A-102-1 Electric Duct Heater Brochure - Brasch

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UL/NEC Requirements*REQUIREMENTDOUBLE SAFETY PROTECTIONUL 1996, Paragraph 23.3.1:"A duct heater shall be equipped with one or more automatically resetting temperaturelimitingcontrols, as determined by 23.3.3, that will disconnect the heating element or elementsfrom the supply circuit to prevent temperatures from exceeding the limits specified.These temperature-limiting controls shall be factory-installed as an integral part of theheater."NEC Article 424-64:"Limit Controls. Each duct heater shall be provided with an approved, integral, automaticresettemperature-limiting control or controllers to de-energize the circuit or circuits."Secondary ControlNEC Article 424-64 (continued):"In addition, an integral independent supplementary control or controllers shall be providedin each duct heater that will disconnect a sufficient number of conductors to interruptcurrent flow. This device shall be manually resettable or replaceable."UL 1996, Paragraph 23.3.9:A duct heater shall be provided with one or more manually resettable or replaceable backupprotective devices of the type specified in 23.3.7, that will, with the contacts of theautomatically reset limit control permanently closed, limit the temperature to comply withthe requirements specified in the Back-up Protection Tests, Section 33.Paragraph 23.3.10:The manually resettable or replaceable protective devices specified in 23.3.9 shall befunctionally independent of the automatically reset limit control. The following types ofcontrols comply with this requirement:A. On or more thermal cutoffs, nonresettable limit controls, or manually resettable limitcontrols connected to open a sufficient number of ungrounded conductors to permitthe unit to comply with the specified temperture limits.B. A combination consisting of one or more normally open magnetic contactors andthermal cutoffs, nonresettable limit controls, or manually resettable limit controls. Thethermal cutoff or limit control shall be connected in the coil circuit of the contactor.The combination shall be intergral witht he product; be able to open a sufficient numberof ungrounded supply conductors to permit the product to comply with the specifiedtemperature limits; and be independent of control by an automatic cycling devicewith the unit.CONTROLLERS AND DISCONNECTING MEANSNEC article 424-20:(a) Serving as Both Controllers and Disconnecting Means. Thermostatically controlledswitching devices and combination thermostats and manually controlled switchesshall be permitted to serve as both controllers and disconnecting means provided all ofthe following conditions are met:HOW BRASCH MEETS REQUIREMENTEvery heater is furnished with an automatic reset thermal cutout of the bimetallic disc typeThis device is sol located that the airflow through the heater can be either left- or righthandor vertical up and the device is serviceable without having to remove heater fromduct. On larger heaters, where UL requires additional thermal cutouts, these are providedat no extra charge.Brasch heaters have always had double safety protection as standard and without additionalcharge. To meet the requirement for a manually replaceable cutoff, a sufficient numberof secondary cutouts are provided in every heater. Secondary cutouts are:1. Factory prewired in the power lines of the heating elements and are not dependentupon back-up contactors or other devices in the control circuit which may fail to open.2. Spread throughout the terminal box to give protection to the particular elements whichthey serve. Thus they will sense unsafe conditions even if they occur in th lower portionof the heater.3. Easily replaced with locally stocked factory replacements once the unsafe conditionhas been corrected. Unlike the manual reset thermal cutouts which invite being resetwithout the cause of the unsafe condition having been determined, secondary cutouts,by requiring replacement, point out that something is seriously wrong and must first becorrected.Brasch heaters are available with optional manual reset thermal cutout and can be wired:1. In series with the automatic reset thermal cutout (in addition to the secondary cutoutwhich serves as secondary protection),2. In the power lines (in lieu of secondary cutouts), and3. To operate back-up contactors.A secondary cutout and back-up contactor combination is unnecessary since the secondarycutouts are rated to carry the load without need for back-up contactors. A manual reset thermalcutout and back-up contactor combination while optionally available is not recommendedfor Brasch heaters since secondary cutouts will be provided instead and offer better protection.Back-up contactors are an unnecessary expense.This requirement means that as long as the thermostat with an off position is not an integralpart of the duct heater, a de-energizing contactor as described on page 9 can be used.Disconnecting break contactors are recommended for all applications and some local codesmay require them as in Chicago and New York City.(1) Provided with a marked "off" position.(2) Directly open all ungrounded conductors when manually placed in the "off"position.(3) Designed so that the circuit cannot be energized automatically after thedevice has been manually placed in the "off" position.(4) Located as specified in Section 424-19.* Quoted from 1999 NEC and UL Standard 1996.24 BRASCH MANUFACTURING
REQUIREMENT(b) Thermostats That Do Not Directly Interrupt All Ungrounded Conductors.Thermostats that do not directly interrupt all ungrounded conductors and thermostats thatoperate remote control circuits shall not be required to meet the requirements of (a) above.These devices shall not be permitted as the disconnecting means.UL 1996, Paragraph 26.11"A contactor or similar device, such as a silicone controlled rectifier required for use with alimit control, shall be provided by the manufacturer of the heater, but need not be mountedon the heater."ZERO CLEARANCEUL 1996, Paragraph 44.5"A duct heater rated 50 kilowatts (kw) or less shall be tested for installation with zero spacingbetween the duct and combustible surfaces. A duct heater rated more than 50 kw maynecessitate that such spacings be larger than zero. See Paragraph 52.2."CONTROL TRANSFORMER CIRCUIT OVERCURRENT PROTECTIONUL 1996, Paragraphs 20.8 and 20.920.8 Except as indicated in paragraph 20.9, a transformer having a rated output of not morethan 30 volts and 1000 volt-amperes (National Electrical Code, ANSI/NFPA 70-1984, Class1, power-limited circuit) shall be protected by an overcurrent device located in the primarycircuit. The overcurrent device shall be rated or set at not more than 167 percent of the primarycurrent rating of the transformer. See paragraph 20.10.HOW BRASCH MEETS REQUIREMENTThis paragraph requires that the duct heater manufacturer furnish control, back-up andsafety contactors or an SCR controller as part of the heater (either built-in or in aremote control panel) whenever the thermal cutout is incapable of carrying the heaterload directly.Brasch heaters, both slip-in and flanged types, are UL Listed for zero clearance, includingthose rated over 50 KW (up to 2000 KW maximum). However, it is not recommended thatany combustible material be allowed to touch any electric duct heater or immediate surroundingareas.These requirements mean that when a built-in 120 volt secondary transformer is supplied,it must be provided with primary fusing: when a built-in 24 volt secondary transformer issupplied, it does not require primary fusing unless it is above 100 VA.20.9 A transformer that directly supplies a National Electrical Code, ANSI/NFPA 70-1984,Class 2 circuit (see paragraph 2.2) shall, in accordance with the Standard for Class 2 andClass 3 Transformers, UL 1585, either limit the output current (inherently limited transformer)or be equipped with an over current device (not inherently limited transformer), andneed not comply with the requirements in paragraph 20.8.SUBCIRCUIT OVERCURRENT PROTECTIONNEC Article 424-22 (b) and (c):(b) Resistance Elements. Resistance-type heating elements in electric space heating equipmentshall be protected at not more than 60 amperes. Equipment rated more than 48amperes and employing such elements shall have the heating elements subdivided, andeach subdivided load shall not exceed 48 amperes. Where a subdivided load is less than 48amperes, the rating of the supplementary overcurrent protective device shall comply withSection 424-3 (b).(c) Overcurrent Protective Devices. The supplementary overcurrent protective devices for thesubdivided loads specified in (b) above shall be: (1) factory installed within or on the heaterenclosure or supplied for use with the heater as a separate assembly by the heater manufacturer;(2) accessible, but shall not be required to be readily accessible; and (3) suitablefor branch-circuit protection.To meet this requirement, Brasch heaters were one of the first to offer UL Listed heaterswith built-in fuses. Note: NEC requires overcurrent protection only on heaters exceeding48 amperes total line current. Automatic circuit breakers also meet this requirement.If overcurrent protection is not ordered built-in, all heaters exceeding 48 amperes total linecurrent must be divided into a sufficient number of subcircuits, each provided with the lineterminals for connection to remote overcurrent protection and this remote overcurrent protectionmust be supplied by the heater manufacturer.Where cartridge fuses are used to provide this overcurrent protection, a single disconnectingmeans shall be permitted to be used for the several subdivided loads""The overcurrent protective devices required by Paragraph 18.1 shall be provided as anintegral part of the heater or shall be provided by the heater manufacturer as a separateassembly, for independent mounting, for use with the heater. See Paragraph 42.15."AIRFLOWNEC Article 424-59:"Air Flow. Means shall be provided to assure uniform and adequate air flow over the face ofthe heater in accordance with the manufacturer's instructions.This paragraph requires that the duct heater manufacturer furnish as an integral part ofeach heater an acceptable means of interlocking the heater with the fan.Heaters installed with 4 feet (1.22m) of the outlet of an air-moving device, heat pump, airconditioner, elbows, baffle plates, or other obstruction in duct work may require turningvanes, pressure plates, or other devices on the inlet side of the duct heater to assure aneven distribution of airover the face of the heater."BULLETIN A102-125
Page 1 and 2: Bulletin A102-1© Brasch Manufactur
Page 3: Ratingsand SizesYou specify it—we
Page 6 and 7: Construction DetailsAutomatic reset
Page 8 and 9: Step ControllersStep controllers ar
Page 10 and 11: Special ConstructionsHeaters forDuc
Page 12 and 13: Special Constructions (cont.)BOTTOM
Page 15 and 16: Finned TubularSLIP-IN AND FLANGED
Page 17 and 18: Use these formulae as rough guideli
Page 19 and 20: How to Calculate Line CurrentsTo de
Page 21 and 22: Wiring Diagram Control System 2Mult
Page 23: Wiring Diagram Control System 4Tota
Page 27 and 28: Express Duct Heaters 14 Day Shipmen

A-102-1 Electric Duct Heater Brochure - Brasch

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