One circuit 125V, others 117V, why?

[IGot2P]

Approximately 8 years ago I built (with the help of a contractor) a

1,200 sq. ft. shop detached from our home (nice shop with central heat and air, half bath, hot water, etc.).

Our home has a 200 amp box so I simply put in a 100 amp breaker and run it to a sub panel in the new shop which has a 100 amp breaker box. Everything in both the shop and house has worked fine since the beginning and still does but I did find something somewhat unique.

I have one item in the shop that draws 23+ amps on a 115 volt circuit and to my surprise had never popped a 20 amp circuit breaker. All outlets and lights are wired with #12 wire so I know that 23+ amps is a bit too much but so be it. Well, I moved the item a small amount and happened to plug it into a different outlet which happened to be on a different breaker and it popped the breaker after running for about 20 minutes. Tried it again and the same thing happened. Out of curiosity I checked the voltage and that particular circuit (the one that the breaker pops on) has 125 volts and all of the others run in the 115/117 range.

Anyone have a clue of how this could happen when they are all coming out of the same box and are approximately the same distance from the box?

BTW - if you intended reply contains the word "code" or "insurance" please don't post as it has nothing to do with my question.

[bob_villain]

You most likely have a slight difference on each side of the 230 volt panel. Like the center-tapped 115 volt is not exact. No biggie.

[Don Y]

Not without your further clarifying the conditions under which you are obtaining these measurements!

How, where and UNDER HAT CONDITIONS are you measuring the potential? Have you also looked at the line at the "supply end"?

Wasn't this question asked (and answered) previously?

[clare]

Both circuits on the same "leg" of the service, or?

If one leg is higher than the other, there is likely a neutral problem somewhere and a load inballance.

[gfretwell]

Clare pegged it, You haver a loose neutral. Try checking it at the main lugs. If it is bad there call the PoCo. If it is bad at your sub, investigate your neutral connections or look for a serious load imbalance.

[Paintedcow]

It's possible there is a neutral problem, but you could just have a pole transformer that is not exactly center tapped. There could also be some load on one leg, pulling down the voltage. Measure the voltage at the MAINS on both legs with everything turned on. Then do it again with everything turned Off.

If it's still unbalanced with everything OFF, it's just a transformer that's a little unbalanced. Not to be worried about, if that's all it is.

You did not say what the device is, which is using 23A, but you'd be wise to run #10 wire and use a 30A breaker for that device. It would help of we knew what it is, because a motor load can vary from when it starts up to when it's running, while a resistive load, such as a heating device has a pretty continuous power draw.

And if it's something like an air compressor, they can use a bit more current after the tank gets full, causing a heavier load on the motor (and when it starts in cold weather). I had to repair some air compressor wiring for a guy who said in the summer it worked fine, but in cold weather, it tripped the breaker. It was obvious that the cold compressor would not allow the motor to get up to full speed when it first started. The solution was to either move the compressor into a heated space, or use a bigger motor and upgrade the wiring to a heavier gauge wire and bigger breaker. A motor was costly, and the wiring upgrade even more money. He said he could not afford to heat his garage all the time. I suggested moving the compressor to his basement and just running a longer air hose to his garage thru a small piece of pipe in his foundation, and cauking around it, or even putting an air chuck on the foundation wall.

He decided to move the compressor to the basement, so all I had to do was run a dedicated outlet for it from his panel. He said he's buy more air hose and just stick it thru a basement window because it was just for occasional flat tires.

[bob haller]

te breaker that trips may have tripped a lot in its past, and be worn. for lack of a better term.

i would first try replacing the breaker that trips

[Paintedcow]

Yea, and the breaker that DOES NOT trip could be defective or even internally seized up, which is dangerous. I'd also try replacing that one too, and see if the new breaker trips in the same panel location.

[trader_4]

+1

If it's with no load, then it would suggest a possible problem with a bad neutral connection. If it's with substantial load, then it could be normal.

[My 2 Cents]

We can solve this through the process of elimination, Is there an Amish heater on the same circuit?, push 1 for yes or 2 for No If you selected 1, unplug the Amish heater and set it by the curb If you selected 2, unplug the Amish heater and set it by the curb

[Bud Doobie]

Forget the jack-leg hacks, a 23 amp tool needs a proper circuit. Upgrade your system to meet all NEC regulations. (This will keep your fire and casuality company happy.)

Do it right. Run a new circuit with a 30 amp breaker, #10 copper and use a 30 amp receptacle.

[John G]

Call your power company and have them check the service drop to your house. A bad connection could cause some voltage drop.

[gfretwell]

Huh? They don't arbitrarily "center tap" the transformer wherever they want,. It is wound at the factory and it will be tapped exactly at the center. This looks more like a 5-6% voltage drop in the neutral. That is far beyond the NEC recommendation and the utility standard.

[Stormin Mormon]

Sounds like it's not to code, and will affect the OP's insurance?

[burfordTjustice]

How? You gonna go tell on him?

Why don't you go to Africa and tend the "poor"

[Gallaxial]

[bob_villain]

+1

[HerHusband]

Did you install a double-pole breaker and run four wires to the subpanel for 240volts?

Or is this a single pole breaker, three wires, and only 120volts available at the subpanel?

If you know the device is drawing more than 20amps, you should really install 10 gauge wire and a 30amp breaker. Just because the breaker isn't tripping doesn't mean it is safe to do.

That said, things with motors often use a lot more power when they first start up, but the draw drops once the motor is running. Startup current usually won't trip a breaker and won't cause any harm since it's a short duration.

The first breaker is probably defective, allowing you to draw more current than it is supposed to.

You have a voltage drop somewhere. Unplug everything and check the voltages again. You may have something else loading down the other circuits.

If you still see the voltage difference, open up the breaker panel and measure the voltages there. If they're all the same, you probably have a bad connection somewhere between the panel and outlets.

If it's a 240 volt panel (two hot leads coming in), check both halves of the panel. If the voltages are different between the two phases, the problem lies somewhere between the main panel and the subpanel. Could be the connections, could be the 100amp breaker back at the main panel, could be the wiring between the two.

Check the voltages back at the main panel to see if they are the same there. If the voltage is signficantly different on the two hot leads coming into your main panel, you should call your power company.

Good luck,

Anthony Watson

[burfordTjustice]

Unlike you (apparently) and the Jesus freak with 5 wives and door knocker I don't give a rats ass about the poor in Africa. Their leaders don't why should I?? I tend to me and mine the rest can get a job or die makes no difference to me.

[IGot2P]

A 24 bulb tanning bed and each bulb is 110 watts. Kilowatt meter shows it drawing 23.6 amps. Only motors are two very small muffin type fan motors.