I'm making a lamp, this lamp has two bulbs in it. Presumably I'm gonna connect this directly with a plug to the wall. To switch the thing on and off I've acquired two on-off switches from and electronic I don't use anymore. On the side they say 3A 250VAC and under that 6A 125VAC, with a simply google search it says houses deliver 20A through outlets. I was told by someone it doesn't matter the amperage of the house because my lamp will only draw as much as it needs, but in the event this is not the case.

How would I go about lowering the amperage of the lamp?

Switch: https://images-na.ssl-images-amazon.com/images/I/71kV5rxckGL.SL1500.jpg

I've been only using DC stuff up till now, new to AC

  • 2
    \$\begingroup\$ If total lamp current rating (lamp 1 current rating + lamp 2 current rating) is less than switch current rating (6A or 3A, depending on mains voltage), and if switch is only used to control lamp, then it is ok to use. It also depends on how lamps are connected, series or parallel. I have given worst case. \$\endgroup\$
    – User323693
    Jan 7, 2017 at 4:33
  • \$\begingroup\$ What wattage is the lamp? I'm assuming you're in the US so 110V is your house supply? \$\endgroup\$
    – crowie
    Jan 7, 2017 at 4:33
  • \$\begingroup\$ As long as the power consumption of the two lamps together is somewhat less than 750W, you should be OK to use the switch. Note that 125V * 6A = 250V * 3A = 750W. Make sure the switch is installed in such a way that you cannot touch the electrified contacts in the back. If you touch 125V or 250V, you will probably get a strong and unpleasant shock that you will never forget. \$\endgroup\$
    – user57037
    Jan 7, 2017 at 4:36
  • 2
    \$\begingroup\$ The bulbs added wattage is about 65 watts and yes I'm in the US \$\endgroup\$ Jan 7, 2017 at 5:28
  • \$\begingroup\$ Are these switches going in the lamp, or in a separate wallbox? \$\endgroup\$ Jan 7, 2017 at 15:50

1 Answer 1


In terms of Ohm's law, power, and resistive circuits (such as a lamp), AC and DC are the same. The amperages you are referring to aren't "delivered" amps, they are "rated" amps. Connecting something that draws more than the rated value will cause them to either trip or be damaged.

First, standard household outlets. In the USA, normally these are actually part of a circuit rated for 15A (not 20A) but to be sure you would have to look at the circuit breaker feeding the circuit. This is the most amps all of the outlets on the circuit can deliver combined without tripping the breaker. This hypothetically could be one outlet delivering 15A and nothing connected to the rest, but usually that's not the case. Further, you would not normally run the circuit above 80% of the trip value continuously, in the example I'm using, 12A. The breaker is likely to wear out over time above this level.

Second, the value on the switch is how much the switch can deliver without damage. Since a standard outlet in the USA is 110-125V, if you are in the USA you would use the 125V value, which is 6A. You cannot connect a load that would exceed his value.

As your friend stated, the lamp will draw whatever it draws in accordance with Ohm's law and the power equation P = IV (same as DC). For example, a 120W lamp would draw 120 W / 120V = 1A.

If it is just a lamp, you're probably OK as this switch could power 125V x 6A = 750 W (this power is the same regardless of voltage/country since 250x3A is also 750 W), and most lamps are well under that.

AC and DC differ most when applying highly inductive (or, less likely, capacitive) loads, such as an AC motor. In that case standard DC equations do not work and you cannot merely add currents, or divide power by voltage to get current. Since you are using a lamp, it is basically the same as DC so I'm not going to go into those AC calculations here. As pointed out in the comments, another difference is an AC rated switch may not be suitable for DC as it might arc or even get welded shut in a DC circuit.

  • 1
    \$\begingroup\$ Thanks for trying to answer. Your answer is OK, but you should probably mention that switch ratings for DC are usually much lower than switch ratings for AC, and some switches may not have any DC switching current listed (should not be used for DC). This has to do with arcing during switch bounce. Also, you are assuming the OP is in the US. Actually we don't know that. So the OP could be using 250V. \$\endgroup\$
    – user57037
    Jan 7, 2017 at 5:22
  • \$\begingroup\$ Thank you very much, I understand this much better. With the combined wattage of the bulbs being 65 I should be good then! \$\endgroup\$ Jan 7, 2017 at 5:31

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