A question for those who have understanding of electricity:
If your house is equipped with electrical outlets that have only the 2 holes (for 2-pronged electrical cords) could you protect your home from electrical surges using the following method: Plugging an adapter to the 2-slot wall outlet and then plugging a 3-pronged surge protector into the adapter, then plugging an additional surge protector into the surge protector connected to the wall. If one were to plug an electrical device into the last surge protector, would the ground function and stop the surge before it reaches it?
This question has been in my mind for a couple of weeks (cause I have old wiring in my house) and I wondered what a pair of surge protectors would do to save something like my computer.
Yes, but so would just one surge protector. The thing is, though, that you’ve got to connect the two-to-three prong adapter correctly. That little green ear on the two-prong side needs to have the screw that holds the coverplate on your outlet run through it. That screw should be grounded, and attaching the adapter to it creates a grounded three-prong setup.
Of course, it’s possible that the outlet box is not actually grounded, and the screw won’t act as a connection to ground. If that’s the case, a second surge protector will be just as ungrounded as the first and you’ll have no way to make your electrical system safe for your computer (or yourself, other living things, and other appliances) except getting an electrician to properly ground your wiring.
You should be able to test the ground by plugging one of those outlet testers with the LEDs into your properly-hooked-up adapter. If it says you’ve got a bad ground, get it fixed. You don’t want to live in a place with unsafe wiring.
This will protect against “common-mode” surges only - ie: between the hot and neutral lines. Differential-mode surges (hot to ground or neutral to ground) will not be affected, since you’ve got no ground.
I agree with the post by Saltire above, however, note that surge protectors do not necessarily need a functioning ground in order to provide protection. Most half decent surge suppressors have MOVs connected both between the hot and neutral lines and between the hot and ground lines. Any voltage surge above the clamping voltage of the MOVs (typically 300 V or so), will be diverted either across the circuit being protected and/or to ground, if present. Nevertheless, as said above, you want a functioning ground for safety reasons.
You’ve got that backwards. Common-mode surges present an equally high voltage with respect to ground on both hot and neutral lines. A differential-mode surge has a high voltage on either the hot or neutral line with respect to each other and to ground. I’m sure there’s a better way to word that, but you get the idea.
I agree with Q.E.D. While it is true most surge protectors provide protection against voltage spikes between all three conductors (hot-neutral, hot-ground, and neutral-ground), there’s no reason you’ll lose surge protection by using an adapter. Think about it… if you’re not using the ground, the device is only susceptible to a hot-neutral voltage spike. Assuming, of course, the device is not connect to earth ground via another path.
But as others have mentioned, defeating the earth ground connection using a 3-to-2 adapter is not a good idea for safety reasons.
Actually, after opening up a number of those outlet boxes in older homes, I’d say the chances are very good that the box is not grounded.
Check with a tester and if it’s not grounded you can run a wire to something that really is grounded (like a water pipe that’s metal all the way to the ground – unfortunately, with plastic pipes, that’s less common these days).
Yes, I’d say you were just lucky.
I have always had my power lines surge-protected, but after my modem card got fried, I made sure I always have a surge protector with a phone jack, too.
The device’s third prong (i.e. ground) needs more than a connection to “earth ground.” Most importantly, there needs a low-impedance path back to the breaker box.
In other words, you can’t connect a device’s third prong to a nearby copper rod in the earth (or water pipe, or whatever) and say, “It’s safely grounded. I’m done.” The third prong must be connected to a copper wire going back to the breaker box. And if you’re going to do that, there’s little reason to also connect to a nearby copper rod, since the breaker box is already connected to its own copper rod.
Before I had a computer, the transformer behind my house was struck with lighting. It took out everything in my house that had a 120 volt transformer **except ** one TV. On this TV I had it plugged into a cheap, (no name) one outlet, surge protector… well, it blew that little surge protector all over the room but the TV wasn’t hurt. The outlet was properly grounded. (you will be surprised on how many items you have in your home that have 120 volt transformers)
If you expect any protection from lighting, the outlet for the protector must be grounded.
APC surge protectors come with a Lighting Protection Policy… if it is plugged into a properly grounded outlet.
I have APC surge protectors on all my major items: Central heater/air conditioning controls, power supply for TV’s computers, security system, sprinkler system, etc. I sure don’t go around unplugging everything in the house every time a cloud comes up for I live in a very lighting prone area.
At the breaker box, all the neutral returns, ground wires and the powerline neutral (from the pole) are bonded together on a bus, and this bus is then tied to an earth ground connection, most likely a long copper-clad rod driven deep into the ground. This provides a nice zero-volt reference point. At thsi point you may be asking “If the ground and neutral wires are tied together anyway, couldn’t the neutral be used as a ground too?” And the answer is “No.” The reason is that the neutral wires carry current. As such, each point has a voltage with respect to ground, per Ohm’s Law: V = I x R. If you have 1 Ohm of resistance in the wire between you and the ground bus and 20 amps of current are flowing through it, you’ll contact 20 Volts between you and a zero-volt ground, such as a copper cold-water pipe. Under the right conditions, this could be dangerous, or at least painful. You’re probably not very likely to come into direct contact with the wires themselves, but if you’ve got a piece of equipment with a metal case, or metal parts you could contact, should one of the wires come loose and touch the case or metal bits you could get a nasty surprise. So, the metal case and other metal bits that both you and one of the wires could touch are connected to a third wire–the ground. This has no current flowing, so zero voltage. If the neutral touches it and has a current, this will be diverted to the ground through the low-resistance, rather than through you, since your resistance is much higer. If the the hot wire makes contact, it will creat a short circuit and blow the breaker, saving both you and your house wiring. The above is somewhat simplified, but hopefully answers most of your questions regarding grounding.
My follow-up question is what specifically is the difference between the hypothetical earth ground, and the ground wire going back to the breaker box? The breaker box simply connects to the earth ground anyway. What is the difference?
Q.E.D.: A lot of folks believe the neutral is not used as a safety/chassis ground due to the common mode voltage that can appear on it as a result of current flowing through it (V = IR). While it is true some voltage will appear due to V = IR, it’s usually not high enough to justify a safety problem, assuming the system is in good order.
The primary reason we don’t want to use the neutral as a safety/chassis ground is to guard against shock in the case a break occurs somewhere in the neutral line. If there’s a break in the neutral line and you happen to be touching the chassis (and assuming you’re grounded), current will flow through the hot conductor, through the appliance, into the chassis, through you, and into ground.
A “break” in the neutral line occurs more often than you think. In fact, a “temporary” break happens all the time. Think about it… when you stick a 2-pronged plug into a receptacle, do you think the neutral always makes contact first? I’d wager that 50% of the time the hot makes contact before the neutral. This means there will be a time span (typically a few tens of milliseconds) where only the hot is making contact. If the neutral were connected to the chassis, and you happened to be touching the chassis while sticking the plug in the receptacle, you’d get zapped (assuming you’re grounded).
LivingInThePast: Dirt and clay are not good conductors. If you simply connect an appliance’s third prong to a copper rod in the earth, there will likely be a significant amount of resistance between this copper rod and the breaker box’s copper rod. This part of the path is very important, since current must flow through it during a ground fault. There’s a very good chance this resistance will limit the current during a ground fault to the point that the breaker will not trip. That’s why the appliance’s third prong must be tied back to the breaker box via a copper wire – to ensure the breaker reliably trips during a ground fault situation.
The copper rod into the earth really doesn’t do anything regarding ground of the wiring in the house. (More later). Think of the ground wire as an alternate path back to the source of power. Let’s start at the transformer on the pole or in a box on the street. It is grounded to the earth. It is the source of the 3 wires to your breaker box. - hot, neutral and ground. All the wiring iin your house is connected to each of the 3 wires, discretely. There is an electrical field in the earth because it is grounded to earth. This is the ground potential at that spot.
Let’s pretend your breaker box isn’t grounded to earth. Now a neutral in your house fails (this is an “open neutral”). The ground is now being used as the neutral. You have power flowing in the ground wire (which is normally not the case). The problem is, nothing fails. The circuit works fine. But the earth around your house, the water pipes and all that stuff is at a different ground potential than the circuit. It is now possible for you to be a “better” ground than the circuit ground. Grounding the breaker box through a rod into the earth, puts it (and its circuits) at the same ground potential as the source and everything connected to the breaker box. It makes all paths to ground “equal”.
The other forms of failure than an open neutral are:
Open hot: No real danger and conveniently attracts your attention by having whatever device quit working. This is what you do when you turn off the breaker.
Open ground: Dangerous (but only if something else happens). If the circuit is GFCI protected it will trip the GFI, again bringing it to your attention. An “ordinary” circuit, continues to work. It is technically ungrounded, but in reality, it is grounding through the neutral, because they are bonded at the breaker box. It is however, experiencing a similar ground potential problem described above.
Okay, let me completely expose my ignorance here, and hope it’s close enough to the OP to continue…
I know there must be something to this “hot” and “neutral” wire business, since just about every electrical component I’ve seen (switches, outlets, etc.) mentions them.
But since we’re talking about alternating current here, in which (as I used to understand it) the polarity reverses 50-60 times per minute, I am baffled as to how one wire can be considered different from the other. What distinguishes the two, relative to the flow of current?
Purely a definition. By common consent the white wire, which is connected to the green, safety ground at the circuit breaker panel is called the “neutral.” The colored wire then varies in voltage from 120*sqrt(2) positive with respect to the voltage of that neutral to the same voltage negative with respect to it and it is callec the “hot” lead.
Ahh, the light glimmers. So the “neutral” and “hot” are simply conventions so that when folks are wiring things up, they will all connect back to the power line in the same way. And because one of them gets wired to ground, that’s called the “neutral” one. Right?
