I live in an apartment.One evening, there was a problem with POCO neutral (disconection)and single phase supply to my apartment was off. It was high summer and no UPS in my apartment. My family members could not manage with candles. To alleviate the discomfort and to be sleep through the night, the neutral was connected to ground after the POCO meter and Lo and behold! The power supply to my apartment resumed and we slept peacefully. Next morning, the POCO neutral was set right. At the end of month I received POCO bill for electricity consumption for my apartment. I was shocked to find the bill amount was three times my usual bimonthly amount. I surmise that the return current that flowed over ground instead of through neutral during that neutral broken period might have encountered significant resistance, the power loss of which might have. increased the POCO meter reading. What are your views? Thanks.
Reason for increase in my POCO bill
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mbrooke
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Is your supply normally TN-C-S or TT? Does your meter only "measure" (meter) the live?
Its possible that the neutral is being metered by mistake and when grounded down it was measuring parallel current from the POCO neutral. Another possibility is that the high impedance of the earth was causing excessive voltage drop and motors/compressors were stalling repeatedly cycling on their overloads.
It is TT. The POCO meter is single phase, electromechanical type with phase and neutral input and output terminals.
mbrooke
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Thanks- is it wired correctly?
Yes please.
mbrooke
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In that case I can't think of a circuit scenario that would cause a grounded neutral to read more. It would have to be load and voltage drop related IMHO.
You mean a power loss taking place only in the energy meter outgoing neutral due to its increased resistance would not be measured by the energy meter?
mbrooke
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The increased resistance of the ground return would cause motors to stall drawing more current. That extra current would be measured by the meter.
Thanks mbrooke. I now remember the refrigerator was on for some hours. Now the picture is clearer because of your deliberation. I hope the next bimonthly PoCo bill due in July would be normal again.
mbrooke
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Thanks mbrooke. I now remember the refrigerator was on for some hours. Now the picture is clearer because of your deliberation. I hope the next bimonthly PoCo bill due in July would be normal again.
Welcome- hopefully you will never have an open neutral either. But also consider yourself lucky despite the bill- here in America an open neutral often results in damaged electronics which amass greater $$$$$.
JFletcher
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The problem could also be in a way that they read or estimated your meter in the previous months... If they went by an estimation, then read your meter, the differences between the two could amount for the high bill. Could have read the wrong meter, could have read the meter incorrectly, etc.
The only time that I have had a exorbitantly high bill at a residence is when I was doing a ton of laundry in preparation for a move... All that hot water and electric drying really ramped up the bill...not entirely unexpected tho...
Edited to add... If the neutral problem existed at your residence just for 12 to 24 hours, and nothing else changed that month, you would have to have something like 90 times your normal electric draw during that period to get a true 3x higher than normal bill.
The only time that I have had a exorbitantly high bill at a residence is when I was doing a ton of laundry in preparation for a move... All that hot water and electric drying really ramped up the bill...not entirely unexpected tho...
Edited to add... If the neutral problem existed at your residence just for 12 to 24 hours, and nothing else changed that month, you would have to have something like 90 times your normal electric draw during that period to get a true 3x higher than normal bill.
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They charged/punished you for sneaking around the neutral!
kwired
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Resistance in the return path puts it in series with the load(s). Might make a motor draw more current, but unless if it is a high enough resistance they can't necessarily do any useful work, and either burn out or open overload protection, at which point they stop carrying any current. Resistance loads simply are in series with another resistance and see less current. If this goes on for long period, then you would have long run times and added loss where the additional resistance is, but if just for overnight, I can't see it making a noticeable difference in the energy bill.
mbrooke
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Ok- you both got me- I missed this part:
I assumed the N was tied to ground for a whole month. If not the case then you guys would be right, a LOT of current would have to be drawn in 24 hours to equal 2 months of electric bill.
I think JFletcher is right here, the bill might have been estimated until it was actually written down when the neutral was hooked back up. And it would make sense in some areas that are heavily populated.
mivey
Senior Member
2S metering does not use the POCO neutral. It uses the two line currents and the line-line voltage.
Current returning to the transformer through the earth is still the same current as what left and was metered. I doubt you could have tripled your usage in one night and still run your unit adequately. You would have had to shunt around your unit with a lower resistance causing a huge increase in energy use, not add a series resistance.
Current returning to the transformer through the earth is still the same current as what left and was metered. I doubt you could have tripled your usage in one night and still run your unit adequately. You would have had to shunt around your unit with a lower resistance causing a huge increase in energy use, not add a series resistance.
mivey
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Is this a 2-wire meter?
mbrooke
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Correct- though if metering only two legs of 120/208Y, you would need a 12S (ie, 5th jaw). Assuming the OP's profile matches the location in question most likely its a single stator, single current coil meter (2 wire) which would require a neutral for the voltage coil:
Very true, I agree.
But here is one theory I have: If the neutral and line are somehow swapped at the meter, grounding the neutral after the meter can cause current flow from the utility neutral through the meter's current coil and down through the ground going back to the LV supply transformer. This current could be substantial given the right network conditions, ie if all the customers are TT and the voltage drop across the utility neutral is great enough.
mivey
Senior Member
If the wires are swapped and the line grounded, how does that solve the open neutral problem for the load and how would the load function well with a faulted supply?
mbrooke
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Swapped only at the meter (the neutral is going through the current coil instead and line/load rotated as to not spin backwards), thereafter the neutral is still grounded down in our contingent scenario. The meter does not care about polarity relative to earth. Only that current flow through the coil heads toward the load and that the voltage coil sees a 230 volt potential. In the normal ungrounded neutral state the meter will function without arising any suspicion. When the neutral opens, the load stops working-- the neutral is then grounded down. The resistance of the building grounding electrodes and the LV substation electrodes is low enough that the bulk of the voltage drop is across the load and as such they function desirably. This basically proves we have a low resistance path between the structure and transformer X0. The meter at this point does not spin, however, when the neutral is reconnected a portion of the POCO neutral current uses the building's electrodes to get back to the X0. This current is registered by the meter and may be large enough to cause high readings between restoration and when the neutral was eventually ungrounded at the building. This would probably be unheard of in the US, but 400 volt systems in many parts of the world are supplied by 250-750kva transformers and run considerable distance with the neutral often being grounded at few (if any) points passed the transformer location.
I know its a bit of stretch, but its the only scenario that I can think of that would cause the meter to actually register so much power in a short amount of time.
Yes it is a 2 wire meter with phase and neutral incoming and outgoing.
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