I'd like to get some opinions on UL 924 from some people other than lighting controls salesfolk. From what I have seen, there are two methods that people are achieving this, bypass shunt relays or entire panels.
In terms of relays, the shunt relays are normally closed relays that opperate in parallel. since they use a normal power circuit to remain open, they have to be in a separate section than the normally open relay fed by emergency power that controls the lighting under normal circumstances. This method could be considered better because of redundancy but now I have all these extra relays or contactors, which could also mean more failure points, and more difficult troubleshooting/maintenance.
Emergency panels have a single device that triggers the panel to close all relays on when normal power is dropped. This means that the relays are probably all normally closed, or the panel is fed by emergency power to close normally open relays. Theatrical dimming panels use this method too to turn on any dimmed loads in an emergency. This method may not have the redundancy, but it is simple and straight forward. And considering relays are rated for thousands if not millions of switching cylces these days, I don't think I am too concerned.
My specific problem is this. I have designed lighting controls for a jail. In my LCPs I have 120V normal, 277V normal, 120V UPS (Not emergency), and 277V emergency. Some of the 277V loads, both normal and emergency are actually 2-pole, 480V loads for site lighting. All of the lighting control manufacturers say they can handle this, which turns out to mean different things. The submittal I got was of the relay type, but 4-pole contactors were used instead of relays. Most won't fit in the panel, so I will have all these contactors outside the panel! I asked about them, and the sales guy started talking about the two types of UL 924 systems I mentioned above and proceeded to tell me that the panel style, where all the relays go closed, "wasn't really" a legitamate way to do it. Why is it UL 924 rated then? I am a big fan of the KISS principle and this submittal doesn't seem to follow that.
Any other experiences to share or advice?
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