BillConnerFASTC
Well-Known Member
When fixtures were all 500-1000 watts, all 12 ga made sense. When they are all 120 watts or so, I don't think it does. That's all.
@BillConnerFASTC What's the amperage rating of the breaker powering the circuit, at what voltage and what's the total peak current drawn upon initial powering?When fixtures were all 500-1000 watts, all 12 ga made sense. When they are all 120 watts or so, I don't think it does. That's all.
@BillConnerFASTC Century Strand, (Strand Century on your side of the walls) on some models of dimmer racks (possibly SV's) used to offer lower wattage dimmers with something like 17 or 18 amp magnetic trip breakers. Shaun Johnson includes 13 amp breakers on some of his installation racks; there's an installation of four of Shaun's 24 dimmer racks for a total of 96 dimmers all with 13 amp magnetic trip breakers in an amateur group's theatre near me. (That particular installation uses duplex 15 amp twist locks in all six of their distribution troughs [3 FOH & 3 back stage plus several one and two circuit boxes on the stage side of their prosc' and on the undersides of mezzanines on both sides of their stage.]) The group went with duplex 15 amp twist locks and 14 gauge cables when they built their building in 1953, long before ETC employed 15 amp twists for specialty applications.Name plate load around 1200 watts before diversity - 120VAC - 20 amp breakers. Inrush - less than 10 ms - maybe twice or more the current - but that is not going to heat anything up.
It just seems silly to drag a 12 gauge jumper to a single 120 watt light at the end of pipe or on a boom. Might as well require every practical to be fed with 12 gauge - and we don't.
If you could find a slow 10 amp breaker, will you still insist on 12 gauge? I suspect some will, because they are used to it, having grown up with 1kw lighting fixtures.
Name plate load around 1200 watts before diversity - 120VAC - 20 amp breakers. Inrush - less than 10 ms - maybe twice or more the current - but that is not going to heat anything up.
It just seems silly to drag a 12 gauge jumper to a single 120 watt light at the end of pipe or on a boom. Might as well require every practical to be fed with 12 gauge - and we don't.
If you could find a slow 10 amp breaker, will you still insist on 12 gauge? I suspect some will, because they are used to it, having grown up with 1kw lighting fixtures.
Erring on the side of caution and prudence is not, IMNSHO, a bad thing.
I wonder if we will see a new trip-curve introduced for LED distribution breakers? Seems like a waste of resources to have to design everything based on the first second of operation.
@Malabaristo Let me guess; is your expertise based on your proximity to ETC, does your expertise rise exponentially the closer you live to work??Not even the first second: inrush from electronic power supplies can often be 1mS or less. Many/Most circuit breakers have undefined behavior in that short of a time frame, but are unlikely to trip even if it's technically in the "may trip" range on the curve. In some ways, this kind of inrush is much less of an issue in practice than it sounds like it should be in theory. Not only is the time very very brief, but you also only hit those huge, peak values in ideal/worst-case conditions: fixtures located very close to a large current source, plus switching on at a 90 degree phase angle (peak of the sine wave). By the time you add a hundred+ feet of 10-12AWG wire the additional resistance and inductance involved will limit how much current can actually flow before the power supply settles down. ...and just to keep things confusing: inrush doesn't actually add linearly for each fixture. Two fixtures of a given type will often draw less than twice the inrush current of a single fixture.
Unfortunately, there aren't really any generic rules you can apply based on nominal LED fixture power because it's highly variable depending on the power supply design. One 100W fixture might have a 75A peak inrush, while another might have almost none. The best you can do is follow manufacturer recommendations (if they provide any...), and remember that will be based on those worst-case theoretical values for inrush that you're pretty unlikely to see in real life.
Erring on the side of caution and prudence is not, IMNSHO, a bad thing.
Therefore, I choose the conservative route and say not more than 10
@BillConnerFASTC What's the amperage rating of the breaker powering the circuit, at what voltage and what's the total peak current drawn upon initial powering?
@Jay Ashworth, @Pie4Weebl, @TimMc and @sk8rsdad What're your thoughts??
Toodleoo!
Ron Hebbard
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