True1 <--> PowerCon converters?

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.
 
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.
@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.
Toodleoo!
Ron Hebbard
 
As a general principle the Code requires all branch circuits to protected commensurate with the ampacity of conductor and attached wiring devices.

The question would be "is a JUMPER an extension of the branch circuit wiring or it is *strictly* appliance wiring and subject to a different part of the Code"?

A practical consideration is one of having difference jumpers of varying ampacity. I'm a big believer in ONE cable size/type to prevent misapplication. Erring on the side of caution and prudence is not, IMNSHO, a bad thing.
 
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.

BTW, current NEC does not require a 12AWG portable cord on an 20A branch circuit. Section 240.5 allows a portable conductor as small as 16AWG on a 20A circuit. Now, that does not mean you are allowed to draw 20A through a 16AWG conductor, just that it's allowed on a 20A branch circuit to feed a load appropriate for 16AWG as determined by table 400.5(A)(1).

And, the Listing of any fixture will specify the maximum branch circuit size it can be connected to. And, it may come with a supply cord as small as 18AWG, and still be code compliant and Listed (think about a table lamp) for use on a 20A branch circuit.

The problem comes when the fixture includes a feed-through outlet rated at 20A (almost an entertainment industry norm in 2019). Now all bets are off, and we need a 12AWG cord, because we assume the user will just keep daisy-chaining until the breaker trips. In this case, the fixture is acting both as a portable cord and a listed utilization device. So, the 12AWG cord is no longer optional, it's required by the conditions of Listing--no matter how small the current draw of the fixture itself.

For more electrical esoterica in this vein, see the attached article from the Spring 2019 issue of Protocol.

ST
 

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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.
 
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.

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.
 
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.
@Malabaristo Let me guess; is your expertise based on your proximity to ETC, does your expertise rise exponentially the closer you live to work??
Toodleoo!
Ron Hebbard
 
Therefore, I choose the conservative route and say not more than 10

Well, we agree, and I use 1200 watts as the load schedule. (Because I was told once by an ETC rep a ColorSource is 120 watts - but checking before I posted here I see by datasheets the spot is 147, the cyc is 133, and the par doesn't say. Maybe I'll up it to 1470)
 
"@billConner What kind of meter measures the stiffnes of a circuit and what units is it measured in?" Units are amps, measured with a very FAST ammeter. But you'd best need to calculate the impedance of the power co's feeders, the step-down transformer (or the poco will give you this number), the feeder to the dimmer rack (or other source of power to the circuit in question), and the circuit you're dealing with to know the number. Just like calculating max short circuit current when designing a panel or its components. Conservative guess, 10 kA.
 
Googling doesn't add much clarity. One answer:

"Stiffness is definded in IEEE Std 100-1996 (Electrical Dictionary) as:
The ability of a system or element to resist deviations resulting from loading at the output."

Clearly a lot of different ideas of what this is but "abstract' is a term that comes up s lot and impedance, so maybe measured in ohms.

Seemed to be a concept that use to come up in relation to measuring rise time of dimmers. Less stiff service resulted in longer rise times.

Nice to know that there are still things for future generations to figure out.

I did wonder if all LED systems were less susceptible to less stiff (flaccid?) service because the load varies less.
 
I would, absent any other standard, measure and express "stiffness" in terms of the series impedance in the Thevenin equivalent circuit. For a purely ohmic impedance, a voltmeter and ammeter and loading resistance are all that would be needed; if capacitive or inductive values must also be considered (and they probably ought to be), I think one would need to consider the changes over (short) time periods following a step change in the load, or do something else equivalent.

This isn't very much different from how a car battery gets load tested, among other things. It's not exactly voodoo, even if it's not an especially common or standard test to make on an electrical supply system.
 

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