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Correspondence N ELC200?-oe`f70 - 71 , 61/ til R0( � W .. Electrical • ' Contractor Services N.W. , Tuesday, September 29, 2009 Gary Noble City of Tigard Senior Electrical Inspector 503- 718 -2446 garyn@tigard-or.gov Re: Available Fault Current Concern, 7904 SW Hunziker, Tigard, OR • Dear Gary: • We are working for Plas2Fuel Corporation in Tigard and are going to be connecting loads to existing panels. We are concerned about the existing service /panel which is currently being installed and its ability to safely interrupt faults. Our goal is to provide a quality electrical installation to our customers which is essentially free of any hazards. Our primary concerns are: • The existing panels and their ability to withstand the new fault levels. • Is the 400arrip 480volt panel near the new electrical service capable of withstanding the roughly 33,000 amps of available fault current which is available at the main terminals of the panel? • It appears as the contractor installing the service is using standard dual element fuses, not current limiting type. This presents a safety hazard as the panel is not rated to handle the AFC and therefore the panel will have to be replaced with a panel that is properly rated. • IF Current limiting fuses are used, it presents a coordination issue. Current limiting fuses are only capable of reducing the.AFC to approx. 9,000amperes(see ref. below). For example: IF The 400amp panel is rated for . • 10,000amperes and has undergone testing to verify its proper operation. When there is a short circuit downstream of the 400ampere it is likely that the current - limiting fuse /s will open instead of the branch circuit breaker. This will cause the entire process to shut down. We have completed a preliminary fault current analysis and this has raised some questions. See diagram below for the system arrangement and fault ratings. Segment 1: 2sets Segment 2: 1set 4/0 Segme 250AI in Metallic Al in Metallic Al i Raceway - 10' Raceway - 30' Rac PGE 36,063A 32,545A 24,507A Pad Mount MOP P-4 ATS 480v 4B9v � 2 — • Electrical Contractor Services NW • 3335 NW St Helens Rd • Portland, Oregon 97210•Phone (503) 366 -6060 CCB 01554600 FAX (503) 296 -5518• Tony Oliverio • Email lonyo ©ecsnw.net • • • The following references below relate to the concerns we have with the current system as it is currently being installed. Minimum Interrupting Rating NEC® Article 100 defines interrupting rating as: The highest current at rated voltage that a device is intended to interrupt under standard test conditions. An overcurrent protective device must be able to withstand the destructive energy of short- circuit currents. If a fault current exceeds the interrupting rating of the overcurrent protective device, the device may actually rupture, causing additional damage. NEC® 110.9, requires equipment intended to interrupt current at fault levels to have an interrupting rating sufficient for the current that must interrupted. This article emphasizes the difference between clearing fault level currents and clearing operating currents. Protective devices such as fuses and circuit breakers are designed to clear fault currents and, therefore, must have short circuit interrupting ratings sufficient for all available fault levels. Equipment such as contactors and switches have interrupting ratings for currents at other than fault levels, such as normal current overloads and locked rotor currents. NEC® 110.10 states "The overcurrent protective devices, the total impedance, the component short- circuit current ratings, and other characteristics of the circuit to be protected shall be selected and coordinated to permit the circuit protective devices used to clear a fault to do so without extensive damage to the electrical components of the circuit. This fault shall be assumed to be either between two or more of the circuit conductors, or between any circuit conductor and the grounding conductor or enclosing metal raceway. Listed products applied in accordance with their listing shall be considered to meet the requirements of this section." This requires that overcurrent protective devices, such as fuses and circuit breakers be selected in such a manner that the short- circuit current ratings of the system components will not be exceeded should a short circuit occur. The "short- circuit current rating" is the maximum short- circuit current that a component can safely withstand. Failure to?limit the fault current within the short- circuit current rating may result in component destruction under short- circuit conditions. The last sentence of NEC® 110.10 emphasizes the requirement to thoroughly review the product standards and to apply components within the short- circuit current ratings in these standards. Simply, selecting overcurrent protective devices that have an adequate interrupting rating per NEC® 110.9, does not assure protection of electrical - system components. To properly comply with NEC® 110.10, current limiting overcurrent protective devices may be required. Minimum Interrupting Rating NEC® 240.60(C) states that the minimum interrupting rating for a branch - circuit cartridge fuse is 10,000A. NECID 240.83(C) states that minimum interrupting rating for a branch - circuit circuit breaker is 5,000A. The circuit breaker or fuse must be properly marked if the interrupting rating exceeds these respective minimum ratings. These minimum interrupting ratings and markings do not apply to supplemental protective devices such as glass tube fuses or supplemental protectors. • • Electrical Contractor Services NW • 3335 NW St Helens Rd • Portland, Oregon 97210•Phone (503) 366 -6060 • CCB 41554605 FAX (503) 296 -5518• Tony Oliverio • Email tonvo®ecsnw,net • • Normal Current Operation • 51.41.000U5'10 RR � �,, pp1T',,ppppRLJ1BBCAMp1V IWWYR RRENT \ _ I HAT OTBGTR6 GUR REM %, I . OYERCURRENT • PROTECTNE ir MACE • ',' �iC.1 i ��p�i QJR O , 6n Ave) ERZIEcia LUIUTE) Short - Circuit Operation with Inadequate Interrupting Rating • .O0 CATEBANE pppppp �N OF MADMAN A UIW r TERRUPT R�O.N INI me nse Ram VIOLATION OF NEC* 1160 OYERGUTRENT • PROTW ME DENCE EI DESTROTE= - ' DAN ERTEANBAND WARM !I DF Short - Circuit Operation with Adequate Interrupting Rating p�rEgGpT�EpT p pEyIC ADE04il1E INTERNUVTK NABNC III CON LAME Will NEC* 110a 19 UNfUTACED • • - ~ f +� BNORTdRCUT - Ewa WELT FLOOD OATEB HAW: • ADECAUn* L H T RATION D - 1 BMW INTERR PTED If you have any questions, need additional information, please call. Best regards, • Ton Electrical Contractor Services NW • 3335 NW St Helens Rd • Portland, Oregon 97210•Phone (503) 366 -6060 CCB #155460• FAX (503) 296 -5518• Tony Oliverio • Email tonyo ®ecsnw,ne( . • a • • • • This is an example of a current limiting let - through current value. This is the lowest available let - through Bussman offers. LOW - PEAK YELLOW Class J; Dual - Bement Time -Delay Rises LPJ_SP Fuse -RISE Let-Through Currents (kA) LPJ 8P • Fuse Size Prusp. Short 15 30 60 101 210 400 600 ' --- - - ----• ..IM_..ONA -W MI C.C. lams Imo ta.s 4+.s lams ts.s Wes TEE :.� :::M:::::0 = : :..- rte.• C .... = _m-...l .... Co. i ....C.rna • , r' ...........n.M. Maian ■.nwn.r.....nnEr.sr soa► 1,000 1 1 1 1 1 1 1 ,n, lowingotwoussommooluolo wrisaiNsamoP i ma —.........ii-......-..... �...�i.•::ii■ -- i. 3,000 1 1 1 2 2 3 3 ,, �r.�iee��a111 ■t►_: �:i orinimIr∎ ,.� 5,000 1 1 1 2 3 5 5 1 I ■11■811■81111� •1 � al � fan! �i 811 ■11!.: %lIMiil ■111Misli■g 'o m I � �� /�: /i! epA 10,000 1 1 2 2 4 • 6 8 1 �� .1.: :�C::'iC::•'.�CC...i::-'- :�::7: 16,000 1 1 2 3 4 7 9 d MR - E ■ -■ l 1l: �El 11 . ■. . _ :— g . = .wt- � .■ 20,000 1 1 2 3 4 7 10 .0 ■ .... i n —. ::'� 2,y 000 1 1 2 3 5 8 10 a .. s......■. .ns•:�.■■ ^1..itnsr•�i.ir.■.v�.■■ ' 1 !i g " -110,10,■ow- ■hums in i3 30 . 1 2 3 5 8 11 1 35,000 1 1 2 4 5 9 12 A7, .. . =►��::C::CG: ==:i'.=. {G =' 40 000 1 2 3 4 6 9 12 a MAI MEP a.-.-r-.0 ..Ila ∎. ■........a.a- -a... ■aat� .. , 3 0 semi :....■•.......ss.... ■.nss. well y.n....■ '=:: == = - 50 000 1 2 3 4 6 10 13 : m -- '. iii. ' ..� .. .s' . .. m. • • .. = m ann i m'in�Si- C ' ,„ ' w m-.= r■ a..... .r-......mm'■�i..■.r —.-'� 60,000 1 2 3 4 6 11 14 omm Ia� s' .al......■ . .I.m ■......n ....■ .f m Qr�oi nium NuuaUurt�ma■ =■81811 ■8111 ■11811■11111r ■■■11■II111� ■■i 80,000 1 2 3 5 7 12 15 .. • i1111111r1 (11111111111P111I1111111I11Ui11 100,000 1 2 4 5 8 12 17 s - 5 5 ®Oi:ll . i a ®3 § §91 a 1: MR i i 150,000 1 2 4 6 9 14 19 PFIOSPEGTN6 SHORT •CRCUT CURiENT.6YMETRGLRYBAYFEREB 200,030 2 3 4 6 9 16 21 250,000 2 3 5 7 10 17 23 • 300,000 2 3 5 7 11 18 24 Note: For lm value al 300,000 amperes, consult Factory. • • • • • • References: 2008 NEC() Cooper Bussman Bulletin EPR -1, Electrical Plan Review • • • • Electrical Contractor Services NW • 3335 NW St Helens Rd • Portland, Oregon 972 10•Phone (503) 366 -6060 CCB #1554605 FAX (503) 296 - 55185 Tony Oliverio • Email tonyo@ecsnw.net • • •