Accidents & failures

chsdiyer · September 2017

So I haven't seen a separate category for this subject and wasn't sure exactly where to post it but this seems like a fitting place. I'm active in a woodworking forum and they have a category for "shop safety". When I was first getting into it, I was clueless as to the power of these tools and things like kick backs. So I was wondering in the world of RE where a lot is done DIY it seems, what are some failures or accidents people have had? Either from component failures, improper installs, or just accidents. I've seen lots of kick back consequences and cut or lost finger photos to make me be a lot more cautious when operating my tools. Perhaps others can learn from mistakes or be made aware of how bad things can get in this field.

littleharbor2 · September 2017

You might want to read up on Arc Flash dangers.

Image: https://us.v-cdn.net/6024911/uploads/editor/2w/gmalpb3c33s2.jpg

mike95490 · September 2017

Avoid using your watch or ring, for arc welding battery terminals

chsdiyer · September 2017

I'm familiar with arc flashes...my brother had the same thing happen to him in that picture. Fortunately he was wearing the proper protective equipment. Bill shared with me a wealth of knowledge that I thought would be good to post here.

I do not have any specific knowledge about how often fires occur off grid... However, there are things that make it more probable:

Store Generator fuel
Generators plumbed to fuel (gasoline, diesel, propane, etc.).
Lead Acid Batteries do vent hydrogen gas (typically, smaller in-cell explosion and spraying of electrolyte/acid).
When lead acid batteries age/fail, they do take more charging current. One interesting report I read said that when a LA battery is drawing ~2% or more of its capacity while on float (i.e., 100 ah battery, taking 2 amps or more), the chances for a battery to overheat and catch fire go up greatly.
Many installations have exposed batteries (wiring/caps) where metal items can fall on bank and cause shorts.
Many folks do not put fuses/breakers on cables that come from the battery bank. Their loads can be >200 amps pretty easily, and big breakers/fuses can be expensive and difficult to wire nicely.
Many installations used exposed wiring runs. Easy to damage insulation, a fire in one wire can drip burning insulation on to another cable, etc. Using cable trays and conduit to run electrical wiring can be much safer.
In commercial installations, most solar systems would be in a locked room or cage to control access.
Many folks mount exposed wire runs on wood panels. Makes wiring easy, but a big fire hazard if the wires overheat.
Similar for floors--Many system are in unfinished rooms with wood floors--Fire hazard.
Mounting hardware on concrete backer board, and using backer board under the solar/battery installation to reduce chance of fire spreading helps (or other fire resistant materials). Note that "flame resistant" plastics, still burn very nicely with enough heat.
For systems we use perforated metal or screens to prevent burning plastics from dripping outside of enclosures. Even a metal shelf under the electrical hardware helps (if not enclosed/fire "proof" materials).
Comparing 12 VDC systems with 120 VAC systems... 120 Watts at 120 VAC is only 1 amp. At 12 VDC that is 10 amps--Basically, on the DC side of your power system, the current is 10x that of the AC power system. Also, heating from current is P=I^2R (current squared * resistance). The same resistance with 10x more current is 100x more heating.

There is also a big difference between AC current and DC current for fire safety... Once you get above >~12 volts, DC current sustains arcs much better than AC current... for example:

And you need DC rated breakers/fuses to work safely in DC power systems:

With solar panels, there has been a big issue with shorts and failing electrical connections causing sustained arcing. With batteries, if there is a short circuit. a fuse or circuit breaker will cut the current flow. With solar panels, they output X amps of current, whether into a battery bank or Grid Tied Inverter or dead short. Circuit breakers "do not" protect solar panels and wiring against shorts.

It is not to say that you cannot design and build a reasonably safe off grid power systems... It is just that there are so many ways things can go wrong. And, even so, electrical fires in homes still happen around 24,000 times a year:

https://www.firerecruit.com/articles/1206100-5-common-causes-of-electrical-fires

According to the U.S. Fire Administration, in 2014, electrical fires accounted for 6.3 percent, nearly 24,000 fires, of all residential fires, 11 percent of the fires where someone died and 7 percent of the fires where someone was injured.

The months with the most electrical fires are December and January due to increased use of heating appliances and lights. Most electrical fires start in the bedroom, but the highest number of fatalities occur with fires located in the living room, family room and den.

Some electrical fires happen because of problems in house wiring or appliance failure, but many occur due to mistakes that homeowners make like overloading electrical outlets or extension cords.

-Bill

chsdiyer · September 2017

Some other links to read:
http://forum.solar-electric.com/discussion/3380/another-fire-n-back-to-ground-zero (generator fire)
http://forum.solar-electric.com/discussion/3375/panel-fire-question ("gray market" solar panels failed)

Solar panel "arc failure" test:

https://www.youtube.com/watch?v=hyx8gh-tUOM

Wiring arc demo with 4x panels in series:

https://www.youtube.com/watch?v=S9a2oPCIMr0

In general, anything over 12 volts and a couple of amps is not considered "touch safe" by UL/NRTLs. And anything over 60 volts is only to be accessed by trained personal (locked cabinets/doors) and never safe to touch (interestingly, they do not specify AC or DC or Both). And is a 48 VDC battery bank charging/equalizing at 62 VDC a hazardous voltage or not.

More or less, any voltage that can drive > 5 mAmps through your body (i.e., heart) is dangerous. And over ~10-t15+ mAmps can be fatal (stop your heart).

With AC, a ground fault circuit is very easy to make. Basically a couple windings around hot and neutral wires (this is actually a current transformer)--If hot-neutral current flow is >5 mAmps, such as through ground/water/etc.) and a circuit that trips at over >~5 mAmps. Accurate and reliable.

With DC, not so easy. Hall effect transistors are fast and accurate--But they drift (need rezeroing every few minutes for accurate measurements). There are now GFI Breakers for DC systems, but they trip on the order of 0.3 amps:

https://www.solar-electric.com/morningstar-gfpd-150v-ground-fault-protection-device.html

Not fully useful to protect people against electric shock through ground faults.

What happens when a solar panel shorts? You basically design the wiring to support Isc of the panel (or 1.25x Isc). That way, if there is a short, none of the wiring will overheat and cause a fire. However, if the failure is an intermittent connection (arcing), no breaker will stop that.

There are AC arc fault breakers--But these can be a pain as brushed/universal motors such as vacuum cleaner and mixer motors do arc internally. So false trips are not uncommon. There are some devices, such as the full Midnite Classic charge controllers, that do have an internal arc fault detector in them.

Mounting panels on roofs, besides the possible increased fire hazard, there is also the problem with little chewing animals making nests under the panels and gnawing on the wiring (not good either). Mounting away from the home--Some good reasons to do that.

And even if you design to prevent fires from expanding into the rest of the building, smoke and heat damage still pretty much means stripping the room(s) down to the studs.

And the problem with fire suppression--Batteries are their own electrical power source--Pouring water/foam/etc. on batteries does not stop the electro-chemical reaction.

Some building departments are requiring master disconnects for solar panels and/or battery banks so the firefighters/owner can stop the power (flowing to short circuits) and reduce the chance of electrocution when fighting the fire.

http://www.midnitesolar.com/products.php?menuItem=products&productCat_ID=44&productCatName=RAPID-SHUTDOWN-SYSTEM-NEC-690.12

I suggest a fire ax and heavy pair of cable cutters mounted near the battery bank/power system so you can cut cables easily and safely (nothing like seeing glowing red hot cables and no way to cut the power).

When doing safety, there are two ways (for me) to look at the issues. First is to design things not to fail (breakers, correctly sized wiring, metal enclosures, fire proof materials, no sharp edges near cables/insulation, no sharp edges around fuel lines, flex for fuel lines and solid mounts for transition from flex to fixed fuel lines, etc.).

The second is to assume that something failed--Now what. For example, during 9/11, one building fire (NY emergency center) had its own problems. Generators on an upper floor, fuel tanks in a lower floor, electric transfer pump to move fuel from basement to gensets. And in that case, fuel line was broken in between from plane/building debris. And the electric transfer pump kept the fuel flowing to the upper floor of the building, and kept the flames fueled.

-Bill

Estragon · September 2017

I agree with everything Bill just said, but I'd just add that we're all going to die of something. By all means be àware of the risks, but don't let it stop you from moving forward.

chsdiyer · September 2017

Yeah, my point in this is not to create fear, but an awareness to the hazards, and hopefully keep people safer. I've known a lot of people who try to do their own home wiring and really shouldn't. I've also done renovations and seen the work others have done and thought....there is no way they had a clue what they were doing. Well hopefully providing awareness on why to do things safe and right will help some people avoid accidents...at least the ones that can be avoided. When I got into woodworking, I had no idea what a kick back was or how easy it is to lose a finger until I looked in the shop safety section of the forum. I learned a good bit from those posts and videos and it definitely made me more cautious and focused when I'm working with my tools. And that's with tools that have large blades spinning loudly in your face. Electricity I feel can be easier to become complacent and negligent with since you can't see it until it's too late. I don't know...just thought this would be helpful.

DanS26 · September 2017

Poor electrical connections are probably the #1 cause of problems in the home and small single phase electrical environments. Few electricians and even fewer DIY'ers torque electrical connections to the manufactures recommendations. It is estimated that 90% of electrical failures occur at connections. A great waste of human life and property which can be mostly avoided.

http://www.ecmweb.com/contractor/do-you-have-calibrated-arm

mcgivor · September 2017

During my electrical apprentishp, we had to attend and pass a safty course as part of qualifications, one of the points driven into us, was never to use the term hot, to refer to a live conductor, hot is a reference to temperature.
Fast forward to when working in Canada, where the term hot is commonly used in reference to live, an apprentice I was working with, was pushing a metalic fish tape towards a panel which was live, the fish tape curled around when entering the panel and hit the bus bar. Needless to say there was a major short circuit, the fish tape was visibly red hot, the apprentice ran into the main distribution and shut the panel off, upon returning, he went to grab the fish tape in the panel, I shouted don't touch it, its hot, he responded, no its not I've turned it off and proceed to grab it. Smoke left his hands that day.

wellbuilt · September 2017

Good post , now I'm scared all over again

Aguarancher · September 2017

mcgivor, the best advice I ever got from an electrician was when working in the service panel, always keep one hand in your back pocket. Doesn't mean you're not going to get bit, but that you won't provide a path to ground through your heart.

Marc Kurth · September 2017

Aguarancher said:

mcgivor, the best advice I ever got from an electrician was when working in the service panel, always keep one hand in your back pocket. Doesn't mean you're not going to get bit, but that you won't provide a path to ground through your heart.

That habit served me while I was in the process of breaking several other rules - and ended up touching my right elbow to a hot 480v circuit. My left hand was behind me instead of holding the steel framework that I was standing on. (Rooftop HVAC unit control panel.-Trane "boxcar" for those of you who know what that is)

Stars and a headache, but no worse for the wear. Well, my wife may not agree.......so that might explain why I can be a jerk at times. :-)

chsdiyer · September 2017

Mcgivor, apart from someone being hurt, that's funny. I hope he was ok! I had an HVAC company at my house one day and they told me about one of their guys being killed on the job. Apparently he was under the house and went to solder a pipe. Well an electrician (they assumed) had been working on something in the attic and left a live wire on the air handler. When their technician went to solder he grabbed the pipe which was energized and couldn't let go. I was shocked when I asked if they've put any new safety procedures in place and he said, no...we just tap the pipes now to check before grabbing them.

Good point Dan. I worked on a project where a power supply was using the screws that held the board in the case as a via for power traces between boards. Well being that this was for vehicles the screws would loosen over time making weak connections. Needless to say, a lot of those boards caught on fire. There's also a problem with over tightening too.

Sorry wellbuilt...not trying to scare, but I would say a healthy dose of fear is a good thing when dealing with electricity. I was trying to strip out excess insulation off some cables coming in my panel box. I must have accidentally cut through one and when I went to pull the insulation off the one I was working on, my pliers shorted out the other two wires. I got a nice fireball in my face, but I guarantee you I was a lot more careful/focused after that and will be in the future.

Estragon · September 2017

A healthy dose of fear is absolutely a good thing when dealing with electricity. It's not a problem until it is, and when it is, there often aren't a lot of obvious signs there's a problem. My rule is to always assume a conductor is live until proven otherwise. I forget my rule sometimes in haste, but have (so far) lived to tell the tale.

peakbaggger · September 2017

I was working near an area of rural VT (the NEK) several years ago. On occasion I would go to parties and would run into former off gridders. Generally it started out with them describing how they used to be off gird until; the big fire, the inevitable mid winter battery failure, the major electronics failure, the having to run the generator all winter story and the occasional divorce due to the lack of reliable power. I did work with a few off gridders for a company that built off grid systems that were installed all over the world. They usually had spent years and thousands to get to a level of reliability they could live with but almost everyone of them would hook up to the utility in heartbeat if it happened their way (or at least their spouse would).

At a prior employer they had a modular receptionist station in the middle of the floor. It was wired into one circuit. It had been there for years until an engineer tried to hook up to printer fed from the station via long extension cable with ground shield fed from another circuit. When the cable was connected smoke ensued and the circuit popped. When the station had been wired someone mixed up the leads. As long as it was isolated no one knew there was problem.

The electrical shop at that employer had a collection of partially vaporized hand tools. Most folks survived but few didnt. 13.8KV is not forgiving stuff and most insulation on tools and leads are generally rated for less than 1000 volts.

lzhome · October 2017

Great thread here. Let me add that Youtube.com will make you a genius or a smoking idiot. Proceed with caution and remember all shortcuts leads to the ER.

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