Sub blowing Christmas lights?

I can't imagine that the sub is doing it. I can't think that an over load on the circuit would blow the fuse in the lights. It would blow the circuit breaker. I am sure the plug on the lights are polarized so you can't try turning the plug 180 degrees and see if it is a polorization issue. Does it occur as soon as you plug the lights in or as soon as the sub comes on? Do you have a surge suppressor that you can plug into the shared outlet then plug the lights into the surge suppressor?

I assume the fuses are installed in fuse holders built into the plug of the light string.

The only thing I can think of is heat generated from poor contact pressure of the receptacle contacts against the plug contacts. Does the plug fit loose in the recept?

The Sub power supply is sloppy and the fluctuating power needs of the sub are messing up the voltage in the A/C supply. The mains are being drawn down and bouncing way over the standard voltage by the sub.

I think that you may very well be pointing in exactly the right direction, Elizabeth. I'm thinking that what is known as an inductive kickback effect, from the power transformer of the sub's amp, may be putting a large voltage spike into the lights.

Inductive kickback, which results in what can often be an extremely large voltage spike, is what happens when the current through an inductance is abruptly changed. Power transformers have lots of inductance. The abrupt change might be related either to the sub's "fluctuating power needs," as you put it, or conceivably to the sudden change in line voltage that may occur when the lights are plugged in and start drawing current.

"Back emf," though, is probably not the best term to use for this. The back emf voltage produced by a woofer or other speaker driver results from a different effect -- the motion of the voice-coil continuing for some amount of time after the input signal has stopped or changed, which causes the driver to act as a generator until its motion gets back in sync with the signal.

Sprink, it would be helpful to know some further details: Does the fuse blow precisely at the moment the lights are plugged in, or at random other times? When it blows, is the sub turned on, and is it playing music?

Regards,
-- Al

electrical folks (AL?) could this be a grounding issue? Even with the sub doing something to the circuit a bad ground seems like a possible cause?

That's a logical question, Paulsax, but I can't envision how either a missing ground or a miswired outlet could cause something like this. No matter how the outlet were miswired or ungrounded it would seem that no more than the normal 120V or so line voltage would be put across the light string (unless, as Elizabeth and I suggested, the sub is adding a transient voltage spike on top of the 120V).

Regards,
-- Al

If it happens when the sub shuts off,there could be a spike from it.When I unplug the walwart for my cellphone,I get a spike.In the bedroom,it even interferes with the tv by unplugging it.I checked it with my Fluke meter,and sure enough a small spike.

Also beside the sub turning off/on doing it,there could be a loose connection in the outlet amplifying the problem if that is the cause.

Al as a rule a fuse will not add protection, blow, in an over voltage situation. I could see bulbs burning out due to over voltage....

The bulbs I assume are a filament type purely a resistive load, I = E/R. I would agree the current will spike with the voltage increase but the fuse should not see the spike, jmho......

At any rate it seems "Sprink" has left the building. Without some further input from he or she we may never find the answer.
Jim

Jim, the famous fictional detective Sherlock Holmes once remarked something to the effect that when you've ruled out everything else, whatever remains, no matter how improbable, must be the explanation :)

In this case the only explanations that seem to present themselves are the ones you and others have offered, the voltage spike possibility (which of course would result in a proportional current spike), and the possibility that it is all coincidence (meaning that the fuses will eventually blow on other outlets as well).

Sprink's words that "the lights have blown twice WHILE plugging in to this outlet" would seem to give credence to the spike theory, because the spike would be adding to the already large current surge that occurs during the first second or two after the lights are connected (due to their low resistance when cold). You appear to be saying that the spike would be either too brief or too small to blow the fuse, but given all the foregoing my feeling is that it is a close call as to whether that possibility or coincidence is the least unlikely possibility.

Sprink -- When you respond, it would also be helpful to know the ratings of the fuse (amperage, fast blow/slow blow, etc.), and how many lights are in series with it, and what their voltage and wattage ratings are.

Regards,
-- Al

Being he didn't complain about other things blowing around the house sounds to me that a poor neutral connection in the service opening intermittently somewhere causing a voltage problem could be ruled out.One rare exception would be if that outlet is split,and running off of two separate phase legs.

Thanks for all the informative info. The sub is off and not playing. However, I found a short in the Christmas lights. BOTH sets. I took the second set, put new fuses in them and plugged them in another outlet, and they came on. When I sat them down, they came back on. I did the same thing with the second set. I plug a third set into the outlet and they worked just fine.

Hello,
It is not the sub doing it most likely as it is simply the amount of load (in Amperes of current) on that particular circuit. Plug less stuff, whatever it may be, into that circuit and use others that are less loaded down already if possible.
Hope this helps,
Tom

So forget Christmas and enjoy your sub. Man, you gotta get your priorities straight.