A couple general electrical questions
I’m trying to figure out some basics on general electricity, but I can’t seem to find the answers (maybe I’m not searching for the right things)
When I look at what comes into my house, I’ve got 3 wires coming in. My two hot, and one neutral, correct? In some homes I see the neutral tied to all the grounds on all the circuits. I’ve also seen a seperate ground bar as well in some houses. I’m sure there are code requirements to have seperate (I assume), but will it hurt anything if it isn’t changed to a system with a proper ground?
And I’m also puzzled about 220v power. I understand basic AC power, but the 220 is a little confusing. I see 110v fed off of each leg, but put the two hots together and you have 220? Is the 220 measured across the two legs (are they just two 110’s in an opposite sine wave pattern?)
I’m not going to try messing with anything, but I’m just trying to get a more basic understanding of how this all works. Thanks in advance.
Replies
Well, your questions are not bad, and our system is a bit different than what is used in most of the world. Let me try to explain it in simple terms.
Let's start at the Power company transformer. What is a transformer? Why it's two coils of wire, places right next to each other, not quite touching. The key words here are 'coils' and 'close.'
Electricity is also magnetism; you can't have one without the other. Just as one magnet affects another, one wire carrying current affects other wires near it. In a coil of wire, the current affects it's own flow through neighboring coils. That's why a coil of wire is not a 'short circuit.'
The current flowing through one coil will cause current to flow in another coil placed near it. Change the size of the coils, and you change the voltage. That's what makes a transformer work.
Let's just assume that a certain coil 'creates' 240v. of electricity. If you cut that coil to half length, it will create half the voltage, or 120v. Make sense? And, yes, these two 120v circuits will be exactly opposite each other. Think of that 240v. circuit as two 120v. circuits flowing in opposite directions).
At the PoCo teansformer, you have three wires coming out. One wire is at either end of the coil, while the other - the neutral- is connected to the middle of the coil.
Now ... as for your house ...
Electricity wants to "go home." In this case, that means it has to return to the transformer to do any work. So, for every circuit, we have a wire 'from' the transformer, and a wire 'back to' the transformer. This explains the connections of the 'hot' wires and the 'neutral' wires; what about the 'grounds?'
What happens if a wire is damaged? Well, it's possible that electricity will find a way back to the transformer. If it does, current will flow. If this path is left to chance, the chance is that bad things will happen - fires will start, people will be hurt, etc.
To reduce this danger, we have ground wires. Ground wires act like electrical 'drip pans,' catching any 'lost' electricity, and giving it a very good path back to the transformer. The better the path, the more current can flow; if enough current flows, the fuse will blow and the danger removed.
The trouble is, electricity will take ALL paths home, not just the easiest one. Since we don't want current to flow through our pipes in the normal course of things, we bond the ground wires to the neutral at only one place - where the power company neutral enters the building. That way, there is only one path back to that transformer.
Getting "lost" electricity back 'home' to the transformer is what 'equipment grounding' and the 'grounded conductor (neutral)' is all about. This has nothing to do with the ground rod.
The 'ground rod' is there for one reason: lightning. The only electricity that has to 'get home' to the dirt under our feet is static electricity - of which lightning is but the largest example.
Some may quible over the details of the story I've just told you, but let's leave those details aside. What I've told you is enough for all the various code requirements to make sense, in every situation.
At one place in the house, at the service entrance, the neutral from the transformer, the neutrals to the loads, the grounding electrode conductor (the wire to the ground rods, etc), and equipment grounding conductor (the green or bare wire to the receptacles) are all connected together.
That location is usually the "main" panel. Now because of the way that different panels are made and different electrician practices you might find the neutrals and grounds mixed on one or more bus bars or much might see all of the neutrals on one and the grounds on another.
But if this is the service entrance the ground and neutral bus bars will be bonded together and to the case. In some cases this is a strap between the 2 buses that also attaches to the case. In other case the the one bus bar is directly connected to the case and the other bus bar is insulated from the case, but has an optional bonding screw that electrically bonds it to the case (and thus the other bus bar).
In some cases there is a separate disconnect switch which usually at or near the meter. In that case that disconnect is the service entrance where the neutrals and grounds are bonded. In that case the "main" panel is actually a sub-panel and the neutral bus is isolated from the case and ground bus. In that case 4 wires is run to the panel from the disconnect, 2 hots, a neutral, and an equipment grounding conductor.
"(are they just two 110's in an opposite sine wave pattern?) "
Exactly.
Think of 2 flashlight batteries connected together with the plus of the first to the - second. If you connect a wire to those 2 terminals that is the neutral. And if you measure from the neutral to the negative of the first battery you will measure -1.5v. And from the neutral the positive of the 2nd battery you will measure +1.5 v.
If you measure across both batteries you have 3 volts.
William the Geezer, the sequel to Billy the Kid - Shoe
GET THEE TO A BOOKSTORE!
Heck, even HD and Lowes has a pretty good selection of DIY books on home electrical. Look for one with clear illustrations, you will look at those ALOT!
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Rebuilding my home in Cypress, CA
Also a CRX fanatic!
Look, just send me to my drawer. This whole talking-to-you thing is like double punishment.