The power coming into a residential home is 240 volts. How much does this volts fluctuate before that could be

Question

The power coming into a residential home is 240 volts. How much does this volts fluctuate before that could be some damage to any of our appliances or wiring?
Also, if one of the load lines are higher voltage that the other would that cause problems or damage?

Answer 1

Over voltage is typically not an issue. Under voltage, or "brownout" conditions are extremely damaging to most electrical devices.

Ohms law reads V=IR, meaning voltage is proportional to the current times the resistance. For most devices, the resistance is a fixed value. Thus when the voltage goes down, the current goes up. This high current will create heat and burn out almost anything other than a light bulb.

As to the load lines. the 240V is achieved through two 120v lines 180 degrees out of phase. Typical things that utilize 240V are dryers and ranges which will be unaffected by the drop in voltage of one leg. The appliance just won't work all that well. A well water pump however will not fare as well with an extended low voltage supply.

Most devices in the household run on 120V so the circuits running on the unaffected leg will appear to operate normally, while the circuits running low will have all the liabilities mentioned above.

Note that "surge supressors" such as those used as power strips for home computers will not protect against low voltage, and can often cause mose damage than they protect against. By using the switch on the strip, you are allowing the magnetic fields in the transformers of all connected devices to collapse at the same instant creating a surge equal to the sum of all devices to hit the power supplies. Also if the switch used in those cheap $20 power strips is not rated for the current actually being drawn by everything plugged in, it will arc, creating multiple mini surges during the several milliseconds it takes for the contacts to open or to close.

Another myth that the manufacturers perpetuate is that a cheap 75 cent varistor acting as a shunt between poles will protect your computer against voltage spikes. In reality, the response time for such a component is so slow that a true surge will be well by the varistor long before it shorts out, and in the mean time, the power supply on your PC will be toast.

By the way, DAV above is mostly correct. What he is recommending is a line conditioner, or power conditioner and can be achieved however without batteries, and can maintain full output at a 40% under voltage. Where he is wrong, is that a good UPS "battery backup" is not only a backup, but also a power conditioner. Some UPS devices are active and are always in-line conditioning power, others are passive and typically run in standby mode waiting for a power failure before cutting in. The protection is never provided BY the batteries, but by the power conditioning circuitry.

Answer 2

Generally the voltage is plus or minus 10 per cent. Most stuff won't be harmed at 10 per cent plus or 10 per cent minus the 240. It's not possible to give you exact points at which harm will come as it depends on the type of load and how hard they are being worked. Motors and compressors will be damaged first, lights don't much care (they'll get dim), hopefully electronic equipment will shut off at low voltage.
If one line is lower than the other it shouldn't make much difference if the voltage is still within the 10 percent limit. I may not be thinking of all possibilities so some things might act a little funny.

Answer 3

Unless you live next to an auto plant, your incoming power quality should be pretty stable.

Most of these answers have some truth to them but the most important question to be answered is why you have voltage fluctuation. This could be caused by loose connections anywhere withing the wiring system from the utility company transformer to the circuit breaker (or fuse) panel.

If you are seeing your lights dim and then get brighter regularly, this, often times, indicates a loose neutral connection.

You can start buy contacting your electrical utility company and asking them to check the incoming voltage and connections. They may tell you to contact an electrician first but it's worth a shot. If the utility company does check and find no problems, you should consult an electrician.

Answer 4

Well.... the lines fluctuate a *lot*, and over time will damage appliances, especially computers. Each fluctuation is a "hit", and repeated hits add slightly to the damage to the appliance. Over time the appliance dies.... just as a person would if they were repeatedly hit in the head like a professional boxer. For most people they use surge protector strips for their most sensitive equipment such as computers and printers. If you really had the money, then you would get an industrial strength surge protector whose size matched the number of appliances you wished to protect. Such an industrial strength surge protector uses batteries between the power lines and your equipment. The power lines charge the massive massive batteries, and the batteries then by their nature smooth out the power to a very smooth and dependable level, and it is then the batteries that supply the smoothed out power to your equipment. Do not be fooled by "back-up" battery powered supplies, as their batteries only kick-in during a power failure and do not supply power to your appliances during normal daily operation.

Answer 5

Yes, having substantially lower voltage on one or both phases can damage electrical equipment. Best way to completely protect everything in your house from voltage spikes and brownouts (voltage drops) is to install BOTH a surge suppressor AND a surge capacitor in your service panel. Best done by an electrician. It may cost you $150 to $400, depending on where you live.

If you are seeing a big difference between the amp load on the two 120 volt phases of your service, you may have an imbalance in your circuits (too much load on one side.) This can result in dangerous induced current on the neutral so you should have it checked and corrected by having an electrician rearrange the circuits in the panel.

Answer 6

Not a single appliance will be damaged due to drop in voltage.

The reason is that all motors made today are thermally protected and if the voltage drops, heat increases within the motor and the thermal switch switches the motor power off. So no damage occurs.

The Mixer and Grinder, those countertop appliances will not be damaged either. Those are induction motors and have the same protection as your AC, your Refridgerator WasherDryer and so on So dont worry about this at all.

Answer 7

Yo James M, not all motors are thermally protected. You need to check the nameplate on the motor to see if it is protected.