Studio wiring advice

[black taj]

It doesn't really work like that. An AC circuit simply bounces "back and forth" between the neutral and the hot. The neutral is what is known as the "grounded conductor". Note it is not the grounding conductor. There are systems that actually employ a grounded hot conductor called grounded B phase or corner ground systems. These are rare, and the neutral is the generally accepted term for the grounded conductor.

I don't want to seem like I'm hijacking this thread. I'm sure there are people who'd like to know this, I just don't want to get too far afield. I'd start an Ask An Electrician thread, but the thought of all those eager fingers inside panels makes me nervous.

[Pure L]

double post

[Pure L]

Lots of food for thought up in here. Thanks for the replies.

So my detached garage (~25 from my house) has its own power box (containing six 20 amp circuits) running from the service panel in my house.

I'm wondering about something though.......

Since both the house and the garage power boxes are grounded to their own respective grounding rods, will this be a problem?

I remember reading somewhere that this (the double grounding) could indeed introduce EMI problems.

Any truth to that? Is this required by code? (It was an electrician who did this.)

Also, is it advisable to do IGs for all of my outlets? Or just the ones I'll be using for audio-type stuff?

How about lights? Anything I should think about there?

Many thanks.

[ptay]

black taj,

I was just trying to figure out what you meant by neutral currents flowing on the ground wires. The green wire should have no AC current flowing on it, right? It's just there to trip the breaker. Right?

[black taj]

black taj,

I was just trying to figure out what you meant by neutral currents flowing on the ground wires. The green wire should have no AC current flowing on it, right? It's just there to trip the breaker. Right?

Correct. What I mean by circulating neutral currents is this:
Your water pipe (called the grounding electrode) is connected to the neutral in the service panel via a copper wire (called the grounding electrode conductor or GEC) The neutral is bonded to the electrode because the earth is a lousy conductor and would never generate enough current to trip a breaker in a ground fault condition. Want to test it? Take an isolated ground outlet, power it up like normal and tie the ground wire from the outlet to just a ground rod that isn't bonded. What you'll end up with is an arc welder.
Now, since a good number of houses share the same method of grounding to the same electrode that is the water pipe. Since ALL the neutrals are bonded to the pipe, there is a certain amount of current flowing on that pipe. Sometimes it is due to faulty wiring in one house, but the cumulative effect is that there will be current on the pipe. This will "backfeed" onto your system simply because of the connection to the water pipe. As I mentioned, the chemical ground rods are really the only way to totally separate your system.

[black taj]

Lots of food for thought up in here. Thanks for the replies.

So my detached garage (~25 from my house) has its own power box (containing six 20 amp circuits) running from the service panel in my house.Just make sure that the neutral is not bonded to ground in the garage panel.

I'm wondering about something though.......

Since both the house and the garage power boxes are grounded to their own respective grounding rods, will this be a problem? No. NEC requires the use of a second ground rod at any outbuilding containing anything larger than a single 20 A circuit. A ground rod's only function is dissipation of lightning strikes on the service mast.

I remember reading somewhere that this (the double grounding) could indeed introduce EMI problems. Double grounding is when you bond the neutral in more than one place, giving the ground parallel paths

Any truth to that? Is this required by code? (It was an electrician who did this.)

Also, is it advisable to do IGs for all of my outlets? Or just the ones I'll be using for audio-type stuff? As stated before, I believe in a non metallic raceway, isolated grounds are pointless. You could install them for your audio equipment and be perfectly fine. A suggestion was made earlier to run a star topology ground. There is a standard grounding system in commercial high rises that might make this installation more elegant. If you'd like, PM me and I can tell you how to install a Hogan ground

How about lights? Anything I should think about there?Electrically, the loudest thing there is are HID lighting and fluorescent ballasts. If it's not a pain, separate the lighting circuits from your power and you'll be fine.

Many thanks.

[ptay]

Black taj,

Isn't illegal to double ground, and to not bond to the water pipes?

[black taj]

If by double ground, you mean to bond the neutral at a sub panel, then yes that is a violation. There is no requirement to ground to the water pipe. The language calls it a grounding electrode. The water pipe is the most common here, but not where PVC pipe is used, or in well systems. You can achieve this in other ways (Ufer ground, chemical ground, high resistance grounding etc.)

[ktone]

I've been thinking about this wiring for studios a bit after having done so a few times. If I were to do it again I would simply wire the whole thing for 240V. Ideally I would have a dedicated feed to do this and use a star topology for ground and outlet circuits feed. Quite simply this takes all the load off the neutral (because there is none) and also reduces any leakage to the ground. Sort of a poor man's balanced power supply but without all the code problems and weirdness you get with a 120 balanced power supply. This might also help with any induced line noise from switched mode power supplies or whatever.

Especially for a digital studio, this would be easy considering 95% of the computers and gear that has some digital processing either has a universal switched mode supply or an external wall wart that can be easily replaced with a 240V version. I guess the only annoying thing would be swapping all the AC plugs to 240V NEMA 6 and making (or finding) your own NEMA 6 power strips. Another option would be IEC power strips but there is no protection from plugging in a 120V device by mistake.

For 120V gear just use a portable 240>120 (non-autotransformer) isolated winding type transformer to maintain the balance.

[ptay]

If your 'star' pount is anywhere except in the dist. Panel you're inviting trouble.

I don't know your location (Honk Kong or some thing ?) but something seems fishy about running all the 220/240 lines and stepping down. The added transformers will radiate magnetic fields ... And do so closer to your instruments and gear.

I see what you mean by the power becoming balanced. But i would argue that return currents are the same whether there on a grounded conductor or a second hot. I wonder if you know of any other studios that have done this. Sort of an interesting idea.

[black taj]

I would agree that it's an interesting idea. The neutral and ground is not your only source of noise. Your hots will carry noise just as well.

I'm not sure what you mean by portable transformers. But to my knowledge, aside from autotransformers, line and load windings are not electrically connected. That is to say, they are not holding hands. The windings simply transfer power via magnetic fields generated.

[ktone]

Return current becomes an issue is if there is a neutral that is shared by more than one outlet. This is where the resistance of the neutral wire creates a voltage drop that is reflected as difference in potential between the neutral connections of different outlets on the same neutral. This is especially a problem with electrically noisy gear where the noise is also reflected on the neutral only to be picked up by other sensitive gear sharing that neutral.

Return current also becomes an issue by having a ground and neutral connected at one point (as they should be). Under heavy current use, the resistance and resulting voltage drop on the neutral causes a difference in potential between the neutral and ground at an outlet that has a heavy load. This then appears at every outlet sharing that neutral.

But i would argue that return currents are the same whether there on a grounded conductor or a second hot.

There is no return current that matters because both hots are both return and supply. With no neutral, every 240V outlet regardless of load, distributes the current flow evenly between the two hot legs.

There can even be a difference of potential between two outlets sharing a pair of hot legs but it has no effect because it occurs on the hot legs equally. Any noise on the line, whether internal or external, is also reflected equally and oppositely on both hots and cancels itself out as well. The ground always sits exactly between the two hot legs and never encounters the stress of having a different potential than the neutral.

The star topology makes the balanced system just that more effective.

I wasn't proposing having a bunch of transformers for stepping down. I was proposing everything running on 240V and if you do have a 120V piece of gear, using a (non-autotransformer) transformer retains the balanced effect for the 120 V gear.

This will not work here in Hong Kong or the UK (HK follows the UK system) because they use a neutral and suffer the same problems. This would only work in the US/Canada because balanced 240 is available everywhere.

As far as noise from stray magnetic fields from transformers, this is usually not an issue. We all already know how to manage this from having used tube guitar amps and other gear with big AC transformers (like just keeping your mic cables away from them). Toroid transformers are better regarding stray magnetic fields - use those.

[black taj]

Return current becomes an issue is if there is a neutral that is shared by more than one outlet. This is where the resistance of the neutral wire creates a voltage drop that is reflected as difference in potential between the neutral connections of different outlets on the same neutral. I'm not sure if I understand this. Are you saying that the neutral is losing voltage because it's shared with another outlet? Where are you measuring the drop from? Hot to neutral? This is especially a problem with electrically noisy gear where the noise is also reflected on the neutral only to be picked up by other sensitive gear sharing that neutral.

Return current also becomes an issue by having a ground and neutral connected at one point (as they should be). Under heavy current use, the resistance and resulting voltage drop on the neutral causes a difference in potential between the neutral and ground at an outlet that has a heavy load. Again, I'm not sure if I get this. The voltage doesn't drop on the hot in a resistive circuit? The neutral is gaining a voltage potential relative to ground?This then appears at every outlet sharing that neutral.

But i would argue that return currents are the same whether there on a grounded conductor or a second hot.

There is no return current that matters because both hots are both return and supply. With no neutral, every 240V outlet regardless of load, distributes the current flow evenly between the two hot legs.

There can even be a difference of potential between two outlets sharing a pair of hot legs but it has no effect because it occurs on the hot legs equally. Any noise on the line, whether internal or external, is also reflected equally and oppositely on both hots and cancels itself out as well. The ground always sits exactly between the two hot legs and never encounters the stress of having a different potential than the neutral. The neutral sits between the hots as well. The potential is the same as ground because of the electrode being bonded to the neutral. It's the reason that a balanced neutral carries the difference of opposite phases rather than the sum of the currents.

The star topology makes the balanced system just that more effective.

I wasn't proposing having a bunch of transformers for stepping down. I was proposing everything running on 240V and if you do have a 120V piece of gear, using a (non-autotransformer) transformer retains the balanced effect for the 120 V gear.

This will not work here in Hong Kong or the UK (HK follows the UK system) because they use a neutral and suffer the same problems. This would only work in the US/Canada because balanced 240 is available everywhere.

As far as noise from stray magnetic fields from transformers, this is usually not an issue. We all already know how to manage this from having used tube guitar amps and other gear with big AC transformers (like just keeping your mic cables away from them). Toroid transformers are better regarding stray magnetic fields - use those.

[ptay]

Shared neutral or not, all the loads you're applying have transformers. The primary of each of these, some.capacitances aside, is floating.

So say one dirty little box has a switching psu, or a failed TVS, and once every cycle pulls in a brief but high current pulse on the load side of the transformer. The primary has to supply it, so you have a pulse of current and volatage fluctuation on the two wires connected to the primary. It is actually happening all the time ang because this pulse is Normal Mode it gets into other loads even if they're on different circuits. ... Even if you use a star wiring layout.

The only thing to recommend this from how I understand it would be that the fields radiated by the two conductors would be the same. Perhaps our dirty little pulse is not put onto the facility ground eith, which seems good. I just dont think it will lower radiation in the studio with noisy loads or has anthying to do with shared neutrals.

[black taj]

^^^^agree it has nothing to do with sharing neutrals.

[ktone]

Again, I'm not sure if I get this. The voltage doesn't drop on the hot in a resistive circuit? The neutral is gaining a voltage potential relative to ground?

I'm sure you have all seen the lights in a room dim when someone has a big stereo blasting in their house. If that sag (voltage drop) exists along the 120V hot it also exists on the neutral and will raise the neutral above the ground as much as the hot line sags. Now consider some newbie wiring 10KW of amps on four circuits off the same 120V leg of a distro. 2.5KW is on each circuit hot but they may all return on one neutral that now has to carry 10KW. I've measured 10 volts or more at the mixing desk when measuring from neutral to ground from amps drawing large amount of current on big high volume surges like a kick drum. I've had problems with this doing large reinforcement systems (of 50KW of amps and much greater) so I'm a little touchy about this sort of thing.

So say one dirty little box has a switching psu, or a failed TVS, and once every cycle pulls in a brief but high current pulse on the load side of the transformer. The primary has to supply it, so you have a pulse of current and volatage fluctuation on the two wires connected to the primary. It is actually happening all the time ang because this pulse is Normal Mode it gets into other loads even if they're on different circuits.

Exactly, because if you consider this nasty pulse occurring in the above 120V scenario then that noise travels along the neutral to another circuit that suffers the noise even though it has a separate and quieter hot.

So if this nasty pulse of yours were to occur on a 240 circuit without a neutral, it occurs equally on both legs of the 240 supply. It also occurs in opposite polarity which means the nasty pulse is common mode on the balanced supply and does propagate into other loads in the building to any significant amount. This also works in reverse of course as there is no neutral to bring noise into your studio and anything on the hots is cancelled as long as the 240 feed is dedicated.

The only thing to recommend this from how I understand it would be that the fields radiated by the two conductors would be the same. Perhaps our dirty little pulse is not put onto the facility ground eith, which seems good. I just dont think it will lower radiation in the studio with noisy loads or has anthying to do with shared neutrals.

You are correct to mention that the pulse, being common mode, stays away from the facility ground and of course has nothing to do with any neutrals. This is a big advantage.

I never considered magnetic radiation from the AC supply to be a big problem either, however a balanced supply could reduce whatever there might be by quite a lot, particularly if you tightly twisted the hot pairs before installation.

[ptay]

Wrong, the pulse is normal mode. One leg goes up while the other goes down.

So all other loads feel the pain.

[ptay]

Wrong, the pulse is normal mode. One leg goes up while the other goes down.

So all other loads feel the pain.

[ktone]

I really had to think about this and I'm still not 100% sure so you may be right, but you said "pulls in a brief but high current pulse". I took this to mean that for an instant the load increased for a brief period of time. Increased current means the two legs are closer together in potential as the current "pull" sags both lines equally and oppositely and in common mode.

If the sloppy PSU was tossing back some weird harmonic EMF, I could certainly believe that may be normal mode.

[ptay]

I took this to mean that for an instant the load increased for a brief period of time. Increased current means the two legs are closer together in potential as the current "pull" sags both lines equally and oppositely and in common mode.

The voltage between the two legs (either neutral-to-hot ... or hot-to-hot) changes equally and oppositely (ohms law worked out for the Iglitch * Z line/2) ... but their average w.r.t. ground stays the same. This is the definition of normal mode.

If the sloppy PSU was tossing back some weird harmonic EMF, I could certainly believe that may be normal mode.

That would be common mode. An idea power transformer would not pass this signal. The problem is transformers in audio gear are usually not electrostatically shielded, so nasty transients will go through the transformer's capacitance or even magnetically if the transformer isn't well balanced.