ECN Forum Forums Technical Discussion Electrical Theory and Applications How does Electricity flow?

How about this.

What is the purpose of grounding the panel?

Several years ago I was summoned to a residence. The owner showed me that whenever she turned on the hall light the living room light would dim. When the refrigerator turned on the hall light would get brighter. Etc. Etc.

I checked everything out, tightened every terminal in the panel, tightened the grounding terminals, etc.

The problem turned out to be a broken neutral wire buried in the yard. Seems it was nicked when it was installed ten years before and gradually deterioated until it was open. Current evidently continued to flow through the ground and everything worked OK until we had a drought. The ground at the panel or the broken end of the neutral gave up and 220 volts were distributed throughout the house depending on the resistance of the circuits involved. This could have easily destroyed any electronic equipment or motors.

Moral, when a house seems possessed look for a bad neutral and a ground that lost its integrity.

The local power company replaced the service entrance cable and we made sure the earth stayed damp at the ground rod site. Case closed.



[This message has been edited by dturner (edited 03-02-2001).]

66',

I typed in a mistake on that one! I was editing it when you must have posted your message, so after I fixed it, I saw your current message.

Don't change the way you understand an Ampere. You are correct. I made a mistake while typing the message out. Had a phone call while typing that part of the message out, and was bouncing between the call and the message.

It's fixed now, so go check it out again!

Sorry about that!!

Scott

To Sparky 66WV

In order to measure voltage you are reading the potential between 2 different points. A voltage reading between a hot and a neutral will give you a voltage difference. Taking a reading between the neutral and the ground will be "0" because they are electrically connected or are the same point electrically.
You have to have a difference of potential to have a voltage.

Thinking of it another way if you were to take a pressure reading in a water pipe and it was 150 PSI and you had another water pipe beside it that also had a pressure of 150 PSI what would be the difference in potential between them. 0 PSI

If you were to place your test leads on the hot conductor at the breaker and on the buss bar supplying that breaker the voltage would also be "0" because electrically they are the same point.

Not that I am advising doing this but if you were to disconnect the neutral wire from the neutral buss bar and take a reading between the neutral wire and the buss bar you would get a voltage reading. It may not be 110-120 because your meter would be in series with the load and the voltage could reflect that. The voltage is being conducted back to ground or back to the source (same place in this situation).

[This message has been edited by dturner (edited 03-02-2001).]

[This message has been edited by dturner (edited 03-02-2001).]

Sirs;
very good anologies here! i don't think we've violated the prime directive either

thank you also, Webmaster, for recognizing the significance and gravity of this topic in this forum!

I may bury myself with this next Q....

If i draw a 3 ph sine wave, there are 6 "peaks" , 3 above the line, zero ref, or whatever it is, 3 below it. This has confused me for near 20 yrs. What would i be metering, in the same type of scenario's as above, in the panel, at the load?

Sparky,

I am going to give an extremely brief answer here first, then type up a more in depth message off-line in my word processor, which I'll post later. This might explain the stuff behind your question better.

Just briefly, you are measuring the amplitude of one flow direction - either the one above the zero line, or the one below it. The meter will most certainly show the RMS [Root Means Square] value of that 1/2 cycle. The RMS value of a half cycle is .707 of the peak value. RMS is the AC equivalent to DC when heating is concerned [this is way too brief!! I am truly sorry!].

If the Peak value was 170 volts, the RMS value would be 120 volts [and vice verse]. There's another value, called Average Value, which is something like .63 of the Peak value [I haven't used that value for so long, I can't remember it's percentage! I'll check on it and include with next message].

Very rarely will one need to use Peak to Peak values. This would be something of concern for Rectifiers or maybe Capacitors.

I'll post a better message later tonight!!

Bill,

Great idea having an area devoted to theory! I am sure the rest agree!

Scott.

Scott,

What, no Smiley Guy??

Bill

Sparky,

I need to alter my first message to you.

A few hours after logging off, I started to think about what you were asking in your message. I misunderstood and misinterpreted the whole thing!

You were asking if the Voltage / Current levels can be measured across the sinewave and the corresponding "mirrored" sinewave that composes the flow in the other wire.
I was thinking of the simple - common method; only of single waveforms

In the case of a single phase circuit; where you draw a certain sinewave, which peaks above the zero line, it has an equal, but opposite flowing wave on the other wire that peaks below the zero line - which can be viewed as being directly beneath the other one.

In this case, the total RMS values will be measured across the two waves, so the total RMS voltage will be derived from the above zero wave and the below zero wave. This coordinates more towards how a meter would measure potential [voltage] in the complete circuit.


This is not a common method of drawing sinewaves that relate to generators and such, but is common for drawing sinewaves that feed into Rectifiers! This type of drawing will show how a half wave, or a full wave Rectifier will produce an output DC with pulsations. I was looking at a dry cell, thinking about the charger for it, when I realized what you were getting at!

I'm such an airhead!

You will only see this done with 1 phase 2 wire circuits, as 3 phase 3 wire circuits will be drawn using only the fundamental sinewaves.
There is an exception [I believe ], a 3 phase Rectifier that contains 6 Diodes [could also be called a 6 phase Rectifier] would show the 3 phase waves above the zero line, plus the 3 corresponding waves below the zero line. In this case, the 1 phase scenario would apply.

Let me double check this one first

The whole thing about these sine waves is that they are just to describe how one current gradually increases in amplitude in a certain time until reaching maximum, then gradually lowers intensity, until once again there is zero current flow. At that point, the current flows in an opposite direction, first rising in amplitude to a maximum, then lowering back to zero.
It's a better way to view the event than using Vectors, plus it's somewhat easier to plot the resulting distorted effects to the Fundamental when applying harmonic distortion.

There is another type of graphic plot that uses waves. It's the one for the Power waves.
True power will be a wave that is entirely above the zero line.
Apparent Power [KVA] will have points above and below the zero line.

I'll run through my Engineering manual and add comments from it to that word processor document that I mentioned before. When it looks good, I'll post it to the forum. That way it will be direct quotes instead of "Hit and Miss"

I am getting very tired of posting incorrectly quoted stuff to you guys!! I do apologize fully for the mistakes.

Scott

I think you are short one 0.

6.28 X 10^18 = 6,280,000,000,000,000,000 the way I figure it.

Yep...6 with 18 digits after it.

6,280,000,000,000,000,000

And none of us caught that one!