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Author Topic: Underpowering Speakers  (Read 31071 times)

Rob Timmerman

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Re: Underpowering Speakers
« Reply #60 on: February 12, 2009, 10:40:17 pm »

David A. Parker wrote on Thu, 12 February 2009 22:24

David Buckley wrote on Thu, 12 February 2009 18:/

 

Note that under the 2008 NEC that MWBC are required to have the handles of the breakers mechanically linked, so if you pop a breaker on one circuit of a MWBC, say by turning on too many parcans, then you'll also open the breaker on the other "side" of the MWBC - oops - there goes the PA...




Now that's really messed up. Bad enough for a concert distro, but household wiring? That's totally useless. Must be beaurocrats with no justification for the job besides coming up with new rules. If anyone knows of anything this new rule will help, please share it with me. I learned residential wiring from  my Dad over 40 years ago, and I've never seen any such nonsense, and never seen a problem that this would solve. That would really mess up my septic system, it has a pump and alarm intentionally on separate circuits. So, if I had to link the breakers, and my pump trips the breaker, it will also trip the breaker on my alarm, so I'll get no alarm. Wonderful.



Slight clarification:  a MWBC is 2 or 3 circuits on different phases that share a neutral.  And only opening one of the phases at a time can result in dangerous conditions: what if the neutral is disconnected in the box where the circuit is off, but it is carrying current from another circuit on a different phase?  Missing neutrals have the potential to cause serious problems and injury; this change is not surprising one.  If you need separately controlled circuits, nothing's preventing you from running a second neutral conductor.

Further, the NEC is  publication by the National Fire Prevention Association, and is edited by professional engineers.  It carries no weight on its own.  For it to apply in any given locality, there must be legislation giving the Code the force of law.  Not all localities do this, and others reference specific (usually not current) editions of the Code.
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Art Welter

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Re: Underpowering Speakers
« Reply #61 on: February 12, 2009, 10:50:53 pm »

David,

In typical residential wiring, separate neutrals are run for each circuit, not so for the MWBC.

If your pump has a separate neutral from your alarm, you would not be required to link breakers.

Art Welter
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David A. Parker

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Re: Underpowering Speakers
« Reply #62 on: February 13, 2009, 06:55:56 am »

Art Welter wrote on Thu, 12 February 2009 21:50

David,

In typical residential wiring, separate neutrals are run for each circuit, not so for the MWBC.

If your pump has a separate neutral from your alarm, you would not be required to link breakers.

Art Welter


That's where I'm having the problem understanding. The whole panel shares a neutral(standard residential panel). It seems that situation would exist at all times. The neutral is grounded, so? If I ran two neutral wires to the sewer system, they both go to the same place in the panel, and that is grounded. I already have separate neutral and ground.
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David Parker
Lost and Found Sound
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Art Welter

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Re: Underpowering Speakers
« Reply #63 on: February 13, 2009, 01:55:11 pm »

David,

See Rob’s clarification message #405947.

I don’t make the rules, I was just pointing out a difference- most house wiring in the USA uses Romex 3 conductor wire, neutral, hot, earth ground.  Commercial wiring uses conduit and separate wire pulls.

If three 20 amp circuits with different loads share the same neutral, the neutral wire could be overloaded if the full potential of  3x20 amps were to go through it, so having the breakers tied together in that situation makes sense to me.

And to bring this around to speakers again, the practice of sharing ground on multi way speaker wiring to save a pin is the equivalent of running a smaller gauge of wire overall.

Art Welter
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