SERIOUSLY? Does APC UPS RM series have NO SHORT CIRCUIT protection at all?

[apcthismotherpocker_apc]

This was originally posted on APC forums on 5/26/2018

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Hi. 

Yesterday I experience a very traumatic situation with a rack mounted APC Smart-UPS 1500 RM installation that I would love to share and understand.

An apparently faulty power supply interlock cable, doubtfully rated 10A, started to seriously spark, smoke and then burn the PVC interlock isolator. 

Almost immediately mains differential circuit breaker was triggered, what interrupted UPS mains but NO PROTECTION WAS TRIGGERED FROM THE UPS, which continued to provide electricity to the already sparked, smoked and burnt cable. 

I was lucky enough to be nearby and saw the whole thing from a 2 meters distance, I doubt for at least 5 seconds trying to understand what was going on and jumped to the UPS front siding panel to MANUALLY INTERRUPT UPS OPERATION!

I'm totally sure the interlock cable was to blame here, maybe acting as a fuse or just faulty, but I was more than extremely worried about NO F. PROTECTION WAS TRIGGERED BY THE UPS itself until it could either burn the whole place down to ashes or run out of battery juice.

I have several monitoring services through the APC UPS data port and, even though I understand they are not updated on-second-basis, power consumption does not show any kind of trend that would imply a dramatic load increase anywhere. UPS Load was under the 15%

I have had an implied understanding that UPS, APC or not, do have internal short circuit protections, overload protection and such kind of security features, but clearly It does not appear to. 

What am I missing here?   

[apcthismotherpocker_apc]

This was originally posted on APC forums on 5/29/2018

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Let's drive this on a different direction:

In case a power supply fails and gets shorted, which had happened to me several times in the past and gets to rarely occur nowadays, which UPS protection should be triggered? 

[BillP · Accepted solution]

This reply was originally posted by Liam on APC forums on 5/30/2018

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Hi Robert - 

You do not mention which Smart-UPS 1500 rackmount you are using, but yes, all Smart-UPS feature either breakers or internal fuses on the output of the UPS in case of an overload or short circuit scenario.

On this SMT1500RM2U for instance, you will see a pop out circuit breaker labeled "Push to Reset" to the left of the outlets: 

In addition, larger units will have multiple output breakers as well as an input breaker. All Smart-UPS are UL listed and are designed to meet local and national electric code. Line Interactive units (SU, SUA, SMT, SMC, SMX, etc) also feature an equipment protection policy in case the UPS is somehow unable to protect an attached load from damage due to a power event.

Without knowing the exact sequence of events and configuration, I can't give you a definitive answer as to why your breaker did not trip. Given the severity of the issue, I would recommend contacting our tech support team for further assistance.

thanks

Liam