Determining short circuit rating of circuit breakers. Determining the short circuit rating of the breaker requires knowledge of the prospective fault current at the panelboard. Following section provides a simple method to obtain this current magnitude. Lets start with calculating the prospective current from the nearest transformer. Fault current on the secondary side of the 3 phase transformer   Ampswhere,FLA Full load amps of the transformer Z Per unit impedance of transformer. Buchtitel Autor Ersch. Cases in Engineering Design Fuchs, H. O. editor 1973 110 ways To Improve Your Sound System. Power Transmission Distributors Association is. The short circuit amps obtained from this method ignores the source impedance. If you do have this impedance then use the following equation. Amps. Ofcourse, you will be more accurate with the result now. However, source impedance is not easily available. This piece of information is typically obtained from the utility serving you. Zsource encompasses the impedance of the entire power system, calculated upto the primary side of the indicated transformer. Phase Circuit Breaker. The+grid+of+today+Transmission+network+%28Subtransmission%29.jpg' alt='Transmission And Distribution Handbook Westinghouse' title='Transmission And Distribution Handbook Westinghouse' />The procedure in determining the short circuit rating of a 1 phase circuit breaker in a 1 phase system is same as above except for the modification to the full load current equation of the 1 phase transformer. Click on figure 1 for an example. Figure 1 Calculation of short circuit rating of a single phase breaker. The XR factor. When selecting a circuit breaker be wary of choosing breakers that will become marginally rated i. In circuits with XR ratio greater than 1. Why Well, in AC systems, fault currents have asymmetrical waveform. The asymmetry due to DC offset gradually tapers off to become symmetric. See figure below. The rate at which the asymmetry decays varies as a function of the circuit XR ratio. The higher the XR ratio of a circuit, the higher the fault current magnitude a circuit breaker has to handle. Figure 2 Fault current magnitude following a fault. So, assuming that you are oblivious of the system XR at the point where you are installing the circuit breaker and that the high current magnitude will persist for a while, it is prudent to select circuit breakers such that the calculated fault currents are only 8. Refer to National Electric Code for sizing the breaker. Designations Of U. S. Air Force Projects. Designations Of U. S. Air Force Projects. Copyright 2. 00. Andreas ParschMX Section Copyright 2. George Cully Andreas Parsch1 MX Projects, 1. Weapons Systems 1. Related Codes. 3 Other Projects. Sources. 1 MX Projects, 1. In early 1. 94. 1, the Experimental Engineering Section of the US Army Air Corps Materiel Division soon reorganized as. USAAFs Air Materiel Command, or AMC began to assign MX designators for Materiel, Experimental. R D projects. Issued by AMCs security apparatus at Wright Field, these. R D programs in engineering orders, correspondence, and. At first MX designations were largely limited to aircraft, engines, major components and ordnance. R D topics. and that trend accelerated even more in the immediate post war period. In fact, twice as many MX numbers were issued. WWII. Not all MX numbers resulted in hardware, of course. MX designations were generally assigned very early in a projects evolution, and thus many MX numbers were subsequently. The Engineering Division found the MX system to be a very useful security device, and it was eventually copied. AMC divisions, so that by 1. MP x. RR x, and FT x operating in parallel within the Command. The resulting confusion undermined the systems. It is not certain from the available records just how many MX numbers were ultimately issued. In an R D summary published in January 1. AMC announced its intent to abandon the MX system as of 1 July 1. MX numbers. continued to be used for several years thereafter. The highest number identified thus far is MX 2. Designation List. The MX tables were generated from a list of MX project designators compiled from declassified USAF records by George Cully. Many thanks go to George for this great contribution to the. Designation Systems. Net. Note Subprojects of MX projects were often designated with suffix letters. Original sources. MX 7. 75 A and sometimes without e. MX 7. 75. A. For the sake of consistency, all subproject. MX 1 to MX 4. 99. MX 5. 00 to MX 9. MX 1. 00. 0 to MX 1. MX 1. 50. 0 to MX 1. MX 2. 00. 0 to MX 2. Weapons Systems 1. Related Codes. WSSSOSRS Designators. At some time in the early 1. Air Force started to assign numerical designations to complete weapons systems, support. The designations initially looked like Examples WS 2. AWS 3. 06. BSS 4. L123Note The dash between the designator and the number is often omitted. WS Weapons System. SS Support System. OS Operational Support. RS Research Support2 is the three digit system number. There were blocks of numbers assigned to different general system. Activate Student Account Uwo more. Strategic Systems. Air Defense Systems. Tactical Systems. Support Systems. 50. Operational Support. ResearchExperimental Support. Within each block, the initial numbers were probably assigned sequentially. Later, however, the numbers were apparently. The n. 99 numbers seem to have been used for general studies. Numbers, which had become obsolete, were often reassigned to new systems. Systems in the 1. WS designators, while systems in the 4. SS, OS and RS, respectively. However, the prefixes were not always consistently used. Omission of Prefix below. The suffix letter 3 was usually an A for weapons systems and an L for support systems including reconnaissance. If the same system number was assigned to different actual projects or activities. B, C,., or M, N,., respectively. The use of suffixes was not entirely consistent Different weapons systems for the same requirement were sometimes managed under the same designator with an. WS 1. 07. A 1WS 1. A 2, and were sometimes assigned the. WS 3. 06. AWS 3. B. Different suffix letters were also used, when a weapons system was further developed e. WS 2. 01. AWS 2. B. Omission of Prefix. Beginning in the 1. WSSSOSRS prefix was frequently omitted when referring to a system. This was especially evident for systems in the 4. Dyna Soar project was. System 4. 64. L only. Also, the WS designator was sometimes used, even if another designator. A is usually referred to as WS 6. A instead of RS 6. A. In rare cases, a prefix was used in a non standard way, like RS for Reconnaissance System or TS for Test System. In the designation list, I show a prefix only for those designators, which I have actually seen with a prefix. System Management Codes. The system numbers are still is use today, but are as far as I know now called System Management Codes SMC. Weaponssupport systems, which received a number in the original designation system retained this number as. SMC e. g. the B 5. Weapon System WS 1. A, and today uses SMCs in the 1. H, 1. 01. P etc. Other weapons use newly assigned numbers, including numbers, which had been originally assigned to a different system. These numbers are sometimes related to other designations of the weapon e. LGM 1. 18. A. Peacekeeper ICBM has SMCs in the 1. The suffix letters in SMCs are not assigned sequentially. Instead, some letters are mostly used for a specific. Examples are E Usually designates the engine of an airborne weapon system Z Used to designate all versions of a weapon system as opposed to a specific versionThe designation list contains also the System Management Codes. Because the transition from WSSSRS designators without. SMCs was probably gradual, there are many numbers, for which I cant say if theyre true System designators or should. SMC only. Designators, which I have found only in an SMC listing, are marked with. Designation List. Note Gaps are marked No information only for those numbers, which I believe should exist because of the. WSSSRS designators. Designation. Contractor. Description. WS 1. ABoeing. B 4. 7Stratojet. WS 1. 00. LBoeing. RB 4. 7Stratojet. WS 1. 01. ABoeing. B 5. 2Stratofortress. WS 1. 01. LBoeing. RB 5. 2Stratofortress. DSMCBoeing. B 5. D1. HSMCBoeing. B 5. 2H1. PSMCPratt Whitney. TF3. 3 P 31. 03 engine for B 5. ZSMCBoeing. B 5. GHWS 1. AConvair. B 5. 8Hustler. WS 1. LConvair. RB 5. Hustler. WS 1. 03. ANorthrop. SM 6. 2Snark. WS 1. ANorth American. SM 6. Navaho. WS 1. AMc. Donnell. F 1. ACVoodoo. WS 1. LMc. Donnell. RF 1. ACVoodoo1. No informationWS 1. A 1. Convair. SM 6. CGMHGM 1. 6Atlas. WS 1. 07. A 2. Martin. SM 6. 8 HGMLGM 2. Titan1. 08. 1. 09No informationWS 1. ANorth American. B 7. Valkyrie1. 11No informationWS 1. ABell. GAM 6. 3Rascal1. No informationWS 1. A Possibly the initial designation of WS 3. A1. 16No informationWS 1. LLockheed. Reconnaissance Satellite System. WS 1. 17. M SAMOS Satellite Missile Observation System became WS 2. A1. 18. L KA 2. Camera. PBell. Hypersonic Reconnaissance Manned Boost Glide Rocket. ASMCMartin Marietta. LGM 1. 18. Peacekeeper. WS 1. 19. L Strategic Photo Reconnaissance Balloon System result of MX 1. Gopher program. WS 1. LBoeing. KC 1. 35. Stratotanker, C 1. Stratolifter. 11. CSMCPratt Whitney. TF3. 3 P 591. J5. W5. 9W engines for C 1. ESMCCFMF1. 08 CF 1. KC 1. 35. 11. 9FSMCPratt Whitney. TF3. 3 P 1. 02 engine for C 1. TSMCBoeing. EC 1. YSMCBoeing. KC 1. ZSMCBoeing. C 1. WS 1. A BGM 7. AICBM Advanced ICBM project for a large MIRVed ICBM as a successor to Minuteman cancelled. WS 1. 21. ARadioplane. GAM 6. 7Crossbow. WS 1. 21. BRadioplane. Longbow Anti Radiation Missile. WS 1. 22. AMc. Donnell.