So, a couple issues here. One is ALWAYS ALWAYS ALWAYS check phase-to-phase voltage on every wire before you do a closed transition. I can't tell you how many times we've had to stop a project and move wires around because of this. Checking rotation alone isn't enough. This, however, only applies while the UPS is in bypass. Attempting to close the tie while the UPS is online effectively results in the UPS powering it's own input (at best) or a phase mismatch and blown-up UPS (at worst). I still hear horror stories from the latter happening on a 400kVA system about 20 years ago at one of the sites I work with. Most UPS will sync to the bypass source so that static bypass is always instantly available, but they can lose sync under some conditions, like low input frequency or voltage. Bottom line, there must be an interlock in-place to prevent closing of the tie breakers unless the UPS is in bypass and as you've not mentioned it, I'm concerned you don't have this? Most UPS will have relays you can use to connect a solenoid key release to for use with a kirk key interlock system. Otherwise, the system can only do an open transition. At the very least, lock out those tie breakers so they can't ever be used.
Splitting the neutral like that is not necessarily an issue, but you need to ensure the ground fault protection relays are properly set or it can result in nuisance tripping. High unbalanced current levels from the split can also result in inductive raceway heating. There are special differential ground fault relays you can use for complicated configurations like this. Also, 4P breakers fix the issue, but be careful using them with UPS as many modern UPS require a solid neutral-ground bond and can fail offline even on battery during open transition transfer if that bond is lost and the neutral is left to float.
Last edited by SteveFehr; 05/26/17 05:34 PM.
