Practical Volt/Amp/Lighting Help

H

Homunculus

Carbonite Member
Hey everyone. For someone that's an aspiring amateur DP and will be shooting some upcoming shorts with friends, can you guys give me some instruction as regards to not blowing up one's household when shooting indoors with various equipment.

I don't know anything about home circuits, voltage, amps, all of that stuff and would like to know more about it. Some basic guidelines or anything would be much appreciated. I plan to use some big Mole/Arri lights like 2k, 1k, etc. And along with those, rebulb a lot of the house hold lights/practicals with higher wattages.


1. What do I do to make sure the house doesn't short circuit or a fire starts?

2. How can you properly do the math for how much volts/amps/watts/what-have-you you're running as opposed to how much a particular household/room can handle? Any resources for this?

Thanks
 
WHAT COUNTRY ARE YOU IN??

volts x amps = watts.

a 300 watt bulb on a 110v circuit = 330/110 or 2.73 amps.

IN THE U.S., most newer construction has 20 amp circuits (Check circuit breakers - it's stamped on reset lever). 20 amps @ 110v = 2,200 watt potential max load. Highly recommend a 20% safety factor or 1,760 watts per circuit.

As you can see, a 2k light is going to totally use up a 20 amp circuit.

Also - most light switches are rated for only 600 watts.

Most lighting circuits are 15 amp - not 20. 15 amp @ 110v @ 80% = 1,320 watts.

Older homes/ Farms, Barns and commercial properties are a whole other story. I've actually shot locations which had old post & tube wiring.

Best ask for help if there's ever any question.

Best wishes.
 
When re-bulbing practicals - several additional considerations. Most enclosed fixtures (ceiling lights, spots, cans, etc) have maximum wattages determined by their heat dissipation capability. Usually labeled somewhere on inside. Free standing lights may have plastic bases, cheap switches, and lightweight cords.

300 watts is about the max I'd be comfortable putting through any freestanding fixture I hadn't specially built up. High output florescents are tempting for these applications but they're not dimmable.
 
Just in case you don't know. Many lighting and grip rental houses in North America will rent you a "Stove tie-in" and/or a Dryer plug. These allow you to temporarily unplug the electric stove in the home you are working and the same for the dryer. Both circuits will supply you with considerable more juice and still afford you the safety of breakers since these "tie=ins" have a breaker setup to protect the plugs that they are powering. Check with your local lighting and grip house they will explain how they work in detail but the simple explanation is you unplug the stove and plug in the device and you get 4 clean circuits and the same for the dryer with less load carrying ability. Usually these items rent for around twenty bucks a day.
 
I cannot recommend strongly enough Harry Box's Set Lighting Technician's Handbook, every serious lighting maestro's bible. The Fourth Edition just came out and I have so relied on the past versions that I pre-ordered mine months ago and have enjoyed all the new material.

It's all in there ;) You'll love it.
 
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thanks a lot for the help everyone. I am digesting the info. Slondon I will check that book out asap and probably order it on amazon. It's just I won't have time to receive it and read it before my upcoming gig for which I need all this info, so until then if you have any other useful info to share please do.
For example, how do you test for circuits in a house hold, i.e.

1. how do you know which is a 15amp and which is 20amp circuit and

2. how do you tell which outlets in a given room are part of the same circuit or which are on a different circuit if any?

thanks
 
Homunculus said:
1. how do you know which is a 15amp and which is 20amp circuit and
Click to expand...

As Pixelated said: "Check circuit breakers - it's stamped on reset lever"

2. how do you tell which outlets in a given room are part of the same circuit or which are on a different circuit if any?
Click to expand...

This is always an issue. The only reliable method is to turn off each breaker and see what goes off. Some commercial/industrial sites have the circuit/breaker number labeled on the outlet.
 
Yes.

As stated, to really know whether you have 15 A or 20 A circuits you'll have to identify the circuits at the breaker box and look at the ampacity of the breaker.

Houses vary as to which edition of the National Electrical Code, which comes out every few years, they follow. However, if the house is less than twenty years old it will probably have two 20 A circuits in the kitchen for appliances, one in the laundry and might have one in the bathroom. The rest will be 15 A. Older houses vary greatly. If you're unsure just treat all circuits as 15 A and give yourself a margin of error by figuring 15 A will supply 1500 W (actually, it's probably 15 A X 117 V = 1755 W). When you read Box's book and materials posted by our forum participant nejuicer you'll realize the wisdom of that advice because some loads such as HMIs and even fluorescents draw more than their stated power requirements. Incandescent movie lights do not behave that way.

Commercial buildings usually have one 20 A circuit per wall.

You should carry and use a circuit tester such as this one which will not only tell you if an outlet is hot but also whether it is grounded and wired correctly for the hot and neutral legs and whether, if it is GFCI protected, that it is working properly.

22-2000.jpg
 
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Slondon thanks for input but as far as treating everything as 15amp that's impossible considering I have a 2k light that's about 17-18amps so I need a 20amp to power it.

2. Where can I purchase that doohickie that you posted there? Home Depot?

3. What's the worst that can happen if you plug a 18amp light into 15amp source? Will it just trip the circuit? Or is there any possibility of fire/explosion, etc.........?

thanks
 
Here in the UK, we've more regulation than you have because of our higher voltage (230V officially, 240 for most people if they measure it!)

If you attempt to take 18A from a modern circuit with a 15A circuit breaker, then it should act as the weak link and switch the circuit off. The real problems come when you take just enough that the breaker doesn't trip, BUT the actual circuit wiring is a little dodgy in places. Lots of older places may have had many changes and additions and there's no guarantee that at some point between your outlet and the breaker the cable hasn't been replaced with smaller capacity stuff - which will overheat and potentially catch fire - eventually shorting out and then tripping the breaker.

I don't know about homes in the US, but as the average home is unlikely to require outlets that can handle major current - if anyone's interested, UK practice is not to have lots and lots of radial circuits but a few ring circuits where a number of sockets share a maximum current of 30Amps, yet each outlet can supply 13! We might have quite a few of these on one ring - so in the room here. I have 4 outlets, each one rated at 13A, yet if I go above 30, the circuit breaker trips. Oddly, this never happens - but plug in a few 2Ks and it would.
 
Interesting..thanks paulears. Wow didn't imagine using a 2k light would be so problematic.. now I'm afraid to start a fire or explode something.
 
The kitchen outlet circuits should be 20 A. Go to the service panel and use your Home Depot/Lowe's circuit tester to identify the circuits and confirm this. Make sure nothing else but your 2K is on one of them and you should be good.

How old is the house?
 
Slondon no idea the age of the house but of course it's one of the things I can find out or try to find out from the current owners/renters.
Just don't know if they will appreciate me unplugging their entire kitchen just to run a 2k light...definitely still an option I will explore but are there any other options?
I mean look, I run the 2k fine in my living room and this house here is most likely over 20 years old probably 30-40 if not more (I could be wrong).
 
A 2k on a 20 amp circuit by itself is going to be just fine - just not a 2k and anything else. You don't have to unplug the whole kitchen - just don't run the toaster/blender/microwave etc at the same time.

You unplug the fridge for sound reasons, not power. Most newer homes have the fridge on a seperate circuit.
 
AH ok. So it's fine to have it plugged in as long as no one turns on any of the other stuff?
You guys are a very big help.

By the way, where is it I can get that circuit testing device, home depot? I don't think anyone answered yet that question
 
Homunculus said:
Slondon thanks for input but as far as treating everything as 15amp that's impossible considering I have a 2k light that's about 17-18amps so I need a 20amp to power it.

2. Where can I purchase that doohickie that you posted there? Home Depot?

3. What's the worst that can happen if you plug a 18amp light into 15amp source? Will it just trip the circuit? Or is there any possibility of fire/explosion, etc.........?

thanks
Click to expand...

Well, if the circuit breaker kicks in... all should be well. But I have had devices 'smoke' before the circuit breaker trips, because the load had enough time to 'smoke', but the circuit breaker trip time was longer.

This sort of experience is not from 'lights', but industrial equipment...

I'd probably not go further than 3/4 the 'rated' power on a circuit, especially in a house that already may have stuff on a circuit...

When the Wife and I were more active in wedding photography, we would take a large power pack for strobes. That thing was capable of 'drawing' down a lot of current during the recharge cycle, and would on older homes or facilities, give a flicker/brown out on some of the lights in the room, if the shoot was at night.

As time went on, we tended to become 'very light' when it came to such equipment...
 
Also of importance: making sure the wiring is ACTUALLY rated for the breaker and socket.

As I was renovating my house I found that a lot of the breakers were 20 amp, the sockets were 15 amp(per receptacle) and the wiring was only rated for 15 amps. Plugging a 30 amp load into one of these receptacles while drawing enough load to pop the breaker, would have subjected the wiring to 2x it's rated load(which is much less than it's peak load, for safety). It might not have gone up in smoke immediately but if the breaker hadn't tripped(broken or such) then it would have heated up and potentially caused a fire.


Same thing happens with extension cords/stingers. A lot of new folks try to run some piece of equipment on an inadequately rated stinger and it'll get hot and melt, eventually popping fuses or breakers or catching fire.
 
BrianMurphy said:
Just in case you don't know. Many lighting and grip rental houses in North America will rent you a "Stove tie-in" and/or a Dryer plug. These allow you to temporarily unplug the electric stove in the home you are working and the same for the dryer. Both circuits will supply you with considerable more juice and still afford you the safety of breakers since these "tie=ins" have a breaker setup to protect the plugs that they are powering. Check with your local lighting and grip house they will explain how they work in detail but the simple explanation is you unplug the stove and plug in the device and you get 4 clean circuits and the same for the dryer with less load carrying ability. Usually these items rent for around twenty bucks a day.
Click to expand...

Where electricity can be dangerous if mishandled, I feel compelled to correct the impression Brian Murphy creates in this post. Unfortunately “Stove Tie-Ins” are no longer as simple as Brian makes them out to be. While they were an option years ago when the lighting load placed on them consisted predominantly of incandescent lights (a linear load), they no longer meet code for three wire circuits (H,H,G); and when used on four wire circuits (H,H,N,G), they are ill equipped to deal with harmonic generating non-linear loads like HMI, Fluorescent, & LED power supplies.

For those of you not familiar with “Stove Tie-Ins”, also called “Splitter Boxes,” they are a special distro panel that rental houses made up to split out the two 120V circuits that make up the 240V outlet. But, you have to be really careful when splitting 240 volt circuits. If the 240V outlet is a 4-wire 50A/240V Range plug (the receptacle has four slots: one for ground, one for neutral, and two for hot), one could use a splitter box to power linear loads like incandescent lights as long as it was wired so that each circuit had a ground and neutral. Where you run into trouble today is when the 240V circuit uses a three wire system (the receptacle has three slots: one for ground, and two for hot, and no neutral.) Many household and industrial 240V receptacles use a three wire system (no neutral) because they were wired for the sole purpose of powering single phase motors or heating elements that draw a perfectly balanced load and return no current. A perfectly balanced load doesn’t require a neutral because the single phase service legs are 180 degrees out of phase and cancel each other out – hence there is no return that would require a separate neutral.

You run into trouble with this kind of circuit when you start to pull an unbalanced load on your "Splitter Box." And, where under most production situations you can never perfectly balance your lighting load, the two 120V circuits that make up this 240V circuit will not have 100% phase cancellation and the extra current of the high leg will not have a safe return path because, by necessity, with a three wire system you have had to bond the ground and the neutral in the splitter box (after all what else can you do with the ground and neutral of your splitter box but to bond them when plugging into a three wire 240V circuit.)

There are some people that will argue that it is not such a big deal to carry current on the ground wire. I would argue that it is both unsafe and unwise to carry current on the ground wire. It is unsafe because the ground wire is intended only as a default conduit in the event of equipment failure (which is why it is permissible according to the National Electrical Code (NEC) to use a smaller conductor for the ground wire.) It is unwise because bonding ground and neutral after the service side of a main service head (which is what you have to do with the ground and neutral of a splitter box when plugging into a three wire 240V circuit.) is a violation of the NEC. To quote Mike Holt, of Mike Holt Enterprises, Inc. again: “The National Electrical Code (NEC) requires a neutral-to-ground connection to be made at service equipment only and there shall not be any neutral-to-ground connection on the load side of service equipment [250-23(a), 250-24(a)(5)]” (full excerpt is available online at his website) If some one were to fall off a ladder because they took a non-lethal shock because the cable they were handling was carrying current on the ground wire your liability insurance would be null and void because you were using equipment that need not meet code.

On four wire circuits (H,H,N,G), Splitter Boxes are inherently unsuitable to carry non-linear loads consisting predominantly of non-Power Factor Corrected HMI, Fluorescent, & LED Lights. Since non-linear loads cause current and voltage to be out of sync, the phase currents no longer entirely cancel when they return on the neutral. In addition to pulling the voltage and current out of phase, the Switch Mode Power Supplies of electronic lighting ballasts create harmonic currents that stack on top of one another, creating very high currents returning to the power source on the neutral wire. For this reason, on their website Kino Flo cautions users that some of their lights “will draw double the current on the neutral from what is being drawn on the two hot legs... it may be necessary to double your neutral run so as not to exceed your cable capacity” (FAQ “Why is the neutral drawing more than the hot leg”.) The neutral wires of 240V receptacles are simply not sized to handle the higher return current generated by loads that stack on the neutral rather than cancel out. Splitting a 240V circuit designed to power primarily heating elements and compressors, to instead power field production equipment and motion picture lights is an application for which these circuits were simply not designed.

In the modern world of Switch Mode Power, older power generation and distribution systems, like AVR generators and Splitter Boxes, are simply no longer capable of managing the adverse effects of the harmonics that the Switch Mode Power Supplies (SMPSs) of non-Power Factor Corrected HMI, Fluorescent, & LED lights generate. The 240V circuits Splitter Boxes use, were designed, not for harmonic generating non-linear loads that will generate high neutral returns, but for single phase linear loads like dryers, ranges, heaters, large motors, and compressors, that draw a perfectly balanced load and return no current on the system neutral.

The only safe legal way to pull power from three and four wire 240V wall outlets is to run your lighting load through a 240v-to-120v step down transformer like the one we manufacturer for our modified Honda EU6500is generators. A transformer will convert the 240 volts supplied by household 240V receptacles back to 120 volts in a single circuit that is the sum of the two legs of the circuit. For instance, a transformer can make a 60A/120v circuit out of a 30A/240v dryer circuit that is capable of powering bigger lights, like a 5k or 4k HMI. What makes it safe to plug a step town transformer into three wire 240V outlets is that the transformer automatically splits the load of whatever you plug into it evenly over the two legs of the 240V circuit so that, in the case of linear loads, you have 100 percent phase cancellation. In other words, where there is no high leg, the loads on each leg of the 240V circuit completely cancel out and there is no return that would require a separate neutral. In the case of non-linear loads - like non-Power Factor Corrected HMI, Fluorescent, & LED Lights – a “K” rated transformer and beefed up neutrals in the secondary distribution system will successfully mitigate the adverse effects of harmonics on the secondary side, isolating the power source (in this case the 240V Outlet) from them.

If you do not entirely understand the inherent problems in using Splitter Boxes today, use this link - http://www.screenlightandgrip.com/html/emailnewsletter_generators.html#anchorTransformer/Distros%20verses%20Splitter%20Boxes - to a technical article I wrote for our company newsletter that explains how to use step-down transformers on set. .

BoxBook.jpg

This article is cited in the just released 4th Edition of Harry Box's "Set Lighting Technician's Handbook" and featured on the companion website "Box Book Extras." Of the article Harry Box exclaims:

"Great work!... this is the kind of thing I think very few technician's ever get to see, and as a result many people have absolutely no idea why things stop working."

"Following the prescriptions contained in this article enables the operation of bigger lights, or more smaller lights, on portable generators than has ever been possible before."​

Since a transformer can safely and legally give you access to more house power through common 240V house outlets, often eliminating the need for tie-ins or generators, it is well worth reading. The article is available online at http://www.screenlightandgrip.com/html/emailnewsletter_generators.html.

Guy Holt, Gaffer, ScreenLight & Grip, Lightng & Grip Rental in Boston
 
does anyone know if a school room, class room, or daycare center type room, what sort of recepticals they have? I will be shooting in a few weeks in one of those and wondering if they have 20a circuits and will handle my 2k light?

Also can anyone confirm, is there any electricians tool I can purchase that you plug into an outlet that tells you the amperage or wattage of that outlet?

Thanks
 
No way to tell really. There are no devices that can tell you the maximum current of an outlet either. You might just have to ask the management or custodial department what breaker size they are using for that area. I doubt they put anything more than 15A in though. Also beware that they might have only one circuit for each room too..
 
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