Kurt & friends The rationale for using a 13A fuse in cords with lower amperage ratings is simple: The fuse in the UK plug is essentially in place to take account of the use of the UK 30A/32A ring main distribution system which is uses 2.5 sq mm (or larger) conductors in the building wiring system. At the socket there is a reduction to 1.5mm or smaller conductors which thus require gross over-current protection at that point.
The fuse is an HBC/HRC type which is there to protect the cord in the event of a catastrophic failure of the cord, such as being cut and shorting the conductors together, or to ground - not not the appliance or the cord under normal operation! Furthermore, I think that many people forget that the North American and other European countries do the same - or even worse! You guys generally protect all your sockets with a 15A (America) or 16A (Europe) HBC/HRC fuse/circuit breaker in the building distribution system - and don't generally have ANY local socket fuse protection at all to protect small cross section (18AWG/0.75 sq mm, or smaller!) cords Therefore if you are worried about our system then you had better go and talk to you local code writers (the NFPA et al) and get all your codes and installations changed. Seriously though, the only time we get over-heated cords of correctly rated cords in reality is where the general ventilation around is poor. The other major issue is overheating in the plugs themselves - generally caused by either loose terminal screws and/or fuse clip contacts that are loose/corroded/covered with verdigris. All of these result in high contact resistance and local overheating - sometimes to the extent that the plugs actually get damaged. This is typically a problem of low-cost items (although it is not always the low-cost plugs that are actually the worst!) and long-inservice periods of use with no precautionary maintenance. Regards John Allen Thomson Racal Defence Electronics Ltd Bracknell UK -----Original Message----- From: Andrews, Kurt [mailto:kandr...@tracewell.com] Sent: 31 October 2000 14:22 To: Geoff Lister Cc: EMC-PSTC Subject: RE: International Power Cords >EN60950 (ITE safety), section 3.2.4, permits a detachable power cord of 1 square millimetre cross sectional area for >cords fitted with connectors rated to 16A, provided the cord length does not exceed 2 metres. >In Annex ZB, the spec adds a section to 3.2.4 "In the United Kingdom, a power cord with a conductor of 1,25 mm >squared is allowed for equipment with a rated current over 10A and up to and including 13A." Our unit will be tested under IEC 1010-1/EN61010-1 not EN60950 although we do use that standard for a lot of our units. I just noticed clause 6.10.1 in IEC 1010-1 that states that the mains supply cords shall be rated for the maximum current of the equipment. So it sounds like I need to use a 10A rated cord since our unit will be rated at 10A. We are using one current rating since the voltage rating will be 100-240V. Even if we used split voltage and current ratings such as 120/240V and 10/5A I'm not sure we could use a 5A rated cord since the standard says it has to be rated for the maximum current, not the maximum current at the user's typical input voltage. >Although the 10A fuse is available for the UK BS1363 plugs, it is not commonly available in retail outlets as spares in a >blister pack. The chances are that if the fuse does blow, it will be replaced by a 13A fuse anyway. I do not understand how it can be considered safe to use a 13A fuse in a cord rated for 10A. According to your comment this is done a lot in the UK and this combination (10A cord with a 13A fuse) is also available in cords from Belden and Panel Components Corp. Sure seems like the cord would melt or get very hot before the fuse would blow. Thanks for your insights, Kurt Andrews Compliance Engineer Tracewell Systems, Inc. 567 Enterprise Drive Westerville, Ohio 43081 voice: 614.846.6175 toll free: 800.848.4525 fax: 614.846.7791 http://www.tracewellsystems.com/ <http://www.tracewellsystems.com/> -----Original Message----- From: Geoff Lister [SMTP:geoff.lis...@motion-media.com] Sent: Tuesday, October 31, 2000 6:43 AM To: 'Andrews, Kurt' Cc: EMC-PSTC Subject: RE: International Power Cords Kurt, EN60950 (ITE safety), section 3.2.4, permits a detachable power cord of 1 square millimetre cross sectional area for cords fitted with connectors rated to 16A, provided the cord length does not exceed 2 metres. In Annex ZB, the spec adds a section to 3.2.4 "In the United Kingdom, a power cord with a conductor of 1,25 mm squared is allowed for equipment with a rated current over 10A and up to and including 13A." Although the 10A fuse is available for the UK BS1363 plugs, it is not commonly available in retail outlets as spares in a blister pack. The chances are that if the fuse does blow, it will be replaced by a 13A fuse anyway. Regards, Geoff Lister Senior Engineer Motion Media Technology Ltd. http://www.motion-media.com -----Original Message----- From: Andrews, Kurt [mailto:kandr...@tracewell.com] Sent: 30 October 2000 20:16 To: EMC-PSTC Subject: International Power Cords Importance: High Group, I have a question about International Power Cord Ratings. We have a product using a C14 Appliance Inlet and I am trying to specify the proper cords for international use. The unit uses an autoranging power supply with an input of 100-240V. We are using a single current rating of 10A on the unit and the unit actually draws just over 8A at 100V. It has a 10A circuit breaker approved for international use. I know that in the U.S. the power cord rating must be at least 125% of the current rating of the product. Does this rule also apply to cords for international use? Since the current draw of the unit will only be about 4-5A max. when used at 220V should the international cord ratings be equal to (or 125% greater) than 5A or equal to (or 125% greater) than 10A? Obviously a cord rated for 7 or 8A will cost less than one rated for 13A. I also have a question relating specifically to cords for use in the United Kingdom (BS 1363 cords). What should the power cord fuse rating be for this product? I see they have fuses in 3A, 5A, 10A, and 13A. I'm thinking that the 10A fuse would be the proper one as the 5A would be very close to the current draw of the product. I also notice in both the Belden and Panel Components Corp. catalogs that they both sell these cords with fuse ratings that are higher than the cord ratings. They both have several 13A fuses in cords rated for 10A. Wouldn't the cord melt before the fuse, or at least get very hot? Since the actual current draw at 220V will be less than 5A I'm thinking that we can get by with a cord and fuse rated at 10A. Does this sound right? The product will be covered under the Test Equipment standards, UL 3111-1, CSA C22.2 No. 1010.1 and EN 61010-1. Any insights into this subject would be very much appreciated. Kurt Andrews Compliance Engineer Tracewell Systems, Inc. 567 Enterprise Drive Westerville, Ohio 43081 voice: 614.846.6175 toll free: 800.848.4525 fax: 614.846.7791 http://www.tracewellsystems.com/ <http://www.tracewellsystems.com/> ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. 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