I installed 4 recessed lights in an unfinished (now finished) room of my
house...the leg was installed to that room by the electricians during
original construction. I just replaced the single light with 4 new recessed
lights. Now when I turn on those 4 lights the other lights on the circuit
give a quick one-time flicker. This is a room off the master bedroom and is
on the master bedroom's arc-fault circuit breaker.
Best way to track this down? Loose wire in one of the new lights? Weak
Thanks for the suggestions.
Size of breaker/wiring on this circuit?
Sounds like probably was/is a 15A/14ga lighting circuit and you've now
added too much wattage w/ the new fixtures and are seeing the temporary
voltage drop when the added load comes on.
How much _total_ wattage is now on this circuit when you observe this?
And, how much did you add?
As a quick/easy test, take all the bulbs but one out of the new
fixtures and make it a small one -- say 60W. Now, does the flicker go
away? If so, put the original back in and do the same test
sequentially. I'll hazard a guess after one or two, you'll see the
I don't see how dirty switch contacts would make the other lights do
that bit of flicker.
It sounds to me like voltage drop in the wiring from the surge of
current drawn by the freshly-turned-on lights while their filaments are
Meanwhile, I would suggest to the OP to check total wattage of lights on
that circuit and the wire size and breaker size. If the wire is AWG 14,
maximum allowed breaker size is 15 amps which means 1800 watts.
The code only allows "continuous loads" up to 80% of the breaker rating,
and it appears to me that lighting qualifies as a "continuous load".
I also somewhat remember that wire size is supposed to be adequate to
have voltage drop less than 5% at full current. For 14 AWG at 15 amps,
that is roughly 75 feet from breaker to load. For 12 AWG at 20 amps, that
is about 90 feet. 12 AWG with a 15 amp breaker is good for about 120
feet, and I would mark the breaker box so that nobody in the future
replaces the 15 amp breaker with a 20 amp one on the basis of wire size.
Another note - I remember reading somewhere recently that a branch
circuit must have all permanently installed wiring identical in maximum
allowable overcurrent protection. I do not know for sure this is NEC;
it might be a local building code for all I know. I guess the reasoning
is to prevent someone from putting in a breaker that is too big for all of
the wiring on the basis of seeing only some of it.
Meanwhile, since incandescents briefly draw up to 10-15 times their
normal current during a cold start, some significant voltage drops in
wiring resulting from this can be perfectly normal. Keep in mind that
light output of an incandescent is roughly proportional to the cube of
applied voltage (normally varies a little more drastically than that
even)! A 5% voltage drop causes incandescents to dim by 15-17%.
If 300 watts of incandescents have simultaneous cold starts, that can
mean a brief load of 4000 watts or 33 amps, possibly a little more. This
is allowed. If this surge flows through just 35 feet (breaker to load) of
14 AWG wire, that can cause a brief voltage drop to already-on lights
downstream of this hypothetical 35 foot wire run of 5% and briefly dim
them possibly by 15-17%.
A fix is not required if a voltage drop of more than 5% occurs only
while filaments are warming up. Brief overcurrents are allowable - there
are even fuses and breakers specifically designed to not blow/trip from
more serious allowable brief overcurrents - moderate and moderately severe
overcurrent will not overheat wiring in a split second.
One more solution, should you determine that a fix is needed - put a
junction box only a few feet from the breaker box and split the new
lighting wire run from the existing one at that point. Keep in mind to
have all wiring on that circuit identical in maximum allowable overcurrent
protection and to have all lights not exceed 80% of the allowable
overcurrent protection - otherwise upgrade all wiring in the circuit or
add another circuit.
More questions or if you have doubts that you can competently do any
such needed work yourself - that's what professional licensed electricians
- Don Klipstein ( firstname.lastname@example.org)
I'll add my guess. The new 4 lights are
probably 150 watt floods or something
like that. They have a very low startup
resistance, therefore a high inrush. Now,
if the circuit is fairly far from the
breaker box, you will get a momentary
drop until the filaments get fully hot.
The further you are from the breaker, the
higher the resistance, the bigger the
voltage drop. This is especially seen
with aluminum wiring because of higher
per foot resistance. I see this all the
time in my 2nd floor bedroom/bath. The
4 halogen lamps in the bathroom, when
turned on, will cause a momentary
voltage dip for the other bathroom. BTW,
this circuit is aluminum and is about 50
- 70 cable feet from the breaker box.
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