Consider a communications gateway linking 4 types of network: 1. SELV CANbus network providing power to the product at 15Vdc. This network runs off a power supply in a host product. The power supply meets Reinforced insulation back to the mains, and the CANbus output is not itself earthed, although there are EMI cap's and transorbs from lines to chassis ground and therefore earth.
2. SELV RS-232 port used only for a short run of cable terminating in a Zigbee wireless module 3. SELV RS485 modbus port 4. SELV Ethernet port with integral transformer, for connection of Cat 5 cable Question: Does anybody think this pcb needs to have an isolation boundary between the input circuit and the output circuits? >From a safety point of view, I think the answer is clearly no, as all circuits are SELV and Table 2G of EN60950-1 tells me regardless of whether or not they are earthed, SELV circuits need only Functional insulation between each other. I'm open to rebuttals however. >From a signal integrity, noise, grounding, etc. point of view I'm not so sure. The Ethernet port is transformer isolated in its output connector, and the RS-232 port is not conductively connected to anything that goes anywhere, leaving just the RS-485 port. That one will run to other modbus devices over significant distances, and it may be grounded at one or more of those devices apparently. Does anyone think that port should be isolated from the CANbus network? If so, why? Thanks in advance, Jim Eichner, P.Eng. Compliance Engineering Manager Xantrex Technology Inc. e-mail: [email protected] web: www.xantrex.com Confidentiality Notice: This email message, including any attachments, is for the sole use of the intended recipient(s) and may contain confidential and privileged information. Any unauthorized review, use, disclosure or distribution is prohibited. If you are not the intended recipient, please contact the sender by reply e-mail and destroy all copies of the original message. - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/request/user-guide.html 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] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________
