Actually I need to meet the standard for outdoor enclosures, UL 60950-22, and clause 6.1 refers back to UL 60950-1 clause 2.2.2 and 2.2.3. The difference is the voltage limits are reduced, due to contact resistance of the body being reduced when subjected to wet locations. The clause states the voltage difference under a single fault must not exceed 30 V ac, without any mention of current. Am I reading this correctly?
John Cochran STRONGARM Designs 425 Caredean Drive Horsham, PA 19044 PHONE: 215-443-3400 X193 FAX: 215-443-3002 From: Richard Nute [mailto:[email protected]] Sent: Friday, September 05, 2014 8:05 PM To: John Cochran; [email protected] Subject: Re: [PSES] UL 60950-1 clause 2.2.3 Hi John: Nothing wrong. When the ground is opened, you get about half the mains on the (formerly) grounded parts. All equipment does this, including two- wire equipment. Even a three-wire power cord does this! The voltage is due to a capacitive voltage divider, line-chassis-neutral. The capacitances are in the line filter and the strays due to the wiring. The key is the current. It is (or should be) less than that specified in the standard. This is "touch" nee "leakage" current. Measure the current to ground and you will find any where from 0.5 mA to 5 mA. When you touch the chassis, the voltage drops to about 20 volts or less, and you may feel a tingle. The source impedance (to mains) is about 200 k (capacitive reactance), maybe more, maybe less, depending on the equipment. Best regards, Rich On 9/5/2014 12:49 PM, John Cochran wrote: From: John Cochran Sent: Friday, September 05, 2014 3:47 PM To: '[email protected]<mailto:[email protected]>' Subject: UL 60950-1 clause 2.2.3 I am doing compliance testing on an outdoor computer/display and am having problems with complying with clause 2.2.3 of UL 60950-1 and clause 6.2 of UL 60950-22. When the earth ground is disconnected, there is an AC potential on the chassis ground that is ½ of the line voltage. At 240VAC, there is 120VAC on the ground. Since everything is grounded in the system and it is in an aluminum enclosure, I have this potential everywhere. I cannot find an open frame AC power supply that does not do the same thing. What is it that I am doing wrong. The UL 60950-22 standard says the maximum AC voltage that is acceptable is 15VAC. John Cochran 425 Caredean Drive Horsham, PA 19044 PHONE: 215-443-3400 X219 FAX: 215-443-3002 - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
