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We have been following 2 incomers and a bus coupler scheme arrangement with two buses in 0.415kV switchboard. Normally, each bus section is fed from incomer breaker and bus coupler breaker remains open. Auto change over scheme is employed on this switchboard. It enables automatic closing of...

@Bill : I Agree, Bill. Contactor closing/opening time are not close to those of static switch. That's why we're alerted when we knew that vendor has replaced static switch with contactors :) @Kiribanda : During Output overload / Inverter fault, my concern would be to protect healthy loads +...

Bill & Kiribanda, Thanks for your valuable inputs :) @ Bill : Since contactor is installed on inverter output & UPS will be continuously on; contactor will also be continuously ON. I agree that contactors are reliable, but reliability of static switches is comparatively better for UPS...

Hello Kiribanda, Please find attached SLD. Since this is preliminary, vendor has not shown contactors. I have shown red arrows at locations where there should be static switches, but vendor has replaced them with...

For one project, we have a requirement of 10kVA parallel redundant UPS with common bypass. Till now we have only purchased UPS which have static switches in bypass and inverter path. Recently one vendor has offered a UPS which has a static switch on bypass path, however they have provided...

Thank you ,Bill and Che Kuan Yau ! For taking time out to reply and solving my query.

Could anyone please explain the attached tripping curves on MN type thermal overload relay? Why are there two different hot and cold curves given? what is their significance?https://files.engineering.com/getfile.aspx?folder=7b3be7ff-57f1-4cee-90b9-ee51b0f48146&file=mntyperelay.PNG

I have requirement of 10kVA UPS which will be fed from 415V 3 phase input supply, and output is 110V AC single phase. I have several questions as listed below about the same: 1) Which factors decides the UPS input supply neutral requirement : Several manufacturers are offering UPS with 3ph/3...