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1、This guidance was written prior to the February 27, 1997 implementation of FDAs Good Guidance Practices, GGPs. It does not create or confer rights for or on any person and does not operate to bind FDA or the public. An alternative approach may be used if such approach satisfies the requirements of t
2、he applicable statute, regulations, or both. This guidance will be up dated in the next revision to include the standard elemnt s of GGP s . . . DEPARTMENT OF HEALTH. EDUCATION. AND WELFARE PUBLIC HEALTH SERVICE FOOD AND DRUG ADMINISTRATION ROCKVILCE. MARYLANO 20857 A R 2 e I980 To: A l l Manufactur
3、ers and Importers of Microwave Ovens Subject: Open Door Operation of Microwave Ovens as a Result of Oven Miswiring Recently there have been three incidents in consumer locations in which the microwave oven operated with the door open due t o oven miswiring. These incidents have resulted in expensive
4、 oven retesting and recall programs. It has also been learned that several workers at one manu- facturing location had accidently been exposed t o microwave radiation in several instances during oven testing, due to oven miswiring that re- sulted in the continued operation of the oven after the daor
5、 was opened. The Bureau is greatly concerned that future incidents such as these could occur and result in the exposure of individuals to high levels of microwave energy. To reduce the potential for such open door operation, due to miswiring of the oven circuitry, the Wtreau strongly recommends that
6、 all manufacturers consider instituting design features that will, (1) preclude andagous accidental miswiring -of microwave ovens, or (2) if miswiring occurred, prevent the unit from operating with the door open. It is recommended that all manufacturers consider: 1. Locating one safety interlock on
7、the neutral side of the line and another on the high side of the line. 2 . Locating the monitor circuit as the last circuit branch in parallel with the high voltage transformer, or making the “hot“ A.C. line connection to the monitor circuit the last connection prior t o connection with the primary
8、of tbe power transfomer. 3. Performing a failure mode effects analysis on each unique design t o identify critical connections and wires where the ac- cident& interchange would result in electrically by-passing a l l safety interlocks and the monitor. 4. Designing critical wire terminal connect p i
9、n t s so as to mechanically preclude accidental interchange of these wires to any unsafe configuration. 5 . Covering the terminals ,of critical wires with insulation to prevent any loose wire from being able to contact another point t h a t might result in by-passing the safety interlock or monitor
10、circuit . 6 . Using wire ties to limit the degree of movement of any Kire that could becone disconnected. - 4 . . Page 2 - A l l Manufacturers and Importers of Microwave Ovens 7. Instituting other design features that would prevent the mis- wiring of units or prevent units that are miswired from ope
11、rating with the door open. Manufacturers must be careful not t o introduce design changes that could result in noncompliance with the Federal perforinance standard. It is requested that proposed changes be .submitted to the Bureau for review prior to incorporating the changes on production models- I
12、t may also be appropriate to submit prototype units to the Bureau for evaluation. It is equally important t h a t certain good quality control practices be . observed t o help prevent these undesirable conditions. The Bureau is hereby requesting that all manufacturers now institute, if not already a
13、 part of their quality control and testing program, a specific test of . each unit to determine that the unit w i l l cease operating when the door is opened, and that it cannot be restarted, when the door is open. Any test that provides positive indication of magnetron shutdown upon latch release o
14、r door opening w i l l be acceptable. The test must also include an attempt t o restart the unit while the door is unlatched. This should be attempted both with the unit programed and not programed (for operation)for digital units, and Kith and without time on the timer for nondigital units, i f the
15、 status of these controls could alter the possibility of starting with the door open- W e recognize that these tests require care in order t o prevent the exposure of the operator t o high levels of microwave energy- In each case the door should be unlatched slowly and the operator instructed t o te
16、rminate the test imnediately if a problem is noted. Also a mechanical stop is recommended that would allow the door to be unlatched and opened slightly but which would prevent the door from opening t o a position that would allow hzzardous levels of microwave energy t o leak from the oven. Regardless of the type of test performed the test must be conducted at a point on the production that is subsequent t
