3rd harmonic made simple

Capacitor current calculation made simple

Battery training at the Factory by:




A product manual and site switching procedure should be present at every site where an attending UPS service engineer is expected to take full responsibility for successfully switching site electrical panels and switchgear. These electrical installations are designed and installed by a wide variety of site electrical departments with vastly varying opinions on how to label UPS bypass and isolation switches. An electrical line diagram is the least we would expect to have available, but seldom is it anywhere to be found. All building management departments should have the electrical drawings present, but when asked for them we sometimes gets the old “dunno mate” response.

Often when doing UPS maintenance we are confronted with poor labelling and no drawings to consult.

Guesswork should never be relied upon when switching critical loads to and from bypass, or when isolating UPS kit for maintenance. Fortunately the switchgear at most sites is well labelled, but on the many sites that are poorly labelled the engineer has to figure out the switching procedure from experience. This can be both expensive and embarrassing.

Remember...always be certain that you know exactly where a switch is connected in the circuit before you operate it, lest it go all quiet in the room.

Some examples of poorly labelled isolators and breakers:

INPUT FROM UPS2”(a UPS doesn’t have an input coming from it!)

OUTPUT TO UPS1” (output of what to UPS1’s what??)

INPUT FROM UPS1 BYPASS” (input to what?)

BYPASS OUTPUT TO UPS1”(to UPS1’s output DB perhaps?)

BYPASS SUPPLY FROM UPS1” (from UPS1’s what?)

INPUT FROM UPS1 BYPASS” (input to what from bypass’s what?)

SUPPLY FROM UPS” (to a DB perhaps? What supply? Mains? Protected mains?)

MAINS INPUT FROM UPS” (from UPS’s what?)

SUPPLY TO UPS2 OUTPUT”(what supply from where goes to a UPS’s output????) (BANG!)

I’m certain there are many more variations of confusing panel labels out there, and any examples would be welcome via email, and I’ll add them to the list.

A critical load is just that...critical to someone, regardless of how relatively small that load might be.

Switch with care!