Those of you who recieve EC&M magazine have already read the "Forensic Casebook" column with this name. I'll give a quick recap - then make a few points that were absent from the article.
The story is quite simple; a dairy worker was using a trailer-mounted power washer to clean up the milking area when he was electrocuted. This, by itself, is a sad tale. Yet, as with so many such tales, the death was more a matter of 'when,' rather than 'if.' The column posits a current path from the washer, along the hose, through the worker, and into the grounded structure. I don't question that.
The two points I want to address are equipment selection and maintenance.
The power washer - a trailer mounted unit - had an "open dripproof" motor on it. Supplied that way by the manufacturer, it had alread been replaced once because of moisture and corrosion damage. There was no supplimental enclosure; just a motor and pump sitting on a trailer.
I have a problem with that design; such a machine is sure to get wet, from every direction, in both use and in transport. A TEFC motor is clearly called for. That's my take.
Keep in mind that it matters not that every component was UL listed; the final assembly was not. I don't know if UL has a standard specific to this type of machine - if it does, I cannot imagine the machine being in compliance.
The lesson here is: buy the RIGHT equipment. Machinery is not a commodity, with all "pressure washers" being the same, and the purchase price being the only thing that matters.
This lesson is confirmed by my other issue: maintenance. The pressure washer was freely coated with manure, straw, and other debris. The capacitor cover and 'peckerhead' were held on with a bungee cord. The power cord and plug were damaged. In short, this machine was an accident waiting to happen.
Likewise, the receptacle that was used was severely corroded. It matters not that a "Bell box" was used; the NEC requires that equipment be suitable for its' location, and specifically mentions corrosion as a factor.
A side note: Dairy operations are very corrosive locations, with great amounts of moisture and harsh cleaning / sanitizing agents used. An ordinary receptacle and aluminum box are just not adequate. Try to imagine what equipment you would use if asked to install a receptacle inside your shower, and planned to powerwash the receptacle with bleach and oven cleaner every day. That's what we're up against.
The article addresses the lack of a GFCI receptacle. I doubt that such a device would have worked in this environmnent. A recent article in the IAEI magazine discussed the ways corrosion can prevent a GFCI from operating. A dairy is one place where the use of a GFCI breaker might be a better choice; you can locate the panel away from the wet / corrosive area.
The various signs of damage to the electrical parts suggests that there were regular mishaps at this dairy. Personally, I begin to start thinking in terms of 'criminal negligence' in a death like this.
The power washer in question was commercially manufactured, and sold as a trailer-mounted unit. The 'manufacturer' was a repair shop that decided to 'branch out' and make their own assemblies using components from the various lines that they were authorised to do warranty work for. FWIW, the manufacturer is quoted as discouraging the use of GFCI protection because of 'nuisance tripping.'
The author of the piece was hired by the manufacturer to investigate the incident. The matter was settled out of court.
That's why one of my points was: just because something is 'factory made' do not assume that it is appropriate for your application.
My other main point was that damage and abuse will make anything unsafe.
Farmers (especially dairy farmers and their staff) tend to be rather blas'e about some of their equipment, especially electrical gear.
Over the years, I've seen it all, machinery held together with baling twine or #8 fencing wire, broken flexes "repaired" with strip connectors and a tonne of electrical tape, in some instances, there is more than one of these "field modifications" in the same flex.
Some of these clowns have no respect at all for electricity or other people's safety (let alone their own).
The idea that you can keep a milking machine going by jamming a screwdriver in the vacuum blower contactor, because it keeps going out on the overload, due to lack of maintenance, goes to show a distinct lack of intelligence or any idea how these things are supposed to work.
I could write a book about the dodgy stuff I've seen on farms, not just dairy farms either, there seems to be a part of a farmers psyche that says that the cheaper and the quicker you can do a repair, the better that repair is.
Don't get me started on their lax attitude to HV lines near their properties, that is a whole different kettle of fish.
Re: The Case of the Shocking Power Washer
#196052 09/07/1001:15 PM09/07/1001:15 PM
Don't be afraid of sounding 'jaded.' the pictures accompanying the article made clear that however lacking the design of the pressure washer was, the accident had plenty of 'help' from the victim.
The best equipment will fail when used in the wrong way (for example, when the materials cannot stand up to the chemicals present) or when subjected to abuse. Just to clarify, I am including the building's electric as part of the 'equipment.'
Though I an sorry for the victim, and his survivors, at some point this becomes the "Darwin Principle" at work. Buy the wrong stuff, beat it to pieces, cobble it together with duct tape .... what do you think is going to happen?
I'm sure that the manufacturer isn't all that concerned about the 'listing' issue.
The fact is, there really are not that many appliances that ar rquired to be 'listed' or certified to any particular standard, by anyone - not even by the manufacturer, let alone by UL.
In the electrical trade, we get used to seeing some form of listing, but tht is only because UL has a particularly strong presence in our field. Many, many markets are pretty much free from UL involvement.
For example, even in 'hot tubs' UL has a weak presence. The very 'creator' of the market, Jacuzzi, does not list their products. Similarly, most pumps are not 'listed' by anyone.
I want to thank Doug for finding the link ... in the past, EC&M has been a month or so behind in posting their stories.
Looking at the pictures of both the pressure washer and the receptacle, it seems clear that the 'responsibility' falls squarely on the dairy operation. I'm not that concerned with that particular angle, though ...
Rather, I am concerned by the routine use of "Bell" boxes in environments that quickly corrode the box and its' contents. Whether they be in concrete or the ground, it's only a matter of (little) time. I've lost count of the inadequate enclusures I've seen in sump pits.
With all due respect to Chicago, there IS a time and a place for plastic. There is also a role for panel-mounted GFCI's.
IMO, Article 110 precludes the use of aluminum where it will corrode, and it certainly refers to the matter of different metals corroding each other. Yet, too many inspectors look no further than the "UL lable." IMO, the lable is but an aid, and not the final word. Nor can we expect there to be a specific classification for every situation. (A similar issue arises with regard to 'subject to damage).
These are design decisions - and the electrician is the professional who is expected to make them.
We can't bring the guy back to life ... but we can help prevent the situation from arising.