Basic electrical questions
February 14, 2010 12:42 PM   Subscribe

Just some random, basic questions about electric and avoiding circuit overload...

I recently moved into an older apartment, and I'm a little concerned about my electric usage in this place which hasn't been lived in well over a decade.

For one, all the outlets are 2 prong - so I'm using the 2 prong to 3 prong adapters along with power strips & surge protectors to allow me to run everything I need. My other concern, none of the breaker switches seem to trip the electric where all my stuff is. The kitchen and bathroom both seem to be on the breaker, but the one room where most of my stuff is hooked up is not even affected when I hit the master switch.

So my questions are:
1. Is there any danger in using my 2 prong adapter/power strip combo for most appliances? Should I spread my things around as many outlets as possible, or does that not make a difference?
2. How many watts can a typical outlet support? If I have the typical setup with one outlet on top of another, is it better to divide my usage between the two, or can I plug everything into a single power strip?
3. I'm already low on outlets but there are a ton of light sockets mounted all around the walls - can I use one of those socket to outlet adapters for another power strip? Are these as safe as standard outlets?

I'm worried about overloading the circuit, and since there's no ground I'm not sure what would happen if I did. I saw 2 prong safety extension cords at Wal-Mart, with some kind of circuit interrupter built-in. Would something like that be worthwhile?

Not entirely sure what my usage is for this room (do you think about usage per room, or per outlet?) - right now I have my xbox 360, TV, stereo receiver/speakers, 4 lights, a small fan, Desktop PC and laptop all hooked up. Things are never all running at once, but what if they were?

Sorry for the scattered questions...

posted by pilibeen to Home & Garden (8 answers total)
A 2-to-3 prong adaptor will have a little metal tab on the two-prong end. That connects to the third prong on the (female) 3-prong end.

If you don't connect that metal tab to anything, then it means everything is floating. There's an electrocution risk to you in that case. It means you're relying on the AC common for grounding instead of a real local ground. That's what I'd be most worried about.

Figuring out what to hook it to can be tricky. Usually it gets connected to the screw in the middle of the outlet face plate, which will be metal and will hook it to the metal of the box. If the box is connected via metal conduit to something which is grounded, that will work pretty well. If not, it doesn't help at all.

If the circuit doesn't go dead when you kill the main, then it isn't up to code. Complain to the owner. If the owner doesn't do anything about it, complain to the local building inspector.
posted by Chocolate Pickle at 1:08 PM on February 14, 2010

1. The danger is that you do not have ground protection for those items that have three prongs. If something were to short normally the easiest path to ground would be there, but instead the person touching it becomes the shortest path. Spreading things around will not make a difference other than overloading a circuit. It has no bearing on (normal) grounding how many items you have on a circuit unless you are drawing too many amps.

2. Wattage is a function of voltage and amperage. I assume you are in North America, in which case the line voltage is 110v. Then, the amount of watts you can safely get out of a single circuit is controlled by how many amps you can draw. Watts = volts X amps, so for a 15amp service you can expect to get no more than 1650 watts of power from a single circuit. Most items have their wattage ratings on the bottom, so you can easily add up how much each /could/ use, and then see if the line supports it. Make sure you estimate to the safe side of the maximum wattage a line can handle.

3. Depends. Most of the time light circuits are actually tapped of line circuits. So now you have to wonder which circuit you are tapping off of, and whether you are exceeding some safe value.

The fact that you can't seem to find a breaker that controls your circuits means that we don't know where the fuses or breakers really are. The worst-case scenario is that the wires in the walls start to act like fuses, which is something you really, really don't want to happen. Nor are we sure if you have 15, 20 or 30 amp service, or a mix of all three. So it can be hard to estimate circuit power draw unless you know that.

Honestly, the landlord needs to update the electrics. The best you can do is to spread your electric use around to different outlets, though the problem might be the building is wires with several lines going from basement to top floor, with everything tapped off of it. In which case most outlets will be the same circuit no matter what.
posted by clvrmnky at 1:10 PM on February 14, 2010

Ok, knowing the actual age of the wiring in the apartment would be very useful. No having a ground prong (the third prong) is not dangerous if everything goes right, this means no overloading, no power surges, no faulty equipment, no grounds (such as getting shocked while standing in a pool of water). Next thing, in general, using light sockets to power non light bulb loads is not a good idea, they are not built for it and may not withstand it without danger. Using a power strip for anything is always a good idea, but without the third prong i don't think they will work right.

Most home circuits are built for a 20 amp load. Wattages are calculated as amps x volts (it is more complicated than this but for this discussion it will do). So to figure out the wattage you can support find out the amperage of the circuit than multiply by 120 (voltages in the us are between 120 and 110 usually). The wattages your devices are drawing is somewhat harder to figure out. They will almost always have a wattage listed but this usually the full draw the can pull, not necessarily the average or usual draw. For this you need an actual meter. A multimeter is the best tool to figure this but is somewhat challenging to learn to use properly. So go get a kill a watt meter from the hardware store. This neat device plugs in then you plug stuff in to it and it will tell you the actual draw of the device. Anyway, if you have reason to believe you apartment is unsafe contact you landlord and if he/she is unresponsive call your local building department. Most hardware store will have a book section with something relating to wiring code and is not a bad place to start. However I hire a professional to do anything complicated (which includes evaluating existing wiring) because getting it wrong can kill you and burn your house down. A couple of hours of professional advice is way cheaper than a house or funeral.
posted by bartonlong at 1:21 PM on February 14, 2010

Let me address a couple of issues before getting to your questions. First, it appears as if you may have a sub-panel that deals with your kitchen and bathroom circuits. If there are other rooms in the house that are not affected by the breakers in this panel, there is another main panel somewhere that controls the circuit(s) for these rooms. You need to have the landlord show you where this main panel is and which breakers control what circuits. You will need to know this when, inevitably, you trip a breaker. Additionally, you will be able to read the amperage of each breaker as it is stamped right on the switch front.

Second, you need the help of someone who knows and understands electricity and who can safely remove a cover plate from an outlet. He might discover that the outlet boxes are metal and grounded. If that is the case, he can install three-prong outlets for you at minimal cost by grounding the outlet to the box. If the box is not grounded, this is not possible in a practical way. This electrician or handyman can also help you evaluate the wiring size and breaker size to determine what your safe loads are.

As to your questions:

1. You are probably safe from electrical shock in the room with the toys in it if you never have any kind of water or other beverage in the room with you. Most of the toys you have don't carry a risk of shock from the case, but anything can happen. Grounded outlets are far safer than non-grounded, but whole generations of people grew up with only a few of them getting zapped by their lamps. However, combine water and electricity and you have a lethal problem.

2. The wattage that an outlet can support is based entirely upon the size of the wires serving it and the size of the breaker on the circuit. You need an electrician to help you determine what is the case in your home.

3. Again, you need an electrician to tell you what the size of the wiring is and to evaluate the load you are planning to place on that circuit. There are no rules of thumb when it comes to individual electrical problems.

Hire somebody to help you with this. It is a cheap investment.
posted by Old Geezer at 4:28 PM on February 14, 2010

Prior to the late sixties/early seventies grounding was not common (much less GFCI). While the situation you describe isn't optimal, it's not like you're taking your life into your own hands every time you turn on the lights. (I think a GFCI will work even if it's not grounded so it might make sense to have those in your kitchen and bathroom.

I'd have said most circuits can handle 15 amps. You multiply amps by voltage to get wattage (in the US it's easiest to just use 100 and it gives you a bit of wiggle room). If your circuits are sub-average that is going to be of small comfort. Also note, it generally doesn't matter how many things are plugged into a particular circuit, just how much power is being drawn at any given moment. The list of things appliances you describe probably doesn't add up to more than 1000 watts and so your circuits can probably handle it. Probably.

To what Geezer said about the size of your wires and breaker, I'd add that the size of your breaker should be governed by the size of your wires - if someone put too big a breaker on a circuit to keep it from kicking off all the time, they deserve a good beating.

I would be most concerned about the living room not going off when you pull your main. There's probably another panel somewhere - you need to know where that is or beat on the table with your shoe if your living space isn't fused at all.
posted by Kid Charlemagne at 5:24 PM on February 14, 2010

However, combine water and electricity and you have a lethal problem.

No, not necessarily. There isn't anything magic about water; it depends on how much there is of it and what else it's touching. It forms a decent conductor (salt water is even better) but it can't conduct if there's nothing for it to conduct to. A puddle of water on a wooden floor isn't any more of an electrocution hazard than the floor would be if it was dry.
posted by Chocolate Pickle at 5:59 PM on February 14, 2010

Response by poster: Thanks for all the great answers so far...

I'm definitely now making it a priority to find the breaker for the living room, whether it exists or not.

Also...what exactly happens if you overload a circuit on a line which isn't fused?
posted by pilibeen at 7:51 PM on February 14, 2010

Also...what exactly happens if you overload a circuit on a line which isn't fused?

Worst case is that overloads may eventually causes an electrical fire as some part of the wiring starts to act as a slow-blow fuse.
posted by clvrmnky at 8:08 PM on February 14, 2010

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