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There is a lot of info in the archives, but much of it is contradictory. There are some great posts by knowledgable electricians w/ references to online sources like EC&M magazine. Here is an article titled "The Earth is Not a Bonding Jumper"I just want to make sure that I have everything straight before doing anything that could risk frying my system or life.
The transformer is listed as Model # H 1.0 0.005
120/240V, 50/60Hz, Eff. Cap < 0.005 pfd
Two primary and secondary windingsElgar was bought by Cummins and no longer lists these transformers on their website.
The primary side has a 5 terminal wiring block numbered(left to right) H1, H3, H2, H4, H5. In the provided diagram below the terminals, H5 is the electrostatic shield, H1 & H3 are one winding, and H2 & H4 are the other. A jumper is between jumper H3 & H2. A seperate ground screw "GND" is directly below the terminal block, it connects the metal plate the terminal block is on to the chasis.
I wired up an AC line with the blue(neutral) wire going to H1, Brown(live) to H4, and green/yellow ground to GND screw. I left the electrostatic shield floating because I didn't know if it should be wired to GND or not.
The secondary has the exact same diagram except it is numbered X7, X9, X8, X10, X11. X11 is the electrostatic shield. With the center legs X8/X9 jumpered and used as ground for measuring, X8/X9 to X7 reads 60V and X8/X9 to X10 reads 60V. Reading X7 & X10 together gives the full 120V.
My questions are:
1) are the GND points of the primary and secondary isolated from each other or connected? (see below)
2) If not, how do I ground the secondary or is it necessary?
3) Do I connect the electrostatic shield terminal to ther respecitve GND on both sides? If so, why didn't Elgar do that stock?
4) Can I get balanced output from this transformer?
5) Will driving a 6 foot grounding spike into the ground outside my listening room and connecting that to secondary ground help? (see below)EC&M's article cited above illustrates one common misunderstanding of isolated ground, then shows the proper connection.
This common configuration has problems. First, you already know the resistance between the two electrodes (connected only by the earth) is neither low nor reliably consistent. This means you have a high potential between the two ground rods. That freestanding electrode, though buried in earth, is not grounded. As electricity seeks the path of least resistance, it will seek a path other than the earth bonding jumper between that freestanding rod and the service-entrance ground rod. Because of the high resistance in your earth bonding jumper, that electricity will build up potential before it can start to flow. Instead of the volt or two you'd have on your copper wire, you may have several hundred volts of difference building up and suddenly discharging through equipment or people. So, you can see the grounding arrangement in Fig. 2 is unsafe. However, it would be safe if you bonded the two electrodes with a copper wire. Does that bond cause other problems that justify the safety risk of not having it?
This configuration provides some isolation from the rest of the load side, by connecting to ground so close to the main electrode. This means that noise generated by a particular device will propagate into the mass of the grounding system and the various low paths of resistance before it even gets to your connection. The impedance of that length of isolated grounding conductor also helps. For nearly all installations, this arrangement has proven to be a more than adequate defense against noise coming from the grounding system.Because omitting that bonding jumper is an open invitation to electrocution and equipment damage, omitting it is ethically unacceptable. It's also a violation of Art. 250 - which makes it unlawful in most jurisdictions.
So, now back to my question #1 - does the primary and secondary GND posts of the isolation transformer perform the function of a bonding jumper between the primary/secondary and their respective circuits?
Follow Ups:
which I strongly suggest you to do, then H5, X11, and the X8&X9 connection should all be connected to normal electrical ground. There is and should be only one electrical ground in a house. Any other separately derived electrical ground is illegal. Other types of dwellings may have more leeway in terms of what is legal. Technical grounds and addtional ground rods should (shall) not be used in a residential dwelling.There will be no isolation from normal electrical ground and the ground that goes to your stereo, assuming it uses one. You would not want isolation. In order to prevent hum all grounds need to be at the same potential, as in the same impedance to earth.
With balanced power, which is what you now have, there should be no current flow through the ground wire unless there is an wiring fault. Hence the ground doesn't really matter (untill needed).
I am sure many will take exception to my comments. I don't care. I have been working with electrical circuits for 30+ years, most of it in a hospital setting where balanced power has been used for a very long time.
Rus
A curious question What is wrong with having more than one groung rod as long as they are connected together. I am in an older house with updated wiring (circuit breakers) but the original ground rod looks suspicious. I was going to drive another and hopefully longer rod in and run a new wire in and ground it to the house ground. For safety reasons I did not want to disconnect the original ground
There is nothing wrong with having more than one ground rod provided there are all in the same location and tied together with one continuous wire. In fact some areas require three ground rods. They have to be arragned in certain ways so you simply must check your local code. Buy a copper coated rod. It will look better longer.Sorry for the confusion. What is not okay is for audiophiles to simply drive a ground rod outside the listening room and use it for an isolated audio ground.
Russ
thanks for the info. I have been watching the potential difference between nuetrql and ground which should be zero. It varies between 2.7 vac and 3.4 vac on my fluke dvm. I get similar readinds on a couple of other cheapie dvm also. This why I wanded to add to the grounding of my house. Am I on the right track
hanks for the advice, Russ, I really appreciate it. I want things done according to regulation, no need to risk equipment, house, or life for a hobby.My house was built in 1968 (Los Angeles, CA) and was wired with only 2 wires - live and neutral/ground. There is no third wire, nor is there anything like a copper pipe to ground to in my living room walls. Obviously, the Romex pipe or outlet box do no good either.
What is your suggestion for this situation?
I'm kind of leery of connecting ground to the neutral wire.
BTW, did I have this x-former figured out wrong.
This is how I had it wired:
This is how I should have had it wired according to the manual:
If there is conduit then the conduit is intended to serve as the ground. If you only have Romex you are kinda screwed unless you want to upgrade/rewire. Somewhere/someplace the neutral wire is connected to ground.I can't really read the labels on your diagram. The electrostatic sheild needs to be tied to ground, not hot or neutral. Perhaps the transformer was inttended to be simply an isolation transformer and you unknowingly wired it to provide balanced power, i.e. 60VAC---0VAC---60VAC. Balanced power is better but usually the transformer has to be derated by 50%.
I have to run but I'll take a look at your post tomorrow if time permits and see if I can figure out your wiring diagram and explain it all to you. But the way you had things sounds best to me. As a quick check verify primary current draw is little to nothing with the secondary open.
Russ
Someone on DiyAudio suggested:
"Put your meter on AC. If you read 120VAC between Hot and the box, 120VAC between Hot and Neutral, and 0VAC between Neutral and the box, you are sitting pretty. "It worked, so everything is hunky-dory there.
The numbering on the schematics I posted follows from top to bottom on the left side X1, X3, X2, X4, X5(shield), GND.
On the right it goes X7, X9, X8, X10, X11(shield), GND.
I tried both methods suggested in the manual and they both caused my SET monoblocks to buzz. Tonight, I will try tying the shield to hard GND terminal instead of neutral as you suggested and see if that makes a difference.
Neutrals are strange and are defined as a "grounded current carrying conductor". But we want to think of ground as a place to send current to but never a place that could supply current. However we are stuck with the fact that AC voltage swings back and forth between a positive and negative value.Without going into the full deal of what that all means I'd encourage you to adopt a different view inlight of how neutrals are commonly used.
A device cares not where it's voltage comes from and only knows what the potential is from wire to wire and what it is to consider a "common" (and do notice I don't say ground). It is common practice to use one neutral for up to 3 different phases. What I mean by this is; let us say I am an electrician wiring your house. I have to provide circuits to your refrigerator and dishwasher which require separate circuits. I am allowed to do this with 4 wires, two hots on separate breakers (provided they are different phase), one neutral to be shared by the two separate circuits, and one shared ground. Let us say that the refrig draws 10 amps and the dishwasher 3 amps. The neutral wire will then carry the difference or 7 amps.
For audio it would be in our best interest if the neutral current was zero (for our stereo screw the dishwasher). Now how to get there? In the example above, let us suppose that the dishwasher and refrig were 240VAC. Now no neutral is involved. The appliances simply have no choice but to draw equal amounts of power from each phase and since these different phases ( which they actually are not...but that's for a different discussion) are 180 degrees out of phase, the currents cancel. This is not unlike how balanced audio with XLR connectors can offer noise reduction and is related to how balanced power helps you.
There is much to learn and as such my comments might mean nothing. Or your knowledge may be such that it fills some blanks. I am here to help when time permits and you may email me at Rbrunt(at)mercymiami(dot)org.
I do warn that my idea of what one needs leans towards the extreme. I am also concerned that you may of intended to have an isolation transformer and instead have inadvertantly wired it for balanced power (which is a great thing BTW) and as a result might have undersized your transformer.
Russ
one neutral to be shared by the two separate circuits, and one shared ground. Let us say that the refrig draws 10 amps and the dishwasher 3 amps. The neutral wire will then carry the difference or 7 amps.That's the part I could have never figured out on my own. At first, I only understand half of our explanation, but while walking the dogs it all sanpped into focus.
I am also concerned that you may of intended to have an isolation transformer and instead have inadvertantly wired it for balanced power (which is a great thing BTW) and as a result might have undersized your transformer.
Bingo!! I had no idea it was balanced even when I typed that I was getting 60-0-60 volts. Go figure! At that point I was just trying to get standard 0-120.
"Bingo!! I had no idea it was balanced even when I typed that I was getting 60-0-60 volts. Go figure! At that point I was just trying to get standard 0-120. "This may or not be obvious, but this setup (figure 3) is NOT balanced unless you ground the output mid point (X8-X9 jumper).
I connected the jumpered secondary X8/X9 midpoint and both Shields to to their respective GND screw. But, not the jumpered primary X2/X3.And thankfully, this Elgar turned out to be one of the quiet transformers - no buzzing at all. I have read posts of others who've gotten units that buzzed noticably. Mine is dead silent, so it's no problem having it in the listening room.
There is manual in Elgar's obsolete products section:
- http://www.elgar.com/pdfs/manuals/Elgar/HIT Series/HIT Series - High Isolation Transformers.pdf (Open in New Window)
nt
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