As an academic exercise; In an electrical circuit, that is prone to popping a breaker when running a device, if I add a 50 extension cord as a resister, would I reduce the chance of popping that breaker?
If it is popping a breaker, it means it is exceeding the current limits. Extension cords have lower current carrying capacity than house wires, so you are taking more risks.
That resistance you are adding is going to heat up and may cause a fire.
If you are sure that the wiring and fittings can take more current, and that the breaker is undersized, get a higher amp rated breaker.
As an academic exercise, yes, you will reduce the chance of popping the breaker. Very very slightly.
As an example, let’s take the first 50 foot extension cable that popped up on google, which is #16 wire. The resistance of #16 wire is about 4 ohms per 1000 feet, so figure roughly 0.2 ohms for 50 feet of it.
For this academic exercise, 120 volts at 15 amps yields an effective resistance of 8 ohms. Add in your 0.2 ohms and now you have 8.2 ohms, which reduces the current to 14.6 amps (approx). So in order to pop the breaker, you now need to lower the resistance to at least 7.8 ohms.
Keep in mind that running 15 amps through #16 wire is going to generate about 45 watts of heat in that wire. That’s a fair amount of heat to dissipate.
In the real world, it’s a horrible idea. Breakers don’t trip at exactly 15 amps. If you are lucky, the breaker is still going to pop. You might think that’s not so lucky, but in the real world, the unlucky result is that the breaker doesn’t pop and you instead continually overheat the extension cord and possibly the outlet, and at some point something gives and you end up with a fire. Worst case, your house burns down and people die. Keeping the breaker that close to the edge is also a really bad idea as you can damage the breaker. You really don’t want to be running more than 80 percent of the circuit’s capacity for continuous loads, and if you are borderline popping the breaker then you are most definitely well past 80 percent capacity.
Is this the only device on the circuit? If so, then you need to move it to a dedicated 20 amp circuit, which in most homes means that you will need to install a dedicated 20 amp circuit. If it’s not the only device on the circuit then you need to move things around and plug them into different circuits so that you stop popping the breaker.
As an academic exercise, this is a really good example to use as a teaching lesson for how NOT to solve a breaker popping issue.
When you trip a breaker, it usually means the load is a short circuit or has very low resistance (< 1 Ω). Adding a 50 foot extension cord won’t matter; the breaker will still trip.
But for the sake of argument, let’s assume the following: the voltage is 120 VAC, the circuit breaker is rated for 15 A, and the load is pulling 15.8 A. The breaker will trip, though it will take quite a bit of time. This also means the load is 7.595 Ω.
Now let’s insert 50 feet of 16 AWG extension cord. The cord will have a resistance of 0.4016 Ω at room temperature. Let’s bump this up to 0.42 Ω to also account for two additional contact resistances and a slightly elevated temperature of the conductors due to self-heating. So now the load is 8.015 Ω and the current is 14.97 A. Which means (theoretically) the breaker won’t trip.
But that’s a carefully constructed scenario and is very unlikely to happen in real life. For real life, reread the first paragraph.
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2 cases that may work against this:
One thing to consider is the device will get lower voltage with the extension cord. That’s all well and good for some things and it will just run perhaps slower or dimmer. However some devices will demand more current to compensate for the lower voltage.
You can also get yourself into trouble when a large starting current is needed, starve power at that point that and you are going to delay startup, requiring the high load for a longer time, and circuit breakers don’t just work with current, but current over time. So even if the current is lower overall, it is still too high and now too long and the breaker may trip when it would’t have before.
Also you may shorten the life of the device as well by running it with so much resistance.
If I had a circuit breaker that regularly tripped, I’d probably want to have an electrician check it out and see what’s wrong with my wiring/electricity use. Because that seems like a problem waiting to happen.
That’s a good point. In my model I assumed the load (without extension cord) was a constant resistance. And while it certainly could be a constant resistance, it could also be constant power. Or a resistance that is a function of current. Or something else.
Modeling these things can be can get complicated if you’re striving for accuracy. For an accurate model you would have to take into account the TCR of copper, ambient temperature, insulation type (since it affects the temperature of the conductors), contact resistances (which are nonlinear), the wiring in the walls in the house, the I²t trip curve for the circuit breaker, etc. And then add in tolerances and uncertainties.
I don’t know if this happens in the USA, but in Australia, the consumer can be so far away from the generator that the voltage is reduced.
The company I used to work for supplied machinery to the catering industry and sometimes we had motors specially wound to accommodate the low voltage.
For domestic appliances it didn’t really matter, but for an industrial pie moulding machine that would run for 18 hours a day (they eat a lot of pies over there) it would overheat and run at the wrong speed.
Yes, bob_2, that does sometimes happen in rural areas of the US. I’ve never heard of appliances custom-made for lower voltage, but it wouldn’t surprise me.
Yea, voltage drop due to a long extension cord (and/or the cord have too small of a wire gauge) can be a real problem. Other than the obvious solutions - reducing length of cord and/or increasing gauge of cord - there’s not much you can do when connected to the power grid. However, I have seen generators that have special control circuitry to keep the voltage from drooping too low at the load. There are two techniques I know of:
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An extra set of wires connects between the generator and the load. The generator uses these wires to monitor (“sense”) the load voltage. It’s a feedback controller: when the controller senses the load voltage going above the setpoint voltage, it reduces the source voltage, and when the controller senses the load voltage going below the setpoint voltage, it increases the source voltage. This is the “best” solution, but it requires an extra set of wires connects between the generator and the load.
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If the length and gauge of the extension cord is known and fixed, the generator can simply monitor the source voltage and current and adjust the source voltage to maintain a constant voltage at the load. How does it do this? Well, since the generator “knows” the length and gauge of the extension cord, it can calculate the voltage drop on the extension cord based on the current. It then knows what the source drive voltage should be in order to keep the load voltage at the setpoint voltage. The advantage of this technique is that you don’t need an extra set of wires. The disadvantage is that it won’t work - and could even result in a dangerous situation - if the length or gauge of the extension cord is changed.
In the US, you do have the issue that the voltage tends to drop a bit in rural areas or other areas where long distribution lines exist or heavy loads exist. A few decades ago, the power company would typically specify +/- 10 percent, so your voltage could be anywhere from 108 to 132 volts. Most power companies these days specify +/- 5 percent, or 114 to 126 volts.
One of the things that they do to prevent the voltage from dropping too low is the use of voltage regulation transformers, which will boost the voltage on longer lines. These are adjustable and are sometimes automatic so that they will keep the voltage in range as household loads vary.
I have never seen equipment in the US designed for lower voltages due to this type of voltage sag.
What is common here is 3 phase power. Transmission and distribution lines are always 3 phase, but for home use, typically every home gets a split single phase transformer attached to one of the three phases. With this, you get 120 volts from either line to neutral, and 240 volts from line to line. It’s pretty rare in homes these days, but in some neighborhoods (I believe New York and Chicago still have some homes wired up like this) the homes get 2 lines from a 3 phase system. Line to neutral voltage is still 120, but line to line voltage is only 208 instead of 240. 3 phase supplies like this are rare for homes, but are very common for apartment buildings and businesses. A lot of things like electric clothes dryers and ovens will work at the lower voltage, but won’t heat as quickly. You do find dryers and ovens designed to work on 208 volts. You also can often find office equipment like photocopiers that has a different power supply installed depending on if it is expecting to run off of 208 or 240.
Industrial equipment or things like catering equipment might be designed for 208 instead of 240, but that’s because of 3 phase power, not because of long power lines.
Also to note that voltage plays a much smaller part than frequency when speed of AC motors (induction) are concerned.
Hence in industrial settings, we have to buy very expensive VFDs (Variable Frequency Drives) for controlling motor speeds.
An Australian factory/bakery would normally receive 415 volts/50 Hertz on four wires. I have no idea how far from the transformer they would have to be for the voltage to be affected, but I do know that we were supplying specially wound motors on occasion.
We shipped machinery worldwide and the Royal Navy (with very exacting requirements) was also a customer, so fitting unusual motors and more sophisticated controls was not that unusual.
It’s very easy to overload a circuit with high-current devices. Running an electric space heater and a microwave oven at the same time could do it.