[Tfug] [OT] Voltage Spikes and Drops

Sat May 16 22:43:13 MST 2009

On Sat, May 16, 2009 at 22:29, Choprboy <choprboy at dakotacom.net> wrote:

> On Saturday 16 May 2009 20:39, Tyler Nienhouse wrote:
> > Ever since I moved into my current house, I have had one big problem. I'm
> > not completely sure what it is, but my guess is that it has to do with
> > voltage spikes and drops.
> >
> > In the living room of this house, the electronics have a tough life.
> Almost
> > every time there is a change in electrical usage in the house (for
> example,
> > dish washer cycles changing), something messes up in the living room.
> [snip]
>
> STOP, stop right there! If you do not have a good handle on electrical
> systems, stop what ever you are doing and RUN FOR THE NEAREST
> ELECTRICIAN!!!
>
> What you are describing sounds like a faulty neutral connection. That is to
> say, the neutral bar is not correctly bonded to ground and back to the
> service transformer. This is an EXTREMELY dangerous condition, a surge
> protector will not protect you, your electronic devices will be destroyed
> in
> time, including computers/microwave/dishwasher/refrigerator/TVs/etc. Where
> the hell is that electrician, why haven't you called him yet???
>
> OK... some background. Standard household power in the US is provided (by
> the
> utility) from a central-tapped 240V transformer, located on a pole or in a
> ground cabinet near your house. The center tap is the "neutral" and is
> bonded
> to ground (typically) for safety and short-circuit clearing purposes. The
> two
> output legs of the transformer are 180deg opposite in phase, resulting in a
> 240V leg-to-leg voltage and 120V in leg-to-neutral voltage. The two legs
> and
> the neutral are brought to your house distribution as a 240V service. A lot
> of people call this a "two-phase" service or think of their panel as
> two-phase, though technically it is single phase service.
>
> So... what happens when you plug something in. When you turn on your 240V
> water heater, current flows from one leg of the transformer, thru one bus
> bar
> in your panel, and thru the resistive element in the water heater. The
> return
> current travels back to the other bus bar and eventually the other
> transformer leg. As this is an AC system, the direction of current changes
> 120 times per second, creating a 60 cycle or 60Hz system.
>
> When you plug in your TV or computer, something slightly different happens
> though... These appliances are 120V, so current travels from the
> transformer
> leg, to your device, and then back to the neutral bus in your panel. In an
> ideal world, you have an equal amount of power usage on the opposite
> transformer leg, so the current travels from the neutral bus, out to the
> second device on the other 120V circuit, and then back to the opposite
> transformer leg. Of course, this is not an ideal world, and the power
> dissipation is rarely balanced between the two legs. The amount of
> difference
> between the two legs is known as the "unbalanced current" and returns to
> the
> transformer via the neutral connection.
>
> So... for a moment, imagine what happens when the neutral connection is
> broken
> or damaged and has a high resistance. This can occur do to a bad connection
> in your house panel, or damage to the utility's transformer. You turn on
> your
> dishwasher, which normally uses 5A at 120V, 600W. The current travels from
> the transformer leg, thru your panel, to the device, and then back to the
> neutral... But the neutral connection back to the transformer is damaged so
> the current can not return directly, it must pass thru devices on the
> opposite leg. Lets say the opposite leg has a TV that normally uses 60W of
> power on a 120V circuit, only 0.5A. Obviously, that is not the same amount
> of
> current (which must be equal to return to the transformer), so what
> happens?
>
> Well, the answer is "it depends", but we will assume the neutral is
> completely
> broken and the loads are resistive, so we can make a good approximation
> with
> Ohms Law (V=IR). The first leg is seeing, in a normal condition, a 24ohm
> equivalent load to neutral (120V/5A=24ohm). The second leg sees a 240ohm to
> neutral. As the neutral is now broken, the equivalent circuit is now a 240V
> drop over a 264ohm load, resulting in 0.91A flowing between transformer
> legs... So what is the result on each leg?
>
> Using the 0.91A of total current flow and Ohms Law again, we can see the
> voltage across the dishwasher is now 21.6V and the voltage drop across the
> TV
> is now 218.4V. So... your dishwasher is now starving for power at 22V
> instead
> of 120V, and your TV just fried itself being fed with 218V.
>
> In all seriousness, what you are describing can be a symptom of several
> different things: faulty breaker/bus bars, bad grounding, bad service
> cords,
> etc. But a faulty neutral connection is a very real possibility. It will
> kill
> all our your electrical items in time. As I said before, this may be a
> fault
> in your service panel, or it may be a problem on transformer/feed. You need
> to get an electrician to diagnosis it ASAP, he/she will need to come out
> and
> measure the voltage and current present on each leg and the neutral
> connection. If the two legs, with differing power usage on each, are not
> very
> close to the same voltage to neutral and/or the current difference betwen
> the
> two legs does not equal the neutral unbalanced current, it is highly
> probable
> the neutral connection is damaged. If the problem exists at the utility
> transformer, then your neighbors are experiencing the same problem and your
> neighbor turning on their dishwasher may be frying your TV!
>
>
> Adrian
>
>
> _______________________________________________
> Tucson Free Unix Group - tfug at tfug.org
> Subscription Options:
> http://www.tfug.org/mailman/listinfo/tfug_tfug.org
>

Thanks for the help!
That sounds almost exactly as I suspected, having a faulty ground/neutral.
It's obviously not too serious of a case because the house is 15 years old
(I've been in it for two of those 15 years) and none of our electronics have
been completely ruined, but I'll definitely be having someone come and look
at it.

Many Thanks,
Tyler
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://tfug.org/pipermail/tfug_tfug.org/attachments/20090516/500d2b73/attachment-0002.html>