(1) *Don’t* — under any conditions — attempt to use the “UPS Maintenance Bypass wraparound breaker circuit on an operating UPS unless the UPS’es authorized service person has studied the “one-line” and says it’s OK to do so! Engaging the wraparound bypass in effect shorts the output of the UPS back to the input, and may be catastrophic. There is a correct sequence to do this; your authorized service person should know this.

(2) Discuss the MOPs (Methods of Operations & Procedures) with the authorized service person before doing the maintenance. Make sure you both understand exactly what will be done and the possible effects.

You specifically said “UPS maintenance” as opposed to “repair”. Most scheduled maintenance such as battery testing or replacements, inspections, etc., can be carried out using the UPS’es internal Static Bypass. While the load is not protected by the UPS during this procedure, it doesn’t require use of the “wraparound bypass”. Your authorized service person will know what needs to be done.

(3) Due to new OSHA requirements regarding Arc Flash safety, operation of certain breakers (such as external maintenance wraparound ones) may now require proper Arc Flash protection, upto and including an arc-flash protective suit and operation only by trained personnel. These requirements are fairly recent so “I used to be able to do this myself” may not apply! Remember, as bad as an outage may be, it’s nothing compared to an injury or death. Your authorized service person should have received training in the new OSHA regulations. Discuss this beforehand. In some cases, the operation of breakers required to switch the load to/from generators may now require an electrician or trained service personnel to do it..

(4) If you have generator backup and one or more ATS’s, once again, be sure you understand how they really work! I saw a case were a operator used the ATS to start the generator and transfer the load, but the ATS said “hmmm.. the utility feed seems OK” and transferred the load back off the generator midway thru the UPS maintenance! Since the UPS was in bypass, this resulted in a brief power outage, enough to take down almost everything.