Electrical Load Mystery

[bobmcc81]

Newbie here that has not ventured into the computer controlled lights yet but give me time!

My latest static light display includes 5 strands of C9 incandescents. I kept blowing the inline fuse in light string number 1 closest to the power source. Power source is a #12 awg 25' extension cord plugged into a dedicated 20 amp GFCI breaker.

I get out my Kill-A-Watt meter and learn the draw is 5.96 amps with a 5 amp fuse. I figure I have some room there so I replace the fuse with an 4 amp/240 volt which I believe should give me 8 amps at 120 volts. I install the new fuse and 1/2 hour later the power cunsumption at the outlet is the same and wire on string 1 is not warm so I figure all is good.

1 hour later new fuse is blown.

What am I missing?

Thanks for any education

Bob

[LabRat]

Loose wire in the string? As the wind blows, it could be shorting, thus "upping" the current draw and popping the fuse.

(just a theory.. I don't have any C9's.. only minis, and now some LEDs)

[EasyGo]

If the string came with a 5-amp fuse, you very likely are exceeding the ratings of the string with five strings strung together.

Secondly, the voltage rating of a fuse is just the maximum it can safely interrupt; you still need an amp rating as big as your load.

[chesterspot]

It's cheaper to buy another extension cord than it is to have a fire because you over loaded the string.

[ErnieHorning]

1 hour later new fuse is blown.

It’s trying to tell you something Bob. Never replace a fuse with anything other than the original type and value. The wire probably will handle more than 5 amps but all of the connectors won’t.

Fortunately for you, you figured the current incorrectly. 5 amps is 5amps, whether its 5 volts or 1000 volts. Had you put in an actual 8 amp fuse, you most likely would have started a fire.

Only add enough strings to stay under 5 amps. Use an extension cord to power the rest.

Stay safe Bob and welcome to DIYC.

[bobmcc81]

Thanks for the polite education everyone without calling me stupid. I guess I'm confusing current draw with fuse capacity. I live I learn.

I will figure out how to power the last two strings from another extension cord.

Thanks again

Bob

[chesterspot]

Bob,

Get a three way adapter like this: 21zyuKWnalL._SL500_AA300_.jpg

Plug it into the end of your extension cord. Plug one string of lights into the adapter and then a 25' extension cord into the other. Run that extension cord along the first string using zip ties or wire ties and plug it in to the remaining 4 strings. This way you don't have to run an extension cord from another location.

[DaveJZ]

I believe... in using C-7 and C-9 lights for much of my displays until this year... You should not connect more than 75 working bulbs together... If you are lucky you can push 80. I say bulb count because when using c-7 lights there are many areas I put "dead" bulbs and may have 4 strands attached together but total lighted count would be around 80.

My guess is your overloading the fuse. They take awhile to "pop" so it may seem just fine at first until the fuse gets hot enough to blow.

Like others I suggest dropping the amount of lights attached.