Determining the switch rating for a lamp

by mar2194
Tags: current rating, lamp, switch
 P: 10 I'm in the process of repairing a lamp that I found with a broken switch. I know the lamp mechanism is functioning because I've bypassed the switch and plugged it in and it works fine. I needed to buy a new switch and they all have a current rating. I'm using 1 60 W bulb with a standard North American 125 V outlet. I thought P = IV --> I ≈ .5 A. Using this info I purchased a toggle switch rated at 5 A for 125 VAC (so at least 5 amps of current can flow through it right??) and tried adding it to the lamp. Didn't work! Does anyone know what I might be doing wrong or how to determine the current rating for the switch I'm attempting to add? Any help is appreciated. I bought the switch at RadioShack if anyone is interested. Thanks!
 P: 10 NVM problem solved; there were 3 connectors for 2 different voltage ratings. I just fiddled with it a little.
Mentor
P: 41,104
 Quote by mar2194 I'm in the process of repairing a lamp that I found with a broken switch. I know the lamp mechanism is functioning because I've bypassed the switch and plugged it in and it works fine. I needed to buy a new switch and they all have a current rating. I'm using 1 60 W bulb with a standard North American 125 V outlet. I thought P = IV --> I ≈ .5 A. Using this info I purchased a toggle switch rated at 5 A for 125 VAC (so at least 5 amps of current can flow through it right??) and tried adding it to the lamp. Didn't work! Does anyone know what I might be doing wrong or how to determine the current rating for the switch I'm attempting to add? Any help is appreciated. I bought the switch at RadioShack if anyone is interested. Thanks!
What do you mean it doesn't work? It sound like it's rated fine. If it weren't rated high enough, it would catch fire, not "doesn't work".

BTW, you do know that the hot lead for lamps needs to go to the inner button on the bulb socket, right? Not to the outside screw part. That's why lamps in the US use a polarized 2-prong power cord.

 Mentor P: 41,104 Determining the switch rating for a lamp Ah, glad it works now. Does my comment about the hot/neutral polarity make sense?
P: 10
 Quote by berkeman Ah, glad it works now. Does my comment about the hot/neutral polarity make sense?
Yah, all I was doing was taking a spliced wire and putting in a switch. When I said it didn't work I just meant that when I flip the switch, nothing happens. I realized I was using the portion of the switch that was rated for 3 amps @ 250 V instead of 6 amps @ 125 V. However, the switch didn't fit the hole so I'm going to buy another one that will be rated at .5 amps. Will that be rated high enough?
Mentor
P: 41,104
 Quote by mar2194 Yah, all I was doing was taking a spliced wire and putting in a switch. When I said it didn't work I just meant that when I flip the switch, nothing happens. I realized I was using the portion of the switch that was rated for 3 amps @ 250 V instead of 6 amps @ 125 V. However, the switch didn't fit the hole so I'm going to buy another one that will be rated at .5 amps. Will that be rated high enough?
That sounds kind of marginal. I'd go with a rating at least 2x or higher than the steady-state current. And be sure to mark the lamp for 60W bulbs maximum or similar.
Mentor
P: 12,070
 Quote by mar2194 ... I purchased a toggle switch rated at 5 A for 125 VAC (so at least 5 amps of current can flow through it right??) and tried adding it to the lamp. Didn't work! Does anyone know what I might be doing wrong or how to determine the current rating for the switch I'm attempting to add?
Glad things worked out eventually. Just FYI, at this point I would have used an ohmmeter to test whether the switch is working properly.

 Quote by mar2194 Yah, all I was doing was taking a spliced wire and putting in a switch. When I said it didn't work I just meant that when I flip the switch, nothing happens. I realized I was using the portion of the switch that was rated for 3 amps @ 250 V instead of 6 amps @ 125 V. However, the switch didn't fit the hole so I'm going to buy another one that will be rated at .5 amps. Will that be rated high enough?
I'll echo what Berkeman said about the 2x rating. Also, any chance you'll use the lamp for a 100 W or 150 W bulb? I would figure out the current at 150 W, and go to twice the current rating of that. So, 1.25A @ 150W, try to get a switch rated for 2.5 Amps. Or if you're absolutely sure 60 W is the maximum you'll use, then 1 Amp.

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