Racking equipment live is one of the most dangerous things we can do in the electrical industry. Some people do not understand why, so lets talk about it. If you open that circuit breaker, are you sure all 3 poles (A, B, & C) opened? Most of the time you cannot even see the moving contacts on a circuit breaker, you just hope that little "OPEN" flag is correct and not lying to you. Now it's time to rack out the circuit breaker. You assume (because you cannot verify) that all three poles opened correctly. When you are racking out that circuit breaker, if one pole is still closed (faulted CB) then that slow moving connection you are opening when you rack out the CB becomes the new unintended point of isolation. Let's just hope the current is zero when you do this, because if not, then you will know really fast. Racking a circuit breaker is the slowest moving opening sequence in free air, and that air gap opens so slowly that it can result in catastrophic damage. Moral of the story: 1) De-energize the circuit elsewhere and rack out dead if you, if you can not: 2) Use remote operations when you can and pull the humans out of the danger zone, if you can not: 3) Use your PPE and any other protective measure to reduce the harm from a potential failure. Hope for the best, but plan for the worst. Follow me on YouTube: https://lnkd.in/dgaR6ktU #NETA #NICET #electricalmaintenance #testing #electricalsafety #electricalengineering #electricalindustry #powerdistribution #powertransmission #testingservices #training #teaching #electrical #team #tech #lovewhatyoudo
Why not standing on the mat?! Where is the safety person? Shepherds hook not utilised?
Trying to rack out a closed switch gear which is still under load, you know the moment you touch the lever. If Main Switch can't be opened, pray and hope for the best. Front blast cover reduces the risk but doesn't make it 0.
Dear br. Thomas Wire according to NFPA70E to avoid the electrical hazard you should put the insulated mat in the front of the Switch gear god bless you
before racking out , can we open the isolator also ?
It is early this morning and I’m on my way home, so I may have misunderstood, but if you confirm that the breaker is faulted, showing voltage on the load side, I was taught to de-energize the bus feeding the faulted breaker by opening an upstream device.
"Reduce" the harm instead of "stop" the harm... Shows how dangerous it really can get! 😵
Personally I have seen the effects of a circuit breaker that had failed with the contact closed. An Ottermill LV ACB and the window annunciator was showing open. Breaker was racked out and caused an arc behind the breaker and that quickly developed into a phase to phase to ground fault. Devastating. Positive indication of the contacts opening is needed. if not then is a gamble. And a gamble that you dont want to be taking. So power off, or simple remove the person from the task and have automation take over. if were wearing arc flash kit then we are concerned. if we are concerned then should we be doing it. The question should be asked. As there is always a way to reduce that risk or remove it from the person.
I have yet to see a real reason for anyone to rack in or out on a live bus.
Switches are going to be the death of someone. I can’t tell you how many times I go into plants to service and test equipment and the prior company tightened the joints to get the ductor readings down. Causing the switch to not open or partially open. Sometimes even close and break the push rods. Instead of taking the time to properly disassemble clean,lube and adjust to manufacture specs. It’s amazing how many people will fight a piece of gear all day trying to adjust to get it to work instead of taking five minutes to read the adjustment out of a manual and it almost always works first time if the parts are still good and in spec. One site we did 3 years ago had over 27 switches that would not operate cause pivot point and contact points were tightened to the max.
Engineering Consultant at HV Engineering, LLC
1mo...and if you can't de-energize, use maintenance mode / ARMS to reduce the risk...and make sure you understand which maint mode / ARMS switch to operate. I've seen many times that the operator turns on the maint mode on the main breaker (which reduces the incident energy on the bus, not the incoming line) to rack the main breaker in/out.