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How many 2K's?


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#1 Allen Benson

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Posted 28 September 2010 - 04:40 PM

Hey, I'm new, can anyone please tell me, How many 2K’s can go in to one 20A circuit?

Thank you.
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#2 Chris Millar

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Posted 28 September 2010 - 04:50 PM

Where in the world are you going to be plugging in this/these 2K's ?
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#3 Allen Benson

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Posted 28 September 2010 - 04:52 PM

into a wall at my school. A college classroom. Just one right?? Thanks.
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#4 Allen Benson

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Posted 28 September 2010 - 04:54 PM

and lets say i have a 12 gauge wire curcuit
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#5 Adrian Sierkowski

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Posted 28 September 2010 - 05:06 PM

If you have a 20A circuit, and you're sure of it, you can plug in 1 2K and nothing else. Don't forget, W=VA or Watts=VoltsxAmps
I round to 100V here in the US to keep things simple and give me headroom so in this case:

2000W=100VX20A

BUT, you have to make sure it really is a 20A circuit...
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#6 Phil Rhodes

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Posted 28 September 2010 - 05:23 PM

...and for those calculations you have to be in a 110V mains part of the world, which is the meaning of the first question. Which our correspondent probably is, statistically. But we need an answer: Allen - where are you?

P
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#7 Adrian Sierkowski

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Posted 28 September 2010 - 05:26 PM

Please Phil we all know the world Consists just of American, Not-America, and Canadia. And the only place that matters is AMERICA.

I assume he's US, as I don't think you'd have a 20A breaker elsewhere in the world (I think it's 13A primarily in the EU).
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#8 Phil Rhodes

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Posted 28 September 2010 - 06:00 PM

So do I, but with my even-more-grumpy hat on, that's the sort of assumption that leads to people staggering about shrieking about the shards of metal embedded in their corneas.
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#9 Stuart Brereton

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Posted 28 September 2010 - 06:06 PM

(I think it's 13A primarily in the EU).


It is indeed, but at least it's at 240v. Being able to run a 2.5kw hmi from house power is very handy.
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#10 John Sprung

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Posted 28 September 2010 - 07:30 PM

My friends in the Netherlands have 16 Amp circuits and three phase at home. In the UK, I understand that they run loop circuits instead of the straight runs we have here.

For the original poster, given that you're in the U.S., yes one 2K is the most you should put on a single 20 Amp circuit. And you have to make sure that there aren't any other loads on it, like a toaster or hair dryer, that would trip it immediately.

A 2K nominally draws 2000/120 = 16.7 Amps, but there's a starting surge when you turn them on, so you want to leave yourself about a 20% pad. Your 2K can share a circuit with some really small loads, say a clock or a battery charger. But nothing big. This being a school, be sure you have access to the right breaker panel. Bigger buildings often have many panels, and they might not be clearly identified.




-- J.S.
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#11 JD Hartman

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Posted 28 September 2010 - 09:29 PM

Shoot, I musta done missed somethin in my years workin as a commercial/industrial 'lectrican. I always thought, incorrectly I guess, that a 2K fixture (Fresnel, blonde, mighty) is a purely resistive load, where does the "starting surge" come from? A single 2K alone, isn't going to trip on 20A branch circuit.

Why don't you mention the 2K plugging rule?
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#12 James Steven Beverly

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Posted 28 September 2010 - 10:29 PM

Why don't you mention the 2K plugging rule?


OK, I'll mention it, what's the 2K plugging rule? :D
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#13 Chris Millar

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Posted 28 September 2010 - 11:26 PM

Please Phil we all know the world Consists just of American, Not-America, and Canadia. And the only place that matters is AMERICA.

I assume he's US, as I don't think you'd have a 20A breaker elsewhere in the world (I think it's 13A primarily in the EU).


I live in the 240v demihemisphere - at work I could point to some example 20A single phase outlets ;)
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#14 Zander Kroon

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Posted 28 September 2010 - 11:51 PM

Hey, I'm new, can anyone please tell me, How many 2K’s can go in to one 20A circuit?

Thank you.

1. A 2k pulls 20 amps (safe math), 17 amps true load.


Edit: Ignore my post. Didn't see the responses.

Edited by Zander Kroon, 28 September 2010 - 11:53 PM.

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#15 John Sprung

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Posted 29 September 2010 - 01:06 AM

where does the "starting surge" come from?


The resistance of the tungsten filament varies with temperature, much lower when cold, like about a factor of 10 or 15. It heats up fast, in just a few cycles, but it does pull a current spike.

For instance, try a 100 Watt 120 Volt bulb. Should draw (100/120) = 0.833 Amps, so its resistance should be (120/0.833) = 144 Ohms when it's on. Put an Ohmmeter on one, and you'll get something more like 10 - 15 Ohms usually. With a clunky old analog meter, the needle will actually jump to about 10 then settle down to a higher resistance as the current from the meter heats the filament a little. The filament is just a piece of wire after all.

The thermometer at USC that crapped out the other day after recording a record of 113 F also works by measuring the resistance of some kind of wire, per the news report on that.

In Tremaine's Audio Cyclopedia, there's even a crude AC voltage regulator circuit from long ago that worked by using the thermal variation of the resistance of light bulb filaments.

Indeed the 2K starting surge by itself won't trip the 20 Amp breaker. But if you already have 3-4 Amps elsewhere on the circuit, it gets chancy. More so with fast fuses than with breakers, though.




-- J.S.
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#16 Phil Rhodes

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Posted 29 September 2010 - 07:17 AM

In the UK, I understand that they run loop circuits instead of the straight runs we have here.



A ring main, in the parlance. For 13A mains in houses and light industrial premises, yes, with each ring ideally being fused at 32A. A house might have a master fuse at 63A, so with over 15kW of power available, a domestic residence in the UK is not a terribly awful place to work. Needless to say, older or much-modified installations may vary, and I would reinforce Mr Sprung's feeling that it's critical to know where the breakers are before you trip one out, and to have replacement fuses of the right type available if that's what the installation uses. Householders or businesses get irate very quickly if you turn off their power for them, so it's as well to find these things out ahead of time. In the worst cases, you can end up calling out a caretaker with a set of keys and it can get hugely time-consuming. Something to do on the recce.

P


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#17 JD Hartman

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Posted 29 September 2010 - 10:34 AM

The resistance of the tungsten filament varies with temperature, much lower when cold, like about a factor of 10 or 15. It heats up fast, in just a few cycles, but it does pull a current spike.

For instance, try a 100 Watt 120 Volt bulb. Should draw (100/120) = 0.833 Amps, so its resistance should be (120/0.833) = 144 Ohms when it's on. Put an Ohmmeter on one, and you'll get something more like 10 - 15 Ohms usually. With a clunky old analog meter, the needle will actually jump to about 10 then settle down to a higher resistance as the current from the meter heats the filament a little. The filament is just a piece of wire after all.

The thermometer at USC that crapped out the other day after recording a record of 113 F also works by measuring the resistance of some kind of wire, per the news report on that.

In Tremaine's Audio Cyclopedia, there's even a crude AC voltage regulator circuit from long ago that worked by using the thermal variation of the resistance of light bulb filaments.

Indeed the 2K starting surge by itself won't trip the 20 Amp breaker. But if you already have 3-4 Amps elsewhere on the circuit, it gets chancy. More so with fast fuses than with breakers, though.

-- J.S.


If an EE spent the (un-necessary) extra time to consider the resistance, at temperature of his resistive lighting loads, he'd never get his branch circuit designs and calculations done. It's simply not a factor that needs to be accounted for. Even more so in lighting for film. Before plugging a 2K in on location, you should know if there are already other loads on the branch circuit. A clamp on ammeter applied to the hot leg of the circuit at the panelboard, will tell you that.

Fast blow fuses? Where would you encounter them? In an older building (again USA), such as an apartment, it would be more likely that you encounter a fusebox where the super or the Tennant has replaced all the 15A fuses with 20A fuses, disregarding the fact that the wiring is only adequate for 15A. Something to watch for.

The 2K rule (USA only): when connecting a 2K load, use the top part of the receptacle, this designates it as "used up". You might even go so far as to place a strip of tape over the lower part of the receptacle. This is a more difficult practice to enforce on location unless all the branch circuits have been traced and marked out.

Edited by JD Hartman, 29 September 2010 - 10:38 AM.

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#18 Bob Blankemeier

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Posted 29 September 2010 - 12:42 PM

If you use paper amps, a 2k = 20amps. However it is actually

1000w/120v= 8.333amps x 2 = 16.66 amps

Answer = You can only run one 2k on a 20a breaker.
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#19 John Sprung

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Posted 29 September 2010 - 01:06 PM

If an EE spent the (un-necessary) extra time to consider the resistance, at temperature of his resistive lighting loads, he'd never get his branch circuit designs and calculations done. It's simply not a factor that needs to be accounted for.

Fast blow fuses? Where would you encounter them?


True, it need not be computed in detail. It's part of why we use 20 Amps for a 2K instead of 16.66.... Using 20 handles it.

As for fast blow fuses, those miserable things still exist. You can accidentally buy them at Home Depot if you don't check the boxes carefully. There are lots of 1920's - 50's buildings here that still have fuses. If you see a blown screw-in fuse in a box, often the tenant has used the old trick of putting a penny under the fuse. Very dangerous, of course -- the current is limited only by the main fuse or the failure of the branch circuit wire.



-- J.S.
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#20 Ed Conley

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Posted 08 October 2010 - 10:53 AM

into a wall at my school. A college classroom. Just one right?? Thanks.


Hey Allen,

As mentioned and what you seem to already know.. yup only One 2k in the 20amp receptacle... BUT.. it gets a little tricky since there are very few Dedicated 20amp receptacles on location.

What this means is that when you walk in to a room and see several receptacles they are usually on the same Circuit Breaker. Depending on the size of the classroom you may have 2 Circuit Breakers that feed separate receptacles to work from but if yer in a Home most rooms are on One Circuit breaker. Plug in a 2k and that pretty much makes the rest of the Receptacles useless for any other lights.

12/3 extension is good to have since you can try another room for power.
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