BYRD]

Phase Converter=yes
Transformers=no
Machine Ground Tied To Service Ground=yes
Does Anyone Run Their Machines In A Lightning Storm?
Thanks

[Al_The_Man]

Generally if lightning strikes the incoming service there can be extremely high voltages being transferred through the system, and to some extent any amount of grounding is not going to protect the machine, personnel, maybe.
Most parts of a CNC machine do not take to excessive over-voltage.
There are expensive devices to either eliminate or decrease the chances of damage, one is SOLA regulators, these consist of Transformers that run around saturation so surges are not processed through them, but they tend to be inefficient, power wise due to running very hot (saturation).
One of the things that often suffer the most are things like SCR drives etc, that operate across the line.
Due to nothing to buffer them, the spike causes havoc with the firing sequence and often, either takes the fuse out, if you are lucky or blows the expensive switching device.
Al.