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Distribution

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The definition of distribution is - something distributed; an allotment. noun.

In this portion you are going to be shown the electricity being distributed in some form or fashion. Large amounts of electricity come into the building, and need to be distributed correctly in order to share the overall power.

It's more important for you to understand safety and products in this section. If you make the wrong decision on a certain breaker to install, you are putting the client and the maintenance electrician at risk in the future. We want to show you the risks involved, and the proper way to choose the right "gear."

This is an extremely important portion of an electrician's job, and you'll see after we're done, why only a few are chosen to do this on a larger jobsite.




Types of Circuit Faults and Shorts


- Overload. This is caused by too many devices running on a circuit that is pulling more power than the circuit is protected for. An example would be a vacuum, lights, and space heater on one circuit that only allocates 1800 Watts on one 15 Amp breaker. If this type of "tripping" is allowed over a period of time, the insulation of the wire is compromised, and a fire could result from damaged insulation.

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Short Circuit - This is caused from an object perforating the wires, a faulty connection, or from long time overheating - causing the insulation to become bare. Once this happens, there is little or no impedence to the "new" circuit. If you have the proper protection (circuit breaker) installed, it will interrupt the circuit safely.

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Overcurrent. This is basically the same thing as a short circuit. This is current that is NOT contained in the circuit. It may be caused by a fault upstream, or by short circuit.

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Ground Fault. This is a short circuit between an ungrounded conductor, and a ground. This is contained within the circuit.

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Fault Current. This is an enormous amount of current flow. This is usually caused by a short circuit, or fault in the line. These can come from transformers upstream, or another generating source much larger than the service being fed. There are three types.
1) Phase to Neutral
2) Phase to Phase
3) Phase to Earth


The Effects of Circuit Faults and Shorts

- Mechanical Forces. The magnitude of the short circuit can cause a mechanical force within the conductor. If the conductors are not held securely, the mechanical forces can move them close to an unenergized surface creating an arc.
Proper mechanical Strength MUST be used in order to support the conductors from high current movements. This is also the reason that time is a factor for protection devices.

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Thermal Energy. This is the measure of the thermal stress, or thermal energy let through by a fuse during short circuit interruption. There are many formulas for this effect, but the two most common are - I2t and Q=I2Rt.
Q = joules
I = current, amperes
R = resistance, ohms
t = duration of current, seconds




Types of Fuses

It is imperative that fuses are sized regarding voltage and amerage. Rated low enough to interrupt an overloaded circuit before it reaches high temperatures, and that the interrupt ratings are sufficient enough to safely interrupt the fault current or short circuit. When people use pennies or copper bars to bypass a fuse, they are endangering themselves, and others, by their actions.




Cartridge Type Fuses
These may not be used in capacities larger than 600 Amp or in circuits more than 600 Volts.
- Class CA, CB, CC, G, J, K, L, R, T, ot HRCI-MISC can be used where a class H is permitted. 135% current carrying.
- Class C rated at 160% of current capacity. Only to be used as fault and overcurrent protection. Overload must still be provided by Class H, CA, CB, CC, G, J, K, L, R, T, ot HRCI-MISC.




Plug Fuse. (CEC 14-202.)

- shall not be used in circuits exceeding 125V
- 10,000 Ampere interrupting capacity
- must be installed so that they are non interchangeable
- on existing panels you can install rejection washers
- not rated any higher than 30 Amps



Supplemental Fuses. These are cartridge fuses ranging from 0-60 Amps. IC= 100,000 RMS Symmetrical.



Types of Circuit Breakers


- Moulded Case Circuit Breaker (MCCB - Low Voltage)


- Miniature Circuit Breaker (MCB - Low Voltage)


- Vacuum Circuit Breaker (High Voltage)


- Air Circuit Breaker (High Voltage)



Common Moulded Case applications worth mentioning

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GFCI (Ground Fault Circuit Interrupter) This device installed in residential/commercial branch circuits is intended to prevent electric shocks, and burns. There are receptacle, breaker, and portable GFCI's. These devices recognize ground faults, and interrupt the circuit before large doses of electricity can harm the person. They are preset to trip at 6 milliamps of leakage. Pressing the trip/reset button on all of these devices will ensure the device is working correctly, and must be tested periodically.

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AFCI (Arc Fault Circuit Interrupters) This circuit breaker is installed in bedroom branch circuits and is designed to recognize an arc in the circuit. If it recognizes an arc, it will interrupt the circuit before an electrical fire takes place. They have filters and logic devices that allow them to sense an arc just before it produces sparks, and intense heat. Once again, these breakers have a "trip/reset" button, and must be tested periodically. 26-722 CEC.



Ratings and Characteristics of Fuses and Circuit Breakers

- Voltage Rating > 14-302 CEC states that each circuit breaker has voltage ratings not less than that of the multi-wire branch circuit. The higher voltage ratings can be determined by apparent power, which is the higher reading.

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Continuous Current Rating > This is current the overcurrent device can still operate safely at without opening, causing damage, or exceeding temperature.

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Interrupting Rating > The interrupting rating must be at least equal to the available fault current. This is the most it can take in short circuit, without damaging the device.

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Time / Current Characteristics > This is dependant on the type of fuse and the strength of the overcurrent. Choosing the proper rating is important for all circuits and devices. Overload vs. overcurrent.

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Inverse Time / Current Characteristics > These characteristics are driven by the manufacturer of the fuse/breaker. The higher amperage that passes through the device, the quicker it opens the circuit because of dangerously high currents. This is to protect the electrical circuit, and the device from dangerous and damaging loads.

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Ambient Temperatures > Excess temperatures in some installations might be another consideration for fuse/breaker installations. If an area has excess heat, for an example, and might effect the performance - this must be considered for additional protection.

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Excessive Vibration > This can be caused by anything from a motor, generator, transformer, ship, or transport vehicle. Not all electrical installations are in buildings that remain stationary. Some installations require vibration dampening. This term means dissapation (damping) of vibrational energy. Installing flexible fittings between the motor and the conduit prevents damage. There are also breakers that can be installed that have higher vibrational tolerances. An example is ships, planes,etc.



Switchgear

Is the combination of electrical disconnects and/or circuit breakers used to isolate electrical equipment. This provides protection from line to ground, phase to phase, and line to neutral faults. This type of circuit control makes building management possible. Two common types of switchgear are;
- Metal Clad
- Metal Enclosed
These distribute medium to low voltage equipment and circuits.



Switchboard

This serves as a service, or a main connection from the feeding transformer.This main portion is the one metered from the power utility - locally. These have large buses that are capable of making multi-connections. This type of service must be rated for the purpose, and a label on the equipment, stating this.