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over voltage

Brad It maybe a loose neutral, however Mr Wallace is working on a 208 to 240 volt piece of equipment and there is not a neutral involved or at least we know of none. Currently Mr. Wallace is testing from A leg to B leg and his readings are not where he feels they should be. Your coworker is correct that a floating neutral can drive one crazy as well as damage equipment. Best Wishes J.Lockard

Comments

  • ed wallace
    ed wallace Member Posts: 1,613
    over voltage

    have a customer who has a 3 ton single phaze central a/c thats rated at 220 volts I am getting 153 volts each leg to ground electrician looked at it today said over voltage is ok I am of the belief that overvoltage is bad for the condenser need any and all comments

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  • Charles G.
    Charles G. Member Posts: 113
    Over voltage

    Generally voltage variances are +/- 10%. A generic spec sheet in front of me says voltage spec is 197-253 V.A.C. What is the voltage between the 2 legs? Anything over the above spec will make things run real fast for a real short period of time. The good news is it won't do that for very long...
  • Eugene Silberstein
    Eugene Silberstein Member Posts: 1,380
    Distribution Transformers

    The didtribution transformer takes the high voltage from the power company and reduces it to the 220v/110v supplies that are used in reseidences. These two, 110 volt secondary power supplies are in phase with each other and should, under normal circumstances, add together to give you your 220 volts.

    Since you are reading 153 volts to ground on each of the two hot legs, it would appear that you are supplying 306 volts to your condensing unit. Is this indeed the case?

    I would check the voltage at the circuit breaker panel in the house and, if the situation is present there, the power company should definitely be called in. If the power at the circuit breaker panel is "normal", I would check the line running from the breaker panel to the condensing unit, looking for sources of magnetic field interference.

    It sounds like there is voltage being induced in the line, in a manner similar to that when a rotating motor causes voltage to be induced across the start winding.

    The voltage reading of 153 volts is actually the peak value of a 110 volt power source. The RMS value is the peak voltage times 0.707.

    Is it possible you are not using an RMS meter?
  • ed wallace
    ed wallace Member Posts: 1,613
    over voltage

    I am using an UEI 832 meter its a true rms meter can i safely go from leg to leg with out shorting out the meter ??

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  • jim lockard
    jim lockard Member Posts: 1,059
    Mr Wallace

    You can and you need to connect your meter line to line and read the voltage. What is you voltage from line A to Line B.? You could have any number of transformer connections that could give you a high reading, Such as an open delta or a grounded delta configuration that will give you a high leg voltage. Listen to your electrican most likly he knows how the local power company works. Best Wishes J.Lockard


  • My old boss said never go to ground when checking voltages because there are to many variables with the ground. He said to always check from one side of your source to the other and I've had very good success that way. I too am curious what the voltage is between the legs.
  • Techman
    Techman Member Posts: 2,144
    Voltages

    Testing "leg to leg "is manditory on all 208/230v 1phase and 3phase systems,and so is testing each leg to ground.When testing any 115v or 24v systems ,one meter probe gets connected to the neutral/ground leg and the other probe to the "hot "leg.Each test has its purpose in troubleshooting.On 1phase, a loose /broken neutral will require a "ground" connection to figure out what is wrong in the system.Good Studying TO All!Over?under?voltage. Both will kill any motor/compressor.
  • Empire_2
    Empire_2 Member Posts: 2,343
    Check the Unit Loaded and Unloaded

    If you are checking loaded you are essentially reading the run cap in the circuit. Try it Unloaded or off and check your line side. This should set you at ease.

    Mike T.
  • ed wallace
    ed wallace Member Posts: 1,613
    voltage testing

    I am more familiar with 24volt and 110 voltage circuits thank you for the advise will check the voltage this weekend niether the outdoor fan or compressor are working so either the contactor is burnt out or both motor and compressor are burnt out i will take 2 digital meters and check the system out will post what i find

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  • Brad White_91
    Brad White_91 Member Posts: 25
    Floating Neutral?

    Is the voltage consistent across the legs? I had similar voltage fluctuations once, 145 volts per leg then down a few, up a few and difference between each (hot to neutral).

    What brought this to my attention was the frying of several electronic components and my UPS going haywire (activating on my computer circuit).

    I spoke to an electrical engineer co-worker and he immediately suggested a "floating neutral" was a good possibility. It was.

    What happens is that the neutral becomes loose and the potential between that and any associate hot leg fluctuates accordingly. The neutral in question was just outside the 'peckerhead' at the overhead service connection. Good mechanical coupling and she was done. No problems since.

    Just a thought.

    Brad
  • Marty
    Marty Member Posts: 109
    digital meters

    UEI= unreliable electrical instruments

    That being said any digital type meter true rms or not can produce some very strange readings to ground
  • Jim Bergmann_3
    Jim Bergmann_3 Member Posts: 5


    Lets get back to the basics here. Are the batteries in you meter good? Even a Fluke meter will show strange readings with bad batteries. Second, this is a residential system; each leg should be 110, 115, 120v maybe as high as 132 at +10%. Neutral and ground have the same potential in a 240v single-phase system. A loose ground or no ground could cause some of the same erratic readings. ALWAYS read from leg to leg and leg to ground. If there is no path back to ground you will read 0 volts even if power is there. You need to have a meter that is CAT 2 or 3 for your application a Fluke 16 is about $120.00 and is one of the best meters for the money. You can also get a Fluke 16-322 kit that includes the amp probe for about $230 with a hard case. If you are really having these high voltages lights in the house would be very bright, and other appliances would be failing. You measured voltages would be far above the safe operating voltages for most appliances.
    Attached is a handout I use in some classes

    Thanks
    Jim Bergmann
  • jim lockard
    jim lockard Member Posts: 1,059
    Good point

    Jim we can saftly assume that the light bulbs are not blowing in the home. J.Lockard
  • Ed Wallace_3
    Ed Wallace_3 Member Posts: 2
    over voltage

    I went to work on the a/c this morning checked leg to leg got 243 volts on line side of contactor removed wires from load side got 0 volts changed out the contactor the out door fan does not run but gets warm to the touch compressor hums and trys to run then locks out on overload tried calling goodman to check the size of a/c was on terminal hold for 30 minutes this morning and again this afternoon anyone know who the local distributor is for goodman in the metro boston area ?
  • don_156
    don_156 Member Posts: 87
    Sounds like

    a bad dual capacitor to me.
  • jim lockard
    jim lockard Member Posts: 1,059
    I was thinking

    the same Don change the cap Mr. Wallace and lets put this post to rest. Best Wishes J.Lockard
  • Ed Wallace_3
    Ed Wallace_3 Member Posts: 2
    over voltage

    if i had been able to reach tech support at goodman today maybe i would have been told the capacitor had gone bad Jim I am sorry i took up valuble space on this portion of heating help.com thought i would get better support here then at some other hvac site sorry didnt know i needed your permission to ask for help
  • Techman
    Techman Member Posts: 2,144
    Hi Ed!

    Totally opposite on Jim,s last reply Mr. Wallace.As was said "Best wishes"
  • jim lockard
    jim lockard Member Posts: 1,059
    Mr Wallace

    sounds like you took my post out of context. Best Wishes J.Lockard
  • Techman
    Techman Member Posts: 2,144
    Hi Ed !-Mechanic to Mechanic

    I ask questions here ALL the time.Some questions from other people are baffeling sometimes,sometimes I think I know the answer,and sometimes I do know the answer.Helping is what this is about.So ask away ,say away,learn away,but don't go away.
  • Eugene Silberstein
    Eugene Silberstein Member Posts: 1,380
    I Sincerely Doubt

    I sincerely doubt that Jim meant anything by the remark.

    Let's all play nice.... Now pass me a beer.
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