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IDEC Smart Relay Update, National Electric Code
Original poster: "David Sharpe by way of Terry Fritz <twftesla-at-uswest-dot-net>" <sccr4us-at-erols-dot-com>
I have taken possession of 5 of these relays (FL1A-H12RCE). Briefly recaping
they are a new micro-PLC with 8 digital inputs, and 4 hard relay (isolated NO)
outputs. Inputs I5 and I6 are rated at 1kHz count capablility, and I7 and I8
are
0-10V analog input. I built a VTTC controller with filament heating and real
time
grid and plate current monitoring. The control ate only 50% of total relays
resources :^). The entire development kit including relay, software and
download
cable is ~$300. I built a development station and tried on the real
article and
it
worked like a champ! Even has five alphanumeric operator prompts (E.Stop,
Guards, Fils Heating, and Grid/Plate Over current Trip. The amount of time
saved by reduced wiring and more flexible control is amazing.
I forwarded info from a National Electric Code refresher class to Jim Lux
(Hi!).
The object was to determine the pieces of the code that have legal "teeth" and
direct impact to TC building and construction in general. The following
are the
definitions and code sections that impact our work. This information is
provided
as is, and is truly not meant to belittle anyone's work. The major abstract
points
of below post are:
1. A disconnection means and overcurrent protection must be provided for
branch
circuit loads (read Tesla Coil). Feeders and protective equipment in new
installations should not be loaded above 80% of capacity.
2. Neon sign transformer "Farms" are explicitly disallowed in the code
("...transformer secondaries shall not be connected in series or
parallel..."
3. From neon sign section of code, requires 1.5" to ground at 7.5kV. This
suggests that 3" separation is needed at 15kV. I know there are many
confounding variables (BIL of equipment, lightning exposure, power
capacity,etc)
but this is first time reasonable distances in protected environments for
current limited
HV equipment is mentioned.
4. From induction and dielectric heating section, any capacitor larger then
0.1uF
at a voltage of 250VDC or greater must be provided with suitable bleeder
resistors. This equates to any stored energies greater then 0.003 J.
5. If you want to check my comments, be sure to use the 1999 Code. There has
been a
massive revision between the 1996 (and earlier) and 1999 Code, to the point
that
a cross reference table in the 1999 code had to be provided to find
applicable
sections in earlier code(s).
6. Again, not trying to start a flame war, and comments are welcome. Each of
the articles in the National Electric Code are included usually because of a
casualty event (i.e. death, injury, or property damage).
Regards
Dave Sharpe, TCBOR
Chesterfield, VA. USA
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National Electric Code and Relevance to Tesla Coil construction
WARNINGS:
1. The National Electric Code is NOT intended as a design manual
for untrained persons.
2. “Good Engineering Practice” will often require more conservative
design then the NEC states. The NEC is a MINIMUM standard.
3. “Compliance with the NEC will result in an essentially hazard free
installation, but not necessary efficient, convenient or adequate for
good service or future expansion.”
4. This information is provided “AS IS” with no warranty expressed
or implied. User assumes all liability with use.
Article 100 Definitions
Disconnecting Means
Overcurrent Protective Device (OPD)
Fitting
Equipment
Clearance
Utilization voltage
Qualified Person(s)
Overload
Overcurrent
Short Circuit
Ground Fault
Interrupting Rating
Ground
Grounded
Grounded conductor
Equipment grounding conductor
Grounding electrode conductor
Articles 110,200,400
1. Examination, installation, and use of electrical equipment
2. Identification of disconnection means
3. Working clearance (around enclosures)
4. Branch, service, and feeder circuits
5. Use and identification of grounded (neutral) and grounding conductors
6. Ground Fault Protection
Working clearances Table 110-26a
Dedicated space (Article 110-26f)
No storage of materials
No piping, ducts, or foreign equipment allowed
Ingress, egress and panelboard clearances
Door Access; allow 90deg opening of doors (Article 110-26(a)(2), page 70-79
Illumination of work areas (Articles 110-26d & 410-4,5)
Protection from Live Parts (Articles 110-27a) “shall be protected by the
use of:
“
Total enclosed enclosure
Room (implied locked and access allowed to “QUALIFIED
PERSONNEL ONLY” )
` Vault
Physical Elevation
600V or less 8 ft
0.6 - 7.5kV 8 ft 6 in
7.5kV 35kV 9 ft
OVER 35kV 9 ft + 0.37 in / kV above 35kV
Over 600V utilization equipment will be posted by “DANGER-HIGH VOLTAGE”
Placards
Grounded (neutral) conductors Articles 200-6(a)(b) identification
Branch Circuits
Conductor Identification Article 210-5
Grounded (neutral) conductor Article 200-6 - colored with white or gray
overcoating
Grounding (ground) conductor Article 250-119 - colored with green or
green/yellow
IEC/CE coloring
Overcurrent protection continuous and non-continuous loads (Art.
210-20(a) )
Continuous Load Load is expected to continue for 3 hours or more.
Rate overcurrent protection at 125% of continuous load + 100% of
non-continuous
load.
Size overcurrent protective device at value or next larger standard trade
size.
Disconnecting Means
Article 225-31… Means shall be provided for disconnection of all conductors
that
supply or pass through the building or structure.
Article 225-32… Means shall be readily accessible at point of entrance of
conductors .
Articles 230-71,72… Services to a building shall consist of not more then 6
switches or circuit breakers. ( 6 arm movements or less to isolate all
power
to a building or system)
Articles 240, 310-Overcurrent Protection
1. Proper Sizing
2. Circuit breakers versus fuses application
3. Matching wire size
4. Preventing electrical explosions
5. Interrupting Fault Current
Overcurrent Protection Article 240
Tap Rules (Article 240-21 and exceptions), 10 feet, 25 feet, over 25 but
less
then 100 feet, over 100 feet
Location of OCD -- Article 240-24
OCD’s not located where exposed to physical damage
OCD’s not located in vicinity of easily ignitable material
Article 240-83
Every circuit breaker having an interrupting rating other then 5kA shall
be so
marked with rating.
Grounding Articles 250
1. Grounding overview
2. Understanding grounding language
3. Grounding electrode conductor
4. Grounded conductor
5. System grounding
6. Enclosure grounding
7. Grounding connections
8. Different type grounds (analog, digital, power)
9. Portable equipment
10. Sizing of ground conductors
11. Sizing of bonding conductors
Article 250-2
Circuits and systems grounded to limit:
Voltages due to lightning, EMI/RFI
Line surges
Unintentional contact with higher voltage lines
Stabilize circuit voltages during normal operation
All conductive materials bonded together to prevent local differences of
potential (all metal cases on a system as an example)
Facilitate OCD operation with a ground fault
Article 250-6
Grounding system shall be installed in a manner to prevent the flow of
objectionable currents. Alterations to stop currents:
Discontinue one or more grounding connections
Change locations of grounding connections
Interrupt continuity of conductive path interconnecting the grounding
connections
Other actions satisfactory to authority having jurisdiction (inspector)
Comment: Changing grounds from a daisy chain (“looped”) to
a common point star grounding methodology
used for
analog, signal, digital and power grounds is an
example
of the above.
Article 250-20 systems required to be grounded
Where system is separately derived
Transformer is not grounded
Supplied by overhead conductors outside of a building
Maximum voltage to ground on ungrounded (power) conductors is 150
volts or less
Article 250-24
Location of grounding connection between grounded (neutral) conductor
and the grounding (ground) electrode shall be made at the service
equipment
(Neutrals and grounds MUST be isolated in control panels and utilization
equipment, UNLESS a new source is being derived.)
Article 250-24
Grounded conductor shall be bonded to case of all service disconnection
means.
(All equipment in a Tesla system with a metal case MUST be grounded to
service equipment ground; and ISOLATED from RF ground)
Article 250-24 (Table 250-66)
Grounding conductor not smaller then the electrode conductor size in
Table 250-66. Equipment grounding conductor size is listed in
Table 250-122
Article 250-50
Grounding Electrode System shall be made up of
Metal water pipe
Metal Frame of building
Concrete encased electrode
Ground ring
Driven ground rods
Article 250-56
Ground rod resistance shall be 25 ohms or less. Additional ground rods
separated by at least 6 feet can be used to augment (reduce) grounding
resistance)
Article 450 Transformers
General rule is transformers should have overcurrent protection at 250%
of full load transformer rating, if no secondary overcurrent protection is
used. Under certain conditions and exceptions (authorized personnel
only, restricted space, etc. ) up to 600% full load overcurrent settings are
permissible. Transformer saturation effects are nearly always seen at load
levels of 250-300%, so 250% is a good working figure with NEC support.
Article 490 Equipment over 600V Nominal
Entire article applies, particularly to high power pole pig or PT powered
systems,
clearances, interlocks engineering controls, isolation and enclosure
requirements
should be carefully studied.
Comment: The “excessively” large clearances are necessary to guarantee
adequate BIL rating of air insulated equipment in
indoor/outdoor
environments. If switching or lightning
transients are
not a design
issue, and equipment will be housed in an indoor dry
environment;
spacing may be significantly reduced (see Electric Sign
Spacing,
article 600-32 below for less than 15kV wiring).
Chapter 6, Special Equipment
Article 600 Electric Signs and Outline Lighting
600-5b -- Branch circuits shall not exceed 20A, and will be dedicated to
lighting
load. Computed load per branch circuit will be a minimum of 1200VA
600-6a Sign will have dedicated disconnect, can be located within or outside
of line of sight, should be lockable in all cases
600-7 Signs will be grounded. Listed metal flexible conduits, or metal
liquid
tight conduits shall be used as a grounding means as long as conduit
lengths do not exceed 100 feet.
600-23 Transformers and Electronic Power Supplies;
All will have GFI with following exceptions
- Transformers with isolated secondaries shall have maximum open
circuit voltage of 7500V or less
- Transformers with integral porcelain or glass secondary housing
for tubing requiring no field wiring of secondary circuit.
Voltage will not exceed 15kV nominal under any load condition, voltage
to ground will not exceed 7.5kV under any condition from any output
terminal.
Transformers or electronic power supplies will have a secondary
circuit current rating of not more than 300 mA.
Secondary connections will not be connected in series or parallel
<< NO NST “farms” ALLOWED >>
Transformer or power supply must be marked to indicate that it has
secondary fault protection.
600-32 Neon secondary conductors over 1000V nominal.
Wiring methods wiring to be run in approved raceway or on insulators
Conductors will be rated for voltage, not smaller then #18 AWG, and have
minimum temp rating of 105 deg C
No sharp conductor bends allowed (corona, dielectric loss)
Conductors to be spaced 1-1/2” MINIMUM from each other and all other
objects other then insulators or neon tubing.
Comment: This may be a good working rule for TC equipment that
HV conductors will be no less then 1-1/2” between energized
conductors and ground and 3” between energized conductors.
This spacing is only valid for voltages up to 15kV between energized
conductors and 7.5kV energized conductor and ground.
Insulators and bushings shall be rated for purpose
Dwelling occupancies Equipment exceeding 1kV shall not be installed
in or on dwelling occupancies. <<NOTE>>
Cable length shall not exceed 20 feet in metallic conduit or tubing and
50 feet in non-metallic conduit or tubing.
Article 660 X- Ray Equipment
Guarding, enclosures, conductors, interlocks and controls all applicable
due to similarity of hazardous voltages and conditions
Article 665 Inductive / Dielectric Heating -- (Vacuum Tube/Solid State Tesla
Coils
Defacto Rules)
Enclosures Completely enclosed, non combustible and deadfront
controls construction.
Doors or detachable panels shall be used for access. Where doors access
compartments with greater then 500-1000VAC/DC, locking means or interlocks
will be provided, above 1kV AC/DC mechanical interlocks or locking means
and electrical interlocks will be provided. Detachable panels not normally
used
for access will be fastened in a manner to make them inconvenient to remove.
DANGER HIGH VOLTAGE KEEP OUT shall be posted on all
compartments with voltages greater then 250VAC/DC, and where unauthorized
personnel may contact energized parts
Bleeder resistors shall be used on all capacitors exceeding 0.1uF having
voltages greater then 240V to ground. This includes auxiliary supplies for bias
voltages, tube keying etc. Interlocked access doors will be used on coils
(work
coils/induction heating) with voltages above 150VAC, or at any DC potential
above ground
Comment: 0.1uF -at- 250VDC = 0.003J (3mJ) This hazard level is
probably chosen due to startle involuntary reaction
conditions
which could cause secondary injuries (lacerations or
cuts), or
throw body/limb onto high(er) power conductor(s),
possibly
resulting in additional severe/lethal injuries.
Grounded and bonding per Article 250 will be used. Wire sizes will be #18 or
larger. High voltage terminals will be guarded to prevent accidental contact.
Step
down transformers for controls or auxiliary (filament) circuits will have
primary
overcurrent protection, sized per Article 450.
Additional General Rules (wiring/workmanship):
1. Wires in a raceway are required to have insulation class of highest present
voltage in raceway. This is generally why separate conduits are run for
power,
control, and signal conductors.
2. Most installations are now installed with THHN and this class
insulation is
rapidly becoming a national standard, due to size reduction, higher
temperature
class. #18 of smaller AWG is generally 1kV class insulation, #16AWG or
larger is 600V class insulation.
3. Overloading of conductors in certain conditions is allowable by code
provided
that inverse timing is allowed to limit thermal rise on conductors.
Electrical
installations are normally for continuous operation (greater then 3 hours),
while
Tesla Coils even under most aggressive use are intermittent operation. So
power
conductors sized to code requirements in intermittent duty (100% ampacity)
should provide adequate safety factors under most use conditions.
NOTE: This list is a first blush attempt to link legal requirements of
National
Electric
Code to Tesla Coil construction practices. Many of these rules make good
common
and engineering sense. Again, realize that these rules are ENFORCEABLE under
the
United States Uniform Building (BOCA) Codes, and generally a dwelling can
not be
occupied until electrical inspection confirms these “terms and conditions”
(i.e.
the
electrical installation) have been met. Also again be aware the NEC is a
minimum
standard, building to a higher standard usually involves more cost and is
generally
avoided by contractors, unless the end owner is willing to deal with the cost
adders.
Also, the requirements of the Occupational Safety and Health Administration
(OSHA),
particularly in regards to Personal Protective Equipment (PPE), Labeling, and
Training
are significantly more stringent then requirements in NEC.
This information is provided “AS IS” with no warranty expressed or implied.
User(s)
assume all liability with use.
D. E. Sharpe
3/8/2001, Rev. 01-- 3/16/01