Sometimes you need to laugh at the little things you find. Good luck deciphering this panel. None of the ones labeled for receptacles, or even #4 "retesticals", killed power to the outlet circuit feeding a motor I needed to replace. And some of these cannot be shut off, so I couldn't just go one by one until I found it. I had to shake my head and walk away for the day. I'll get one of the plant's in house guys to figure it out for me tomorrow.
My motor is fed via the conduit off the side of the outlet box and through the wall. I'm told they scabbed power off the receptacle circuit. But they'll need to verify that for me so I can lock it out properly.
No joke. This is at a large cast iron foundry. They have a lot of equipment that runs at 4160. The largest I mess with is the 480 stuff. None of my equipment runs on anything larger. Takes special skill and big balls to play with the 4160 circuits.
Used to work at a scrap processing plant. There were two automobile shredders - one natural gas with two 2200 HP engines and the other was electric. It had a large 4160 motor that was started "across the line". Hated even going in the room where it was. Had to wear all sorts of safety gear and use hot sticks for even the simplest tasks. My first rule of junk yard electricity became "assume nothing" as some of the older installation work in the plant was done by non-electrical people.
I've been through arc flash training, I'm required to wear the gear and practice the steps on the job. I've never witnessed an arc flash, but I've seen videos and the aftermath. The power released is amazing.
Saw a failure in a 13.2 kV generator terminal box. I believe it was a loose connection that turned into a bolted fault. Bear in mind, generators are limited in short circuit current. When we opened the box after the event, there was nothing left. Nothing. All the phase terminals and wires had vaporized or melted.
Yeah - you don't want to fool around with this. Or even 480V for that matter. If you seen or heard a 480V single-phase to ground fault close up, you are quickly moving in the opposite direction. Its scary.
I've been involved in the restoration of 2 arc flash incidents...
One was a bus duct failure @ 13.8kv - surprisingly minimal damage, given the power involved...
Other was a large-case breaker failure (3000A breaker) @ 600V... It took 3 weeks of 24 hour shifts to rebuild the switchboard. There was an outline on the wall across from the cell that blew, that clearly showed where the electrician that was racking in the breaker, had been thrown against the wall.
The bomb suit saved his life; he was released from hospital the next day, and was back on the job, working on the repairs, the day after... Until that day, I'd been pretty lax about wearing my suit. Now, I gear up every time.
Great. Pretty sure at least something on our panel will get labeled retesticals now.
It will certainly cross my mind every time I think of receptacle.
As for large power, there was a large transformer unit (??) at a new building on an Army property in the area. IIRC, a couple of low voltage techs were working on it, to run a control wire to it (but I can't remember, it may have been JIW, or these were Tech I's, either way, no excuse) and the idiots were using a hole saw. On a live unit. Drilling DOWN into it. Things went poorly.
It was toast, feed to the outside was toast, think the utility had some work outside to do...the guy not drilling was lucky he had half turned away when shit blew.
FFFFFFFF that. We working down at Metro airport and running our cables, (cat-5, cat-6, video over IP and data for additional information screens at every gate) and in a few locations we were over the transformer rooms. Just being in the rooms with them big fella's should give you respect for them, you can feel the thrum through you. Every now and then we had to climb on em to get some supports up or feed cable, and man, did we move quick. :P
As a HVAC controls and Building Automation tech, we get to interface with power monitors and such...
We had to run a Modbus cable from each of four "substations" back to our JACE to be able to monitor them. (Daisy chain). We submitted what we had to do to the customer, and they said okay, but flatly rejected our electricians... They wanted their electricians to do the panel penetrations... hot 480 3P panels.... yeah... we didn't argue with them.
What's got me worried now is here in a few months, we are going to be starting to retrofit their chiller plant to new controls... and their chillers run on 4160..... Now I'm afraid to go in there! -- "Oh me, oh my. A lovely day is dawning. Oh what a joy I didn't wake up dead. So I can go to [work] and then resume my yawning, and get my sleep [on site] instead of in my bed."
I work with varying voltages throughout my job.... 24VAC, 120VAC, 240VAC, 277VAC, 480VAC... and maybe some in between there... On the higher stuff... 277 and 480, I've never worn any kind of special clothing, or really did anything out of the ordinary... mostly because I didn't know any better... I've never been trained on *proper* procedures for working with 480... For example...
My job requires me to work inside a 480V VFD. (I have to bring in 24VAC control circuits and wire them to the control board of the VFD.) I would consider the drive HOT... only because there is power going into the disconnect. (Even though the disconnect is off.) The electricians keep the panels locked, and the electrical rooms locked. So I would have to go to an electrician, and ask them to turn the circuit off.... and would promptly be laughed at for it. So I do what I can do... stay away from the bottom of the drive.
I know it doesn't make it right, but there is a small twinge in the back of my head that says "What is going to happen if I'm sitting in front of this drive, and something goes horribly wrong with this disconnect?" If anything, I have learned that when I turn something back on, I don't stand in front of it. I stand to the side, and try to do it at arm's length.... and have been laughed at for doing it.
I think as we move into this chiller plant, that before we do, I am going to push my company to do some training with working around higher voltages. We may not have to go into panels with 4160 in them... but I'd rather be trained and not need it, than to need the info and not know it. Hell... maybe it would be a good idea to forward my project manager and his boss the above video... -- "Oh me, oh my. A lovely day is dawning. Oh what a joy I didn't wake up dead. So I can go to [work] and then resume my yawning, and get my sleep [on site] instead of in my bed."
My employer's policy is to wear arc flash gear for anything 40 volts and above. I know that seems a bit over the top, but it is what it is. There are different rated clothing for different voltage. For example I don't have to wear the full space suit when working with 120v. But it still gets a few chuckles or comments of disbelief from some of my customers that don't care or sometimes don't even know what an arc flash is. I just tell them that's our company policy, and since I enjoy being employed I follow it. I've never had anyone give me more serious grief beyond that. If they did I would stop work and call our safety office for further direction.
We carry up to cat 2 on our trucks. I have yet to run into any equipment calling for anything more than cat 2, except for some 4160 motors. In those cases we work with a qualified electrician.
There are different rated clothing for different voltage. For example I don't have to wear the full space suit when working with 120v.
Lurch, you should know that the level of PPE has no direct correlation with the voltage you are working at; although voltage is one characteristic. The only way to know what level of PPE is appropriate, is through the arc-flash sticker on the equipment, which would be there is an actual arc-flash study had been done. (Now a code requirement.) The arc-flash sticker will tell one what the arc-flash energy and boundaries are; and the PPE category.
When there is no label, then yes; one would have to take an educated guess. The level of energy is what dictates the PPE level. From a simple perspective, arc-flash incident energy = t x V x I
't' = time for the fuse to blow or breaker to trip 'V' = voltage 'I' = available fault current (3-phase bolted short circuit current)
Voltage is actually the least concern; although system design based on the voltage can have a large effect on the amount of energy. Some rules of thumb, assuming the over-current protection works and has an instantaneous setting; i.e. current-limiting fuse; thermal-magnetic breaker; etc. See below.
Warning, the following rules-of-thumb are estimates only. In all cases, one use the information on an arc-flash label; or consult with a professional engineer skilled in determining arc-flash incident energy levels.
- 208 or 120V on the secondary side of a transformer no larger than 75kVA = PPE 0 or 1
- up to 600V on the secondary side of a up transformer no greater than 500 kVA = PPE 3
- Any voltage from a utility 'grid-style' network (i.e. 208V utility in NYC) = PPE 4 or 'Dangerous' (meaning no level of protection will save you)
- Voltages over 1000V, from substation transformers 2MVA and larger = PPE 4 or 'Dangerous'
Personally, unless its 120/208V from a small transformer; if there are not labels on the equipment, I would use the highest level of PPE available. If the equipment has a 'maintenance' setting, that lowers energy levels (by reducing the amount of time for a breaker to trip), it should always be turned-on before servicing the equipment. These are not very common, except in new, high-end equipment.
Yes, I just left it simple. Voltage is usually the biggest factor in the equation from my experience. The higher the voltage, generally the higher the requirements. All the newer equipment I work on has the sticker, but most of the equipment I work on is not new.
Actually it has more to do with the available bolted fault current than anything else. Using voltage alone can be deceiving because the level of protection from the next upstream OCPD can vary wildly. This is exactly why the labels whizkid3 posted are now required.
neonhomer it sounds like you really might benefit from NFPA 70E training. If I were you, I'd follow up with your plant's safety officer not only about the training requirements for your job classification but also the safety culture being perpetrated by the maintenance electricians.
The best example for a high level of protection needed for low voltage systems are the bus bars from a 48V or 60V battery room. Whatever conductive material you drop on those bars will be instantly turned into a hot plasma cloud.
Low voltage does not mean safe, especially not if it can deliver a huge current. -- Got some spare cpu cycles ? Join Team Helix or Team Starfire!
You are not doing anyone a favor working like that.
Ask your self this question: Who will take care of your loved ones when something goes wrong?
A a very bare minimum, LOTO and PPE will apply to any device you work on that has energy in it. It does not matter if you are a full time employee, a part time cleaner or contract worker: You are responsible for your safety. You must be in control the the energy available in and to the device you are maintaining.
Yes, you need to approach the company about this situation. It is not just for your benefit but point out to them that if something goes wrong and you have not been properly trained, the company is in deep dodo. -- The difference between genius and stupidity is that genius has its limits.