The Electrical Contractor Network

ECN Electrical Forum
Discussion Forums for Electricians, Inspectors and Related Professionals

Books, Tools and Test Equipment for Electrical and Construction Trades

Register Now!

Register Now!

We want your input!

Featured:
   

2017 NEC and Related
2017 NEC
Now Available!

   
Recent Posts
Sprinklered equipment 26-008
by bigpapa
12/02/16 04:24 PM
On Delay Relay with Auto Reset
by Potseal
12/01/16 09:59 AM
Wow, that was close!
by jraef
11/28/16 07:06 PM
Earthquake in New Zeeland
by RODALCO
11/27/16 11:25 PM
Calling all Non-US members!! (Non-US only)
by Tjia1981
11/27/16 06:33 AM
New in the Gallery:
12.5A through 0.75mm˛ flex (just out of curiosity)
Shout Box

Top Posters (30 Days)
gfretwell 13
HotLine1 9
Texas_Ranger 8
sparkyinak 7
Trumpy 6
Who's Online
1 registered (geoff in UK), 133 Guests and 5 Spiders online.
Key: Admin, Global Mod, Mod
Page 1 of 2 1 2 >
Topic Options
Rate This Topic
#2137 - 06/23/01 01:34 PM i give up
Cindy Offline
Member

Registered: 06/23/01
Posts: 196
Loc: PDX, OR, US
how can the black wire be hot and the white wire not be hot if the electricity alternates back and forth from the black wire through my stuff and back over the white wire, if its not going back over the white wire then why have a white wire?
dont be mean when you answer
C

Top
Work Gear for Electricians and the Trades

Work Gear for Electricians and the Trades
Work Gear for Electricians and the Trades
Arc Flash Clothing, Gloves, KneePads, Tool Belts, Pouches, Tool Carriers, etc. etc....

#2138 - 06/23/01 01:54 PM Re: i give up
sparky Offline
Member

Registered: 10/18/00
Posts: 5545
Hi Cindy;

white wires can be 'hot' in a switch loop, is that what you are refering to??

p.s.- most of us have had our rabbies shots !


Top
#2139 - 06/23/01 02:15 PM Re: i give up
Cindy Offline
Member

Registered: 06/23/01
Posts: 196
Loc: PDX, OR, US
ummmm, no actually this is a more basic question, my dumb meter is pegged on really really... ummmm, empty
i think i'm asking what is the difference between the white and black, i guess.
like why can i touch a white wire and not get shocked, assuming i can, i'm not going to try though
it just seems like you would get shocked by touching either the W or B wire if the switch is turned on to something and the electricity is going through both of them. know what i mean? seems like they would both have the same ouch factor, i think you call it potential maybe
C

Top
#2140 - 06/23/01 02:15 PM Re: i give up
Fred Offline
Member

Registered: 04/30/01
Posts: 461
Loc: Straughn, IN 47387
Cindy,
In a 120V circuit, say to an outlet in your livingroom, you have a black, white and a bare or green wire connected to the outlet. The black wire is always "hot" as long as the circuit is turned on. You would always be shocked if you touched the exposed copper of the black wire whether you had anything plugged into the outlet or not. The white wire is the grounded conductor. As long as there wasn't anything plugged into the outlet, or any other outlet on this particular circuit, you could touch the exposed copper of the white wire and not be shocked. But, if there was something plugged into this circuit, using electricity such as a fan, you would be shocked by touching the exposed copper of the white wire.
Why?
Because when an appliance plugged into an outlet uses electricity, the electricity "flows" through the appliance making it work and has to return to it's source. Think of it as a water wheel on an old mill. When the water flows over the mill's wheel it makes the wheel turn and the excess water flows back into the river. When they stop the water from flowing the wheel stops moving and there isn't any water returning to the river. The water is still there, it has just been stopped from flowing over the wheel.

Top
#2141 - 06/23/01 02:31 PM Re: i give up
Anonymous
Unregistered


>why can i touch a white wire and not get shocked,
You could. But it is not usually likely because usually by a margin of 9999:1 the copper is a better conductor than you, so too little current travels through you for you to be able to feel it, i.e., <1 mA.

Hey, often one can touch a hot conductor and not get shocked, you know, like when standing on dry nylon carpet.

>it just seems like you would get shocked by touching either the W or B wire if the switch is turned on to something and the electricity is going through both of them.

That is somewhat true.

But juice on the black side is available in a large quantity. Juice on the white side is curtailed by the load and has a clear path to get back to the transformer already.

>seems like they would both have the same ouch factor
If you disconnect the neutral from the bus bar in the panel, that is pretty close to correct - at least as far as killing a human goes.

In the switch loop sparky mentioned, white is an ungrounded conductor, is on the line side (ahead of the load), and is actually an extension of black from the source at the fixture junction box, and in new installations should be marked to indicate that it is ungrounded.

Top
#2142 - 06/23/01 03:46 PM Re: i give up
Cindy Offline
Member

Registered: 06/23/01
Posts: 196
Loc: PDX, OR, US
sounds pretty simple i guess, so is that all there is to it? must be more. like why do you get sparks when the B and W wires touch each other accidently? seems to me like the waterwheel idea would mean that the water would just like to keep going down the river. you said the hot wire juice is hotter or there is more of it than in the white wire because some[?] of the electricity is used in the load. and you said that it is going back to a transformer. does the transformer not want to get all of it back or something like that? in any case, it sounds like the white wire is also hot when the fan or whatever is running, maybe just not as hot as the black, maybe, is that right?

Top
#2143 - 06/23/01 04:07 PM Re: i give up
amp-man Offline
Member

Registered: 06/23/01
Posts: 144
Loc: Sacto, California US of A
Cindy,

Hey, I think you asked a good question!

Fred and the other posters have explained it nicely, and here's another way to look at it.

When the appliance or other load is "on", there's just as much electrical current flowing through the neutral as is flowing through the hot. What's different is the "pressure" or voltage behind the current. There's less "push" or voltage on the neutral side of the load because the load has used that energy to do whatever it does. Keep in mind that it's the current that's dangerous.

There are certain situations where you are more likely to get shocked if you touch the neutral. One is if there is a poor connection in the neutral anywhere between where you might contact the neutral and the common grounding point in the panel (the "ground bus"). A poor connection makes the neutral conductor a fairly poor pathway for the current to return to ground, and so YOU become a more "appealing" path for the current to flow on, back to earth potential.

This situation is made worse if you happen to be in contact with the neutral and standing on concrete (which is in turn in contact with the earth), or touching a water pipe or the like. It's even worse if you're barefoot, and you're wet or sweating. These things all make you a much better conductor of electricity.

Keep in mind that it takes VERY LITTLE current to interfere with the electrical signals that make your heart beat normally. For most people, 6 milliamps can cause electrocution. That's why GFIs (or GFCIs to be more exact) will open the circuit if there's 6 mA of current leaking to ground (not returning on the neutral wire) for more than a few seconds.

BE careful out there!

Top
#2144 - 06/23/01 04:40 PM Re: i give up
Anonymous
Unregistered


> why do you get sparks when the B and W wires touch each other...?
Because electric wants to travel from black to white. Black is the top half of the hill. White is the bottom half. We put loads in the middle.

>you said the hot wire juice is hotter or there is more of it than in the white wire because some[?] of the electricity is used in the load. and you said that it is going back to a transformer.
Correct. When the black wire comes from the transformer, that is the top of the hill. When the white wire returns to the transformer, that is the bottom of the hill.

>does the transformer not want to get all of it back or something like that?
If it were sentient, it would want it all back desperately. Actually, the electric power has been pushed out on the black side. It wants to get back in, but the white side is the only way back in.

>it sounds like the white wire is also hot when the fan or whatever is running, maybe just not as hot as the black, maybe, is that right?
Kind of. The white wire has current flowing in it. The white wire is its best hope for getting back to the transformer where it wants to be. If you touch it, and you offer it a path, it will take it. But a human is a lousy path compared to the white wire which is a metallic path straight back to the transformer.

Now when you touch the black wire, it's a different story. There is more current available there than can get by via the light bulb or whatever because the light bulb offers resistance and limits how much current can flow. So there is current available on the black wire waiting for any possible means to get back to the transformer.

If you touch the black wire, as much current as can travel through you will do so limited only by the amount of resistance you offer.
(On the white side, you are competing with a copper wire. And the copper wire has a better bid than you by a thousand times over - so it gets the bulk of the current. But if you cut the white wire, you can be the winning bidder.)


[This message has been edited by Dspark (edited 06-23-2001).]

Top
#2145 - 06/23/01 04:48 PM Re: i give up
Anonymous
Unregistered


>if the electricity alternates back and forth from the black wire through my stuff and back over the white wire
The white side is there passively (we call it neutral).

The black side is doing the pushing and pulling. So while it is true that the current alternates, power is coming from the black side only. (It's not like the black side pushes then the white side pushes it back.)

Top
#2146 - 06/23/01 05:18 PM Re: i give up
Cindy Offline
Member

Registered: 06/23/01
Posts: 196
Loc: PDX, OR, US
so if i use the water analogy some more here, you are calling the electrical pressure voltage like the water pressure in a hose maybe, but its still water, or current, or electricity, you are just describing it in different terms, maybe?
and after the hose is turned on and runs the sprinkler or whatever then just less of the water, or voltage and current, is left to deal with maybe? the water pressure stays at 40# like the voltage stays at 120 volts. you can feel the 40# and the actual effect of the cold water, so maybe the temperature effect of water is like the current effect of electricity, they both are in conduits, ones solid, ones liquid, they both have pressure behind them, then we want to use the effect of the pressure somehow..... maybe the water thing is getting crazy here whatever, just one more thing that i wanta know is if the 120 volts in the black wire just goes straight through the fan or something to the white wire trying to go back to the ground then would a circuit breaker trip in the garage? so does that mean that the white wire is never supposed to be able to let that much current or voltage go back to the ground or transformer or ground bus you referred to? after reading what everyone said, it sounds like the white wire has current whenever something is turned on, but not as much as the black wire because some is used by the fan or load but it looks like they're always the same size wire, seems like the white could be smaller. sorry, too many questions, but this is kinda interesting.
C

Top
Page 1 of 2 1 2 >



ECN Electrical Forums - sponsored by Electrical Contractor Network - Electrical and Code Related Discussion for Electrical Contractors, Electricians, Inspectors, Instructors, Engineers and other related Professionals