open neutral and energy usage

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Re: open neutral and energy usage

Originally posted by canman:
Peter,then are you saying that the statement that the voltage in all parts of a parallel circuit will be the same is not true?And are you also saying that the resistance of a given number of resistances is not always less than the smallest one of the resistors in question when they are placed in parallel?
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No, not at all. :) As Wayne and Ed have demonstrated, when the neutral is opened we no longer have a purely parallel circuit.
 
Re: open neutral and energy usage

peter d,

"True, but the cold resistance of a heating element or a light bulb is still a fixed value.

Is my water heater example incorrect? Ohm's law must surely still apply. When you apply less voltage, the element does not get as hot, therefore it has less resistance than it would at a higher voltage. [higher temp = higher resistance]. But isn't this offset by the lower voltage?"

Your example is correct in principle, but resistance of heating elements, etc., is a strong function of temperature. The heater would reach some steady state temperature at the lower voltage, and power would be somewhat more than the one quarter you have predicted. Also, the resistance would be somewhat stabilized by the temperature of the water. It is a tricky little problem.

This problem has been made too complicated though. Simply put, we have one group of parallel loads tied to one leg in series with another group of parallel loads tied to the other leg. We then have a voltage divider which changes as the loads change.
 
Re: open neutral and energy usage

rattus,

I think we need some context for the discussion. :) I was just attempting to explain this comment that canman made:

If you put the pencil to it i beleive that you will find that in this scenario with a given resistance power usage increases 4x.
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Hence my water heater example.

The heater would reach some steady state temperature at the lower voltage, and power would be somewhat more than the one quarter you have predicted. Also, the resistance would be somewhat stabilized by the temperature of the water. It is a tricky little problem.
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Right, I agree. But the 1/4 less would still bring us to a ballpark figure if we halved the voltage of the water heater, and in most cases, is close enough. :)

This problem has been made too complicated though. Simply put, we have one group of parallel loads tied to one leg in series with another group of parallel loads tied to the other leg. We then have a voltage divider which changes as the loads change.
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Not necesarily. We are all saying the same thing with different words. I do like the simple way you described it, but many times we need to look at the math to truly understand and explain something. I think Ed's diagrams do a good job of uncomplicating things. :)
 
Re: open neutral and energy usage

Canman, my opinion on your story which I believe was the subject of a Mike Holt newsletter, is that the neutral was open on the primary side of the POCO transformer rather on the secondary service side. Since the primary and secondary neutrals are tied together at the transformer, this would put primary voltage on the service neutral which would then try to return to ground through the service grounding electrode and the well pump which as I remember was destroyed along with the wiring. There was no municipal water to bond to. Depending on the resistance to ground this would put many thousands of volts on the service neutral and consequently all neutral conductors in the house.

This would be the ONLY explanation for the exploding light bulbs and the surge suppressor fire. If you pay attention to what has been said about the division of current and voltage when the service or multiwire neutral has been lost you will see that the 240 volt loads would be unaffected and the 120 volt loads may not even see 240 volts. Even if they do that should not be cause for light bulbs to explode or surge suppressors to catch fire and as I remember, the other "pyrotechnics" that ultimately caused the house to burn to the ground.

Nope, that voltage was WAY higher than 240.

-Hal
 
Re: open neutral and energy usage

Back again!Merry christmas everyone.All have made some good points but this is how it looks to me.If you only had two circuits in your home made up of multiple resistances in parallel and you lost your neutral then you would indeed have a series -parallel circuit until all resistance burned up on one leg or the other,however this is not true in most cases as you generally have at least 10 or 15 circuits.All of these circuits have their loads in parallel between the hot and neutral and this does not change.Then as the neutral goes away each circuit could be looked at as 1 total resistance on one phase or the other.To complete a circuit a resistor from phase A must find a path to phase B.This can only be done through the parallel resistance on phase B, placing all loads on circuit A phase A in series with circuit B phase B completes a path.However you must remember that you have many more circuits matching up in the same way at the same time as all 15 circuits are energized and possibly carrying a load.This will cause another parallel circuit to occur because you have multiple circuits with no neutral.So it looks like to me that you would have parallel circuits in parallel across phase A and B until you got down to 2 circuits,and they would all be at an elevated voltage for at least part of the time.By the way when it happened on my house it was on the underground between my house and the transformer,I still had both hots,power company came out in the snow and strung a temporary cable to my house from the transformer.One of the few times that it snowed in Texas.
 
Re: open neutral and energy usage

thanks for all the info lets look at undervoltage as stated when tested there was 180 -195 volts showing by poco
now the furnace is running lets say at 180 volts instead of 220 elements not heating up to proper state therefore heater would run for longer to aquire temp in the house same senario with hot water tank and stove correct?
 
Re: open neutral and energy usage

Chevy,

Low voltage would mean that the heaters would draw less current and stay on longer, but the total energy usage would remain the same.

Now, induction motors, say on a residential AC of 3 to 5 hp, would draw excessive current and perhaps trip breakers. If they had a heat pump augmented with resistive heat, that might explain the high bills and high currents.

From experience, I know that an old 3-ton AC draws about 20A @ 240V. The breakers are 30A.

[ December 27, 2004, 08:21 PM: Message edited by: rattus ]
 
Re: open neutral and energy usage

well thanks everyone for the quick responses i guess customer has just a freak of nature thing happening will suggest putting in claim for damages thanks anyway
 
Re: open neutral and energy usage

No freak of nature.Power is equal to volts x volts divided by resistance.2x the volts =4x the watts.Look at your earlier post on page one where you said power consumption went from 150 to 35 or 40 per day after the service was changed.Do not take anyones word just use the formulas and you will see that if the voltage is reduced by one half,power reduces to one fourth as discussed in previous posts.Isnt it interesting that your power was reduced to about one fourth?
 
Re: open neutral and energy usage

What if the floating neutral messed up the control circuitry to the point that the heaters and AC compressor were running at the same time? That is, they were fighting each other.
 
Re: open neutral and energy usage

rattus, that is a posibility and i have seen it happen.And would exsplain breaker tripping.Most AC that i seen have a 240 to 24 volt transformer but i won't rule out that something like this did not happen
 
Re: open neutral and energy usage

well before we trail off to much there is no ac
the furnace is only a backup source lights alone were equting to 2700kw/mth in the summer without ac furnace is forced air electric the same unit as a gas forced air but with electric burners
 
Re: open neutral and energy usage

canman the service as i stated was damaged between the hous and the transformer just as you say yours was i,m taking it your underground neutral was burn,t off also between house and transformer . question is, was there any decrease in your usage after it was fixed?
 
Re: open neutral and energy usage

Just talked to the smartest man I know. He suggests that some sort of fault in the dwelling caused the neutral to burn out. This fault continued to waste energy until the neutral was replaced. Then there was enough current to clear the fault, and all was well.

Could have happened!
 
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