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DAY 17 CHAPTER 28 OVERCURRENT PROTECTION FUSES AND CIRCUIT BREAKERS FIVE CIRCUIT CONDITIONS 1. NORMAL LOADING 2. OVERLOAD 3. SHORT CIRCUIT 4. GROUND FAULT 5. OPEN NORMAL CIRCUIT THE CONDUCTORS CAN SAFELY CARRY THE CURRENT. THEY DO NOT GET HOT. THE 15A FUSES DO NOT OPEN. CONDUCTORS RATED AT15A CONDUCTOR RESISTANCE=0.001Ω 15A FUSE 240V SOURCE SOURCE R=1mΩ 9.99875A 24Ω LOAD RESISTANCE 15A FUSE I THRU CIRCUIT E 240V 240V 9.99875 A R 24 1m 1m 1m 24.003 OVERLOADED CIRCUIT THE CONDUCTORS BEGIN TO GET HOT, BUT THE 15A FUSES WILL OPEN BEFORE THE CONDUCTORS ARE DAMAGED. CONDUCTORS RATED 15A CONDUCTOR RESISTANCE=0.001Ω RLOAD 15A FUSE 240V SOURCE SOURCE R=1mΩ 19.995A 24Ω RN 24 12 N 2 24Ω 15A FUSE I THRU CIRCUIT E 240V 240V 19.995 A R 12 1m 1m 1m 12.003 SHORT CIRCUIT THE CONDUCTORS GET EXTREMELY HOT. THE INSULATION AND THE CONDUCTORS WILL MELT UNLESS THE FUSE OPENS QUICKLY. LOAD RESISTANCE CONDUCTORS RATED 15A CONDUCTOR RESISTANCE=0.001Ω 15A FUSE 240V SOURCE SOURCE R=1mΩ RLOAD R1 R2 24 0 0 0 R1 R2 24 0 24 80,000A 24Ω 15A FUSE SHORT CIRCUIT PATH I THRU CIRCUIT E 240V 240V 80,000 A R 1m 1m 1m 0.003 GROUND FAULT 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. HOT CONDUCTOR SOURCE GROUNDED CONDUCTOR OPEN CIRCUIT THE CIRCUIT HAS AN OPEN, NO CURRENT WILL FLOW. CONDUCTORS RATED 15A CONDUCTOR RESISTANCE=0.001Ω 15A FUSE OPEN 240V SOURCE SOURCE R=1mΩ 24Ω 15A FUSE ANY OPEN HAS INFINITE RESISTANCE LOAD RESISTANCE 0A I THRU CIRCUIT E 240V 0A R 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. SCREW BASE FUSES HAVE RATINGS FROM 0 TO 30AMPS 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. REJECTION BASE, TYPE S FUSE DUAL ELEMENT FUSE 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. CARTRIDGE FUSES ARE RATED FROM 1/8 T0 600 AMPS IN BOTH 250V AND 600V CARTRIGE FUSES CAN BE USED AS THE MAIN DICONNECT MEANS 115KV FUSE FUSES 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. DUAL POLE SINGLE POLE THREE POLE BREAKER WITH HANDLE TIE TWO POLE 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 MULTI WIRE BRANCH CIRCUITS MUST HAVE HANDLE TIES ON CIRCUIT BREAKER FOR SIMULTANEOUS TRIPPING. OCPD (OVERCURRENT PROTECTION DEVICES) LOCATIONS 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. Overcurrent devices shall not be located in the vicinity of easily ignitible material, such as in clothes closets. (E) Not Located in Bathrooms. In dwelling units and guest rooms or guest suites of hotels and motels, overcurrent devices, other than supplementary overcurrent protection, shall not be located in bathrooms. (F) Not Located over Steps. Overcurrent devices shall not be 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 not less than 100 amperes, 3-wire. Noalox Anti-Oxidant Compound Reduces galling and seizing on aluminum conduit joints Suspended zinc particles penetrate and cut aluminum oxide Carrier material excludes air to prevent further oxidation Improves service life of aluminum electrical applications