electrical phase

I'd like to point out one error in Albert’s post. It has two do with two 120volt phases one row on the left side one row on the right.

A panel is configured so that a (full size) breaker and the breaker directly underneath it are on opposite phases. That way a two-pole breaker can be plugged into two spaces right next to each other (or one on top of the other) producing 240volts.

To truly isolate one half of a residential panel 120/240 volt. You would have to configure your breakers top to bottom skipping every other space.

I hope that makes sense. In all practicality there is no possible way to isolate any one phase for audio unless you have a three-phase panel with no 3-phase loads present in that panel.

My best advise is to always pull a dedicated neutral (white wire) with every hot. In addition add an isolated ground and I.G. receptacles

While I'm on the subject I'd like to mention that there is no such thing as two phase power. 120/240 is derived from a single transformer and is refered to as single phase power in the electrical trade in general.

3 phase power can only be 120/208, 277/480, or 120/240 with a high leg(Not very common except where lots of motors are present) These are standard 3 phase voltages used in the USA

Glen, I have three phase as pointed out in my post, it is 120 / 240 as I mentioned already.

My comments are correct for my particular configuration and did explain that there are two supplies coming into my home. Are you saying that in most home electrical drops the panel does not get power from two different 120 volt supplies?

I have two panels in my utility drop closet. One three phase that runs the AC and one that does not contain the third leg, that has two 120 volt AC drops.

Inside the house is three panels, two are 100 amp Square D and both have two different voltages supplying them (they always meter differently).

The third panel is 220 only, and the two hot legs measure the same as each of the 120 Volt supplies.

The power coming in is a four line double zero cable, and a 750 amp box with a amprobe type meter (pull the meter, the power stays on).

Albert,
Your 3-phase power is probably 120/208. My guess is your reading 120v phase to ground, but if you put a good meter phase to phase it probably reads in the neighborhood of 208v. Check it with a high-grade meter (Fluke) sometime. This is a typical 3-phase voltage used in the USA no matter where you live.

If your reading 240v phase to phase then you probably have 120/240 with a high leg. That means one of your legs will be reading 277v phase to ground. I doubt you have this kind of power in a residential neighborhood.

In a typical residental service the panel does derive power from two separate 120v supply lines, but the supplying transformer is a single-phase transformer capable of producing 240volts. (This does not apply to you)

It does not take two transformers to produce 120/240

And without two or three transformers you cannot get two phase (No such thing) or three-phase power.

If Memory serves the transformer on the pole has a center tap (Neutral/ground), which allows for a reference point on either leg. Thus there are not two phases present just two hot's and one Neutral (Ground reference) derived from one transformer (One phase of a three phase system) on the pole

Hot to hot reading 240v
Hot to neutral reading 120v (when grounded to earth)
(Again this does not apply to you)

Your house has one main drop three phase derived from three single phase transformers on a pole or in an underground vault near by. These three transformers are configured to produce the desired voltage you seek which is typically 120/208 based on what you've told me already. This is in fact your main power at your main panel. 120/208 three phase.

From that three phase panel two hots and a neutral are sent to a single-phase panel (in the same closet). Even though we typically refer to this panel as single phase (Standard terminology) you are in fact feeding it with two phases. (ONLY BECAUSE YOU HAD 3 PHASES TO START WITH) This is a little different than a normal residential installation and in fact would be treated as a commercial installation.

Let's talk about the reason the two panels inside your house have different voltages. They are 120/240 panels which means you are using *A phase* and *B phase* tapped from your main three phase panel to feed one. *B phase* and *C phase* tapped from your main 3 phase panel to feed the other. You see that each panel has at least one different phase than the other. That's why the voltage reading is never the same at both panels.

It would be a little hard for me to believe that you’re only reading 120 phase to phase at these panels. You should be reading 208 phase to phase. There is no way an electrical contractor would do this type of installation unless he doubled the size of the supply neutral, you would also have to run a dedicated neutral with every hot comming out of the panel.

As for your meter That's called a CT meter (Current transformer) when you pull the meter you do not disconnect the line power, just the ct's. Pretty common in Commercial installations.

I am reading 241 Volts phase to phase with a Fluke 2860 A. Phase to ground is 120 on each leg.

On the topic of this thread. Would audiophiles not benefit from my suggestion of keeping one of the two 120 volt supplies as the primary power for the stereo and the noisy stuff on the other?

Other than the confusion about the set up of the breakers in the box and the fact that I have 3 phase, it seems the two 120 volt supplies most readers (probably) have could still benefit from Killerpiglets idea of separate runs.

Also, why could everyone not use a meter to differentiate between the two 120 volt drops? I do this often behind my equipment. I just meter several plugs, and the one that is the low leg gets the digital equipment, as I keep it on the opposite run from the analog gear.

I would be surprised if two runs coming in were EXACTLY the same voltage, and this would be an easy way to tell them apart. It always works here, the voltage may change a little during peak usage periods, but the two supplies stay almost the exact number of volts apart, day or night.

Albert,

Are you reading all three phases 120v to ground?