I have just bought a brand new house. New like just built and I got to
choose some of the things like carpet color, cabinet style and tile
color. But when I came upon the house the drywall was up and taped, so
I didn't get in on the ground floor, so to speak. According to the
builder, and to the label on the electrical panel I have an 150 AMP
service. Since the stove and clothes dryer are gas, this should be
more than enough. But (and here finally is my question), whenever the
air conditioner turns on, or more frightening when the dish washer
starts a new cycle, the lights in the house dim for a second. Should this be
happening? What could the builder and/or the elecrician have done to
make this occur. Each of the major appliances has its own circuit
breaker and there are quite a number of circuit breakers for the
lights. Why wouldn't I have enough juice to keep this from happening?
Is it dangerous?

---

Clarification of Question by beauregard-ga on 01 Sep 2003 20:46 PDT

Let me clarify what happens when the air conditioner turn on, or the
dish washer starts a new cycle. The lights flicker, but come right
back to full strength. But I lived in a 20 year old apartment before
owning this house, and even with that cheap electrical system I
experienced no such phemoninon when the air conditioner came one.
Here, the lights almost go off, there's so much current drain at these
times. Come right back, but I don't like this behavior.

---

Clarification of Question by beauregard-ga on 04 Sep 2003 00:02 PDT

I had No. 10 wire installed to replace the No. 12. Everything I've
read about this situation leads me to believe that the size of the
wire connected to a certain circuit must be big enough to support the
number of AMPs the circuit breaker is rated for. The breaker must
"pop" before the wire melts and catches fire. The device on the other
end of the wire is inconsequential.

No. I'm not going to pursue this any farther. The builder contends
that the wire was adequate for the original A/C compressor which he
installed and that my problems were caused by upgrading the
compressor. This is nonsense. I know it and he knows it. But I'm not
an electrical engineer and there may be mitigating circumstances at
work here. My lights still dim slightly but there's a device called a
"kickstarter" which I will have installed. Presumably this is a
capacitor of some sort that eliminates the instantaneous load placed
on the house circuits at compressor start-up. Maybe my 150 AMPs for
the house isn't enough? I don't believe this, because I'm never using
more than a few electrical appliances at any one time. Don't have an
electric stove nor electric clothes dryer: These are gas. 150 AMPs
should be more than enough for a single man living with a very small
cat.

So even if the lights dim now, at least I can rest assured that if
there’s a problem, the house won’t burn down. Or, at least, I hope I
can rest assured of this. I may schedule a full house electrical
inspection of my own, but I’m so overwhelmed with responsibilities of
a new house and having to work to support it, that I can’t imagine
doing so in the near future. If you suggest that I should do it
immediately, then I would.

But you’ve already saved my life. You may close this question, if you
like, and I will give you the highest possible rating. And with the
vast sum of money you’ll receive from Google, you can think about
retiring to Florida.

Thank you
Andy

Hi beauregard,

Here are a few links that have some
related info regarding "voltage sags"
in your home's electrical system.


[ http://www.dotznize.com/electric/?a=tr ]
[ http://muextension.missouri.edu/explore/agguides/agengin/g01409.htm ]
[ http://www.pge.com/002_biz_svc/002c1c_understanding.shtml ]

 -=-  -=- -=- -=- -=- -=- -=- -=- -=- -=- -=-
ELECTRIC MOTORS AND BACK EMF
[ http://galileo.phys.virginia.edu/classes/202.sc2k.spring03/chap22/chap22.html ]

{two types of motor to consider}
DC motors, where a coil carrying a
DC current (provided e.g. by a
battery) is put into rotation
by the torque generated by the
field on the current. {and}
also AC motors, where the
current in the rotating coil is
the Alternating Current supplied 
by the power company.

For either type of motor we
have to deal with a special
effect, again due to
electromagnetic induction, that
goes under the name of back
EMF. Here is what goes on :
as a coil rotates in a magnetic
field region, it sees a varying
flux and, as usual, it tries to
oppose the change. In other
words, as the motor rotates,
driven e.g. by the 120V from
the Electric Company, it
produces itself an EMF, at all
times opposing the one that
puts it into motion. As a
consequence, when the motor
turns at full speed, it does
not see the whole 120V, but
only the difference between
120V and the induced EMF.
It takes some time for this 
back EMF to build up within
the circuit, when the motor 
just starts up it sees the full 
120V voltage and it draws a 
very large current. This is why 
you notice a dimming of the
lights when a heavy appliance
kicks on : the (initial) very large
current through the appliance causes
a drop in the line voltage.


-=-  -=- -=- -=- -=- -=- -=- -=- -=- -=- -=-


Although it may seem that dimming
is something that may naturally occur
in certain situations, please be advised
that without the inspection of a trained
professional, any reference to "what
appears to be happening," will be 
mainly subjective. If you do not feel
confident with the wiring installation
please call in a 3rd party to properly
inspect the wiring and load capacities
versus the actual demanded load.

-AI

sounds like your panel is 150amp, but the electric utility can't do 30
amp.  who to blame i do not know.  do your neighbors have the same
problem?  you're probably on the same transformer.

Your answers may well have saved my life and the life of my cat
Beauregard. I did as you suggest and had an expert look at the air
conditioner wiring. Turns out, on this 30 AMP curcuit, they wired with
No 12 wire. Much, much too small if the device actually decided to
draw 30 AMPS. The problem will be repaired tomorrow. Tonight I just
don't use the A/C. It's cool, so that's not a problem. Thank you
again.

Hi again beauregard
and hi to your owner  :o)
...

Glad to hear it was looked at.
Did they get you all fixed up?

Are you going to pursue this
further with the home-builder?

Any other homes that might need
to know about a similar situation?

-AI