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Electrical Wiring FAQ (Part 2 of 2)
Section - Noisy fluorescent fixtures, what do I do?

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Top Document: Electrical Wiring FAQ (Part 2 of 2)
Previous Document: Can I install a replacement light fixture?
Next Document: What is 3 phase power? Should I use it? Can I get it in my house?
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	Many fluorescent fixtures tend to buzz, objectionably so when used in
	residential (rather than warehouse or industrial) situations.  This
	tends to be the result of magnetic/physical resonances at the
	(low) frequencies that standard fixture ballasts operate.  You
	can eliminate this problem by switching to electronic ballasts,
	which operate at a higher (inaudible) frequency.  Unfortunately,
	these are quite expensive.

Subject: Noisy lights with dimmer switches, what do I do?

	Often, after installing a dimmer switch, or replacing bulbs controlled
	by a dimmer, you'll start hearing objectionable buzzing or humming
	from the bulb.  Sometimes it even interferes with televisions or radios.

	A little theory first.  The voltage on the wiring in your house looks
	like this - a sine wave (forgive the lousy ASCII graphics ;-):

                  ...             ...              ~ +160V
                 .   .           .   .
                .     .         .     .
              ------------------------------------ 0V
                        .     .         .     .
                         .   .           .   .
                          ...             ...      ~ -160V
	Most dimmers work by having a solid-state switch called a triac
	in series with the light bulb.  Whenever the voltage passes through
	zero (it does this 120 times per second), the triac turns itself off.
	The control circuitry in the dimmer provides an adjustable delay
	before the triac turns back on.  So, the resulting wave form looks
	like this:

                  ...             ...              ~ +160V
                  |  .            |  .
                  |   .           |   .
              ------------------------------------ 0V
                          |   .           |   .
                          |  .            |  .
                          ...             ...      ~ -160V

	As you can see, by varying the turn-on point, the amount of
	power getting to the bulb is adjustable, and hence the light
	output can be controlled.  Voila, a dimmer!

	This is where it gets interesting.  Note the sharp corners.
	According to the Nyquist theorem, those corners effectively
	consist of 60Hz plus varying amounts of other frequencies that
	are multiples of 60Hz.  In some cases up to 1Mhz and more.  The
	wiring in your house acts as an antenna and essentially
	broadcasts it into the air.  Hence TVs and radios can be
	effected.  This is called EMI (Electromagnetic Interference).

	As far as the bulbs are concerned, a bulb consists of a series
	of supports and, essentially, fine coils of wire.   When you
	run current through a coil, it becomes a magnet right?  If
	there's any other metal nearby, it'll move.  Just like a
	solenoid.  Further, when the amount of current flow abruptly
	changes the magnetism change can be much stronger than it is on
	a simple sine wave.  Hence, the filaments of the bulb will tend
	to vibrate more with a dimmer chopping up the wave form, and
	when the filaments vibrate against their support posts, you
	will get a buzz.

	Worse, some dimmers only do half-wave switching, such that the
	one half of the chopped wave form will be absent.  Which means
	that the current flow during the present half will have to be
	much stronger to produce the same amount of light - more EMI
	and more tendency to buzz.

	Solving buzzing problems:  If you have buzzing, it's always
	worth trying to replace the bulb with a different brand.  Some
	cheap bulb brands have inadequate filament support, and simply
	changing to a different brand may help.  Try "rough service" or
	"farm service" bulbs.  They're usually much stronger and better

	Chance are, however, that switching bulbs won't make that much
	of a difference.  Perhaps the buzzing will go away at some
	dimmer settings, but not at all.

	Buzzing bulbs are usually a sign of a "cheap" dimmer.  Dimmers
	are supposed to have filters in them.  The filter's job is to
	"round off" the sharp corners in the chopped waveform, thereby
	reducing EMI, and the abrupt current jumps that can cause
	buzzing.  In cheap dimmers, they've economized on the
	manufacturing costs by cost-reducing the filtering, making it
	less effective.  Perhaps the dimmer will be okay at some
	settings, but not others.  Or be very picky about what bulbs to

	It is our belief that most buzzing problems can be traced down
	to cheap (<$15 dimmers), and most effectively solved by going
	to mid-range ($25-$35) dimmers from respected companies, such
	as Leviton.  One of the authors of this FAQ, after learning
	this lesson, will still use $.89 outlets, but insists on better
	dimmers.  By all means, try a different bulb first.  You may
	get lucky.  If not, it's time to swap dimmers.

	If you have EMI problems, it's almost certain to be a cheap

Subject: What does it mean when the lights brighten when a motor starts?

	This usually means that the neutral wire in the panel is
	loose.  Depending on the load balance, one hot wire may end up
	being more than 110V, and the other less than 110V, with
	respect to ground.  This is a very hazardous situation - it can
	destroy your electronic equipment, possibly start fires, and in
	some situations electrocute you (ie: some US jurisdictions
	require the stove frame connected to neutral).

	If this happens, contact your electrical authority immediately
	and have them come and check out the problem.  If you say "loose
	neutral", they will come.

	Note: a brief (< 1 second) brightening is sometimes normal with
	lighting and motors on the same 220V with neutral circuit.  A
	loose main panel neutral will usually show increased brightness
	far longer than one second.  In case of doubt, get help.

User Contributions:

Report this comment as inappropriate
Dec 21, 2011 @ 12:00 am
In a fire protection circuit, circuts are shown witha no example 6,8,4etc. what it mean?these circuits are connected between smode detector,junction box etc
Report this comment as inappropriate
Dec 24, 2011 @ 12:12 pm
My daughter dropped a small necklace behind her dresser. The necklace crossed a plug terminal and shorted the receptacle.
I bought a new receptacle and installed the same. I still have no power I suspect there could be a bigger problem,this is aluminum wiring.
I've killed the breaker and call an electrician but am curious as to what happened.P.s. there is a dimmer switch on the same circuit.
Report this comment as inappropriate
Feb 24, 2012 @ 11:11 am
Regarding new construction wiring and running 12/2 and 14/3 wire in the same box.

I have multiple switches to lights. Ran 12/2 and 14/3 into switch box and inspector wrote correction needed.

What should I have done instead?

thank you
Report this comment as inappropriate
Nov 26, 2012 @ 9:21 pm
Does a grounding electrode facilitate the operation of a OCPD, to clear a ground fault ?
Report this comment as inappropriate
Mar 18, 2013 @ 10:10 am
Assuming you are installing two switches in a two switch box, you probably should have used 14/2 and 14/3 instead of replacing 14/2 with 12/2. If you are only installing one switch in a one switch box, you should only have one cable in the box.
P k
Report this comment as inappropriate
Jan 26, 2014 @ 10:10 am
I prefer to use nothing smaller than12 awg /the smallest sized wire on a circuit determines the allowable ampacity
Ex: 15 amp-14awg. 12awg-20amp only rule for thumb other factors such as continuous load,heating and others if you do not know the safe NEC rules then please call a qualified journeyman Electrician better be safe

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Top Document: Electrical Wiring FAQ (Part 2 of 2)
Previous Document: Can I install a replacement light fixture?
Next Document: What is 3 phase power? Should I use it? Can I get it in my house?

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Last Update March 27 2014 @ 02:11 PM