One thing you have to make sure is that your power supplies are the same type. A person can have two 130A AC power supplies, but if you have one Type 8 power supply and one Type 4 power supply (something I've tried) you will see the exact behavior you describe - power one off and the entire rack goes down momentarily and everything restarts. My experience has been that as long as your two power supplies are exactly identical, the failover works perfectly. I've had several occasions (last night, in fact, while switching out the UPS) where I have to power one or the other off, never disconnect a user while doing it. - Joel -----Original Message----- From: Joshua Coombs [mailto:jcoombs@gwi.net] Sent: Monday, April 07, 2003 9:38 AM To: Discussion relating to the 3Com/US Robotics Total Control modem systems.; alex@wanex.ge Subject: Re: [USR-TC] PSU question As long as both UPSs are running within normal tolerances, fail over should work as expected. Note I have observed powersupply fail over tripping over itself in the past using 130A 120v powersupplies on dual feeds. Both power supplies were green, power down one and the chassis rebooted... so your milage may vary. Sometimes it works, sometimes it doesn't, even if they are on the same power source. Joshua Coombs On Monday 07 April 2003 08:32 am, alex@wanex.ge wrote:

This chassis is connected to 2 UPS-s in case of 1 fails another will work. What will happen if voltage (or amperage or freq.) of one UPS is different from another?

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