DAY 17 CHAPTER 28 OVERCURRENT PROTECTION FUSES AND CIRCUIT BREAKERS
Jan 14, 2016
NORMAL CIRCUIT
THE CONDUCTORS CAN SAFELY CARRY THE CURRENT. THEY DO NOT GET HOT. THE 15A FUSES DO NOT OPEN.
CONDUCTORS RATED AT15ACONDUCTOR RESISTANCE=0.001Ω
15A FUSE
15A FUSE
LOAD RESISTANCE240V SOURCESOURCE R=1mΩ 24Ω
AV
mmm
V
R
EI CIRCUITTHRU 99875.9
003.24
240
11124
240
9.99875A
OVERLOADED CIRCUIT
THE CONDUCTORS BEGIN TO GET HOT, BUT THE 15A FUSES WILL OPEN BEFORE THE CONDUCTORS ARE DAMAGED.
CONDUCTORS RATED 15ACONDUCTOR RESISTANCE=0.001Ω
15A FUSE
15A FUSE
240V SOURCESOURCE R=1mΩ 24Ω
19.995A
24Ω
122
24
N
RR NLOAD
AV
mmm
V
R
EI CIRCUITTHRU 995.19
003.12
240
11112
240
SHORT CIRCUIT
THE CONDUCTORS GET EXTREMELY HOT. THE INSULATION AND THE CONDUCTORS WILL MELT UNLESS THE FUSE OPENS QUICKLY.
CONDUCTORS RATED 15ACONDUCTOR RESISTANCE=0.001Ω
15A FUSE
15A FUSE
SHORT CIRCUIT PATH
240V SOURCESOURCE R=1mΩ 24Ω
80,000A
AV
mmm
V
R
EI CIRCUITTHRU 000,80
003.0
240
111
240
LOAD RESISTANCE
024
0
024
024
21
21
RR
RRRLOAD
GROUND FAULT
SOURCE
HOT CONDUCTOR
GROUNDED CONDUCTOR
WHEN A HOT CONDUCTOR COMES IN CONTACT WITH METAL AND THE RETURN PATH HAS HIGH RESISTANCE THE BREAKER WILL NOT TRIP. THE METAL WILL HAVE THE SAME VOLTAGE AS THE HOT.THE VAULE OF RESISTANCE CAN VARY GREATLY DUE TO THE DIFFERENCE COMPOENTS ALONG THE CIRCUIT PATH, MAKING IT HARD TO FIND THE GROUND FAULT CURRENT VALUE.
OPEN CIRCUIT
THE CIRCUIT HAS AN OPEN, NO CURRENT WILL FLOW.
CONDUCTORS RATED 15ACONDUCTOR RESISTANCE=0.001Ω
15A FUSE
15A FUSE
LOAD RESISTANCE240V SOURCESOURCE R=1mΩ
0A
24Ω
AV
R
EI CIRCUITTHRU 0
240
OPEN
ANY OPEN HAS INFINITE RESISTANCE
FUSES/CIRCUIT BREAKERS: PROTECT CIRCUIT FROM CURRENT OVERLOAD.
SHORT : UNWANTED PATH THAT CURRENT TAKES.
PARTIAL SHORT :ONLY PART OF LOAD IS SHORTED OUT.
DEAD SHORT : ALL OF THE LOAD IS SHORTED OUT.
Fuses have two types of bases, the Edison Base (Type T fuses) and the Rejection Base (Type S fuses), also known as a "tamper-proof base". The Edison Base Type T fuse works with the typical socket used in the fuse box seen in older homes and the fuse base looks like a light bulb base. A Rejection Base Type S fuse actually consists of two components, an adapter base that screws and locks into the Edison socket in the fuse box, and the fuse itself. Each different amperage rating of a Type S fuse has a matching socket base adapter with a different sized thread that prevents mismatching (rejection base). It stops a person from putting a 20 Amp rated fuse in a 15 Amp circuit.
The Bussmann S Series Plug Fuse is for all-purpose applications. It's like two fuses in one. Features include a simple link element for short-circuits and dangerous overloads, plus a series-connected element which lets the harmless overload starting currents of motors pass without opening. It uses less energy, operates cooler, and provides superior protection.
DUAL ELEMENT FUSE
CIRCUIT BREAKERS: TWO TYPES: THERMAL,MAGNETIC
THERMAL:CAN BE RESET MANUALLY OR AUTOMATIC. AUTOMATIC RESET OCCURS AFTER BREAKER HAS COOLED.
Circuit Breaker: A device designed to open and close a circuit by nonautomatic means and to open the circuit automatically on a predetermined overcurrent without damage to itself when properly applied within its rating.
MAGNETIC CB: WHEN A OVERLOAD OCCURS A BIMETALLIC ELEMENTS UNLATCHES THE INNER TRIP MECHANISM. A MOMENTARY OVERLOAD DOES NOT CAUSE THE BREAKER TO TRIP. IF THE OVERLOAD IS HEAVY, A MAGNETIC COIL CAUSES IT TO TRIP.
Circuit Breaker Animation & Working http://www.youtube.com/watch?v=GSh0f94JwaA
240.24 Location in or on Premises.(A)Accessibility. Overcurrent devices shall be readily
accessible and shall be installed so that the center of the grip of the operating handle of the switch or circuit breaker.
(D) Not in Vicinity of Easily Ignitible Material. Overcurrentdevices shall not be located in the vicinity of easilyignitible material, such as in clothes closets.
(E) Not Located in Bathrooms. In dwelling units andguest rooms or guest suites of hotels and motels, overcurrentdevices, other than supplementary overcurrent protection,shall not be located in bathrooms.
(F) Not Located over Steps. Overcurrent devices shall notbe located over steps of a stairway.
230.79(C) One-Family Dwellings. For a one-family dwelling,the service disconnecting means shall have a rating of notless than 100 amperes, 3-wire.
OCPD (OVERCURRENT PROTECTION DEVICES) LOCATIONS
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Noalox Anti-Oxidant Compound