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Old 02-14-2010, 03:34 PM   #1
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no voltage between legs of a 230v circuit


I went to repair an electric furnace when I noticed that I had no voltage reading between the two hot legs of my 230v circuit. I had a reading of 110v +- on each leg.

The heating equipment in this home is on a seperate meter from the rest of the house. It feeds a subpanel on the side of the house that has one breaker for the furnace and one for the heat pump. When I flip the main in this panel the problem goes away temporarily but invariably returns. Is this a loose hot in the meter box or somewhere on the power company's side?

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Old 02-14-2010, 03:43 PM   #2
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no voltage between legs of a 230v circuit


How are you measuring the voltage at the furnace and with what test equipment? Multimeter?

And how are you measuring the voltage at the panel and with what test equipment?

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Old 02-14-2010, 03:47 PM   #3
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no voltage between legs of a 230v circuit


At furnace with all furnace wiring disconnected I read 110 +- from each leg to ground, and 10v between legs.

At the panel I am getting the same readings with the equipment breakers switched off.

I took all readings with a Fieldpiece sc77 multimeter.
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Old 02-14-2010, 04:07 PM   #4
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no voltage between legs of a 230v circuit


just to check a couple things:

the main to the sub-panel is a 2 pole breaker, yes?

the breaker to the furnace is a 2 pole breaker, yes?

are you saying when you flip the main (in the sub) off and then back on you then get 240 between the 2 legs at the furnace or the breaker going to the furnace?

and when you say the power is disconected at the furnace (to check the voltage), you have simply 2 wires dangling there connected to nothing except at that breaker?

and from this panel, it goes directly to a meter (but not the main meter)



so, when you have this problem, do you have 240 volts on the line side of the main breaker (of the sub panel)?
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Old 02-14-2010, 04:17 PM   #5
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no voltage between legs of a 230v circuit


One of your hot legs has a loose connection. You are measure the working hot leg voltage through the furnace. If you disconnect the power wires from the furnace and measure with a solenoid tester you will probably find that only one leg has power.
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Old 02-14-2010, 04:18 PM   #6
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no voltage between legs of a 230v circuit


Everything you said is 100% correct nap. Voltage on line side of main breaker comes and goes.
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Old 02-14-2010, 04:19 PM   #7
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no voltage between legs of a 230v circuit


Quote:
Originally Posted by brandonmcginnis View Post
At furnace with all furnace wiring disconnected I read 110 +- from each leg to ground, and 10v between legs.

At the panel I am getting the same readings with the equipment breakers switched off.

I took all readings with a Fieldpiece sc77 multimeter.
Good a multimeter! (Yeaaaa!)

Try turning off all the breakers at the panel and see what you get.

(It could be that something which is "on" is feeding power back into a non-working leg...)
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Old 02-14-2010, 04:26 PM   #8
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no voltage between legs of a 230v circuit


I'm at a different location now, I can't do any hands on. I got the same readings on the line side of the main breaker with the other breakers in either position.
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Old 02-14-2010, 04:36 PM   #9
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no voltage between legs of a 230v circuit


if you are getting a bad voltage on the line side of the main breaker, it is something from that point back to the POCO supply. If you have nothing between the panel and the meter and from the meter to the POCO supply, I would contact them to have them check their power.


when you are having these problems, check your main power on the line side of the main in the main panel as well. You may be losing a leg there as well and just not realizing it.


the one this that is odd is that flipping the breaker corrects the problem. Not sure what to make of that.
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Old 02-14-2010, 04:58 PM   #10
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no voltage between legs of a 230v circuit


The panel is connected to the meter box by a very short piece of pipe. Im wondering if vibration or movement from the physical act of resetting the breaker is causing a spotty connection in the meter box to make/break intermittently.
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Old 02-14-2010, 05:22 PM   #11
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no voltage between legs of a 230v circuit


I had similar thoughts. In fact, I repaired a very similar situation where the pinch pieces of the meter base had rusted away almost completely with actually almost identical symptoms as you have posted.



the problem is: to check it out, the meter must be pulled out. Not knowing where you are, what your POCO would say about it, and what you are capable of, I hesitate to suggest such actions as

1. it is often illegal to pull the meter without POCO permission

2. you have hot tabs in the meter base, which is quite compact and I strongly recommend against working in a hot meter base

3. If the meter base is bad, you are going to have to have the POCO pull the power anyway so you can replace the base

4. some areas require a licensed electrician to do any of the involved work


btw: by the time I got called out to the job, the connection had completely gone but the dscription of the symptoms before that point were darn near identical to yours.

Last edited by nap; 02-14-2010 at 05:24 PM.
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Old 02-14-2010, 05:34 PM   #12
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no voltage between legs of a 230v circuit


Thanks for all your help nap. I'm definitely not pulling the meter, so it's gonna be a call to Duke power.
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Old 02-14-2010, 06:38 PM   #13
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no voltage between legs of a 230v circuit


Quote:
Originally Posted by brandonmcginnis View Post
Thanks for all your help nap. I'm definitely not pulling the meter, so it's gonna be a call to Duke power.
Yes. Nap is right on. I had a similar problem on two separate jobs. I traced the problem (by checking point to point) to the meter tabs. One of them was burned. Replaced one of the Tabs on the load side of the meter after the Power Company was called to open the meter box. Lucky thing, there was a Main Switch before the meter, in both cases. (Original 100 Amp. service was old.!
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Old 02-14-2010, 07:07 PM   #14
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no voltage between legs of a 230v circuit


Correction: the two cases with the bad Meter Tabs were, that there was no power at all off one leg. The other two cases, where there was 120v. to Neutral on each separate leg, but Zero Volts between the Two legs, was, that they were connected wrong. One case was a freezer in a supermarket. I was called by the refrigeration service co. that there was an electrical problem to the line that was installed. (Probably by a "Fly-by-night" "Mechanic". Turned out that the (2-pole) breaker was not at the correct position in the panel. The second case was at a driving school classroom. Where I did the wiring for the lights and one line for a 240v. A/C. The panel was using temporary (220v.) power. When it was switched to regular power, the A/C stopped working.
The problem was traced to an incorrect connection by the Electrical Contractor who did the Service wiring.!
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Old 02-14-2010, 10:22 PM   #15
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no voltage between legs of a 230v circuit


If it works correctly, 240 volts and all, for a moment after flipping the main breaker off and back on, chances are the problem is at or near the main breaker.

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