Another possibility is that the US equipment may have been designed for a three phase "Y" input with a neutral and was used on a European three phase "delta" circuit. Someone could have then tied the neutral terminal to ground creating a serious hazard as well as a voltage imbalance.
Just a thought... Rick -----Original Message----- From: Rich Nute [mailto:ri...@sdd.hp.com] Sent: Wednesday, October 11, 2000 3:38 PM To: wo...@sensormatic.com; k3...@eurobell.co.uk Cc: emc-p...@majordomo.ieee.org Subject: Re: Neutral/Earth connections Hi Richard and Dave: In answer to Richard's comment: > The neutral is never to be tied to the chassis of equipment. It is not > allowed by any safety standard nor the National Electrical Code. The neutral > is to be tied to earth at one and only one point and that is that the > service entrance or the electrical box fed by an on-premises transformer. I > would have to seriously question if this product was designed to any > recognized safety standard. Even if it does not pop the breaker, is it safe? See IEC 60950, Sub-clause 1.2.12, Power Distribution, and Sub-clause 1.2.12.1, TN-C system and Figure 3. This reference describes a scheme by which accessible conductive parts are grounded via the neutral conductor of the power distribution system. Also, see NEC 250-60, Frames of Ranges and Clothes Dryers, and 250-61, Use of Grounded Circuit Conductor for Grounding Equipment, and 250-61(b), Load Side Equipment, Exceptions. In the USA, the frames of cooking ranges, wall-mounted ovens, counter-mounted cooking units, and clothes dryers may be grounded via the neutral conductor (i.e., the TN-C scheme). However, the TN-C grounding scheme is not permitted for the equipment mentioned in the original posting. In answer to Dave's question: While there is no general rule regarding configuration of exported equipment, there are specific rules for some kinds of equipment (laser, x-ray, medical, etc.) that requires that the equipment must meet either USA safety standards or the safety standards of the destination country. Personally, I find it hard to believe that a reputable USA manufacturer would supply equipment where the neutral was connected to the chassis. So, I wonder if there is some sort of mix-up due to wiring the unit for the U.K.? A USA 240-V unit is provided with three wires: +120 V (typically black) -120 V (typically red) Ground/Chassis/PE (green or green/yellow) A USA 120-0-120 V unit is provided with four wires: +120 V (typically black) 0 (neutral) (white or natural grey) -120 V (typically red) Ground/Chassis/PE (green or green/yellow) So, I wonder if the unit was a 240-V unit, but the wires were identified as +120, -120, and 0/chassis? Then, I wonder if the use of a 120/120 marking implied a neutral? I suspect that there is some confusion because Dave describes connecting the unit to a U.K. 120-0-120 source. I would expect that the unit could be connected to a U.K. 240 V source (phase and neutral) with the third wire connected to PE. I suggest a further study of the unit or its schematic to determine if the chassis is used as a current- carrying conductor (i.e., neutral). Best regards, Rich ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson: pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson: pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org
