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Will I blow a fuse?


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#1 David Sweetman

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Posted 23 January 2006 - 11:13 PM

I hope this is not a over-done topic, but I didn't really know what to search for...

I recently purchased a Mole open-face 2k and a "Mole" clone fresnel 1k.

I know that there are formulas to figure out how much you can use without blowing a fuse. I will be using these in standard US household outlets, I guess 120 volts, but I'm not sure. I would love to hear any methods you use when shooting on location to figure out how much light you can plug in and where.

I recall hearing something about W=AV, watts=amps x voltage. If this is correct, please explain how to use it in a practical manner.

Thanks in advance
-Dave
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#2 David Mullen ASC

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Posted 23 January 2006 - 11:34 PM

You can just round off and say that a 2000 watt (2K) lamp needs 20 amps (it needs slightly less than that but this gives you some wiggle room.) It's easy to remember. So a 1K needs 10 amps, or two 1K's need 20 amps, etc.

Check the fuse box to see how many amps each circuit is wired for. Most modern households have 20 amps circuits, but sometimes you run into 15 amp or 10 amp circuits, especially in older houses (and if shooting in a house with the old screw-in circuit fuses, get some spares, and put the right type in the right circuit -- i.e. don't try and screw in a 20 amp fuse for a 10 amp circuit.)

Now remember that other items may be sharing that circuit, which can cover multiple outlets, often those along one wall, but not always. Refrigerators, overhead lamps, etc. may also be drawing power and add to the load, so just because you have a 20 amp circuit, doesn't mean you can plug in a 2K if other objects are drawing power too.

The best thing is to label every wall outlet with some tape to mark which ones share the same circuit. You can go to the breaker box and turn off every breaker except one, and then go around and plug in a light into the outlets to discover which ones belong to the circuit that is on, then mark that outlet so you know how much power you are plugging into each circuit. Also remember that long extension cord runs can cause an extra load on the circuit.
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#3 Tomas Koolhaas

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Posted 24 January 2006 - 12:15 AM

I hope this is not a over-done topic, but I didn't really know what to search for...

I recently purchased a Mole open-face 2k and a "Mole" clone fresnel 1k.

I know that there are formulas to figure out how much you can use without blowing a fuse. I will be using these in standard US household outlets, I guess 120 volts, but I'm not sure. I would love to hear any methods you use when shooting on location to figure out how much light you can plug in and where.

I recall hearing something about W=AV, watts=amps x voltage. If this is correct, please explain how to use it in a practical manner.

Thanks in advance
-Dave


Hi,
Amps= WATTS divided by VOLTAGE. so a 2000w light on 120v power = 2,000/120=16.66666 which is rounded off to 20 for safety. So as David said most modern curcuits are 20A so you could probably put a 2K and another smaller light(s) on the same circuit, but rounding it off to 20A is safer in case there are any other aditional power drains on the same circuit you are not aware of.
In Europe the voltage is higher so you can run more off a circuit with the same Amperage.
Cheers.
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#4 David Sweetman

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Posted 24 January 2006 - 12:47 AM

Awesome, thanks for the replies.
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#5 Laurent Andrieux

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Posted 24 January 2006 - 06:10 AM

In Europe the voltage is higher so you can run more off a circuit with the same Amperage.


Yep, it's 230 V instead of 120 V. Nearly the double ! B)
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#6 Matt Sandstrom

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Posted 24 January 2006 - 08:39 AM

In Europe the voltage is higher so you can run more off a circuit with the same Amperage.

yes, but the circuits are rated lower accordingly. the typical wattage is the same.

/matt
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#7 Laurent Andrieux

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Posted 24 January 2006 - 08:52 AM

yes, but the circuits are rated lower accordingly. the typical wattage is the same.

/matt


I don't get that... With a 230 V supply, you can get 2300 W from a 10 A plug...
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#8 Matt Sandstrom

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Posted 24 January 2006 - 10:14 AM

i'm not sure what it is you're not getting. by rated lower i mean we have lower amp fuses here in europe, thus the available wattage turns out about the same despite the higher voltage.

/matt
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#9 Laurent Andrieux

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Posted 24 January 2006 - 10:46 AM

lower amp fuses here in europe


Don't know, David was talking about 10 A and 16 A lines, that we also have here in France, I mean in "houses", but also we often have 32 A washing machines commonly...
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#10 Matt Sandstrom

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Posted 24 January 2006 - 11:05 AM

well, whether it's true or not is another question. i though you "didn't get it". :-)

in my fuse box here at the office there are mostly 10 and a few 16 amp breakers. the "washing machine" connector has three 16 amp ones. when i lived in the u.s. we had 20 amp fuses in our apartment, iirc. and i never experienced not being able to plug a 2k into any outlet, which suggests that if 10 amps are used there it's rare. old buildings? hotel rooms?

/matt

Edited by mattias, 24 January 2006 - 11:05 AM.

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#11 Laurent Andrieux

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Posted 24 January 2006 - 11:25 AM

Ok, I get it, from reading again David's post as well.

I realize that usually here, 10 amps fuses are for "built-in" light circuits basically (at the cellar, in walls), not for plugs. You usually have 16 A avaiable in plugs. I mean in modern houses, not old ones.

But ok, I see that in US you more commonly have 20 A for plugs. Thanks for the info.
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#12 John Pytlak RIP

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Posted 24 January 2006 - 12:20 PM

The fuse or circuit breaker current rating used for a given circuit usually depends on the gauge (thickness) of the wire used. In the USA, a 14-gauge wire must be limited to 15 amperes, a 12-gauge wire must be limited to 20 amperes, a 10-gauge wire is normally limited to 30 amperes. The circuit breaker used should be less than the rating of the outlets used (e.g, if the outlet is rated for only 20 amperes, you should NOT use a circuit breaker of over 20 amperes, even if you use thicker gauge wire).

Any circuit used in a damp location or where accidental body leakage electrical ground and "hot" may occur (bathrooms, kitchens, basements, outdoors) should be protected by a ground fault circuit interrupter (GFCI) that shuts off the circuit instantaneously if there is any shock-producing leakage (through your body) to ground.
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#13 Hal Smith

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Posted 24 January 2006 - 12:41 PM

A good place to get more amps is the circuits used for ranges and dryers. For instance: my house has two 50 amp 240 volt breakers for them. If you unplug the dryer or range, all those amps are available for use. You can break down those 240 volt services into two 120 volt services for lighting (a 240 volt service is two 120 volt services back to back with neutral (ground) in the middle). If I unplug both my dryer and range, my house has 24kW of available power lying around waiting to heat up some lights. More or less modern houses usually have at least 48kW of power coming into them (200 amps @ 240 volts). I am talking about RESIDENTIAL power here - larger commercial buildings often have 3 phase "Y" or Delta service, you can "Jeep" into that power safely but the rules get more complicated.

The safest and best way to confiscate some of that power is to build a separate box (distro) out of Home Depot (etc.) supplies. You'll need a matching range or dryer cord, a circuit breaker box with perhaps 8 spaces, 20 amp breakers, conduit quad boxes (METAL!) to mount convenience outlets in, cover plates, misc. short pieces of conduit and matching connectors, and a good DIY household electrics book for reference. You'll probably want to use a 20 amp breaker for each pair of outlets (4 plugs) - remember each 1000 watts is close to 10 amps (actually 8-1/3 amps). Wire the individual circuits with #12 wire - it's rated for 20 amps on reasonably short runs. Don't scrimp on wire size - if its too small it'll drag your voltage down which in movie work will cause lighting color temperature problems - your 3200K halogens may drop down to 3000K, etc. Buying an inexpensive meter to test the voltage at each outlet after construction will avoid any REAL unpleasant experiences such as accidentally wiring the 120 volt outlets with 240 volts - if you do that, your lights will be REAL bright for about two seconds - then you'll need new bulbs. By having "daughtered" your distro off one of the existing range or dryer breakers in the house, if you do something real stupid that breaker will trip and save the house's wiring.

If you're nervous about DIYing the above, find a working household or industrial electrician and beg him/her to build the distro for you - doing it the way I described is child's play for someone who does construction electrics for a living. Or you could find a gaffer. :)

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#14 Phil Rhodes

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Posted 24 January 2006 - 03:18 PM

Hi,

In the UK, each floor of a recent domestic house will generally have a 32A ring main, with perhaps a dozen or so 13A outlets. So, 3120W per socket, or 7680 per ring. There will also be one or more "cooker circuits" which are probably 32A each. However, the company fuse on the incoming mains will usually be 64A, so you have access to a total of just over 15K in a house with diversity.

Phil
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#15 Marc Alucard

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Posted 24 January 2006 - 03:31 PM

To the best of my knowledge in the US if you split a single phase 220/240volt dryer or kitchen circuit you can only pull the original current available from the combination of each leg. The neutral wiring in the house will not be large enough to handle twice the current if you split it as you describe.

Or I could be wrong.

Cheers,
Marc
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#16 Luke Prendergast

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Posted 24 January 2006 - 05:25 PM

you can only pull the original current available from the combination of each leg. The neutral wiring in the house will not be large enough to handle twice the current


Neutral in a multi-phase circuit carries the DIFFERENCE of the current draw on all the other phases ie., 10 amps from one leg, 15 from the other, 5 amps through the neutral. Hence the relatively skinny neutral wire in a multi-phase circuit.
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#17 Marc Alucard

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Posted 24 January 2006 - 05:43 PM

In the US almost all homes have single phase power. For my machine shop tools I need to generate the third leg.

Cheers,
Marc
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#18 Laurent Andrieux

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Posted 24 January 2006 - 05:51 PM

If you have a ground connect, multiphase would be provided by 4 legs, am I wrong ? But in France, when we we have multiphase, it's usually three, meaning 5 legs.
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#19 Luke Prendergast

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Posted 24 January 2006 - 06:00 PM

415v 3-phase (240v between any phase and neutral) is common in Australia, but for industry, not household. Active, Active, Active, Neutral, Ground.
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#20 Laurent Andrieux

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Posted 24 January 2006 - 06:04 PM

Exactly, though in France it's 380 V (or may be was it when it still was 220 V and then would be 415 V since it's 230 V nowadays ?)

Anyway, don't mistake, neutral and ground are not the same, despite what somebody said here before.
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