Electrician in the house, the one I don't want to burn down?
June 6, 2013 4:47 PM   Subscribe

I want to start shooting some videos at my apartment, but I want to do it safely. It will involve using lights which might draw significant power, not always linearly. The building is from 1928, with what I understand is old wiring. I need to find a way to measure the capacity of my circuits.

The building changed ownership several times and I got vague descriptions over the years about the state of the electrical lines here. I was told by one person that the wiring is very old, probably from the original 1928 construction, with failing isolation that is just falling off. I was told conflicting stories about which outlet is on which circuit, with one person telling me that all the outlets and all the lights in my apartment are on the same one circuit (the unit has 4 apartments).

However, I'm not sure how much I can trust any report by semi-involved landlords past and current (who just bought the building).

For example, my apartment has it's own breaker box (a breaker box, not a fuse box, which might indicate more modern solutions), but the wiring that's sticking around looks ancient, with greasy cotton isolation.

Inside my apartment box there are three breakers. One has a 20 on it (I assume amps) and next to it somebody wrote "plugs" with a marker. Two breakers have a 15 on them and next to them in marker "lights".

Now, does the fact that there is only one breaker with "plugs" written on it (20 amps) mean that all my outlets are indeed on the same circuit, while the overhead lights are on two circuits (15 amps)? Also, I was under the impression that really old electrical systems had very low amperage, so I was surprised to see a "20" on the "plugs", rather than f.ex. a "10".

Here is what I want to know:

1)What is the capacity of any outlet in my apartment

2)Which outlets are on the same (maybe all) circuit, and which are on a separate one

3)What is a safe amount of power to draw from my outlets

How can I test this? I understand that it's something of a rule of thumb that household AC power is anywhere between 1500 - 2000 watts cumulatively. So, using the amp=watts/volt formula, a 20 amp breaker means I can pull 2000 watts, right? Ordinarily in the U.S. it's 120volts, but I'm being conservative and going with 100.

So, if all my outlets are indeed on the same circuit, I can use lights that cumulatively pull no more than 2K watts (after I turn off all other electrical devices, like refrigerator, fan etc.). However, obviously I will need to do under that number if I'm using HMIs because those lights pull a huge initial charge before settling down to their rated wattage.

Anyhow, I'm not clear on a few things. If all my outlets are on the same circuit does it mean that I can use any single grounded outlet for the full 2K, or is there still a reason to distribute the lights to different outlets even though they are all on the exact same circuit? Could it be that, f.ex. somehow the main line has been upgraded (hence the 20 amp breaker), but the lines going from that to different outlets are the old original wimpy lines, so it still makes sense to try to distribute all the lights so that the old wiring in any single outlet is not overloaded by a full 2K watts?

How do I test all this? What equipment do I need to purchase? Or should I simply hire a licensed electrician and have him measure out everything?
posted by VikingSword to Home & Garden (13 answers total) 2 users marked this as a favorite
 
Best answer: Not an electrician, just a homeowner who's done a bunch of inspected electrical work on his own home...

First, I'd verify what those breakers actually control. Throw them, and see what goes off. The "15" and "20" are indeed amps, and should correspond to roughly 1800 watts and 2400 watts respectively (to a first approximation, Watts is Volts times Amps, you're on 120 Vold circuits), but in my humble and under-informed opinion you'd be a fool to draw more than 1800 watts (the usual max for a 15A appliance) from any circuit unless you know what the wiring looks like.

You'd definitely be a fool to draw more than 15A/1800 Watts from any socket unless it's got an additional slot for one of the normally parallel pins to be perpendicular to the other (ie: It's actually a 20A socket and not a 15A socket).

I'd also suspect that your licensed electrician can't really measure (non-destructively) what you want to know, which is the state of the wiring and sockets inside the walls, and what the path back to the panel is from any given circuit.

So I think the thing you can answer solidly is #2, and you do that by plugging things in, verifying that you have power, turning off the breaker, verifying that you don't have power.

On the "really old electrical systems had very low amperage": My house was built in 1947, I recently ripped out all of the old Knob & Tube and replaced it with Romex. All that K&T was, at a glance, #14ga or #12ga wire, which is good for 15A or 20A respectively. But when we moved in, the entire house had a 60A feed to a fuse box, and the first thing we did was get that upgraded to a 200A feed to a breaker panel (and I hired an electrician to do that so they'd deal with PG&E). Is upgrading your panel and running a few special purpose circuits (even just a few sockets right by the panel you can run heavy extension cords from) an option?
posted by straw at 5:04 PM on June 6, 2013


Response by poster: Is upgrading your panel and running a few special purpose circuits (even just a few sockets right by the panel you can run heavy extension cords from) an option?

I don't know. I don't own the building, I'm renting. I suppose I'd have to get clearance from the owners, which might be tricky. What's involved? How much $ are we talking about, if I hire an electrician, does s/he need some kind of clearance from the power company?
posted by VikingSword at 5:20 PM on June 6, 2013


Kind of a tangent, but there are some really good modern LED movie lights. One of the best things about them is that they don't use tons of power or get hot, so they're ideal for shooting at home.
posted by drjimmy11 at 5:34 PM on June 6, 2013 [1 favorite]


Response by poster: drjimmy11 - I know all about LED lights. However, they lack in brightness, the quality of light is not very good (multi-shadows etc.), color rendition is generally poor and so forth. They have their uses - and I own quite a few - but they are not a substitute for tungstens and daylights. If you need *hard light*, LEDs are not ready as yet; they are evolving and in time might get there, but today they are still very limited and expensive.
posted by VikingSword at 5:59 PM on June 6, 2013 [1 favorite]


I understand why you don't like LED lights, but you are in a situation where that's probably your only good option. I wouldn't draw more than 1500 watts in your situation since you don't know the condition of the wiring, and that's not enough to do much of anything with standard lights. Better to use LED than nothing at all. If this is a project where using an LED light fixture is going to ruin the project, you need to reevaluate what you are doing. Having a hard light is great, but you aren't going to get enough light for much other than night sequences where you don't have to worry about fighting a bunch of blue light from outside.

The cost of rewiring your place is going to be crazy expensive, and it is doubtful your landlord would even let you do it.

So, my suggestion would be to find some LED lights which you can work with, knowing their limitations, and when you really need that 5K worth of hard light you use a generator outside.
posted by markblasco at 6:59 PM on June 6, 2013


Response by poster: I have experience with lighting, so I've got a pretty clear idea of what I can accomplish with which lights. The biggest light I might use would have a 1.2K draw - you can get pretty intense hard light from a mere 1.2K HMI (for daylight) or for tungsten 750W Source 4 PARs or PARnels, which still leaves room for some 250/150 fills and kickers and still not go over 1500-1600W cumulative. Cameras are so sensitive these days, with native ISOs in the 800 and up you get almost noise-free footage, so I don't need tons of light. Also, since these are interiors, I can always flag or ND windows so I'm not fighting daylight. Exteriors is a different story, but it doesn't apply much, since in my apartment I'll be shooting interiors. What is more important to me is the quality of light than the brightness, and for quality of light LEDs are nowhere near tungstens as yet, so that's where I'm at.

Anyhow, I don't want to derail this too much into discussing LEDs, because I'm well aware of this option, having owned and used a whole bunch of them, this is more about how to not burn down the building.

Of course, if there is no way to tell the quality of the wiring without tearing them out of the walls, then I guess I'm screwed. Not being an electrician, I was hoping there might be something like measuring impedance from one end to the other and getting an idea of the state of the wire conductivity and hence it's general robustness - if you see that you're dealing with 12 gauge wire, but it's pushing through like it's 16, then obviously it's fraying somewhere along the path, etc. - it can't tell you everything about the state of the isolation of course, but I thought maybe there are some tricks I'm unaware of. Anyhow, throwing this out to the hive mind, since I don't know much about this and for me safety comes first - I'd rather pull 1.5K safely than take a risk with 2K never mind what the nominal amperage of the breaker says... and I can live with 1.5K.
posted by VikingSword at 8:51 PM on June 6, 2013


Best answer: an idea of the state of the wire conductivity and hence it's general robustness [ . . .] it's fraying somewhere along the path

The thing is, wire installed inside walls is often (maybe usually) solid-core - one relatively large piece of copper wire inside the insulation sleeve rather than a bunch of very small wires twisted together. So there's not much to really fray or break or reduce the conductivity.

In any case, the potential issue is with the state of the insulation sleeve of the wire. Pull too much current, the wire heats up, the insulation melts, the hot wire comes in contact with something flammable, problems. I don't know of any way to check what kind of shape the insulation is in except visually.

straw's got a point that the standard wall outlet is technically rated for 15 amps. I won't say I haven't pulled more than 15 amps off a single outlet, but I will say that I've seen melted plugs and outlets, and I will say I've never done it in the apartment where I'm living, y'know? So yeah, at the least I'd distribute to different outlets.

Testing the basics is easy; buy a circuit tester for a couple of bucks from a hardware store, or probably even a nearby drugstore. Leave the breaker on and check that all your outlets are on (and wired correctly, while you're at it.) Then flip off the 20 amp breaker marked "plugs" and go back around and check that all the outlets are off. If some are still on, flip the other breakers one at a time and see if they turn off. Turn on your overhead lights, flip one of the "lights" breakers, see which lights go off. If you wind up with all 3 breakers you have access to turned off, but you still have lights on or live outlets, then they're wired who-knows-where, and I'd avoid those outlets for this project. There might possibly be an additional breaker box by your electric meter or in a basement or utility room, if you can get to them.

You might look into renting a small generator. The Honda 2K gennies are what they say on the tin - portable, very fuel-efficient, and very quiet. Maybe not "shooting movie dialogue in the same room" quiet, but if you can figure out a way to put it outside or maybe even in a different room and run a 12 gauge extension cord through a mostly-closed window or door, you've got some additional power available pretty cheap.
posted by soundguy99 at 10:20 PM on June 6, 2013


Best answer: I'm an electrician but obviously I'm not your electrician and I haven't seen your installation (IE: there may be some gotcha that totally invalidates what I'm about to type that you don't even know you are failing to notice). Definitive answers can only be provided by a professional able to inspect the complete premises.

First off breaker panels didn't exist in homes in any significant quantity in 1928 so your wiring has been at least somewhat updated at some time since the apartment was built. Breakers in general didn't really make the upgrade path in small demand apartments like yours until the 70s so it is likely the panel was put in after 1970; a picture of the panel and especially a clear picture of any of the labels could really narrow that estimate down.

That doesn't mean your actual wire was updated. It was (and still is in certain circumstances) legal to connect 1928 state of the art tube and post wiring to modern service equipment. Even the presence of NM in the breaker panel might mean they only upgraded the wire to the first device.

Second it's unlikely that a unit small enough to only need three circuits would have two of them dedicated to lights though there is a lot of YMMV mostly driven by access and existing infrastructure. Is the insulation you can see for sure cotton or is it possibly paper? Impregnated paper over rubber was used into the 80s (recently enough that around here you see it on aluminum wire). The cotton stuff is generally older. Again a picture could help me narrow it down.

Turning each breaker off in turn and seeing what doesn't work is an easy thing that you can do to map out what is feeding what and is a good first step.

Third yes the 20 and 15 is the amp rating of your circuits. Circuit breakers (and fuses for that matter) aren't immediate trip devices. IE: they don't stay closed at 14.9A and then immediately trip at 15.1A or even 16 or 17 amps. You can load a 15A breaker with 20 or 25 Amps for a short period and it won't trip (the less the overage the longer you can load it). Most breakers will handle 10-20% overage indefinitely. So depending on how long and how much your lights draw at start up you might not have to account for the warm up current.

Is the 20A a single breaker or is it physically twice as big as the 15A breakers? It's pretty common for plugs to form a Multi Wire Branch Circuit where a single double breaker controls two circuits thereby doubling the power available to you.

Your lights are a continuous load assuming you aren't turning them off and on every 10 minutes or something. Therefor derating your use to 1500 and 2000 watts is prudent. Also some receptacles are only rated for 12A so spreading your loads out onto different receptacles is a good idea.

straw: "I'd also suspect that your licensed electrician can't really measure (non-destructively) what you want to know, which is the state of the wiring and sockets inside the walls, and what the path back to the panel is from any given circuit.
"

A well equipped electrician can megger the circuits which will give an indication of the condition of the wire insulation and interconnect/splice conditions. They can also tone the circuit out to see where it goes but it'll be a lot cheaper to do that experimentally with a bit of time and a plug tester.


VikingSword: "I suppose I'd have to get clearance from the owners, which might be tricky. "

If it's just an inspection (IE: you aren't asking the Electrician to do any repairs/upgrades) I'd risk it.


VikingSword: "How much $ are we talking about, if I hire an electrician, does s/he need some kind of clearance from the power company?"

An hour or two (say less than $200) for a basic look see. Meggering all the circuits if required (which it probably won't be) would depend on the number of outlets/fixtures but figure quite a bit longer.

This isn't anything your power company cares about. Your electrician won't even need a permit because they aren't changing anything but be aware that your electrician will be legally and morally obligated to alert authorities if he sees something dangerous that your landlord won't fix. The urgency will depend on the degree of the danger. In other words a lack of GFCI in the bathroom isn't a problem but a series of parachute splices or something would have to be dealt with.

PS: You have experience with lighting but have you thought about how much heat 2000W is in a little space with the windows closed? If you don't have central air you might want to consider reserving power capacity for a fan or two.
posted by Mitheral at 11:14 PM on June 6, 2013 [2 favorites]


Another option might be batteries, so that you slowly draw power overnight to charge the batteries, then discharge them "off-line" to power the lights. How many hours a day do you need to power the lights? A computer UPS "uninterruptible power supply" might work for you.
posted by at at 8:20 AM on June 7, 2013


Response by poster: Mitheral, that's an amazingly comprehensive answer, thank you. On the cotton - it's absolutely some kind of threaded criss-cross material, looks like that very old isolation sleeve on phone receiver lines way back when - can't say if it's cotton, but it's definitely some kind of rag. And yes, the 20 amp breaker is about twice as fat as the 15 amp breakers.

Re: heat - yes, it can get hot, but thems the breaks(!), talent has to sweat. Batteries: can't imagine it will be near enough output to power the high demand lights I'll be using. Generator: that has of course been the option all along, though I think I might need something beefier than 2K on account of large initial draws of lights like HMIs.

My next step is to get a circuit tester as suggested by soundguy99 (thank you!) and test all my outlets.

Thank you everybody for your answers! I'll proceed carefully, and hopefully there's no electrocution or fires in my future.
posted by VikingSword at 10:35 AM on June 7, 2013


Best answer: There's a rule for you: do not operate a continuous load over 80% of the breaker rating, so no more than 12A/16A on the 15A/20A circuit, respectively. Or 1440W/1920W in power terms.

Screw-in light fixtures are not rated to handle a high number of amps, so no more than say 3-4A per fixture (so if you have multiple lights drawing 3A each, feel free to plug four into four different fixtures on that 15A circuit).

If you follow the above rules, you are using the circuits as they were intended. Because of those hot lights in a small apartment, I would keep a fire extinguisher handy if you don't already have one.

Strangely enough, often old circuits are heavier wire gauge in older houses because there were only a few separate circuits, so they had to have enough capacity to run everything. A lot of residential outlet circuits are only 15A, while you can see your circuit is 20A.

If you follow the 80% rule, don't worry about the surge of current on initial turn-on. That's part of the reason for the 80% rule. Now, if you turn all your lights on at the same instant, you could get a nuisance trip; just turn the lights on one at a time if that becomes an issue.

It is a good idea to plug into as many separate outlets as convenient even if they are on the same circuit, because the contacts get loose over a long time of use and heat up more than they should. Or you could install a nice, new, high-quality outlet if you only want to plug into one.
posted by flimflam at 1:58 PM on June 7, 2013 [2 favorites]


Batteries: can't imagine it will be near enough output to power the high demand lights I'll be using.

Would drawing 3K Watts for 4 hours work, or do you need 16 hours a day?
posted by at at 12:24 PM on June 8, 2013


Response by poster: 4 hours would be enough under most circumstances; you very rarely would actually shoot for 4 hours a day; time is spent setting up the lights and testing various lighting schemes, but that doesn't necessitate having the lights on during that entire time. When not testing or shooting, you switch off lights (hence the old hollywood cry "save the lights!" as a command to switch off lights the moment the tape stops rolling) to prevent unnecessary heating up, prolong bulb life etc.
posted by VikingSword at 9:32 AM on June 9, 2013


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