Electrical comes into most homes in the US at 240 volt, phase one and phase two.
This means phase one @ 120 Volts and phase two at 120 Volts. These together such as to a clothes dryer or electric oven is how you arrive at 240 Volts.
If problematic household products are on the phase OTHER than the one your audio gear is on, the stereo is isolated from the pollution introduced by these products. The worst of these are refrigerators, microwave ovens and household computers, although any electric motor or pump is likely to cause noise on the line.
If you look at your electrical panel, there are twin rows of breakers or fuses ( usually running vertically top to bottom ). One vertical row is first phase 120 Volt supply and the other vertical row is the second 120 Volt supply.
Basically if all the stereo gear is connected to breakers or fuses on the same side of the panel, they are more isolated than if they share power with the household products that generate noise.
During new construction or a complete replacement of a panel, have your electrician read each of the two supplies with a VOM. Most of the time they are different.
In my neighborhood, readings are usually around 119.5 for one, and 121.7 for the other. I chose the 121.7 to dedicate to audio.
I have the rare luck to have a three phase drop, and dedicate that to the air conditioning system. This further isolates noise from the audio system and saves power. |
Agree with most of AP's post except that many 240 Volt breaker panels are manufactured so that first/third/succeeding odd horizontal rows are on "A" phase and second/forth/succeeding even horizontal rows are on "B" phase. Use a voltmeter to verify construction.
Lighting dimmers can be added to the list of noisy devices to be located on the non-audio phase. |
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Great post Albert! I am pressing print on this one. |
If you should decide to rearrange your household loads in the distrubution box, don't get so carried away that you wholly unbalance the loading of your drop transformer. You want basically equal current loads on both phases, when all loads in the house are operating. I measured all the loads with a clamp-on Amprobe & then put the noisiest ones on the other phase from the dedicated line, maintaining an overall balance as secondary objective. This becomes even more important when commercial power fails for a long time & we have to fire up the backup generator. |
Thanks, fellows.
Albert, great explenation.
I have a 60 amp panel into the sound room.
I asked my brother inb law (he's an electrician) to explain to me how he'd wired it.
I now understand that half the outlets are one one phase, half on the other.
KP |
I'd like to point out one error in Alberts 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 youre 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.
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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? |
Albert,
There's no way to separate a 2-pole 220v breaker to one side or the other. I think we all know that? No matter what you do the noise from your 220 circuits will always be present on either side of the panel.
You could in theory separate all your 110v breakers to one leg of the panel, but that's not necessarily a great idea.
The main objective when terminating a panel is "load balancing" That is to say an equal amount of amps on each side. This will reduce the load on the neutral conductor. When you have 50amps on one leg and 50 amps on the other there is zero amps on the neutral.
However if you had 100 amps on one leg and 10 amps on the other you would have 90 amps on the neutral (Grounded conductor) This poses some serious concerns. Electricians and engineers always seek to reduce the load on the neutral by distributing the load equally to both sides of a panel. The same holds true in three-phase power distribution.
You may also want to consider labeling your outlets with a P-touch labeler. You could mark the phase (A, B or C) plus the circuit number and panel designation. That may come in handy when moving things around.
Take care
Balancing the panel= Best installation |
I am reading the two phases that come into the house, the third phase as mentioned already, goes to the big commercial AC unit that keeps us comfortable during the hot Texas summers. |
Glen, regarding your comment: There's no way to separate a 2-pole 220v breaker to one side or the other. I think we all know that? No matter what you do the noise from your 220 circuits will always be present on either side of the panel.
Looks like from what you said that the 220 shares with both circuits, but the two 120 Volt drops ARE separate, and therefore could be dedicated specifically to the stereo for one drop and noisy ( refrigerator, computers, etc.) on the other.
Back again to the fact that they can be separated, and that is what I prefer to do. Your suggestion to balance the panel is your answer to best sound. So until someone has a bunch of time on their hands to try this both ways (would that prove anything owing to the differences home to home?) we are still two opinions. |
Al, I give up :^)
See you on the next thread |
I've been informed (don't know if it's true) that you/we only have one 'phase' coming into our houses on two seperate 'legs', not 'phases'.
Is this correct, Glen?
I had mentioned in several postings that by moving the amp's circuit breaker to the opposing 'leg' where the other audio circuit breakers reside, I had elminated a fairly audible transformer hum coming from my amp. That is a true statement.
However, I had no idea that affect would occur. I originally moved the amp's circuit to the opposing 'leg' just to see if I would gain any sonic benefits as I had heard that tip from audioasylum or audiogon forums.
I did not notice any sonic improvements.
-IMO |
You guy's need to stay out of your panels before you burn your houses down. You have no idea. Trust me! |
Glen, you union guys crack me up. :)
Just kidding,
Actually, I think I feel more secure with my own work than my professional electrician friend's work who installed my first dedicated line a few years ago.
A few months afterward, I went to change the wall outlet but first shut off the 20 amp circuit breaker and then as an added safety messure checked the outlet for power. Sure enough, it still had juice.
Turns out the electrician had switched lines by connecting the 12 gauge romex and 20 amp outlet to the 15 amp circuit breaker and vice versa for the 20 amp circuit breaker.
Had I not performed that extra safety messure, my toes would have caught fire.
Honest mistake, but I don't think electricians can afford to make too many mistakes without serious repercussions. |
Stehno,
Sounds like a non-union electrician to me :^) |
