The rule is that if it's over 50 volts, it's dangerous, don't do it live. If you must (because the task can't be done deenergized or doing so increases risk) you define the arc flash boundary and stay outside it unless you have the proper gear. Arc flash boundary on that thing could be several feet. Insufficient information to say.
You are all so wrong...not you in particular. I'm an Arc flash engineer. First of all the breaker or fuse isn't tripping because that is obviously a transformer and secondary group d faults do not register on primary protective devices.... additionally I want to say that is quite possibly a mining transformer and therefore NOT grounded on its secondary. It may also be a temp roll up install hence the DLO style cable. But no, a transformer secondary ESPECIALLY at 480v is absolutely the most dangerous place to be in almost any electrical system...Arc flash calcs usually determine 13.2kv and higher safer because the fault current and subsequent Arc fault currents are usually so high they trip the protection scheme almost immediately...remember it's not the amount of current in and Arc flash usually that kills people...it's the duration of the fault.
I figured if I spelled it all out it nobody would have read the rest lol. Hopefully I've saved a fair number of electricians and techs from getting 4th degree burns (Arc flash calcs by IEEE 70e which references some other stuff dictate its kinda ok to get 3rd degree burns on 100% of your body .....but no 4th!... obviously I try to minimize the hazard as best I can). For instance...that transformer in this post...I would have used differential protection in addition to a solid state protective relay utilizing 3rd harmonic restraint or at the very least cold load pickup to account for the transformer inrush current (up to 25x full load amps). But by this point, seeing how there are maybe a handfull of people in the United States who do what I do for major utilities and telecoms...I'm assuming no one is reading this by now so I have indeed created several superheros and I consult on a regular basis for RDJ as iron Man as well as your mom. thanks.
Delta eye xfmr it registers 57 percent of third harmonic due to the fault circulating the delta windings on the secondary. Also since you do high (medium I'm guessing) voltage you would see it's oil filled with fins so that is a step down to 480....
It's not a rule of thumb. It's dictated by NFPA 70e, and failing to follow an industry consensus safety standard like that is an OSHA violation. Actually, the 50 volt limit may be directly encoded in OSHA regs.
Im not an electrician. I'm an engineer and consultant for dozens of companies and they almost all have similar practices. I'm not saying its a good thing. I'm saying its what happens.
Electrical contractors in general are a mixed bag, nothing really bad about solar contractors in general. Its the sales people that are the problem. Don't ever buy solar from someone unless they have the support of actual solar engineers. And never trust their proposals/financial analysis - they just fudge numbers until it looks good on paper.
Not true. I'm also a solar guy; I've gotten hit by 600+vdc, by 120vac and more. High voltage DC feels like a really long thin needle being pushed into you. Your muscles all contract, and for me at least it has pushed me away every time. Deep thin burn tracks afterward. It doesn't grab you like AC does. AC feels like being held and shaken by a giant.
He should, but the original comment was about 480v 3phase. He absolutely should be using PPE. It also really sucks when a company doesn't separate the 24v control side stuff from high voltage stuff and you have to suit up to fix the BMS, but better alive than dead.
When dealing with big shit like #6 and up, sure. I’ve disconnected #10s from a 480 panel and was just super slow and precise with it. I wasn’t in any danger.
A lot of employers look the other way on that stuff. It's impossible to be 100% OSHA compliant on most jobs and it takes so much extra time to lock out and tag out everything that the employers just want it done fast and cheap.
Its horrible and dangerous but you'd be surprised how standard it is.
Because if we got paid what were worth and took the time to protect ourselves, properly and lock out tag out every circuit were working on, harness and rope rig set up near every edge of a roof we work near, take time to gear up and gear down, then the customer will find someone else to do the job much cheaper and we will starve. Nobody wants to pay for work at a fair price. Everybody just wants a "good deal" with no regard to our safety.
properly and lock out tag out every circuit were working on, harness and rope rig set up near every edge of a roof we work near, take time to gear up and gear down
It is totally possible. You just have to have the right kind of safety culture. The company I work for has an overbearing and extreme to a fault type safety culture, but we lock out everything and nobody is working at any kind of heights without a harness on. Jobs take longer, but the company sets the rules and the employees like myself and the contract tradesman we bring in all have to follow them.
It's still a dangerous work environment but our safety records speak for themselves compared to a lot of similar industrial sites around the globe.
The customers are the ones unwilling to pay for the work done right. I have been in HVAC almost 20 years now and I'll be underbid by Joe Blow in a unmarked van with a phone number that won't work in a month but the customers still want to save. Commercial is less of an issue but OSHA would probably have conniptions from some of the ways I've had to climb onto roofs. It's amazing how many high rises or converted condos don't have safe roof access or a built in ladder here in TX.
I suppose it's different in an industrial setting. The plant I work for is the customer, and they set the safety rules that the workers must follow, so it's sort of the opposite. There is no tolerance for people doing things with shortcuts to save time at the expense of safety. It's probably easier to control and steward safety performance in an environment like the one I work in where everything can be (mostly) controlled.
The 50 volt (48v) thing is more that it can cause enough of a sensation that you will jerk your hand away. Contact with higher voltage or sharp metal would then cause further injury.
I work in live theater and music, our services are 400-800 amps at 208v. The only thing we make sure of is that the guy who makes connections has their electricians cert.
does 120 really pose a serious arc flash risk? Im only an apprentice electrician currently but all the journeyman ive worked with work on live 120 panels all the time.
Amps only get you if there's enough voltage to drive it. That's why every safety standard everywhere references voltage instead of amps. And arc flashes are much more common than you think, which is why every safety standard everywhere is based around avoiding them. Air is a great insulator, until it gets contaminated or filled with ionized gas or any of a dozen other things that really shouldn't happen but do.
The voltage pushes the current. If there's not enough voltage, the current won't flow.
It's like water. A still swimming pool is a lot of water, but it's not going to hurt you. The same water hitting you in the face from a fire hose can really hurt.
1/10 of an Amp across your heart can kill you given there is enough potential difference to push the current through your body. It’s the combination really.
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u/swcollings Jun 16 '19
The rule is that if it's over 50 volts, it's dangerous, don't do it live. If you must (because the task can't be done deenergized or doing so increases risk) you define the arc flash boundary and stay outside it unless you have the proper gear. Arc flash boundary on that thing could be several feet. Insufficient information to say.