We've got a breaker that blows regularly. Usually when we use
the vacuum when the pool filter is running. It's a 15amp circuit
and draw is usually close to that. To circumvent this, I've run
a cord to another circuit in the house to run the filter, and all
is well. But sloppy.
What I could do is get a licensed electrician to add a circuit.
But what I think I should do is check to see how much draw is
on each of the circuits and move stuff around to balance the
load. Particularly since the original layout used by the original
owners of this house probably doesnt' really represent the
current distribution of loads on the circuits. There've been
additions, new appliances, etc., etc. in the past 20-30 years.
Would it be best to proceed with what I'm doing -- mapping
each of the circuits to the stuff in the house that's connected
to it, and then move wiring or loads around to balance it?
And if I want to do that, is there an easier way than to track
down each appliance and calculate the load? Or is there a
method of reading the current draw through each circuit-
breaker indirectly? It seems to me that the way to do this
properly is not to just ask a guy to add a circuit, but to
actually have the information for him (or me) to distribute
the loads properly/accurately/safely to put each circuit
as far below maximum as possible. And I don't see how
adding a circuit will do this right -- only add to the maximum
that could be going through the main box.
Ideas? Comments? e-mail is fine if this has been beaten to death.
Map out each circuit device as see what is on each branch circuit. You
might find a branch circuit that has very little load, and add a recept to
the existing circuit. At no time will the amount of the total house load go
up, because you already use the stuff. You could add many recepts on a
circuit, because it only increases the load when something is plugged in.
The cheap way to do it is to map all the outlets and fixtures and figure out
which breaker feeds which item. A second person and two radios/cell phones
cut the time required five fold. HD has a $70 (?) gimmick that sends a high
frequency signal down from an outlet and when you touch the right breaker
with a matching sensor the sensor lights up. You need to trip all breakers
so that you don't have any crosstalk between circuits. You can also measure
the actual current with a "clamp" meter ($50 - $200) if you open your
breaker panel and clamp it on the hot (black) wire that goes out of the
breaker. This means working with exposed wiring with the electricity on, so
If you have a vacuum that draws nearly 15A then you need to have 12 gauge
wire in the circuits and 20A breakers on them. This is because and electric
motor will use more current than the rating on the tag when started. The
Code assumes 125% of rated amperage to calculate the load for a device with
an electric motor. For example, if the label on your vac lists 14A, then you
need wiring and protection for 125% x 14A = 17.5A i.e. 12 gauge wire and 20A
This helps a lot, folks!
And incidentally, how does the above work w/r/t the wire gauge?
That is, how do you get 125% of a wire gauge? I've always been curious
as to how wire gauge is graduated or calculated. Is the gauge proportional
to the relative weight per foot of the wire, and, hence, proportional to
the cross-sectional area of the wires? How much more cross-sectional
area does, say, a 10 ga. wire have over a 12 ga. wire? And is 12ga./14ga.
equal to 16ga./18ga and to 4ga/6ga? Or what? I'm assuming power-handling
capacity for wire is proportional to the current density, and hence to cross-
Sorry to go off on a tangent, but this has always bugged me, and it helps
me understand the whole picture.
You don't really need to get 125% of a wire gauge. You use the 125% to
calculate the load in ampers (you need to include all other loads in the
same circuit as described in the Code) and then pick the next wire gauge up
from a table there. For 20A circuit it happens to be 12 gauge wire. See this
table, which is reproduced in may books on electric work for other loads and
gauges. There are inexpensive tools to measure the gauge of a disconnected
wire (trip the breaker first!). You are most likely to have 14 gauge wires
for 15A circuits in your outlets, unless your electrician was compelled to
think ahead and did use the 12/2 or 12/3 cable.
Here is the definition of the wire gauge from M$ Encarta:
The diameter of a single-stranded piece of wire is designated by the wire's
gauge number. Gauge numbers of multistranded wire designate the diameter of
the entire wire. Various gauges are used in the United States for different
kinds of wire. The standard scale for copper and aluminum wire is the
American (also known as the Brown and Sharpe) gauge, which ranges from gauge
number 0000, which corresponds to a diameter of 0.460 in (about 1.17 cm) to
gauge number 40, which corresponds to a diameter of 0.00314 in (about 0.008
cm). For steel and iron wires, the standard is the U.S. steel-wire gauge,
which ranges from number 0000000 for a wire with a diameter of 0.490 in
(about 1.25 cm) to number 50 for a wire with a diameter of 0.0044 in (about
You're on the right track, but maybe trying to over analyze
it a bit. I take it you've lived there for awhile, and you
probably have a good idea of any other "trouble spots" you might
have. The trick is to map the circuits which include those
trouble spots, and try to break them up.
There's not really a need to have exact current draws for the
offending locations, but rather to recognize what's causing the
problem, just like you have with the pool filter and the vacuum.
You know right now that one of thse two outlets needs to be
moved to one of the new circuits. You might have 2, 3, 4? cases
like that, and then it becomes a question of hashing out a plan
on which ones to move and how to do it without making a real
If your service panel has room for more breakers, consider
having 2 or 4 new 20A circuits added. An electrician can run
two circuits on one piece of 12-3 w/ground and cover two of
your desired locations. Do that twice, and you've now created
4 new circuits, each having an isolated receptacle for a
trouble spot. One of those will be the receptacle for your
pool filter. Another might be the bathroom plug with that
1800W hair dryer plugged into it, or that kitchen outlet
where you run the toaster oven and the refrigerator across
the room is on the same circuit.
Divide and conqueor, but don't over think it.
I think a whole house circuit map is extremely important. As you
already state, there is at least one overloaded circuit in your house.
Having circuits mapped out will allow you to see if there are under
utilized circuits. In addition, you might also discover some fun
surprises. I discovered that a bathroom GFI outlet was added in-line
to a circuit that supplied all the first floor lights. It was a
simple matter to add in another circuit to just the GFI.
You didn't tell us some other information which I consider essential
to provide a reasonable suggestion. How old is the house? Are the
outlets grounded? Is knob and tube wiring present, or ungrounded
cloth romex? Have you tested all the outlets to see if they are
properly phased (hot to small opening, neutral to large opening) and
grounded. You can also do this with light fixtures to see if the
center pin is hot, and whether the switch controls the hot or the
neutral. What kind of panel do you have. Is it a Federal Pacific?
How large of a service do you have to the house? Are there specific
loads (window AC or refrigerator) that cause other lights to dim? Do
you have the recommended number of circuits for your house per the
NEC? A house should be set up so that anyone can live there without
having to calculate loads on various circuits. If you are living that
close to the line on a number of circuits, it maye be time to upgrade.
When we updated, we considered how the house would be used by both
ourselves and other people. We added an outlet on its own circuit
near each bedroom window so a window AC unit could be used without
interfering with other lights or appliances. We put the outlets of
each room on its own dedicated circuit, and spaced the outlets so that
extension cords were no longer needed. The entire kitchen was on one
circuit so we added two more 20's so that the fridge, microwave, and
toaster oven could all run at once.
On 28 Jun 2003 19:23:32 -0700, email@example.com (G. Mark Stewart) wrote:
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