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Understanding Audio Connection and Electrical Safety

Discussion in 'Recording' started by jg49, Mar 2, 2009.

  1. jg49

    jg49 Well-Known Member

    I am starting a new thread to further a discussion begun on page three of the following thread:
    (Dead Link Removed)

    I did research on voltage, current and Ohms Law (which was not passed by an act of congress, suprise) this morning and think I have a better grasp of these ideas. I also came upon this article http://www.rane.com/note110.html which I found helpful in understanding the use of balanced cables.

    So now I have a few questions. When hooking up a guitar to my Presonus unit using the obviously unbalanced cable from a guitar, the manual states that the first two channels are instrument ready. The use of a DI box then is not really necessary is it?

    Is an isolating transformer as mentioned in the above article the same thing as a passive DI? Or is it another creature altogether?

    Should a DI for guitars or bass be active, as my understanding (or lack thereof) of some of Remy's posts are that passive units are not correctly matched in impedance for transmisitting the impedance levels of guitar pickups?
  2. MadMax

    MadMax Well-Known Member


    There's a couple of methods, but the most widely accepted method is a "star" ground...

    This is where each piece of gear goes to a central ground point that is associated with the primary incoming power...

    In a permanent installation, that is usually at the main ground lug in the breaker/disconnect box... or at the main ground rod.
  3. jg49

    jg49 Well-Known Member

    Ok, I see. I guess I will have to drive another ground rod in. My space is in an out building fed by underground conduit back to the mains in the house, this was all done by a licensed elecrician. However when the building was wired it's intended use was as a photo studio, so it has lots of power for lighting. 6' copper rod, ground clamp and 14 gauge wire sufficient?
  4. MadMax

    MadMax Well-Known Member

    OUCH... this hurts...

    I KNOW what I would do, but this is one better left for a real licensed spark-meister.

    If I call it wrong, it's not good...

    Better to hope DaveDog will catch this and tell ya' the right way.

    This much information is gonna be needed;
    1.) Is there a sub panel, sub panel with disconnect or sub panel AND disconnect in the building?

    2.) What is the rating of the panel/disconnect... please be specific.

    3.) What is the size and type line feeding the building?

    4.) You mention driving "another" ground rod in... is it that there is no rod for the building? or that you have no way to access it?

    You'll need to check, or maybe DD will know... but here in my county, all ground rods must be a minimum of 10' in the ground, or firmly on bedrock.

    I'm a firm believer in grounding protection... you get hit by it once... well... it WILL make a believer out of ya'.... QUICK! So... I'd use a #6 or at the smallest, a #8 green to use as your main lug connect to ground... Then, I'd pull no smaller than a #12 green to each piece of gear back to the main lug/#8 or #6.

    A note about resistance and wire... The larger the diameter, the lower the resistance. The lower the resistance, the easier to discharge to ground. (hint: Stranded wire gives you more surface area.)
  5. jg49

    jg49 Well-Known Member

    Ok I will try and answer these questions I know a little about electrical, enough to know I don't know enuf LOL.

    The sub panel (I don't think it has a disconnect at the sub) is in the basement of the main house.
    It has three breakers in it, 2- 20 amps that each feed half the wall outlets, and a 15 amp that is for the ceiling lights and outdoor flood.

    I will have to get back to you on the wire type(s) and gauge. It is some type of copper romex. It is in 1-1/2" Carlon conduit between the buildings.
    Edit: 12/3 w ground and 10/3 w ground
    There is a ground rod at the service panel (by the meter) but it is at the far corner of the house and would be very costly to trench over to (existing gardens, fences, walkways ETC.)

    10' rod sounds right that is what I originally wrote and then edited to 6' because I could not remember what the standard length was.
  6. MadMax

    MadMax Well-Known Member

    Let me be sure I'm understanding this correctly...

    So there is NOT a panel of any kind in the out building?

    You have 3 circuits in the out building fed from some kind of sub panel in your basement.

    These 3 circuits are fed to the out building through a single 1.5" PVC conduit.

    If this is true, you will likely be needing to call your electrician out again, but before we go that far into it...

    As far as electrical, mechanical and your buildings' usage... I would encourage you to read the sticky at the top of the studio construction forum and post your construction concerns there.

    Not that there isn't anything wrong from drifting off topic in this thread mind you, its just that it can quickly become a good thread for others seeking solutions to their electrical problem/situation.

    Disclaimer in place...

    Here's the issue in a nutshell as I understand it.

    Unless you have a disconnect at a panel, you will not have a ground rod. AFAIK, you cannot drive a ground rod and tie to it unless a disconnect is present... but I could be wrong.

    You might be ok to run the star ground runs back to the sub panel, but with the size of a single 1.5" conduit already being filled and the probability of the sub panel not having an associated ground rod, I think yer' SOL.

    Again, this is somewhat speculative based upon experience, not licensed knowledge, but AFAIK, there are very specific circumstances for driving and tying to extra ground rods... and from what you describe, you do not meet those standards or situation.

    Again, hopefully a licensed professional electrician, such as DD will weigh in on this.
  7. Davedog

    Davedog Distinguished Member

    Can of worms indeed.

    Something tells me there are several things wrong with this picture.

    Perhaps its simply a matter of nomenclature, Or perhaps a misinterpretation of the rules by your 'Qualified Electrician'....

    I picture I have is this: There is a MAIN PANEL at the meter on the outside of the house. This panel contains the circuit breakers for the HOUSE and a MAIN BREAKER of some kind for a SUB-PANEL in the basement. Y/N?
    In the SUB-PANEL there are breakers operating the circuits in the DETACHED building you are using as a studio. Y/N?
    There is NO PANEL in the studio building at all.Y/N?
    The cicuits for the detached building are fed through an inch and a half PVC conduit from the SUB-PANEL in the basement and distributed to the devices in the detached building one the conduit enters the structure. Y/N?
    The conduit contains ROMEX cable one of which is a #10-3 w/grnd and the other is a #12-3 w/grnd and these are NOT a UF type of cable.Y/N?
    The PVC is a continuous run to the detached building or is it simply a sleeve leading to the outside of the basement and then the cables are direct-buried the rest of the way. Y/N?
    The wire FEEDING the SUB-PANEL in the basement from the MAIN PANEL is what size and type? Is it also a cable and does it contain a grounding conductor? Is the GROUND BAR in the SUB-Panel separated from the neutrals???
    What is the distance from the house to the out building?

    I can help you if I understand the situation more clearly. These are apparent violations of the National Electrical code. Without being there I cannot determine the safety of this installation without some facts.

    Yes, a bond wire between devices to connect the frames of your rack gear is redundant. Thats exactly what its referred to. This meant as a shunt for any outside RF, lightning, physical harm, etc.
    ALL quality outdoors rigs have a shunt to ground in the system.

    A standard ground rod is 8' long X 5/8" and made of galvanized steel or copper.
    Under certain soil conditions a second rod will be required to meet the impedance necessary to safely operate an electrical system.

    Where I live this is the case.
  8. jg49

    jg49 Well-Known Member

    I'll try and explain the whole system but my electrical knowledge is weak at best. The wires from the street come in overhead and down the side of the building in conduit to a box I'll call the "service" (where the meter and the ground rod are.) Then into the buildings basement via conduit to another box I'll call the "main" where the breakers for the house wiring are. A metal conduit runs from this box across the ceiling to far corner where another panel is that I am calling the "sub."

    This is where the breakers are for the studio (shed.)

    This detached building here is considered a portable shed in the fact that it has no foundation, set on concrete piers, assembled off site and delivered on flat bed truck. It is 2x4 construction, sided, roofed,floored, insulated and now sheetrocked.

  9. jg49

    jg49 Well-Known Member

    Everytime I try to post it f*&%^&* fails and dumps the post I'll try again later
    The sub has separate neutral and ground bars and grounds run between panels and studio. The conduit is continuous basement to interior. Buried 3'.

    Cable is 12/3 and 10/3 w grnd not UF.
  10. jg49

    jg49 Well-Known Member

    If I did not answer everything I will clarify, this is my eight try at posting this so I am a little frustrated, thanks to both you and Max
  11. MadMax

    MadMax Well-Known Member

    aha.... the plot thickens.....

    seriously... sorry to hear about your posting issues...

    It really does help when you explain the entire situation.

    I can just about tell you that DD let out a nice big sigh when he read your post. (as did I)

    I really don't know where to begin...

    All I'll say is that you really should consider starting another thread in the construction forum, COMPLETELY explaining your intent/purpose of the use of this building...including all the details in the read me sticky at the top of the construction forum, (including links to pics, designs or drawings) or realize right now, that it sounds like you're spinning your wheels to get down a road to no where, or you just really like exercises in futility.

    The reason why I put it like this... you seem to be wanting to turn a shed into a recording studio the absolute hardest way you possibly can... well... actually, there's hardly anyway that you really CAN turn a shed (as you described) into anything more than a moderately mediocre mix room. (That is if you are attempting to do anything other than some hobby level stuff.)

    In either case, we've drifted WAAAAY off the subject of means of connecting audio....
  12. jg49

    jg49 Well-Known Member

    I never thought that this question was quite so complicated.
    You mean my shed will never become a world class studio space? I mostly do use it as a mix room with occassional solo tracking. 80% of my recordings are live mobile usually in small clubs and my space here works fine for cutting the long recordings into pieces, rough mixing to determine what songs the bands want to focus on, etc. The final mixes are usually done at at my friend's pro studio if the situation warrants it. Alot of what I record ends up as webpage background music or vanity stuff that the bands are passing out to friends or fans and I have gotten pretty good at processing that here.

    I've read your construction thread and I wish you the best but I am not of the inclination to invest the same kind of money in this economy or the climate of the music industry today as a business venture, but then most of us are doing this because this is what we like to do.

    So can I drive a separate rod or not?
  13. MadMax

    MadMax Well-Known Member

    Here's the deal...

    Your building probably is not going to get approval for a separate disconnect as its not setting on a permanent foundation.

    The space underneath the building is going to be a major source of low frequency problems.

    Those two factors alone are going to impede your ability to legally get above much more than a level of a mediocre mix facility.

    You're limited on power, which will limit your ability to get a good solid ground, AFAIK. Again, someone will hopefully clarify, but IMHO (and non-licensed opinion) you cannot legally put a ground rod down.

    Also, if you do much to treat the building as a "business" or even a "hobby" and you have an insurance claim, you need to be sure that your homeowner's policy will cover your gear.

    I mean, if you want to risk it, go ahead, but I've spent too much money on gear (even before the studio was under construction) to put all my gear in harms way... and I would think you probably have as well.

    There's a lot more to this stuff than a lot of us think about when we get started. Sure, we all love music, and making good recordings is a natural progression, but don't loose sight of the fact that all too often, you should also go back and look at it from an accounting, legal and/or business side.

    That reality check is something I encourage everyone to do at various stages of your "career".

    Getting your building reasonably soundproofed and acoustically treated is only about one third, to one half of the whole picture.
  14. Link555

    Link555 Well-Known Member

    So here is my take on the situation. Your shed should be fine. When you drive a ground rod into the earth your doing it to establish the Ground potential for the house. This might not be 0V, but regardless all incoming voltages are referenced with respect to this ground potential.

    Now the main reason for a ground rod is to protect the mains of the house (and the loads attached to it) from the lighting. If lighting strikes it will hopefully go through the point of least resistance to the lowest potential in the area, i.e. your grounding rod. There are elaborate grounding and lighting protection schemes out there, but this the typical one for household installs.

    Now on to this star point concept. This means all current returns paths (referred to as ‘common’ paths) connect together at the same point. This is not the easiest solution, but it helps minimize the things such as ground loops and maintain a single reference point to ground.

    Think of a wire as a resistor (its not, its really a complex impedance) the longer the wire the higher the resistance. So using Ohms law you can see that if you do not use a star ground there will likely be voltage across different ‘common’ connection points.

    Now onto your place- the sub panel returns its current to the main panel, so yes your circuit return will be star connected at the sub panel not the main panel. This means there will be a potential difference between the main panel ground and your star point reference.

    However does this matter? Not really since all of your circuits can still share the same common reference . Use the same breaker to run your audio gear if at all possible.

    Obviously you cannot exceed the 15A or 20A rating, but you likely will be able to run your recording gear off one breaker. That way your gear all shares the same return path.
  15. jg49

    jg49 Well-Known Member

    All of my equipment is on one 20 amp breaker. There is a second wall outlet circuit also 20 amp but happenstance is that I am not using that one and will make it a point not to, though a lot of times amps and keyboards have been.

    I guess I will have to wait until the electrician returns from the Caribbean March 12, obviously he is doing something right that I am not LOL. Not involved in music perhaps?

    As far as insurance goes I do have a replacement value rider on my equipment. It was originally taken out to insure my guitar collection but has been updated regularly to include recording equipment, amps, etc. i think that this something everyone should consider.
  16. Link555

    Link555 Well-Known Member

    What was the orginal problem?
    Ground noise?
  17. jg49

    jg49 Well-Known Member

    No, just Davedog had suggested in another post that all gear should be grounded from the chassis lug and I innocently asked where it should be grounded to.

    (Humor) Instead I found out my space sucks. LOL
  18. MadMax

    MadMax Well-Known Member

    HA!! Glad you've got a sense of humor about it!

    No one said your place sux...

    Just not optimal... and it's gonna be tough to make great w/o it being a permanent structure...

    About just arbitrarily driving a ground rod... BE CAREFUL! I'm speaking from experience in dealing with fairly complex grounding schemes... do it to code.

    If you do ANYTHING against your local electrical code, your insurance company WILL use that as an excuse to not process the claim, and CAN even sue you.
  19. jg49

    jg49 Well-Known Member

    I am not doing anything without talking to my elecrician, and I do have a sense of humor and no you did not say that.
  20. Davedog

    Davedog Distinguished Member

    A ground rod at your outbuilding will ONLY be for the redundant bonding of the casing and metal parts of the rack an associated gear.It is NOT meant as a grounding electrode. It is mearly a shunt for a fault to the frameworks.

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