tyler.martin
Active Member
Some brands of LED House / Work lights have a UL924-listed programmable internal default setting they can go to should the DMX source be interrupted. So, if the DMX signal system from the House / Work Light Controller goes-down, and there isn't a UL924-listed DMX transfer device, then the lights don't wake-up stupid, they wake-up to a predetermined level.
This does the same thing as a separate UL924-listed DMX transfer device that controls many lights. However, I'd rather have 90% of the House / Work lights come-on correctly (10% failure), than have none of them come on if the single separate UL924-listed DMX transfer device fails. Of course, using the 'department of redundancy department' approach would have you use the separate UL924-listed DMX transfer device AND House / Work Lights that have integral UL924-listed DMX transfer devices.
Another consideration is that the ETC device only drives up to 31 light fixtures, then you have to buy another one for the next 31 fixtures, etc. For a typical auditorium with 100+ lights, this means at least 4 of the transfer devices may be required. The Strand device will drive four lines of up to 31 fixtures each.
The illumination level required by the Fire Code is generally much less than 'FULL ON', so you can set all the LED lights to maybe 10-15% (whatever it takes to meet the code) and the electrical load on the emergency power system (generator / inverter) is significantly reduced. Less load usually means it costs less money. Example: If you have 100 houselights that can normally provide about 50 fc at FULL-ON for 200 watts each, then 100 of them at 10% could provide about 5 fc in a nice even coverage at about 20 watts each. This reduces the emergency power load from 20,000 watts to 2,000 watts. A 2,000 watt UL Listed battery type inverter that is self-monitoring and automatically reports to the Maintenance Department via pre-programmed emails will cut the long-term maintenance labor costs way down from dealing with a plethora of 'frog-eye battery packs'. The initial cost and long-term maintenance cost / hassle of a diesel generator is sometimes prohibitive.
This system design approach provides a whole-house emergency egress illumination rather than the spotty blinding effect of a bunch of 'frog-eyes'. We all know the batteries in the 'frog-eyes' don't get tested and replaced as frequently as they should, so by centralizing the load to a generator (or a single large inverter / battery) the over-all cost of the building is less. You don't need to pay for both LED houselights AND a separate 'frog-eye' system (and all the attendant labor and materials for wire and conduit). You also get the added aesthetic benefit of no 'frog-eyes'. Damn, those are soooo ugly in an auditorium . . .
ETC now makes a version of the DEBC with 6 outputs.
Unsurprisingly when looking at the cost of UL924 certified fixtures, the cost difference between having certified fixtures vs a UL924 front end control is quite high. The certified DMX fixtures having nearly a 20% premium over the standard fixtures. Now IMO, there is another downside of having the fixtures be the DMX transfer, what happens if you lose the DMX signal in a non emergency scenario... then you have your houselights/worklights forced to full because the signal is gone (intentionally or not) I've seen brands that expect a normal power sense and are fed via an emergency source, but the transfer function happens when the sense feed is lost. At that point, the cost of running two power feeds to fixtures is more than likely equal or greater than having the front end emergency control system.
I was also under the impression that a UL924 device had to have a readily accessible test switch for that function (a-la ETC DEBC)