Download Let Your Light Shine

Let Your Light Shine
Matt. 5:16
Let your light shine before men in such a way they may see your good works and
glorify your Father who is ion Heaven.
Destination (region of the world)
Electrical standards for the region
Voltage
Frequency
Plug connection arrangements
Electrical Load Evaluation
Critical Life Support/ Uninterruptible Power Source/non-Critical
Linear Loads
Resistive
Inductive
Non-Linear Loads
Prime Mover Generators
Gasoline Powered
Diesel Powered
Wind
Hydro
Alternative Energy Sources
Solar
Hybrid Systems
Electrical Distribution Systems
Grounding
Lightning Protection
Safety
Learning Objectives
An overview of electrical standards around the world
How do I get plugged in?
Evaluate the Electrical Energy Usage
How is electricity being used?
Appropriate Electrical Energy Generation
How can I generate the needed Electrical energy?
Proper Electrical Power Distribution
How do I get the energy where it is needed?
Shocking Experiences
How do I protect myself and the equipment?
General Observations on Electrical Power Generation and Distribution
Power Generation
1. Fossil Fuel is EXPENSIVE. Diesel fuel for example is at least $4.50 USD in most
of the developing world.
2. Gasoline powered equipment should be avoided because of the danger in handling
gasoline. Also gasoline powered products are generally of low quality in the
developing world and resulting in premature equipment failure.
3. Solar energy is plentiful in many regions and should be utilized. Obviously, solar
energy is a daytime function thus batteries are a necessity for non sunny times.
4. Micro/Mini hydro can be source of renewable energy in the proper setting. Righta-way authorizations, permissions to use or modify stream flow, high capital
investment, and security at the site because it is often remote to an inhabited
facility are obstacles to a successful installation.
5. Wind power can be a source of renewable energy at the proper settings.
Obviously, a constant wind flow of a least 7-9 MPH in necessary for justifying
the installation. Wind turbines have a high profile to the environment and security
of the installation should be considered. The wind turbine should be at least 20
feet about the canopy of vegetation or highest obstruction.
Power Distribution
1. Copper wire is EXPENSIVE. Aluminum wire has inherent problems with wire
terminations.
2. Proper coordination of circuit breakers, wire size, and circuit capacity is essential
to safely squeeze every electron through a power distribution system.
Conclusion
EXTREME conservation of electrical usage with high energy efficient devices is
essential to a sustainable, affordable installation. Renewable energy generation should be
used where feasible to reduce the use of fossil fuel and its associated daily costs.
Configurations – Voltage and Frequency Standards
Americas – except Bolivia
Single Phase – 240/120 VAC; 60 Hz
Three phase – 208/120 VAC WYE connected; 60 Hz
240/120 VAC DELTA connected; 60 Hz
Centered Tap Grounded
European
Three Phase – 380/220 VAC WYE connected; 50 Hz
West Africa Three Phase – 400/230 VAC WYE connected; 50 Hz
East Africa
Three Phase – 415/240 VAC WYE connected; 50 Hz
IMPORTANT NOTE!
240 Volts Line to Line as we find in USA is NOT the same as 240 Volts Line to Neutral
found in most International settings.
Governing Electrical Code
North America – National Electrical Code 2005 (revised every 3 years)
European – International Electrical Regulations Sixteenth Edition
Outside of USA Plug Configurations
See www.interpower.com
Voltage Transformation
Use a step-down transformer from 240 to 120 as needed. Make sure the derived 120VAC
is referenced to ground.
See www.toddsystems.com
Frequency Transformation 60/50 Hz
There is no economical device that transforms 60 Hz power to 50 Hz. In order to verify
that a device rated for 60 Hz will work on 50 Hz, perform the following test:
Measure the current “in rush” and “full load” current at both 60 Hz and 50Hz. If current
at 50 Hz is 10% greater than at 60 Hz or the current at 50 Hz exceeds the nameplate
rating at 60 Hz, the machine will fail prematurely. This applies to devices with motors,
transformers, ballasts such as fluorescent lighting fixtures, and any other devices with
inductive characteristics.
EXTREME WARNING!
Select system voltage and frequency based on the regional standard and not the USA
standard as a long term design decision.
Electrical Load or Device List
Each electrical device needs to be evaluated based on the following criteria:
DESCRIPTION
TYPE
VA/w/Hp
VOLTS
Description
Descriptive name for the device
AMPS
PHASE
CRITICAL/UPS
NON-
DUTY
CRITICAL
CYCLE
Type
Resistive – Applied Voltage and load current in phase
Heater elements
Inductive – Load Current lags the applied voltage by 90 degrees
Motor
Fluorescent light ballast
Transformer
Electronic –
(non-linear)
Load current non linear with respect to the applied voltage
Devices using switching power supplies – computers
VA – volt-amps
W – Watts
Hp – Horsepower
Volts
Nominal Applied Voltage as recommended by the manufacturer – nameplate data
Amps
Full load Current at the rated Voltage and Frequency
Phase
Single phase or three phase
Critical/UPS
Generally refers to life support or process critical device requiring the electrical source to
be constant in voltage and frequency being with no interruptions powered by an
Uninterruptible Power Supply (UPS). A UPS can take the following forms:
Single Conversion
Line Interactive
True On-Line
Non-critical
Loads not requiring power source backup
Duty Cycle
Estimate of device usage in a 24 hour period
Connected Load
The summation of the VA of each device will yield the total connected load. Using the
estimation of the Duty Cycle, multiply the Total Connected Load with an estimate of the
Duty Cycle of the devices, this will yield an estimate of the expected Running Load. In
my experience, the Running Load is about 30% of the Total Connected load.
Example of a Simple Load Study Spreadsheet
QTY
2
1
3
2
3
Description
Office Appliances
Desk Top Computers
Server Computer
Lap top Computer
Desk Top Printer
Small HP Type Printer
Watts
Total
Watts
400
600
200
720
120
800
600
600
1440
360
4
10
30
1
1
3
10
16
50
2
2
6
8000 BTU Split A/C Unit
Variable Speed Fan
40 Watt Single Tube Fluorescent
Light
1/2 Hp water pump
Refrigerator - 15 ft3 energy efficient
water heater
Guest House Appliances
5000 BTU wall A/C
Variable Speed Fan
40 Watt Single Tube Fluorescent
Light
Refrigerator - 15 ft3 energy efficient
Toaster
water heater
850
180
3400
1800
80
1125
850
2400
2400
1125
850
7200
550
180
5500
2880
80
850
1000
2400
4000
1700
2000
14400
Total Estimated Connected Load
20% Load Factor
25% Load Factor
30% Load Factor
35% Load Factor
40% Load Factor
51055
10211
12764
15317
17869
20422
25 KVA (65%) Load Factor
45 KVA (65%) Load Factor
65 KVA (65%) Load Factor
16250
29250
42250
Example spreadsheet for solar installation in Eretria
Load Study Eritrea
Hours per
Description
Refrigerator
Laptop Computer
Laptop Computer
Printer
Fax
Codan Radio
Charger for Palm Pilot
Regional BGAN Terminal
Mini M Satellite Phone
Fan
Low Wattage Lighting
Type
Motor
Electronic
Electronic
Electronic
Electronic
Electronic
Electronic
Electronic
Electronic
Motor
Resistive
VA
120
192
192
280
187
250
60
156
360
60
75
1.15 for
AC
138
221
221
322
215
288
69
179
414
69
86
Day
2
1
1
0.25
0.25
0.5
1
0.5
0.25
10
4
Watt Hr/Day
276
221
221
80.5
54
144
69
90
103.5
690
345
Total
Watt -Hr/Day
System Eff 0.70
5.8KWHr/m2/day
2293
3275
565
80 watts per
7
panel
120 watts per
panel
Batteries
1 day storage
50% discharge
12 volt @ 225
Ahr
Total required
Understanding Electrical Power Measurements
True Power (W)
The term is used to express the rate of doing work or converting energy. True power is
the actual power used in an electrical circuit. True power is measured in Watts (W),
Kilowatts (KW), or Megawatts (MW). In any DC circuit, or in an AC circuit in which
voltage and current are in phase, such as resistive loads, true power is equal to voltage
times current.
Reactive Power (VAR)
Reactive power (VAR) is power supplied to reactive load. The unit of reactive power is
volt-amps reactive instead of watts as in true power. VAR represents a pure reactive load
(inductor or capacitor) component or load. Reactive power supplied to a reactive
component such as an inductor or capacitor should average out to zero and is not
converted to sound, rotary motion, light or heat. The function of power in a reactive
circuit is to produce a magnetic field around a coil or to charge a capacitor.
Apparent Power (VA)
Apparent power is the product of the voltage and current in a circuit calculated without
considering the phase shift that may be present the voltage and current in a circuit.
Apparent power is expressed in volt-amps (VA), kilovolt amps (KVA), or megavolt amps
(MVA). Because apparent power considers circuit current regardless of how it is used,
apparent power is a measure of component or system capacity. This is the reason why
transformers are sized in VA rather than Watts. The transformer must deliver current at a
set voltage regardless of the application that uses current. With small single-phase AC
motor circuits, apparent power is much higher that true power.
Power Factor (pf)
Power factor (pf) is the ratio of true power used in an AC circuit to apparent power
delivered to the circuit. Power factor is commonly expressed as a percentage. The lower
the power factor, the less efficient the circuit and the higher the overall operating cost.
The overall operating cost is increased because every component in the system, such as
transformer and conductor sizes, must be sized for the higher current caused by lower
5
6550
13100
2700
5
power factor. Power factor is lagging for an inductor load, leading for a capacitive load,
and in phase for a resistive load.
Generators with Prime Movers
Although there are two basic types of generators – synchronous and induction – the
former is used almost universally for isolated operation.
A generator produces electricity when magnetic flux lines are cut by a rotating wire coil
(rotor). The magnetic flux lines are produced by the magnetic field present between the
North and South poles of a permanent or electromagnet. The stronger the magnetic flux
lines and the faster the rotation, the higher the voltage produced.
Synchronous Generators
The generators are called “synchronous” because the mechanical rotational of the rotor is
directly related to the phase angle of the AC voltage produced. A synchronous generator
produces its own voltage. The frequency produced will be exactly the revolutions per
second of the rotor divided by the number of pole pairs.
Automatic Voltage Regulator
The Automatic Voltage Regulator maintains a no load to full load steady state voltage to
tight tolerances. The AVR has a volts/hertz characteristic that proportionally reduces the
regulated voltage at reduced speeds. This feature aids the engine during sudden large
additions of load. Single phase voltage sensing can aggravate the voltage unbalance
across a three phase system by monitoring the voltage and current only in a single phase.
Three phase voltage sensing does a mathematical calculation by electronics based on the
current and voltage of all three phases and sets the system voltage accordingly.
The electrical power produced by the synchronous generator set is derived from a closed
loop system consisting principally of the exciter rotor, the main revolving field and the
automatic voltage regulator. The process begins when the engine starts to rotate the
internal components of the alternator. The residual magnetism in the main rotor produces
a small alternating voltage (AC) in the main stator. The automatic voltage regulator
rectifies this voltage (converts it to DC) and applies it to the exciter stator. This DC
current to the exciter stator creates a magnetic field that, in turn, induces an AC voltage in
the exciter rotor. This AC voltage is converted back to DC by the rotating diodes. When
this DC voltage appears at the main rotor, a stronger magnetic field that the original
residual field is created which induces a higher voltage in the main stator. This higher
voltage circulates through the system inducing an even higher DC voltage back at the
main rotor. This cycle continues to build up the voltage until it approaches the proper
output level of the generator set. At this point the automatic voltage regulator begins to
limit the voltage being passed to the exciter stator that, in turn, limits the overall output of
the alternator.
Diesel Generator
Standby Rating – Application for supplying continuous electrical power (at variable load)
in the event of a utility power failure. No overload is permitted on these ratings. The
generator is peak rated. Generally, this rating is for 4 hours or less.
Prime Power Rating – Application for supplying continuous electrical power (at variable
load) in lieu of commercially purchased power. There is no limitation to the annual hours
of operation and the generator set can supply 10% overload power for 1 hour in 12 hours.
Other Considerations
Derate 10% for altitude above 3500 Feet Above sea level
Derate 15% for 50 Hz operation if using the 60Hz specifications
Derate for power factor less than 0.8
www.caterpillar.com
Diesel Engine Mechanical Governor
The speed regulating governor characteristics are accomplished by a mechanical rotating
mechanism coupled to mechanical linage to the injector pump. Generally, the speed
droop on this type of governor is 3% - 5%. Isosynchronous operation is not an option
with this type of governor.
Diesel Engine Electronic Governor
The speed regulating characteristics are modeled in electronics in the form of a
Proportional, integral, and derivative control scheme. Speed droop and isosychonous
arrangements are switchable. The actuator is generally a current to rotational transducer.
www.woodward.com
Wind Power
The use of wind energy has been around for well over a thousand years. However, there are
certain physics that guide us on what it can and cannot do. The proper name of a wind
generator is actually “Wind Energy Converter” that being a device that converts the
potential energy in the wind to another form of energy. This can either be mechanical or
electrical. When the wind blows, the rotor blade stops a percentage of the wind. That
percentage is what is converted into energy. According to physics, the maximum amount
of wind energy that can be converted is 59.3%. This is known as the Betz Limit.
www.eere.energy.gov/windandhydro/wind_how.html
There are a number of types of wind generators. Research has been done on virtually
every possible concept with the objective of producing the maximum amount of power
for the lowest cost at the highest possible reliability. Conventional experimentation has
found that the horizontal axis upwind or down wind design to be the best concept. The
most common designs include:
1.
Horizontal upwind: The generator shaft is positioned horizontally and the
wind hits the blade before the tower.
2.
Horizontal downwind: The generator shaft is positioned horizontally and
the wind hits the tower first then the blade.
3.
Vertical Axis: The generator shaft is positioned vertically with the blades
pointing up with the generator mounted on the ground or a short tower.
There are two basic types of airfoils (blades) a lifting and drag type.
1.
The drag style airfoil is typically what you see with an old Dutch wind
mill or American water pumping wind mill. The blades are generally a flat plat
which the wind hits and causes to rotate. This type of design is great for very low
wind areas and will develop a lot of torque to perform an operation. However, in
medium to higher winds, their capabilities to produce energy are limited.
2.
The lifting style airfoil is what you see in most modern wind turbines and
on airplanes. A properly designed airfoil is capable of converting significantly
more power in medium and higher winds. Actually, with this design, the fewer
number of blades the more efficient this design can be. Two European companies
actually produced one bladed machines however, dynamic balance issues
prevented them from becoming a commercial success
Locating a wind generator is extremely important to the performance of the machine. It is
the difference between a machine that give you lots of energy and a garden sculpture. The
ideal location for a wind turbine is 20’ above any surrounding object within a 250 foot
radius. This generally means your property should be at least one acre in size. You should
have at least a 9 MPH average wind speed at your location.
www.windenergy.com
Hydropower
The basic principle of hydropower is that if water can be piped from a certain level to a
lower level, then the resulting water pressure can be used to do work. If the water
pressure is allowed to move a mechanical component then that movement involves the
conversion of the potential energy of the water into mechanical energy. Hydro turbines
convert water pressure into mechanical shaft power, which can be used to drive an
electricity generator, a grinding mill or some other useful device.
Hydropower is a very clean source of energy. It does not consume but only uses the
water, after use it is available for other purposes (although on a lower horizontal level).
The conversion of the potential energy of water into mechanical energy is a technology
with a high efficiency (in most cases double that of conventional thermal power stations).
The main advantages of hydropower are:
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•
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•
•
power is usually continuously available on demand,
given a reasonable head, it is a concentrated energy source,
the energy available is predictable,
no fuel and limited maintenance are required, so running costs are low (compared
with diesel power) and in many cases imports are displaced to the benefit of the
local economy,
it is a long-lasting and robust technology; systems can last for 50 years or more
without major new investments.
Against these, the main shortcomings are:
•
•
•
it is a site specific technology and sites that are well suited to the harnessing of
water power and are also close to a location where the power can be economically
exploited are not very common,
there is always a maximum useful power output available from a given
hydropower site, which limits the level of expansion of activities which make use
of the power,
river flows often vary considerably with the seasons, especially where there are
monsoon-type climates and this can limit the firm power output to quite a small
fraction of the possible peak output,
Hydropower Feasibility
To know the power potential of water in a river it is necessary to know the flow in the
river and the available head.
The flow of the river is the amount of water (in m3 or liters) which passes in a certain
amount of time a cross section of the river. Flows are normally given in cubic meters per
second (m3/s) or in liters per second (l/s).
Head is the vertical difference in level (in meters) the water falls down.
The theoretical power (P) available from a given head of water is in exact proportion to
the head H and the flow Q.
P=Q × H × c
c = constant
The constant c is the product of the density of water and the acceleration due to gravity
(g).
If P is measured in Watts, Q in m3/s and H in meters, the gross power of the flow of water
is:
P=1000 × 9.8 × Q × H
This available power will be converted by the hydro turbine in mechanical power. As a
turbine has an efficiency lower than 1, the generated power will be a fraction of the
available gross power.
www.microhydropower.net
Hybrid system
Combination of power sources interfaced together
Components of a Hybrid System
Voltage Regulators
Each of the transformer types below has application in developing world facilities.
Voltage swings of -25% to +10% are common throughout the daytime. The largest
voltage swings occur at 6:00 PM to 7:00 PM in the early evening because of residential
lighting loads. Industrial loads are often a small percentage of electrical power usage
especially in the rural settings. Extremely long and under sized power lines aggravate this
problem of voltage sags throughout the day. The voltage regulator needs to carefully
coordinated with the type of electrical load that is connected so as not to cause additional
problems with voltage instability.
www.superiorelectric.com
Transfer Switches
An ATS (automatic Transfer Switch) with built-in control logic monitors your normal
power supply and senses any interruptions. When the utility power fails, the ATS
automatically starts the engine and transfers the load after the generator has reached
proper voltage and frequency.
This happens in a matter of seconds after the power failure occurs. When the utility
power has been restored, the ATS will automatically switch the load back, and after a
time delay, it will shut down the engine. A recommended practice is to wait at least 5
minutes after national power restoration before transferring from emergency backup.
During those five minutes, a national utility can experience voltage and current surges,
switching transients as capacitor banks are energized, brown outs, frequency swings, etc.
as they attempt to pick up the electrical load on the power line.
It is essential to monitor all three phases of incoming power. In the developing world,
single phase national power brown/black outs are common. If a three phase motor is
allowed to continue to run under single phase brown out conditions, it can be destroyed in
a matter of minutes. Often times, the distribution system in a missionary community is
single phase loads so a single phase brown/black out will leave sections of the facility
with poor or no electricity.
www.asco.com
OutBack Inverter/Chargers
Outback Inverter/chargers are the next generation in advanced power management. Each
is a DC to AC sine wave inverter, battery charger and AC transfer switch housed within a
tough die-cast aluminum chassis.
Just like the local utility grid, the inverter produces true sine wave AC electricity for your
stand-alone or backup power needs. Computers, TVs and pumps are just some of the
examples of modern electronics that last longer and run better when powered with true
sine wave electricity from an OutBack inverter. Starting up your air conditioning,
washing machine or well pump is worry-free because of our high surge power capability.
Batteries and generators are the costly consumables when using inverters to generate
electricity. The integrated smart battery charger uses multiple stages to perform quick
recharging while prolonging battery life, saving your batteries and generator from
unnecessary wear. Automatic switching between AC power sources is seamless due to an
AC transfer switch that reacts in less than 16 milliseconds.
Unique networked communication is built into all OutBack products providing complete
integration. Expanding your system with your growing power needs is as simple as
adding additional inverters with modular architecture. Further flexibility is provided with
the ability to be connected at any time in either parallel, series or three-phase power
configurations. Industry leading OutBack reliability is achieved through simplified design
and rugged construction. www.outbackpowersystems.com
www.outbackpower.com
Batteries – Deep Cycle
Deka/MK Battery 8L16, 6 volt 420 Ah
Battery Group: L16
Terminal Type: T875
Nominal Voltage (V): 6 volts
Capacity at C/20: 420 Ah
Operating Temperature: -20F (-29C) to 140F ((60C)
Charge Voltage @ 68F (20C)
Cycle: 2.35 VPC
Float: 2.25 VPC
Resistance: 2.0 Milliohms (full charge)
Terminal: T875
Made in U.S.A by East Penn Manufacturing
Weight: 113 lbs / 51.2 kg
Dimensions (LWH): 11.75"x 7"x 17.3" / 298 x 178 x 435 mm
www.eastpenn-deka.com
Solar Photovoltaic Panels
Sharp ND-208U1, 208 watt PV module
This poly-crystalline 208 watt module features 12.8% module efficiency for an
outstanding balance of size and weight to power and performance. Using breakthrough
technology perfected by Sharp's 45 years of research and development, these modules use
an advanced surface texturing process to increase light absorption and improve
efficiency. Common applications include office buildings, cabins, solar power stations,
solar villages, radio relay stations, beacons, traffic lights and security systems. Ideal for
grid-connected systems and designed to withstand rigorous operating conditions, Sharp's
ND-208U1 modules offer maximum power output per square foot of solar array.
Features
•
High-power module (208W) using 155 mm square poly crystalline silicon solar
cells with 12.8% module conversion efficiency
•
•
•
•
•
Sharp's advanced surface texturing process increases light absorption and
efficiency while providing a more subdued, and natural look
Bypass diode minimizes the power drop caused by shade
White tempered glass, EVA resin, and a weatherproof film, plus aluminum frame
for extended outdoor use
UL Listings: UL1703, UL
Sharp modules are manufactured in ISO 9001 certified facilities
Electrical Characteristics
•
•
•
•
•
•
•
•
•
•
•
Cell: Poly-crystalline silicon
No. of Cells and Connections: 60 in series
Open Circuit Voltage (Voc): 36.1V
Maximum Power Voltage (Vpm): 28.5V
Short Circuit Current (Isc): 8.13A
Maximum Power Current (Ipm): 7.3A
Maximum Power (Pmax): 208W (+10% / -5%)
Module Efficiency Maximum Power: 12.8%
Maximum System Voltage: 600 VDC
Series Fuse Rating: 15A
Type of Output Terminal: Lead Wire with MC Connector
Mechanical Characteristics
•
•
•
•
•
•
Dimensions (L x W x D): 64.6" x 39.1" x 1.8" (1640mm x 994mm x 46mm)
Weight: 46.3 lbs (21 kg)
Modules/Carton: 2
Carton Size: 68.3" x 43.2" x 4.5" (1735mm x 1097mm x 114mm)
Carton Weight: 93.2lbs (42.3 kg)
Modules/Pallet: 28
www.affordablesolar.com
Solar Charge Controller
OutBack MX60 60 amp Charge Controller
Rated for up to 60 amps of DC output current, the OutBack MX60 can be used with
battery systems from 12 to 60 VDC with a PV open circuit voltage as high as 140 voc.
The MX60's set points are fully adjustable to allow use with virtually any battery type,
chemistry, and charging profile. The OutBack MX60 allows you to use a higher output
voltage PV array with a lower battery voltage - such as charging a 24 vdc battery with a
48 VDC PV array. This reduces wire size and power loss from the PV array to the battery
location while maximizing the performance of you system and saving you money! The
OutBack MX60 comes standard with an easy to use and understand display. The four
line, 80 character, backlit LCD display is used for programming and monitoring of the
system's operation including built-in Data Logging with 64 days of memory.
SPECIFICATIONS
MX60
Output Current Rating
60 amps DC Maximum at 12, 24 or
48 VDC
Nominal Battery
Voltage
12, 24, 32, 36, 48, 54 or 60 VDC
(programmable)
PV Open Circuit
Voltage
125 VDC Maximum
Standby Power
Consumption
Less than 1 watt typical
Charging Regulation
Methods
Five Stage: Bulk, Absorption, Float,
Silent, Equalization
Voltage Regulation
Setpoints
Equalization Voltage
Adjustable 1.0 to 5.0
VDC above Bulk
Setpoint
Temperature
Compensation
Programmable slope -2.0mV/oC/Cell
to -5.0mV/oC/Cell
Voltage Step-Down
Capability
Can charge a 12 or 24 VDC battery
from a 48V nominal PV array
Power Conversion
Efficiency
99.1% @ 40 amps Output 97.3% @
60 amps Output
Digital Display
4 line 80 character backlit LCD
Display
Remote Interface RJ
45 Modular Connector CAT 5 Cable 8
wire
Operating
Temperature Range
-40 to 60°C Power derated above
25°C
Environmental Rating Indoor Type 1
Conduit Knockouts
Two 3/4 - 1” on the back; One 1” - 1
1/2 “ on each side; Two 1” - 1 1/2” on
the bottom
Warranty
Two years parts and labor Optional
Extended Warranty
Dimensions
Enclosure: 14.5 “ H x 5.75” W x 5.75”
D Shipping box: 17.75” H x 10” W x 7”
D
Shipping Weight
12 lbs. - 5.4 kg
Electrical Power Distribution
Load Distribution Panels Sizing
Voltage Rating and Configuration
Single Phase
Three Phase
Bus Bar Current Rating
Greater than Connected Load Calculations
Main Breaker or Lugs Only
Number of Circuit Breakers/Spaces
Surface or Recessed Mount
Indoor or Rainproof
www.squared.com/us/products/panelboards.nsf
Circuit Breakers
Coordinate with wire size and electrical load calculations
Wire Size
Based on electrical load calculations and voltage drop for a given length
Voltage drop not to exceed 5% (recommendation)
Grounding
The purpose of electrical grounding is stated as follows from the National Electrical Code
section 250-1:
“Systems and circuit conductors are grounded to limit voltages due to lightning, line
surges, or unintentional contact with higher voltage lines, and to stabilize the voltage to
ground during normal operation. Equipment grounding conductors are bonded to the
system grounded conductor to provide a low impedance path for the fault current that will
facilitate the operation of over current devices under ground-fault conditions.”
To boil this down to understandable terms, a ground is a conduction connection between
electrical circuits or equipment and the earth. A low impedance (resistance) ground path
is a ground path that contains very little resistance to the flow of fault current to ground.
The purpose of electrical grounding is for the protection of personnel from electrical
shocks. Infants and patients in the hospital/clinic setting are particularly vulnerable to
electrical shocks. A few milliamperes of current at 120 VAC can be fatal. Electronic
grounding is used primarily to provide a clean chassis ground to help maintain signal
integrity for sensitive electronic equipment.
How can you tell if your system is properly grounded? The following drawing illustrates
the necessary components for grounding a single-phase and three-phase electrical service
with a grounding electrode. If you are still not sure what arrangement that you have and if
you are properly grounded, measure the voltage with a Digital Multimeter (DMM)
between the “HOT’ and neutral conductor. Then measure the voltage between the neutral
and ground conductor that could be a metal chassis of a piece of electrical equipment.
Now measure the voltage between the “HOT” and ground conductor. The voltage
between the “HOT” conductor and the neutral and the “Hot” conductor and ground
conductor should be the same. The voltage between the neutral and ground conductor
should be less than 0.5 volts. Any other voltage combination indicates a problem in the
grounding scheme.
Note! Personal Safety
If a DVM indicates a relatively high voltage or a voltage that is erratic, the voltage may
be a false indication of the presence of voltage due to the high internal impedance of the
measuring circuit in the DVM. Fluke now sells a STRAY VOLTAGE MODULE for
their DVM. This module lowers the input impedance of the meter to eliminate the
possibility of static voltages. And alternative is the following:
The light bulb test will indicate a current carrying grounding situation. Place a 120
incandescent light across the apparent voltage source and see if it glows or lights up. The
bulb has low impedance.
The major causes of grounding problems are loose electrical connections, reversal of
conductor connections, missing ground wires, improperly installed or missing grounding
electrodes. Another cause of electrical noise and grounding problems is the bonding of
the neutral connection and the ground conductor on the load side of the service
distribution box such as a sub panel or at a piece of electrical equipment. In this case, the
neutral currents will flow in both the neutral and ground conductors. All of these
examples produce electrical noise and safety hazards for personnel.
An additional separate isolated ground rod creates two ground references that are
typically at different potentials. The reason for these different potentials is because the
resistances of the soil between the two isolated ground rods vary at each location. This
results in current circulating (ground loop) in an attempt to equalize potentials. A ground
loop is a circuit that has more than one ground point connected to earth ground with a
voltage potential difference between the two ground points high enough to produce a
circulating current in the ground system.
Unfortunately, correcting the above wiring problems with grounding current loops is time
consuming and can be frustrating. Nevertheless, the place to start your investigation is at
the service transformer or service load distribution box. Check for grounding electrodes
and inspect the connections for sound mechanical and electrical bonding. Next, check
each outlet for the proper termination of “HOT”, neutral, and ground conductors looking
specifically for poor connections, wiring reversals, and missing grounding wires. Often it
will be necessary to unplug other equipment during the investigation to attempt to
localize the problem.
The results of correcting grounding problems can be substantial resulting in better
performance and longer life from electrical equipment especially devices using the latest
technology. Eliminating electrical shocks from the metal chassis will improve the
performance and attitude of personnel.
The color green or yellow with green stripe always identifies a conductor used. Yellow
with green strip coding is international. Green is often not used or only as a control wire
color in the international setting.
A neutral conductor carries current from one side of a load back to the source. The color
white or natural gray is used for the neutral (grounded circuit) conductor in most places.
Check local and country standards for color coding. For example, in Kenya the neutrals
are black and white is not used.
IMPORTANT NOTE!
Failing to know these wiring colors can lead to destroyed equipment and some personally
shocking experiences.
Lightning Protection
As a thunderstorm grows, charges build up in the cloud. The bottom usually develops a
large negative charge while high at the top of the cloud a positive charge develops.
Ninety percent of all lightning flashes occur within the cloud. When a thunder cloud
moves over an area, it can induce an intense charge of opposite polarity on the ground
below. This is called the cloud electrical shadow, and results in unequal and constantly
changing ground potential. Everything within the electrical shadow accumulates and
dissipates this charge at varying degrees:
1. Conductors (metal structures, storage tanks, wiring/piping, and grounding grids)
- collect and dissipate these charges most quickly (microseconds).
2. Products within containers (petroleum, military ammunition) - collect and
dissipate these charges relatively slowly (the rate is highly dependent on
surrounding insulators vs. conductors)
3. Insulators, and some insulated products - collect and dissipate these charges
most slowly.
4. The ground (earth)- collects and dissipates these charges on a grand scale but the
rate is very dependent on geological factors (soil resistivity, moisture,
stratifications, lakes and rivers, etc.)
If all of the above components are interconnected (using an effective common grounding
mechanism), their charges will rise and fall together, keeping the charge across the
system in balance. If the components are not interconnected, then the charges grow and
shrink independently causing ground potential differentials, and the creation of “Bound
Charges”. If the intensity of a Bound Charge becomes big enough, it will try to dissipate
following a path of least resistance which can either be to follow grounding structures or
wiring or to arc to a nearby conductor which has less resistance and/or impedance. As the
storm intensifies, so do the magnitudes of these charges, and when the air between the
cloud and the earth can no longer act as an insulator a cloud-to-ground spark (or lightning
strike) occurs. Lightning always “chooses” to follow a path of least resistance/impedance.
Thunder storms and lightning strikes have the following characteristics:
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Total Cloud Charge: 10 to 40 Coulombs
Average Cloud Charge: 30 to 90 Coulombs are discharged
Charge Transfer per Flash: 25 Coulombs Discharged
Average Transfer per Flash: (EFS) 5 to 30 to 300 kV/m
Electric Field Strength: Dependent on humidity, temperature & pressure
Average EFS for lightning: 10 kV/m (required to breakdown the insulation
threshold of moist air)
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Multiple Upward Streamers: 100 to 300 kV/m (usually under drier conditions)
Peak Voltage: One to Ten Billion Volts, 50% at 100 Million Volts
Peak Current: 2 to 510 kA (usually the return stroke) 99% < 200 kA 50% @ 30
kA
Polarity Negative: > 90%
Duration (99%): 30 to 200 ms (average duration of single return stroke 50ms)
Number of Strokes per Flash: 1 to 26 50% > 4 10% > 9
Lightning RFI Range: 1 kHz to 100 MHz 95% 200 kHz to 20 MHz
Temperature: 50,000 F Pressure 10 atm (causing sonic boom = thunder) Many
bad things happen when lightning strikes, resulting in various direct and
secondary effects.
Direct Effects of Lightning
A Direct strike can have the following effects:
1. Heat: fires, structural damage from instant vaporization of trapped moisture
(example: explosions of concrete or trees)
2. High voltage and high current surges along conductors over long distances (along
lightning rods to grounding rods, and along any electrically or metallically
connected equipment)
3. High voltage and high current surges along the ground over shorter distances.
4. If a strike hits an individual it can cause severe injuries or even death.
Secondary Effects of Lighting
When lightning strikes nearby within microseconds the strike lowers (or neutralizes) the
local ground charge and all interconnected conductors. However, the accumulated charge
of some objects such as the fluid of a storage tank, does not discharge as quickly,
resulting in a temporary “Bound Charge”. People, computers and electronic equipment,
transformers and certain electrical equipment, and flammables do not like being hit by
lightning, or being anywhere near where it strikes.
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intense electromagnetic pulses (EMP)
earth current transients
atmospheric transients
Nature of an Earth Electrode
Resistance to current through an earth electrode actually has three components.
1. Resistance of the electrode itself and connections to it. Rods, Pipes, masses of
metal, structures and other devices are commonly used for earth connections.
These are usually of sufficient size or cross section that their resistance is a
negligible part of the total resistance.
2. Contact resistance between the electrode and the soil adjacent to it. If the
electrode is free from paint or grease, and the earth is packed firmly, the contact
resistance is a negligible part of the total resistance. Rust on an iron electrode has
little or no effect since the iron oxide is readily soaked with water and has less
resistance than most soils.
3. An electrode driven into the earth of uniform resistivity radiates current in all
directions in the surrounding soil.
Generally, the resistance of the surrounding earth will be the largest of the three
components making up the resistance of a ground connection. Whether a soil is largely
clay or very sandy can change the earth resistivity very much. In soil, conduction of
current is largely electrolytic. So the amount of moisture and salt content of the soil
radically affect resistivity. The amount of water in soil varies, of course, with the
weather, time of year, nature of sub-soil and depth of permanent water table.
How to Improve Earth Resistance
1. Lengthen the earth electrode in the earth. In general, doubling the rod length
reduces resistance by about 40%. The diameter of the earth rod has very little
effect on its earth resistance.
2. Use multiple rods. Two well-spaced rods driven into the earth provide parallel
paths. They are, in effect, two resistances in parallel. The rule for two resistances
in parallel does not apply exactly. The resultant resistance is not ½ of the
individual rod resistance but the reduction for two equal- resistance rods is about
40%. When you use multiple rods, they must be spaced apart further that the
length of their immersion. The use of a grounding ring of bare #2 AWG often
serves as a good earthing rod.
3. Treatment of the soil – Chemical treatment of the soil is a good way to improve
earth-electrode resistance when you cannot drive deeper ground rods. Magnesium
sulfate, copper sulfate, and ordinary rock salt are suitable non-corrosive materials.
Chemical treatment is not a permanent way to improve your earthing system
though. The chemicals are gradually washed away by rainfall and natural drainage
through the soil.
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Metal Oxide Varistors
The most common type of varistor is the Metal Oxide Varistor (MOV). This contains a
ceramic mass of zinc oxide grains, in a matrix of other metal oxides (such as small
amounts of bismuth, cobalt, manganese) sandwiched between two metal plates (the
electrodes). The boundary between each grain and its neighbor forms a diode junction,
which allows current to flow in only one direction. The mass of randomly oriented grains
is electrically equivalent to a network of back-to-back diode pairs, each pair in parallel
with many other pairs. When a small or moderate voltage is applied across the electrodes,
only tiny current flows caused by reverse leakage through the diode junctions. When a
large voltage is applied, the diode junctions break down because of the avalanche effect,
and large current flows. The result of this behavior is a highly nonlinear current-voltage
characteristic, in which the MOV has a high resistance at low voltages and a low
resistance at high voltages. The main use of varistors is to protect electrical and electronic
equipment by shunting transients voltages to ground.