UL924 UPS's

[mshields]

I am specifying a 3 phase, 208Y/120V In and Out UL924 Emergency UPS. The vendor I am specifying around is taking their standard model which they modify to meet UL924 by (perhaps among other things) by not eliminating the internal maintenance bypass switch but rather by installing a barrier to the 3 breakers that constitute it. i.e. though it has a MBS, the three breakers are configured for non-bypass and then bolted away never to be altered.


Apparently it is cheaper for them to do this in order to meet the UL924 requirement than it is to remove the three switches and rewire accordingly.


Can anyone tell me, what the rational is for this UL requirement. Do they not want to risk the unit being left in bypass indefinitely thereby causing an emergency circuit not to be backed by the UPS.

And if that is the rational, what of the engineer who comes along and installs an external maintenance bypass switch, thereby causing the same condition they are ostensibly trying to avoid? Which I'm inclined to do, such that they are not without power should a repair need to be made.

Any thoughts?

 

[texie]

I am specifying a 3 phase, 208Y/120V In and Out UL924 Emergency UPS. The vendor I am specifying around is taking their standard model which they modify to meet UL924 by (perhaps among other things) by not eliminating the internal maintenance bypass switch but rather by installing a barrier to the 3 breakers that constitute it. i.e. though it has a MBS, the three breakers are configured for non-bypass and then bolted away never to be altered.


Apparently it is cheaper for them to do this in order to meet the UL924 requirement than it is to remove the three switches and rewire accordingly.


Can anyone tell me, what the rational is for this UL requirement. Do they not want to risk the unit being left in bypass indefinitely thereby causing an emergency circuit not to be backed by the UPS.

And if that is the rational, what of the engineer who comes along and installs an external maintenance bypass switch, thereby causing the same condition they are ostensibly trying to avoid? Which I'm inclined to do, such that they are not without power should a repair need to be made.

Any thoughts?

First question, do they actually have the product listed this way? Or are they just claiming the product meets UL 924?
As to building your own bypass in the field I'd have to ponder that from an Article 700 perspective. Also it would seem that field building a bypass would get messy and expensive as you would have to have something like a Kirk key arrangement due to the possibility of someone closing the bypass while the load is powered by the inverter and thus out of sync with the bypass.