“Grounding Electrical Equipment” for personal protection, good idea, or bad? The highest risk and the perhaps the most dangerous task a person could perform as an electrician/engineer/electrical worker.
I have used this picture for many years in the 70E classes I have presented while discussing ASTM F 855 personal protective grounding and I will refer to this picture many times throughout this blog. I will attempt to cover the subject matter in a blog form however there is just so much to consider when comes to the question of proper grounding. The first question should be “why are we required (above 1000 volts) to ground the bus and what is the purpose in the first place? The NFPA defines this task as a high risk, and a 40 cal flash suit is to be worn during the grounding procedure (provided the point of grounding is calculated to be 40 cal or less).
I need to say something very important before I start this discussion; I have never seen any person or group perform the grounding task correctly, using the correct equipment, cable sizing and ground clamp design, proper PPE, Lighting, space to work, number of workers and the list goes on and on. I have attempted to use trainers that the training company would send out to the class for demonstrating purposes and I just cannot with a clear understanding of what is happening, proceed with this method of instruction because it’s WRONG, DEADLY WRONG!
Let me also say that grounding of an aerial line conductor from an insulated bucket truck, using the proper PPE and hot stick handling tools, is not included in this blog. I am talking about utilities that are trained and equipped to perform the task and grounding in this environment is totally different than the Industrial task of grounding Medium Voltage, Low Voltage Switchgear and Motor Control Centers.
So why do we ground the equipment?
The primary purpose for grounding the switchgear/panel, phase to phase and phase to ground, is to ensure that the OCPD (overcurrent protective device) upstream will trip open when it senses a high current flowing, i.e. upon accidental re-energization of the equipment.
The OCPD cannot operate if the ground path is not a very low impedance allowing maximum ground/fault current to flow. When I use the term “low impedance” I am talking about micro-ohms/milli-ohms which cannot be achieve with homemade grounds, poor connection, improper connectors, undersized cable, etc, etc ,,,,
You might say, looking at this picture, that’s never done! Well, Wrong again! This type of grounding equipment was and is still used in so many Industrial sites that I could not list them here and it’s very scary to think that we are. This is 2017? Yes?
The second reason we ground the equipment is to ensure that if the worker was touching the phase bus or conductors at the time the equipment somehow became hot again, the voltage drop for the cycles it takes the OCPD to trip would not rise to a level that would cause current to flow thru the worker, killing them! If the impedance to ground obtained by a proper grounding set that is correctly installed is extremely low then the breaker trips and you walk away alive.
How does the circuit become “Hot Again”? If we performed the lockout/tagout procedures correctly as stated in OSHA and NFPA 70E on all possible sources, then the possibility of becoming energized is minimized/avoided, so grounding the system is a backup precaution. How many of you folks reading this blog have seen or have known of accidental missed identification of the electrical switches, circuit breakers opened, or all control devices locked out, or?????
As a minimum list of items/tasks that are required prior to grounding:
- Lockout/Tagout completed and verified by visual inspection and testing for Zero Voltage (Energy) as described in the NFPA 70E.
- Arc Flash study completed and expected cal/cm2 posted and verified.
- Job task analysis meeting completed example JSA or JTA
- Only Qualified personnel performing the task.
- Ground cables and ground connectors are pre-selected to fit application. (This step might require additional training to ensure everyone understand proper fit and proper types of connectors and proper sizing of cables, etc. Reference ASTM F 855)
- Insulated hot sticks that have been dielectrically tested and examined.
- Proper PPE; might be 40Cal blast suit, gloves, boots, etc, etc.
The list could even be longer depending on what you are working on and its location/environment.
It comes down to applying the grounds (Man vs Task) and this task is considered the most dangerous task one could perform. SO, SO, SO Is it the only way????
NO!
My next blog will go into detail on the actual task and some things to consider before undergoing this. Here is a question for you to ponder upon before the next blog “Can a mechanical/electrical device perform this task for me?”
Next week