Re: NEC and Tesla Coils

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "David Sharpe by way of Terry Fritz <twftesla-at-uswest-dot-net>" <sccr4us-at-erols-dot-com>

Jim

Excellent points.  The NEC is fixed installation driven.  You could argue
that since
your 20kVA controller has welding or stove plugs on it and casters and can
be moved elsewhere it is a portable appliance and opens up considerably the
design
requirements.

I received a letter from another attendee from the class that illustrates
what can
happen even if everything is done by the book(s).  This occurred in a power
plant somewhere in Georgia recently.  A 4160 3ph breaker on main station
service faulted in some fashion and blew up catastrophically.  The electrical
explosion destroyed two supply transformers for this switch gear lineup and a
480V auxiliary lineup that powered the lub oil system and cooling water system
for a large turbo generator.  A loud BOOM, a 45 minute fire, no lights, and a
generator set that coasted from 1800 rpm to 0 on no oil on bearings, and no
pony gears to keep the turbine spindle rotating.  A multi million $$$$$ KABOOM!
The biggest piece of the circuit breaker enclosure that was recognizable
was the
burned, charred, partially vaporized remains of 'A' phase arc chute protruding
from 1-2' thick amalgam of copper, iron, plastic.  This is what happens
when you
hit a breaker with about 100-200kA on 4160, less then 300' from the generator.
Fortunately, no injuries or fatalities from this incident.  These types of
incidents
go in my BOHICA file, and are a loud warning of what can happen if your
design is less then adequate...

Regards
Dave Sharpe, TCBOR
Chesterfield, VA. USA

Tesla list wrote:

> Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-uswest-dot-net>"
<jimlux-at-earthlink-dot-net>
>
> It occurs to me, reading over David's stuff, and my copy of the NEC, that
> really, the NEC (and the building code) applies primarily to permanent
> installations.
>
> For "portable equipment", NEC regulates some aspects.. things like power
> cords, although it really doesn't aim at that "market". For instance, the
> NEC isn't used to regulate PC's, Televisions, etc.
>
> Also, for instance, NEC prohibits installation of electric sign equipment
> operating at >1kV in a residence.  But, of course, the monitor you are
> reading this on has a 15-20 kV supply that is unequivocally lethal in it.
>
> In fact, there isn't much in the way of legal regulation for these sorts of
> things. If you were to try and sell them, some jurisdictions (Los Angeles
> County in California, for instance, but not Ventura County) require that all
> appliances and electrical equipment be either UL listed, or UL tested and
> approved, or approved by a recognized testing lab, etc...
>
> But, since your average tesla coil isn't being manufactured for sale, these
> laws wouldn't apply.
>
> OSHA rules apply to "occupation"... i.e. work (if you are being paid or
> volunteer...) and don't really apply to owner/operated.
>
> I think that as far as safety regulation goes, "good engineering practice"
> is it.
>
> That said, I think that looking to the NEC and OSHA regs for guidance on
> formulating a set of "design requirements"..  Things like grounding,
> interlocks, bleeder resistors, current ratings of conductors, are all things
> that you need a starting point for.
>
> It's also important to make sure that you don't wind up inadvertently
> getting yourself regulated... If you start out with the (publicly) stated
> intention that you will "meet code", you're probably doomed to failure.
> Which code? Which regulations? Who's doing the inspecting?  This is
> definitely one of those things where you probably don't want to even start
> down the path.
>
> As it is, TC's are a hobby or avocation, not particularly more or less
> dangerous than any other hobby such as metalworking, car racing, shooting,
> sewing (every year more people are disabled in the garment industry than in
> electrical industry, on both absolute and percentage basis).  None of these
> activities are particularly regulated (except, perhaps, shooting) when done
> on a non-business basis, other than common sense sorts of general laws
> prohibiting you from creating a nuisance or hazard.
>
> Everything is different if you are doing it for a profession (paid or not).
> Then it will primarily be up to your insurance carrier and the places that
> you show your coil.  Those of you that have done TC stuff for organized
> haunted houses, school assemblies, film production, all know about what
> hoops you have to jump through. (And they vary from instance to
> instance....)