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Posted: 7/19/2022 5:33:53 AM EDT
[#1]
Quote HistoryQuoted: Do you treat equipment as de-energized just with grounds or do you need a visible air break? Grounds are a last resort protective device that would be layered with a switch or physical air gap (cut jumpers). A properly designed air-break switch in the T&D world will have an air gap 110% greater than the gap to ground. Any voltage, even a surge, should go to ground before jumping the gap. Otherwise it should be treated as hot. It's not common practice to open transformer fuses if a primary is down. That would be an insane amount of extra steps if you're working between gang operated switches or 3 phase laterals. You could always make an air gap on either side of the downed wire by cutting in insulators. That's also not very common and it makes a mess of the wires if you're constantly doing that. Some companies do practice that though and that would be ideal safety wise. I brought the issue up that you can't clearance a line with customer load connected, but it went nowhere. I do transmissiin now and we always have an air gap and grounds, but distribution is a different story. |
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Posted: 7/19/2022 5:50:43 AM EDT
[#2]
Quote HistoryQuoted: That's terrible  I'm a retired electrician and when we worked on high voltage, 480, 4160 or 13,800 we installed grounding clamps on all phases so any back fed energy would immediately go to ground. Excuse my ignorance but do line workers do this also? Like most accidents, the coming investigation will find a combination of safety protocols that were not followed. Sorry about your friend OP. |
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Posted: 7/19/2022 7:19:35 AM EDT
[#3]
Quote HistoryQuoted: Why not install a manual transfer switch? Quote HistoryQuoted: Quoted: the layout of my panel doesn't lend itself to lock switch. i use physical breaker locks and have a checklist taped to the door to use before switching over. the breaker for the genset NEVER goes hot before the lockout is on the main. i trust myself to take the time to get it right and i manually test things every quarter. this isn't rocket science but when you need a generator you are already stressed and here likely sweating your balls off. Missing something is a real danger. Why not install a manual transfer switch? i will be eventually. i will need to run 75' of wire for a new 50amp circuit and the local electrician wanted around 2k for the parts and labor. Sure i can do it myself cheaper, but i'd prefer not too. if/when prices become sane i will get one installed. Until then i lockout the main with a tagout breaker lock before doing anything. |
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Posted: 7/19/2022 7:47:44 AM EDT
[#4]
Quote HistoryQuoted: That's terrible I'm a retired electrician and when we worked on high voltage, 480, 4160 or 13,800 we installed grounding clamps on all phases so any back fed energy would immediately go to ground. Excuse my ignorance but do line workers do this also? This No idea why phases weren't grounded. This is why it's done |
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Posted: 7/19/2022 7:56:14 AM EDT
[#5]
Quoted: Friend of a friend is a lineman of 20 years. Last night he was working on a high voltage line that was de-energized. His leg hit or got close to a line and he was electrocuted. He has second and third degree burns and is still alive but the damage is severe. The line was energized due to a homeowner backfeeding their generator into the grid. The dude has a wife and kids. Even if he makes it he'll never be the same. Will add links if the incident makes the news. I'm posting this because there are many DIY'ers on this forum and the topic of generators comes up frequently. Thats terrible. It must not have been grounded. I ground everything unless I can see both ends and sometimes, I still do. There will be much more of this as people try to deal with the weakness of our power grid on the cheap. They cut corners or are just too damn dumb to hook up a generator. |
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Posted: 7/19/2022 9:09:22 AM EDT
[#6]
Quote HistoryQuoted: Do you treat equipment as de-energized just with grounds or do you need a visible air break? Grounds are a last resort protective device that would be layered with a switch or physical air gap (cut jumpers). A properly designed air-break switch in the T&D world will have an air gap 110% greater than the gap to ground. Any voltage, even a surge, should go to ground before jumping the gap. Otherwise it should be treated as hot. A visible open and grounded to be considered dead is our procedure. That’s from the source though, in the case of a backfeed we wouldn’t have an open downstream. |
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Posted: 7/19/2022 9:24:17 AM EDT
[#7]
Tragic. Hope he recovers.
Curious as how it happened. I would have guessed the feed came off the transformer primary taps onto the neutral/ground and one phase. Wondering if he has actually on the pole or in a bucket. Seen someone blown off a pole once during and accident I was involved in. It would be fairly easy to get into a back feed walking around up on the pole to get to something near a transformer. Guy On the job I was working had taken his belt off to get around something when he got into the primary so when it hit me and him he fell off the pole. |
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Posted: 7/19/2022 9:25:02 AM EDT
[#8]
Quote HistoryQuoted: Did the actual clearing time differ from what your analysis calculated? Fuse selection/sizing is critical as fuses are dumb devices. They sometimes (always) struggle to clear a high impedance fault. I’m not not a protection guy and I didn’t stay in a Holiday Inn. Quote HistoryQuoted: Quoted: Quoted: This is what it comes down to. It’s not dead if it’s not grounded. I’m guilty of just wearing rubbers when a breaker is open without testing and grounding. All it would take is an incidental contact on a line you thought was dead to have problem. We built a scenario with a 50kva and a 3500 Honda Generator. Little single phase tap. Grounded the line 100ft from the pot, energized the generator and closed the fuse. It held and the little red beast kept chugging. Moved the ground closer to the pot, no trip on the generator or blown transformer fuse.We kept moving the ground closer to the pot with no tripping. Shunted at the bushing while the generator was running and finally tripped the breaker. Isolate from known and possible sources of potential, check for voltage, ground and keep hands and feet at the same potential or in parallel with a low impedance ground as close to yourself as practical! A lot of fatalities on “grounded” lines. Always know where you are placing your body in the circuit and work accordingly! Did the actual clearing time differ from what your analysis calculated? Fuse selection/sizing is critical as fuses are dumb devices. They sometimes (always) struggle to clear a high impedance fault. I’m not not a protection guy and I didn’t stay in a Holiday Inn. We did no analysis prior to or after the event. It was done to demonstrate to a crew that isolating from all sources was critical. That utility fused transformers at 300% to reduce nuisance tripping. Time current curves matter! High impedance faults are tough to clear reliably while maintaining system reliability. Not a protection guy either but I did put 43yrs in the trade. 37 of them in the field. |
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Posted: 7/19/2022 9:39:08 AM EDT
[#9]
Quoted: Well that proves that grounds aren’t as sufficient as we are taught in all cases. We sure try to work smart and minimize risk but a third party down the line 5 miles is hardly ever added into the equation. Grounds are very effective when properly sized and placed. Too often they are not properly utilized. I think many people see a ground as a “stopping device” in regard to current flow. They believe current gets to the ground and stops hence the bracket grounding practice. The fact is current will travel all paths. I liked to put an ammeter on grounds in a hot transmission to show apprentices and non-believers how current can flow in a grounded circuit. Establishing a visual opening is also a key concept. |
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Posted: 7/19/2022 9:43:28 AM EDT
[#10]
Quote HistoryQuoted: Like most accidents, the coming investigation will find a combination of safety protocols that were not followed. Sad but true. |
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Posted: 7/19/2022 9:50:38 AM EDT
[#11]
Quote HistoryQuoted: I don't want to give out a few details as everything I got was second hand and this was the account I got. I have been keeping an eye out for any news articles on it. I was involved with the installation of a 350kva backup generator. It used what is known as a "closed transition transfer switch." That is, when power was out the generator would start and the transfer switch would kick over to the generator. After mains power was restored the generator would rotate and sync phase with the mains and momentarily bridge the generator to the grid before breaking connection with the generator. This was to prevent the momentary flicker you'd otherwise get with a standard transfer switch. The installation of this type of switchgear was documented and approved by the local utility so they could take proper safety precautions. I inspected one similar to that on a broadcasting station once. I was told they were doing it so during storms they could power it up before losing grid power so no loss of airtime if the utility went down. Did not look into the detail of how any opening and closing times worked or the opening and closing of the switching methods |
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Posted: 7/19/2022 9:54:12 AM EDT
[#12]
Quote HistoryQuoted: That fucking sucks big time. Electricity is an interesting subject. There appears to be so many variables that determine whether or not you're going to get killed by electricity that it's just a roll of the dice. Some folks get what would be deemed a small "dose," and they get killed. Others get hit by fucking lightning and receive a couple of burns, but are otherwise okay. If anyone listens to Shawn Ryan's podcast, and if you heard DJ Shipley's story about having been electrocuted, you'd know that fella is pretty fucking indestructible. Anytime someone else says electricity is spooky or unpredictable it's simply that they don't know enough about a situation to predict its behavior. It follows every path to ground always, there are formula to predict amps and volts across an object, it's as predictable and consistent as gravity. It's perfection is scary, you get no mulligans. The very first time you fuck up it bites you. |
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Posted: 7/19/2022 10:03:14 AM EDT
[#13]
Quote HistoryQuoted: I understand ATSs MTSs and interlocks.. I have an ASCO300 series to wire up for mine.. However in a somewhat related question, how is this handled when solar being fed into the grid at homeowner level being more and more popular? Do they have a list of people who have solar and just go around and shut off everyone's feed into the grid? If the solar system is installed correctly it has a sensor on the power management unit that shuts the output to utility side down when utility power is cut. |
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Posted: 7/19/2022 10:08:48 AM EDT
[#14]
Quote HistoryQuoted: Dominion is rolling out new meters that have exactly this sort of capability. Rated to disconnect at full load, remotely using a 915MHz to cellular bridge. I don't know if they have active back-feed detection but it wouldn't be hard to implement. Thats great, but I doubt every utility does it unless mandated or it makes financial sense. Safety 3rd. |
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Posted: 7/19/2022 10:10:01 AM EDT
[#15]
Quote HistoryQuoted: I respect electricity because it's perfectly predictable. It's a physical force that follows rules, everytime. Anytime someone else says electricity is spooky or unpredictable it's simply that they don't know enough about a situation to predict its behavior. It follows every path to ground always, there are formula to predict amps and volts across an object, it's as predictable and consistent as gravity. It's perfection is scary, you get no mulligans. The very first time you fuck up it bites you. Simple math! Insert yourself into a circuit or touch something creating a circuit and current will flow. If the math works in your favor you live. If not you’ll learn the accuracy of Dalziel’s research! |
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Posted: 7/19/2022 10:31:31 AM EDT
[#16]
Quote HistoryQuoted: Thats great, but I doubt every utility does it unless mandated or it makes financial sense. Safety 3rd. Quote HistoryQuoted: Quoted: Dominion is rolling out new meters that have exactly this sort of capability. Rated to disconnect at full load, remotely using a 915MHz to cellular bridge. I don't know if they have active back-feed detection but it wouldn't be hard to implement. Thats great, but I doubt every utility does it unless mandated or it makes financial sense. Safety 3rd. I imagine that the primary function is remote disconnection for non-payment. Safety is at least 3rd. |
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