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Thread: Ideas & suggestions for designing a dedicated Sound Room

  1. #31
    Senior Member RMC's Avatar
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    RE "Then there is the problem of the noise being generated on the power lines"

    When equipment is properly wired and grounded, there is no power lines noise for me.

    RE "Even if allowed, the breaker must be designed and rated for more than one wire."

    My 120V breakers from a Square D breaker panel, MADE IN THE USA, have two slots to specifically allow connection of two hot wires on a single breaker, known as double tap. Maybe cheap panel breakers don't allow but mine do.

    RE "Same goes with using 14/3 and 12/3 wire for two circuits."

    That mention implies the two hot wires from a double circuit cable (14/3 and 12/3) are connected to the same breaker, it is NOT the case. When a two-circuit cable is used the black and red hot wires each go to a separate breaker. Stating "Same goes..." seems incorrect. Double tapping (two hots on same breaker) and double circuit cable (each hot going to a separate breaker) are different animals.

    RE (properly grounding the two circuits can be tricky)

    Its not rocket science nor tricky, simply need to know how to do things when neutral and ground wires are shared with the two circuits. There's an additional safety trick most electricians and DIY don't do when installing a double circuit, i learned it from a Master Electrician, you need to put a flat head nail joining those two breakers (there's a hole for this) so that if one trips the other follows. Very logical, good reasons for this, too long to explain here. Other breakers don't have a joining nail, only those for a double circuit.

    RE "or aluminum cable."

    The suggested use of Alu cables is very surprising. Alu cabling for electrical work has been banned for years in many jurisdictions due to connection problems with this "soft" metal, softer than copper which is the preferred one. Moreover, Alu has a resistivity about 1.6 times that of copper. Not a great conductor.

    RE "sub panel providing many more 120 volt circuits"

    The many more may or may not happen since this depends on how loaded the main panel is, and the sub panel can only use the "loose" (amperes) from the main panel. An unused 220V breaker slot would provide two 110V lines.

    As always consult a licenced electrician.

  2. #32
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    [QUOTE=RMC;439635]RE

    When equipment is properly wired and grounded, there is no power lines noise for me.

    Noise can be generated and impressed on power lines from outside or inside your house. Digital sources (CD players etc.), cable TV, lighting, motors within your home (through wiring or through the air) can generate noise in your system. Proper grounding will not eliminate these; it only reduces common mode sources of noise. You should educate yourself on common mode and normal mode noise...

    RE "Same goes with using 14/3 and 12/3 wire for two circuits."

    That mention implies the two hot wires from a double circuit cable (14/3 and 12/3) are connected to the same breaker, it is NOT the case.

    No, two hot leads from two different breakers feeding two circuits sharing the same neutral and ground in a 12/3 cable. In addition to the potential noise from these circuits impressing on the other as stated above (especially in audio power circuits), taking the hot leads from the opposite legs (L1 and L2) can cause several unsafe situations. What could happen if one of the two shared circuits is taken offline and the ground or neutral is mistakenly disconnected? Or the circuit is misidentified on the opposite end and thought to be de-energized before work is started? Many jurisdictions in the USA forbid multiwire circuits in residential structures for that reason.

    RE (properly grounding the two circuits can be tricky)

    Its not rocket science nor tricky, simply need to know how to do things when neutral and ground wires are shared with the two circuits. There's an additional safety trick most electricians and DIY don't do when installing a double circuit, i learned it from a Master Electrician, you need to put a flat head nail joining those two breakers (there's a hole for this) so that if one trips the other follows. Very logical, good reasons for this, too long to explain here. Other breakers don't have a joining nail, only those for a double circuit.

    Proper grounding IS rocket science to someone that does not understand it - I cannot tell if you do. Putting a nail through two breakers is illegal, period. For a multiwire setup (the proper term you are describing) the two breakers must be mechanically connected and designed this way (like a 220v breaker).

    RE "or aluminum cable."

    The suggested use of Alu cables is very surprising. Alu cabling for electrical work has been banned for years in many jurisdictions due to connection problems with this "soft" metal, softer than copper which is the preferred one. Moreover, Alu has a resistivity about 1.6 times that of copper. Not a great conductor.

    Not aluminum cable - aluminum and steel ARMORED cable. Ever hear of those, do you know the difference?

    RE "sub panel providing many more 120 volt circuits"

    The many more may or may not happen since this depends on how loaded the main panel is, and the sub panel can only use the "loose" (amperes) from the main panel. An unused 220V breaker slot would provide two 110V lines.

    Everything you stated in this paragraph is pretty much factually incorrect. You can have a subpanel breaker rating up to 80% of the main panel main breaker rating, and the subpanels branch circuit breaker rating maximums are 80% of the sub's main rating. There is no limitation as you state ("loose amps"? lol) in NFPA 70 that the summation of the values of the branch circuit breaker ratings need to be below the value of the main breaker rating (go to your panel and do the math).

    A 220V breaker does not provide two 110V lines, it provides L1 and L2 to the subpanel from which you can derive both 220V and 110V circuits as in your main panel.

    So expert in grounding, can the ground and neutral in a subpanel be tied together? If you are wrong and wire it up the incorrect way you could kill someone. Only you need to see your answer before you google it.

    I just needed to correct the misstatements you made, so someone doesn't utilize the incorrect information given. I am not going to argue with you - get an electrical engineering degree or a master electrician certification then we can talk.

  3. #33
    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by mmc8180 View Post
    RE "or aluminum cable."

    Not aluminum cable - aluminum and steel ARMORED cable. Ever hear of those, do you know the difference?
    FWIW: Using steel MC cable offers a significantly higher degree of EMI shielding than the aluminum MC cable. Some years ago we measured it at work and the difference wasn't trivial.


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