125v vs. 117v revisited

[IGot2P]

Took some time this evening and checked the voltage on several outlets in my shop and to my surprise I found several at 117v and several at

125v. Then I noticed that the difference voltages were on different circuits. Then taking a look at the breaker box I noticed that each 125v would be directly across from another 125v breaker and the same for the 117v circuits.

Well, that gave me a good clue as to what was happening so I opened the box and took a look and checked some voltages. I took a picture, added the voltages to it, and uploaded it to one of my domains at

so go and take a look.

As I have previously mentioned in an earlier post this is a sub-panel which is supplied from the main panel in my home via a 100 amp breaker. I have not taken time to check but I am almost willing to bet that I find different voltages in my home also. It is going to be interesting to see if what I am getting from the street to my home is also different voltages...how you want to bet?

The home was built in 1993 and these differences have never caused a problem but it will still be interesting to see what is actually happening.

[clare]

You have a poor neutral connection somewhere. Guaranteed. One leg is higher than the other, which means there is more load on one side than the other and your neutral is floating to some extent. Check at the main breaker at the house, from each line in turn to both neutral and ground. If you have the same difference there, call the power company or an electrician to check the problem. (or if you feel qualified, check the torque on all the neutral connections in your service box first - if still off, call the power co) If the house circuits are good and the shop is not, check the neutral wire for the shop circuit, both at the main panel and at the shop sub-panel. There is no other explanation than a bad neutral somewhere. It might not be in your house - it could be anywhere between your house and the transformer. Check with your next door nieghbor to see if they have the same situation - then you know if it is "local" to your house, or more system wide.

[Micky]

I say you're getting 8 volts for free and you shouldn't complain.

If you really can't use them, you might even be able to sell these 8 volts. It's a shame you didn't post before Xmas because that's when people are spending money, but you probably only lost 20% or so.

If you're in a hurry, or don't want strangers coming to your home, contact an electricity wholesaler.

[Paintedcow]

Yep, one "LEG" is higher than the other.

So why didn't you just go in the house and open the panel, and measure the voltages on the MAINS. It would have only taken a few more minutes to pop off that cover and measure it. [Before you posted this]. At least then we would know for sure that your MAINS (directly from the meter) are not balanced.

All electrical stuff is rated for 120 volts, but few homes have exactly

120. Most are somewhere between 115 to 125. All regular appliances and bulbs will work just fine on any voltage in this range. If you get below 110 or above 130, there will be problems. (and 110 and 130 are already pushing the limits).

I have 118 on both legs at the moment...

[Stormin Mormon]

What happens if it's a bad center tap or load imbalannce?

I suggest if your guarantee fails, you need to discuss with IGP what will be your pentalty. Perhaps donate $100 to Salvation Army in the name of IGP.

[trader_4]

+1

Many posters suggested it could be a problem with either a loose neutral on his side or the power company's side. Simple way to find out if it's his side is to check at the incoming service at the main panel.

[gfretwell]

Do the same thing at the house panel, then get back to us.

We can play "spot the violations" later ;-)

[John G]

The grounds in a sub-panel are not to be terminated on the neutral bar. Remove the green screw and install a separate ground bar in your sub-panel for the grounding conductors.

Did you contact the power company? A problem with one of their lines may be causing the voltage drop.

John Grabowski

[gfretwell]

Is that all you saw ;-)

[clare]

The "poor neutral connection" MAY be in the transformer - but it's still the neutral. If it's in the transformer the transformer needs to be replaced to solve the problem because it is either a bad connection or a burned winding.. It is almost definitely NOT an error in the initial winding of the transformer.

My guarantee is a 100% money back guarantee. He didn't pay anything for my opinion. He gets exactly that back if I'm wrong.

And if he proves I am wrong, He will also get my appology.

More than he'd get from many others.

[clare]

He doesn't have a voltage "drop" he has a voltage "imballance". His service voltage is pretty well dead on where it should be at a total of 117+125=242 volts. Only 1% over spec.

[Don Y]

Do the *easy* things, first.

- measure at the *main* panel

- measure at the subpanel (already done)

- open the disconnect at the subpanel and remeasure at the main panel Assuming this isolates the problem to the subpanel:

- remove individual loads from the subpanel (open breakers) and measure

Take good notes.

You should be able to diagnose the problem just from these observations.

[gfretwell]

The voltage drop is in the neutral

[gfretwell]

You are trying to tell us that a PoCo had over a mile of "secondary" wiring. I don't think so. The transformer that takes the medium voltage distribution down to the service voltage is usually within a hundred feet of the service point. The 120/240 or 120/208 will come from that transformer bundle if it isn't coming from a customer owned SDS. I would agree that a problem in their primary could cause bad voltages but all of them would be bad in the same direction (GIGO)

[taxed and spent]

He didn't say that. Perhaps a mile away was their autotransformer.

[gfretwell]

We were talking about imbalances in a 120/240. That happens in the final transformer in the distribution. Everything on the line side of that will be medium voltage in residential, typically a single phase and in commercial that will come from the utility right outside or a customer owned SDS on site.

[John G]

It has taken an unbelievable amount of drivel and misinformation to get down to this simple list of things to do to isolate the problem. :-?

[Don Y]

I am basically lazy. :> As I think most folks are. I would rather do the easy things -- take data and THINK about the problem -- than run around "try this", etc.

Occam's Razor: chances are, it's something in the subpanel/workshop and NOT something with the utility -- *or* the main panel (not counting the subpanel tie-in).

Eliminate the workshop and see if the problem persists. If not, tells you the problem is *related* to the workshop (though may still manifest in something else).

Far better to be able to tell an electrician or the utility: "I did this and this is what I saw" than to just throw a bunch of unrelated observations at them ("Well, did you try *this*?" "No, but I tried something (totally unrelated)!")

We had a neighbor around the corner have his metercenter catch fire! Faulty connection on one of the mains and it just arced it's way into flames. Likewise, had a vault "explode" (coincidentally, near that same home!).

I.e., when things start deviating from normal by too much, Bad Things happen. "You have been warned" ;-)

[Ralph Mowery]

Often it is easy to determin if it is a neutral problem. Meter both sides of the AC. Then with almost everything cut off, plug in a large load such as a bathroom heat or hair dryer to one side. If the unloaded side changes voltage it is almost sure to be a neutral problem somewhere.

YOu can do this in the workshop, then move to the house. If workshop and not house, it is probably your problem, if also at the house and on the main wires, if the neutral is not loose at the box, probably the power company problem

[gfretwell]

Generally speaking, checking at the service disconnect is about as far as you can go because everything on the line side of that is sealed by the PoCo. They will generally fix anything on that side for free, just to keep you out of the metering equipment. Obviously if they determine it is on the line side of the service point (typically the crimps on the drop or the transformer connection on a service lateral), it is their baby anyway.