Fixing Blown Fuse the Hard Way

[G. Mark Stewart]

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.

Mark

[Ron]

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.

[EJ]

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 be careful.

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 breaker.

EJ

[Tom Pendergast]

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 mess.

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.

TP

[G. Mark Stewart]

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- sectional area.

Sorry to go off on a tangent, but this has always bugged me, and it helps me understand the whole picture.

Mark

[EJ]

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

0.11 cm).

EJ

[Mike Hunt]

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.