#17 For Your Information ... Common Neutral Interaction

#17 For Your Information ... Common Neutral Interaction
APPLICATION
NOTE
For Your Information ...
#17
Common Neutral Interaction
Overview
Filter chokes can be wired in series on either the line side
or the load side of the dimmer (as shown below).
Common neutral interaction is interaction or “cross talk”
between at least two dimmers that share the same neutral
wire. When solid-state dimmers are operating, voltage
spikes occur and are transmitted onto the neutral wire.
Normally this is of little concern, except when the neutral
wire is common to two or more phases of a 120V/208V, 3phase, 4-wire system. Under this condition, the voltage
spikes may feed back to the dimmers via the common
neutral wire, causing interaction between the dimmers.
Symptoms
•
•
•
Line Side Installation
Hot
LDC
120V
60Hz
Neutral
Lights flicker steadily at certain dimmer settings.
Lights flash to “full” output at certain dimmer settings.
Light level of a dimmer on one phase inadvertently
changes when a dimmer on another phase is
adjusted.
Load
Load Side Installation
Hot
LDC
120V
60Hz
Recommendations
Lutron recommends the following methods to avoid
common neutral interaction:
1. Separate neutrals
2. Filter chokes
1. Separate Neutrals
The best way to avoid common neutral interaction is to run
a separate neutral wire for each phase of the 3-phase
system (see below).
Neutral
Load
The following filter chokes are available from Lutron:
Model
LDC-10-TCP
LDC-16-TCP
Rated Capacity
600-1200W
1200-1920W
Note: For more information on Lutron filter chokes, see our
Lamp Debuzzing Coil specification sheet,
P/N 360-212.
AØ
Neutral
Load
BØ
Neutral
Load
CØ
Neutral
Load
2. Filter Chokes
If it is not possible to run separate neutrals for each phase
(e.g., an application with existing wiring), you can use filter
chokes to “clean up” the voltage spikes creating the
interaction. One filter choke is required for each dimmer.
The filter choke makes an audible buzz, so care should be
taken to mount it in an area where the noise will not be
objectionable.
Worldwide Technical and Sales
Assistance
If you need assistance call the toll-free Lutron Technical
Assistance Hotline. Please provide exact model number
when calling.
(800) 523-9466 (U.S.A., Canada, and the Caribbean)
Other countries call (610) 282-3800
Our address on the Web is http://www.lutron.com
Lutron and Nova are registered trademarks of Lutron Electronics Co., Inc.
Need additional assistance? Call the Lutron Technical Assistance Hotline 1-800-523-9466
Lutron Electronics Co., Inc.
7200 Suter Road
Coopersburg, PA 18036-1299 U.S.A.
Made and printed in U.S.A. 7/98 P/N 360-283 Rev. C
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