INFORMATION SHEET 2.1 Layout and install Panel Board

Philippine Electrical Code (PEC) provision for circuit protection Conductors-Maximum Ampacity and Size

a) General. Branch circuit conductors shall have an ampacity of not less than the rating of the branch circuit and of not less than the maximum load to be served. Cable assemblies with neutral conductors smaller than the ungrounded conductors shall be also marked.

b) Household ranges and cooking appliances. Branch circuit conductors supplying household ranges, wall-mounted ovens, counter cooking units and other household cooking appliances, shall have an ampacity of not less than the rating of the branch circuit and not less than the maximum load to be served. For ranges of 8 ¾ Kw or more rating, the minimum branch circuit rating shall be 40 amperes.

c) Other loads. Branch circuit conductors supplying loads other than cooking appliances as covered shall have an ampacity sufficient for the loads served and shall not be smaller than 2.0 mm².

Switchgear in a broad sense covers a wide range of equipment connected with switching and protection. A circuit breaker is a switching i.e.

current interrupting or making device in switchgear. The basic requirements of switching in power system practice are two-fold:

1. to permit apparatus and circuits to be conveniently put into or taken out of service;

2. and, to permit appropriate and safe isolation of apparatus and circuits automatically in a pre-determined time period when they develop faults.

Circuit Breaker is an automatically-operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Unlike a fuse, which operates once and then has to be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation. Circuit breakers are made in varying sizes, from small devices that protect an individual household appliance up to large switchgear designed to protect high voltage circuits feeding an entire city.

Typical circuit breakers and schematic symbols.

Small circuit breakers are either installed directly in equipment, or are arranged in a breaker panel.

Photo of the inside part of a circuit breaker

The 10 ampere rail mounted thermal-magnetic miniature circuit breaker is the most common style in modern domestic consumer units and commercial electrical distribution boards throughout Europe. The design includes the following components:

1. Actuator lever is used to manually trip and reset the circuit breaker. It also indicates the status of the circuit breaker (On or Off/tripped).

Most breakers are designed so they can still trip even if the lever is

held or locked in the on position. This is sometimes referred to as "free trip" or "positive trip" operation.

2. Actuator mechanism. It forces the contacts together or apart.

3. Contacts. It allows current to flow when touching and break the flow of current when moved apart.

4. Terminal connection 5. Bimetallic strip

6. Calibration screw. It allows the manufacturer to precisely adjust the trip current of the device after assembly.

7. Solenoid

8. Arc divider / extinguisher

Principles and Operation of Circuit Breakers

Circuit breakers operate using one or both of the two principles:

1. Thermal operation relies on the extra heat produced by high current warming a bimetal strip which bends to strip the operating contacts.

2. Magnetic operation is due to the magnetic field set up by a coil carrying the current which attracts an iron part to trip the breaker when the current becomes large enough.

The Advantages of the Circuit Breaker over the Fuse:

1. The circuit breaker acts as a switch aside from its being an over current protective device.

2. When there is over current, the circuit breaker trips (cut) automatically and after correcting the fault, it becomes readily available for switch on. Unlike the fuses which has to be discarded and replace after it is busted.

3. Circuit breaker can be with multiple poles and can be installed with 1, 2, or 3 poles which will simultaneously protect and switch one to three lines. The fuse on the other hand is a single pole put into a single wire and can protect only one single electric line.

4. Circuit breaker position is easier to detect. It is closed, tripped or open right at the handle.

5. The fuse, on the other hand, is not easily detected because the melted fusible element is within the fuse casing.

6. Circuit breaker can be manually tripped so that in many cases it also acts as the circuit switch.

Functions of fuses and circuit breakers in electrical circuits:

1. it protects electrical circuits from damage by too much current;

2. serves as protection of conductors;

3. serves as protection of electrical loads/equipment;

4. serves as current limiter to the circuit;

5. acts as safety valve for electrical circuits; and 6. serves as disconnecting means

Types of circuit breaker and their operating principle Thermal trip

- If current flow exceeds the rated limit of the breaker, the bimetallic strip heats and bends.

- As the strip bends, the latching mechanism is tripped and the contacts open.

Electromagnetic trip

- As the current flows through the breaker, it creates a magnetic field within the coil. During sustained overload condition, the magnetic field interferes and draws the core into the coil.

- The metal trip bar is attracted to the core forcing the latch to move, thus opening the contacts.

Standard ampere rating for fuses and nonadjustable circuit breakers 15 20 25 30 35 40 45 50 60 70 80 90 100 110 125 150 160 175 200 225 250 300 350 400 450 500 600 700 800 1000 1200 2000 2500 3000 4000 5000 6000

Circuiting guidelines

There are many ways of doing the circuitry but there is no optimum or perfect way of doing it. There are certain guidelines promulgated by the National Electrical Code (NEC) for flexible, economical and convenient layout. They are as follows:

1. The code requires sufficient circuitry to supply residential load of 30 watts per square meter in buildings excluding porches, garages and basements.

2. The requirements of 30 watts per square meter works out to 80 sq. m.

per 20 amps. Circuit (2,400w) or 60 sq. m. for 15 amps. Circuit (1,800w).

3. Good practice suggests that a load should not exceed 1,600 watts for a 20 amp. Circuit or 1,200 watts for 15 amp. Circuit, thus,

a. For a 15 amp. Circuit, -1,200w max. Load –40 sq. m. maximum area.

b. For a 20 amp. Circuit, -1,600 w. max. Load –53 sq. m.

maximum area.

4. The NEC requires a minimum of 20 amp. Appliance circuit to feed all small appliance outlets in the kitchen, pantry, dining and family room.

5. The general-purpose branch circuit should be 20 amps. Wired with no.12 AWG being the minimum size of conductor wires for convenience outlet.

6. Circuit load on a 15 amp. Circuit should be limited to the values given on table of branch circuit requirements.

TABLE OF BRANCH CIRCUIT REQUIREMENTS