Why does my diesel household generator provide better power than my public line?
When the household generator quicks on in an outage, the lights are brighter, the floor fans work better, etc…. When we are using the public utilities current, the lights are dim, the fans are slow and every time our wellpump quicks on, the lights flicker and dim more. AND, when we have the generator on automatic, it turns on every time the wellpump comes on and then shuts off shortly after the wellpump stops. We have had the current checked by public utilities here and they said the volts coming into the house are fine but the amps which should be at 125 is only 17! The utility company (we live on an island in the Caribbean) says there must be a problem both at the pole AND in the house but how can this be when we have no problems in the house when the generator is on? Also, will running our appliances and electronics with such low amp availability damage them?
your power from the mains enters your house from a down lead connected to power from the street. The down lead is then connected to a power meter, then from the meter via a feeder line to the main circuit breaker panel.
Your generator is most likely connected via its own feeder and switch gear to either several circuits or the entire circuit breaker Panel.
This makes the circuit breaker panel or selected individual circuits on it the common point between the two systems.
So the problem lies either from the pole/transformer or on your house to equipment on your home which includes the down lead, Meter, Meter box/socket, or feeder line to the main CB panel.
I cannot completely rule out your circuit breaker panel or generator switch gear yet because I don’t know details of how your have the gen set wired into the system. So depending on where the switch gear is located you could have an issue with the mains power connection there.
Now in terms of amps your main can provide 125A but its drawing only 17. Reading the amperage by itself doesn’t mean there is problem, rather you aren’t using enough power.
What you do need to do is measure the voltage while items are running and look for a voltage drop.
At the pole you have 125V while you have a number of devices connected which result in a current draw of 17A. Ohms law E = I * R
will tell us that you hav roughly 7.5 Ohms of resistance connected to the mains. In a perfect system all of the devices are connected in parallel with zero series resistance. This allows each device to get full mains voltage. What you don’t know is if that 7.5 ohms is just from your equipment or if it includes any series resistance from a loose or bad connection. Series resistance will cause a voltage drop , leaving less voltage available for your devices to operate.
Motors want to draw the same amount of power P = E * I so if they see less voltage and will run at a lower speed and draw more current.. The higher current flow will cause more voltage drop across the series resistance and leave less voltage for the lights which will look dim.
To find the voltage drop try measuring the voltage of a high amp motor while its running and when its off. Compare the two and see what the difference is If you have significant difference more than 5V you have a voltage drop. Work your way back through the system measuring voltages until you possible see the voltage return to something much closer to the 125V no load voltage.
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It sounds like the problem lies between the main breaker box in the house and the pole transformer. You should look for any burned, damaged segments of wire where extreme heat has occurred. The problem may also lie in the circuit breakers between the box and the transformer if you have that feature.
Yes, it can damage your electronics, because if the resistance in the circuit is high (low amperage through is because of the increased resistance), the voltage on the line will drop quite a bit.
In short, there is little you can do, the utility company is responsible for your problem. Their equipment and or installation is bad.
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Before changing anything, you should measure your voltage at different points along the circuit. Use a long copper wire and attach one end to your ground rod at the service entrance. If you do not have a ground rod, this is a potential problem. Attach the other end to your volt meter and measure voltage at you incoming power, before the service box, a the service box and then at each breaker. Each point should be within a few volts of each other, a larger voltage difference infers a high resistance, and this is the source of your problem. If you house has a low incoming current, there must be a high resistance somewhere in your incoming power. The most likely event, is a loose or corrodes connection. This is potentially a fire hazard. If you cannot find it, called a licensed electrician. It might save your life.
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your power from the mains enters your house from a down lead connected to power from the street. The down lead is then connected to a power meter, then from the meter via a feeder line to the main circuit breaker panel.
Your generator is most likely connected via its own feeder and switch gear to either several circuits or the entire circuit breaker Panel.
This makes the circuit breaker panel or selected individual circuits on it the common point between the two systems.
So the problem lies either from the pole/transformer or on your house to equipment on your home which includes the down lead, Meter, Meter box/socket, or feeder line to the main CB panel.
I cannot completely rule out your circuit breaker panel or generator switch gear yet because I don’t know details of how your have the gen set wired into the system. So depending on where the switch gear is located you could have an issue with the mains power connection there.
Now in terms of amps your main can provide 125A but its drawing only 17. Reading the amperage by itself doesn’t mean there is problem, rather you aren’t using enough power.
What you do need to do is measure the voltage while items are running and look for a voltage drop.
At the pole you have 125V while you have a number of devices connected which result in a current draw of 17A. Ohms law E = I * R
will tell us that you hav roughly 7.5 Ohms of resistance connected to the mains. In a perfect system all of the devices are connected in parallel with zero series resistance. This allows each device to get full mains voltage. What you don’t know is if that 7.5 ohms is just from your equipment or if it includes any series resistance from a loose or bad connection. Series resistance will cause a voltage drop , leaving less voltage available for your devices to operate.
Motors want to draw the same amount of power P = E * I so if they see less voltage and will run at a lower speed and draw more current.. The higher current flow will cause more voltage drop across the series resistance and leave less voltage for the lights which will look dim.
To find the voltage drop try measuring the voltage of a high amp motor while its running and when its off. Compare the two and see what the difference is If you have significant difference more than 5V you have a voltage drop. Work your way back through the system measuring voltages until you possible see the voltage return to something much closer to the 125V no load voltage.
References :
Current is strictly a function of the load that you apply to the source. The problem you are experiencing has nothing to do with current. Instead, the things you describe - dim lights, fans less effective - all relate of voltage and suggest that the voltage delivered by the commercial utility is lower than the voltage delivered by your local generator.
There are two possible interpretations - one that your generator is delivering an higher-than-normal voltage, and the other that the utility is delivering a lower-than-normal voltage. It is possible that both interpretations are correct.
I suggest that you first measure the voltage under the two conditions. You will probably see a difference. I assume that you are on a 60Hz system - in that case, the normal range of voltage will be 115-120.
Normally, you don’t want the voltage to be too high because that can cause damage to appliances and electronics. The upper limit is probably somewhere in the 125-130v range.
If the voltage is too low, motors will ‘work harder’ to deliver the same mechanical torque to the equipment they serve. Fans and pumps will be slower, and the motors will run warmer. If the voltage is too low, that additional heat could cause damage. The lower limit is very hard to predict - but if you see a voltage of 100 v or lower, you need to take action.
When you are being supplied by the commercial utility, they probably regulate the voltage at their end of the circuit to be somewhere in that range. But as you (and your neighbors) consume power, that consumption causes a voltage drop in the circuit, with the result at the voltage actually delivered at your site will be lower. That’s not a problem - it’s the way it is. Basic physics.
The solution is for the utility to reinforce their distribution system. That reinforcement can take many forms - it could include reconductoring the circuit (bigger wires will cause less voltage drop), reconfiguring the circuit (so that less load is being served through the set of wires delivering power to your site), or application of some form of local voltage regulation, either inductive voltage regulators or power factor capacitors. These are not inexpensive solutions, and it may take considerable effort by you and your neighbors, together with assistance from whatever government regulatory agency monitors the electric utility, to convince them to make that investment.
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