125v vs. 117v revisited

[IGot2P]

Okay, to the few who have stayed on subject...first I checked most of the outlets in the house and they all read in the 122v range. I then opened the house breaker box and both sides coming in read 122.7v. I also checked the voltage coming out of the breaker that goes to the shop and they also read 122.7. I also tightened all three wires down that go to the shop (actually none were loose). I THINK that this tells me that the problem is in the shop but we are currently in the middle of a rain/sleet/snow storm here in the Midwest so I am no going back out to the shop to look in that box again tonight. In fact, we were totally without power part of this afternoon...the ice probably took a limb down over a line.

Thanks for all of the help and let me know if you agree that the problem is in the shop.

[trader_4]

Given that you have an imbalance at the subpanel, the obvious and easy next step is see if the imbalance exists at the service feed to the main panel. If it does, then call the power company.

[gfretwell]

You have determined that it is in the neutral in the feeder. It might even be worth disconnecting it AFTER YOU TRIP THE BREAKER for that feeder and examine both ends of the wire for corrosion etc. Then examine the lug and reinstall it.

I also did not notice a ground rod connection at the shop end. If you are setting the "way back" machine to a time when 3 wire feeders to additional buildings, you were still required to drive a rod. With that much of a voltage drop in your neutral, you are putting voltage on the case of all of your equipment. A ground electrode will mitigate that a bit. If you really want to address the violations you can also separate the wires on the ground bus (one for each screw) you have plenty of spares. You can double or triple up the grounds in most panels but not the neutrals. They need their own screw. What size wire is that feeder?

[taxed and spent]

A secondary network may be formed with many transformers feeding into a common bus at the utilization voltage. So, a problem a bit distant from the home can cause a problem.

[gfretwell]

Where do they do that? We have something that might look like that when it first meets the eye. This is the middle transformer, of 3, in what looks like a continuous bus that serves 11 houses but if you look carefully, that dog bone on the 2 ungrounded conductors is an insulator so that "bus" is actually 3 separate segments on 3 transformers.

It happens when there were 2 customers, fairly far apart served from one transformer and then the houses start filling in.

[dpb]

On 12/28/2015 6:24 PM, IGot2P wrote: ...

You've isolated to you do not have an imbalance at one end of a wire and do at the other end...that's pretty clear evidence it's in the feeder or the connections there.

How did you run the feed line; possible you got a knick in insulation and are seeing moisture shunting effect in a buried line?

Of course, as gfretwell says, make the simple connection check first.

And, of course, there's still the issues regarding shared commons and grounds, building ground for the shop, etc., etc., ...

[dpb]

On 12/29/2015 11:12 AM, dpb wrote: ...

..

And, if you cut off everything inside that box and the imbalance doesn't go away, you've proven it's in either the feeder itself or the connections, not a large imbalance in load in the box (altho that's pretty well proven already; you can just conclusively demonstrate it to yourself if there's no load and still and imbalance it's gotta' be either the feeder is damaged or the connections).

[John G]

Are you referring to the two different brands of circuit breakers?

[Don Y]

No GFCI's and I suspect there may be some need for them in a "shop" (without knowing what else is in the building).

Two 20A breakers are unused -- both on the same leg (a likely place to suspect a sizeable imbalance)

The bottom right two-pole breaker feeds a 220V circuit wired black/white (i.e., the safety "ground" acting as neutral for any appliance fed from that branch)

[Tekkie®]

John G posted for all of us...

John, this is typical of this group. The posters want everyone else to do their work for them, then they argue and don't follow the information given and most times the result is never known. Follow along in the posts and you will see the offenders...

[clare]

Unless there is no 120 volt component to the device in which case there IS no neutral.

[Don Y]

In either case, the white should be "taped black" in the panel and at the other end(s) of the branch circuit.

[clare]

It should be, but in proactice, at leat for 240 volt heating circuits, it virtually never is - particularly if they are using coloured jacket cabling

[trader_4]

It's actually the reverse. The neutral also serves as a ground for old circuits installed in the days when it was permitted, prior to a separate ground being required. A neutral was always required to support a circuit with both 240V and 120V loads, it can't physically work without it. The concept of requiring grounds came later.

[gfretwell]

I was willing to give him a huss on that. They are probably "classified" for that panel.

[gfretwell]

That is why I asked about the feeder size.

There is plenty of 240v shop equipment that doesn't use a neutral.

[gfretwell]

A fairly recent change. (at least for old guys like me)

[gfretwell]

Actually only for ranges and clothes dryers for the 40 years or so that this exception existed but it was still never legal from a sub panel ... for exactly the reason we are discussing. The neutral is 5 or 6 volts above ground. Do you really want to be laying on a concrete slab with a drill that is putting 5 volts AC in your sweaty hands? That is why I would really want to see a ground rod or two. It is going to be a tingle voltage that may or may not trip the GFCI ... if he had any.

Then we could open the "other metallic path" thing if we are still using the old 3 wire feeder exception.

[Don Y]

You don't know that looking *in* the panel. Put a cover on the terminal Jbox (because you are no longer using that piece of gear) and the next guy coming along opens it to find white (untaped), black and copper. Do you think he's going to assume the white is really a hot and this is a 220V feed? Or, that it's yet another 110V, 20A circuit?

[IGot2P]

Okay, the feeder wire is #2 if I am reading the writing on the wire correctly.

I shut all of the power down and loosened the neutral in the main box in the house and then reset it and tightened it up very tight. It did not appear to be loose or corroded before or after I did this. I also checked once again that the the hots coming out of the 100 amp breaker in the main box in the house were tight and they were.

Now to the box in the shop. I attempted to tighten the hots but they were already as tight as they would go. I then loosened the neutral, checked for corrosion (there was none) and re-tightened it.

After doing the above I checked the voltages again and had the same 125 and 117 as I originally did so no joy.

Then I shut all of the breakers off in the shop panel including the main

100 amp breaker and checked the voltages again. Now things had changed and I had 122v and 120v!

To this layman it appears that it is just difference in the load on the two legs that is making the difference but now that the difference is down to two (2) volts I think that is close enough. I suppose that I could move some of the load from one leg to the other and even things out somewhat. Of course it would depend upon what was turned on at any given time.

Thanks to all who helped,

Don