Electrical Forum - unbalanced voltage in 240 volt / 120 branchs

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Subject - unbalanced voltage in 240 volt / 120 branchs
zimzim	What could be the cause of a sporadic problem that crops up occasionally with this 240 volt single phase main. The main is divided into two 120 volt legs like normal. The problem is that when there is a load applied to either of these 120 volt legs the voltage will drop according to the amount of the load applied to the circuit. At the same time the voltage will increase accordingly on the other leg of the split 240 volt. The sum voltage of the two 120 volt legs is always very close to 240 volt. The variations on the legs have been as much as 60 volts on the low leg and 180 on the high leg. I can turn on a simple single light bulb and cause a big voltage swing. Am I seeing leakage to ground due to faulty wire?
Scott Vickrey	Do you read any voltage between the neutral and ground during the voltage swings? When you read the swinging voltage where you reading them to neutral? If is it differrent when reading them to ground?Check to make sure your neutral is bonded to the grounding system at the first panel and first panel only. Check the grounding system.
electrofried	same as scott said.I would look at the neutral. make sure your lugs are tight .
donnfse	I had a similar situation in my horse barn. I had 120/240 to the barn. I had some work done on my well( had the pump replaced). When the well company was done, my power flaked out just as you had described. I turn something on, the voltage would go down on that leg, and would go up on the other leg by about the same amount. Turns out that the neutral for the barn was tied to the well head casing. It had been accidently disconnected by the well repair company. Repaired the connection, and all was well. So check your neutral connection. It is probably disconnected. IF YOU DO FIND A DISCONNECTED NEUTRAL, MAKE SURE THAT YOU DISCONNECT POWER TO THE CB BOX THAT THE NEUTRAL IS USED FOR. IF YOU DON'T, AND SOMETHING CONNECTED TO THE BOX IS TURNED ON, YOU COULD FRY YOURSELF OR THE EQUIPMENT CONNECTED TO IT.
JimmyDee	If you want a technical explanation of what is happening I will attempt one. The condition is, like that has already been stated, one of a kinda, sorta, open neutral. This puts two loads in series with each other and the one with the greatest load will have the least voltage drop across it. This will put the lesser of the loads with the greatest voltage. (voltage drop across series loads) You probably are getting some neutral effect through your ground rod (s). This is not a good low resistance connection usually that is capable of large current draws like starting a motor. Jim
David Hyatt	If this is happening alot with all circuits it could be also in the meter can. Still think it is a neutral but it could be on the power companys side. If there was no anti-oxident put on the wires it will corode and cause this type problem.
Electricman	Scott hit the nail on the head sounds like an open neutral.
ppesinc	This is a great topic but not for a lay person. If they have an open neutral, as it sounds, the grounding or bond wire must not be broken or loosen. All of the unbalanced current is flowing in it and an arc will happen if this is broken.I would start by calling my power company and have them check from the source to the house. Most power companies in Florida don't charge for this service.
zimzim	I would like to thank all who posted comments to this topic. I now have a few answers to Scott's questions. This is a shop building which has had the main turned off since the last posting. I finally had a few minutes this evening to check on a few things. The Voltage between neutral and ground during the voltage swings is 0. The line to neutral and the line to ground voltage both read the same when the imbalance is observed. My neutral is bonded to the grounding system at the first panel. It is also bonded to the grounding system at an older main panel that was converted to a subpanel. I have checked the neutral connections and tightened them. I have also added another ground wire and rod and bonded it to the main. I still have the problem. Any other suggestions? I do have some aluminum wire to the main and to one of the subpanels. They appear to be good and connections are tight but could corrosion still be the problem?
Scott Vickrey	I'm not getting the whole picture. Is the panel with the problem the main panel or a sub panel. If it's the main I think the problem is on the utility company's side. Call your power provider. Tell them what's going on. They should be able to find the problem.
boccinono	Have you tried turning the sub-panel off? And if so are you getting the same voltage swing when turning on a single light bulb from the main panel. In other words try to isolate the problem. If you still have the problem with the main, I agree with Scott, call the power company. It could be at the transformer. Also the sub-panel should have a isolated neutral. The only reason I say this is because you called it the old main.Please reply back, I am interested in the problem. Hope I helped.
Electricman	The neutral and ground should not be bonded in your sub panel I agree with the others It could be a utility problem. I had a open neutral on an new service twice and both times it was the utility who didnt do the job correctly once they didnt even attach the neutral. It was kinda funny cause they insisted it wasnt them I told them if its me I owe you guys a steak dinner and vice versa needless to say I am still waiting on that steak.