Sawdust on the Floor

I had a neighbor recently ask me about what they thought might be a defective outlet in their home. They figured that the outlet must be bad because every time they tried to use the outlet, a circuit breaker would trip. After a little Q &A, we got down to the real problem, the outlet performed correctly until they plugged in the vacuum cleaner, then the breaker would trip. They went on to explain that when they tried another outlet across the room, everything worked OK. Ergo, the first outlet had to be bad.

While I agree that it might be a defective outlet, there could also be other issues. First, all outlets and light switches in any particular room of your home are never wired to the same circuit breaker. The load for every room is split between two or more circuit breakers. So unless you have a total power failure, no room will ever be left in total darkness. With that in mind, I suggested that they verify that in fact both outlets are on the same breaker. If so then I would replace the suspected defective outlet. If you don’t know which breaker is connected to which outlet, and you don’t want to go about turning off every breaker until you find the correct one, use a Digital Circuit breaker detector.

If the outlets prove to be on separate circuits, then I would want to consider the actual load on that circuit breaker. Circuit breakers are rated in Amperage, or Amps, which is a measurement of the amount of current flow through the circuit. When the circuit breaker trips, it has sensed a current draw over the rating of that circuit breaker.

Now remember that the current load in any room will be split between two or more circuits, so you may have an outlet in your living room on the same circuit as one in the basement, or bedroom. This may not seem logical, but really it is. The electrician who wired your home had to balance the need to keep the number of circuit breakers down, while at the same time not creating a situation where the circuit would normally be overloaded by everyday use. The electrician wouldn’t connect an outlet where a washing machine would normally be connected with one that provides power to a microwave. Both of these devices draw large amounts of current.  If both were every turned on at the same time, the circuit breaker would trip.

So, let’s say that the circuit breaker that always trips is labeled as a 15 A ( 15 Amps) breaker. Can you just replace it with a larger amperage breaker, like a 20A. Not unless you like to see fire trucks parked out in front of your home. Never upgrade the size of the breaker. The wire that connects your circuit breaker with the rest of the house, is rated to carry a maximum amount of current. Typically, you will find that a 15 A circuit has been wired with 14 gauge wire, which is rated for 15 Amps, but not 20 Amps. If you were to replace the circuit breaker on this circuit with a 20 Amp breaker, the 14 gauge wire would heat up to the point that a fire may occur, long before the circuit breaker would ever trip. As current passes thought the conductor( wire), it generates heat, a larger wire can dissipate a larger amount of heat before it causes a fire.

If you are my age, you may remember all those safety messages about not over loading an outlet, with extension cords. Older homes were not wired with the same amount of outlets per room as the current building codes require, so our parents relied on extension cords to multiply the amount of outlets in any room. Your typical extension cord is made of 16 or 18 gauge wire, the larger the number the smaller the wire diameter. So we have a circuit that is protected by a 15A breaker, that is extended using a wire that can carry even less current; a fire just waiting to happen.

Today’s new high tech families are creating the same type of safety issues. Look behind your computer stand, I will bet you have a multitude of power cords, from the computer, printer, monitor and on and on, connected to a buss strip. Unless your room was wired with the intent of connecting this many devices, you will have to use a buss strip. But please use a quality buss strip, one that has a heavy gauge wire to the buss strip, and also contains its own circuit protection. It’s much better to trip the protector on the buss strip then to over load your house wiring, if you create an overload condition.

How many devices can you safely connect to any circuit will really depend on the device. Take a look at any electrical device you have. Some place on the back you will find a label that will contain the normal voltage that the device will operate at, and an Amperage value. The value listed will be the maximum amount of current the device will ever draw. If you were to add up all the devices connected to any circuit, you would soon realize that this just doesn’t make sense. You would have way too much of a current draw. For instance I have a pencil sharpener that is rated at 2.0A, so logic would say that if I had 8 similar devices connected to the same breaker, I would always be overloaded.

Any electrical device will draw maximum current only at two times. Once when it’s first turned on, this is known as starting current, the other is when the device stalls or locks up. Starting current is only present for a few milliseconds, the actual running current is normally about 60 % of that value. So the current draw value, which may also be labeled as full load amps(FLA), is a misleading value, but all manufacturers report it the same way to avoid confusion, or at least that’s their logic.

There is really no way to predict how many devices can be installed on any circuit, unless you were to actually measure the current of all the devices on the circuit and then add them up. Electricians use a device known as a clip on Amp Probe to measure the current draw of any device. this device is simply clamped over power lead in your circuit, As Current passes thru the wire, the current is displayed on face of the meter.

In all of the years that I have been working with this kind of thing,  I’ve learned  that some people want to know every detail about the subject, and there are those who are  happy just knowing the facts, and don’t really care if the egg came before the chicken or is the other way around. If you are the type that needs all of the details, there are mathematical ways to calculate the all of relationships of Current, Voltage and Resistance. The Pie chart below is for you, it is known as Ohms Law, and it defines the principals of electricity. But if it’s “my eyes are starting to glaze over” time for you, then please skip the next section, I totally understand.

The way this pie chart works is this, if you want to calculate the amount of current in circuit, you would use the formula I=E/R, where I is amperage, E is voltage, and R is resistance. Resistance is as the name implies, the resistance to current flow, the larger the resistance, the lower the current flow. It is assumed that the voltage remains constant.

Sorry I got carried away, getting back to our friends problem they had simply over loaded that suspected breaker. So the outlet was not bad, and they now always use the outlet on the other side of the room. If in your case it turns out that the outlet is defective and you’ve never changed an outlet before, see my post from 1/11/09 , “How Do I…Replace a Defective Electrical Outlet?

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1. How Do I…..Replace a Defective Electrical Outlet?
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