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Can this be used safely?

  1. May 8, 2004 #1
    Can this be used safely???

    Sorry for bothering you guys with such an easy question but it has started a huge debate on another forum. Since it deals with Electricity and is probably very simple, but we are all aquarium hobbiest's and dont' knowone REALLY knows the answer.

    Here goes,

    There is a switch beeing used for an auto-topoff device that is rated to have a maximum switching capacity of .28 amperes at 110VAC. This is a float switch made by www.madisonco.com and is part # M8000. This switch also has 22 Gauge leads on it. Ok, so people are using this switch to power on/off air pumps and power heads. The pumps and power heads usually do not draw more then 10 watts and are 110VAC devices. I know that under regular circumstances this switch will withstand the load, but if aftter the switch somewhere in the power head or air pump there was a short. Wouldn't that switch have to be able to withstand the entire load of the circuit? (15 amp Breaker?) My thought is that if there is a short then this switch would be the weakest link and could possible melt or start a fire. Also don't all switches on a 15 amp house circuit have to be able to withstand 15 amps then to avoid buring in the event of a short in that circuit? Any help would be great, I dont' want to see any fellow aquarium enthusiests get burned up in there sleep, especially since there is all the water...

  2. jcsd
  3. May 12, 2004 #2
    Greetings Jeremiah.

    I believe you have no problem here to worry about.

    Some devices connected to house current, such as a lamp are simple and straightforward. The current goes through the cord, then to the switch of the lamp and then to the bulb(Of course, it's AC, but let's forget that right now).
    Under these conditions, the entire circuit is subject to the 15-amp maximum you described.
    The filament of the bulb has a substantial resistance to current flow, which by design heats the filament and gives off light. This resitance means that the current flow at any given time of proper lamp operation is far less than 15-amps.
    In fact, for a 100 watt light bulb connected as such, the current flow throughout the lamp is just less than 1 amp.
    But, because the switch is before the bulb in the circuit and provides negligable resistance, it "should" be rated at least 15-amps or usually more.
    However, because of this simple design, a potential hazard exists.
    If the switch fails, arcing can occur along the switch at the full 15-amps(1650-watts in this case). This arcing can melt components of the switch and cause a fire. This is why UL approved sitches are recommended. They reduce arcing and have an insulating barrier to reduce the potential of fire.
    Hopefully, the house breaker will trip before the potential for disaster happens.

    In the case of your aqaurium(and many other devices) the circuit design is not as simple as that of a lamp.
    Usually, a transformer device is the first device that the house current see's in it's circuit path. The transformer reduces/regulates current flow to the rest of the aquarium.
    What this means is that all of the circuit after the transformer is usually far less than 15-amps.
    So, if a short occurs AFTER the transformer, the arcing is much less and usually of no hazard. Your switch is rated at 1/4th of an amp because that is all that will flow through it(due to the transformer). If the switch shorts, it does NOT short at 15-amps, only 1/4th of an amp.
    So, there is no problem here.
    But do you see where there could be? Yes, the transformer!
    If there is a potential fire hazard, it is with the transformer, not your switch after it.
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