Can I convert these light fixtures from 220-240v to 110-120v?
July 1, 2012 4:15 PM   Subscribe

Can I convert these light fixtures from 220-240v to 110-120v?

We've brought some light fixtures back to Canada with us from China, however they are marked as 220v-240v only (60w, 50-60 Hz).

Is it simply a case of fitting a 110v bulb or do we have to change the entire fitting/wiring? If so, how difficult a task is it? I'm a relative amateur at electrical work, so please explain to my 5 year old self if it's possible or if I need to hire an electrician to avoid burning the house down.

We have some IKEA desk lamps we bought in China that are labelled 110v-240v, so all we'd have to do is change the bulbs to the appropriate voltage, so I'm wondering if that is the case for these lamps.

Items are 2 x table lamps and 1 x pendant lamp. Links are to the Chinese manufacturer's website, however Google translate does a reasonable job.
posted by arcticseal to Home & Garden (10 answers total)
 
What kind of bulbs do they currently have in them? What does the socket look like? Also, is there any point in the lamp where there is something which is designed to step the current down from 220?
posted by hippybear at 4:34 PM on July 1, 2012


Looks like you would at least have to switch out the plug... Also, what is the bubble thing in the cord shown in one of the photos for the first link?
posted by hippybear at 4:38 PM on July 1, 2012


Anyway, if the table lamp needs to be rewired, it's a pretty basic process. Here's a quick online tutorial about how to do it. You can probably get everything you need at a big box home improvement store.

Rewiring a hanging fixture is pretty much the same, except you end up with bare-wire ends instead of a plug, and those bare-wire ends are twisted and screw-capped onto the wires coming out of the ceiling during the installation process.

Generally (and I'm not an electrician, but I've rewired plenty of lamps in my time), I don't think that running lower current through wires built for higher voltage is a problem. It's when you go the other way that you end up overheating and causing a fire.

The only thing I can see standing in the way of you not simply being able to screw a bulb into the lamps and having them work would be if there is something in-line in either lamp designed to step-down the current (basically converting the 220 to 110), which might affect what comes out if you only feed 110 into it to begin with... also, that plug on that table lamp... probably won't fit into your Canadian wall sockets.
posted by hippybear at 4:45 PM on July 1, 2012


Generally (and I'm not an electrician, but I've rewired plenty of lamps in my time), I don't think that running lower current through wires built for higher voltage is a problem. It's when you go the other way that you end up overheating and causing a fire.

That's the thing, in this case. Power = voltage * current, so a 60 watt bulb will draw twice as much current at 120V vs 240V.
posted by junco at 5:09 PM on July 1, 2012


hippybear - No bulbs came with them, but they look to be standard screw fittings. I just screwed a regular screw threaded bulb into the pendant lamp to check.
Not seeing anything that steps the current down, but I could be missing something in a bulkhead?
Bubble thing is just the on/off switch.

I'm OK at rewiring plugs etc. (used to wire up logging units offshore to 3-phase, it's just been 10 years since I had to do so)

junco - would it then be advisable to limit the fitting to a 30w bulb?

Let me know if there's any more info, I can always go take photos of fittings.
posted by arcticseal at 5:15 PM on July 1, 2012


would it then be advisable to limit the fitting to a 30w bulb

Right, that's exactly it.

They say a fixture is rated for, say, 60W, but what they really mean is that it's rated for 60/240 = 0.25 amps. So now that you're on 120V, it's rated for 120*0.25 = 30W. You might want to look at CFL or halogen instead of standard bulbs to get more light out of those watts.

When you rewire, make sure the switch switches the hot, not the neutral. You probably already knew that, but it never hurts to remind, I figure.
posted by mendel at 5:49 PM on July 1, 2012


If we're talking incandescent bulbs, I disagree with junco. The bulb behaves like a resistor (with some nonlinear effects from temperature). Its wattage rating is based on the expected household current where it is sold. A 60 watt bulb would draw half as much current on 120v as 240v.

I don't know if this is true for fluorescent bulbs.
posted by scose at 9:30 PM on July 1, 2012 [1 favorite]


work would be if there is something in-line in either lamp designed to step-down the current (basically converting the 220 to 110)

There's no reason to expect anything like this in a lamp that takes incandescents and uses a simple on-off switch.

That's the thing, in this case. Power = voltage * current, so a 60 watt bulb will draw twice as much current at 120V vs 240V.
Right.

A 60 W bulb designed for the 240 V world will pull down ~0.25 amps when supplied with 240 V. I might be off by √2, "RMS", etc.
A 60 W bulb designed for the 120 V world will pull down ~0.5 amps when supplied with 120 V. I might be off by √2, root-mean-square, etc.

So if you're in the 120 V world, using a lamp designed for the 240 V world, and you screw a local 60 W bulb into it, it will be pulling twice the current through its wiring as when you were using it in 240V-land.

Say the wires, switching or so on have some resistance somewhere, R, and you run a current I through it. That bit heats up, turning electrical power into thermal power.
Power = Current * Current * Resistance.

Say this part of the lamp, the wiring for example, was radiating 5 W of power as heat.
5 W = I * I * R
And now you move to 120 V land, buy a local bulb, and plug it in.
You double the current.
20 W = (2 I ) * (2 I) * R.
so the wiring radiates 20 W of power.
That's not good. That wiring, or that switch is going to get hotter.

That describes the general case of lamps.

In your case, if the copper wires are thick enough, and your switch can handle the double current, there's not much resistance, and it's all good.

If the copper wires aren't thick enough, or there's a wonky bit in the switch, then you've got a house fire.

I would check to see if the copper wires are thick enough.

Use a wire stripper to check, and then look up "gauge", and some table or writeup on line, and then scratch your head and say "I wonder if there's a somewhat formal description of how thick the plastic housing on these wires should be when I'm running twice the current through them". I dunno, myself. And then tell yourself "there's no writing on this switch saying what its max current is."

If you want to use 60 W bulbs in it, you probably should strip out the old wires and bulb mount and put in a new wiring and bulb mount, following a "how to rewire a lamp" writeup.

Or use bulbs rated for half the max power in the old, 240 V country, 30 W instead of 60 W.




If we're talking incandescent bulbs, I disagree with junco. The bulb behaves like a resistor (with some nonlinear effects from temperature). Its wattage rating is based on the expected household current where it is sold. A 60 watt bulb would draw half as much current on 120v as 240v.

You are analyzing what happens to a particular bulb designed for the 240 V when someone plugs it into a lamp in Canada, 120V-land. Your reasoning is correct, but that's not what arctic seal is dealing with.

I agree if the ceramic and plastic bits of the lamp can take the waste heat from a bulb designed to use 75 W at 240 V when it is in China, call it 40 W of waste heat, then that part will be fine in Canada using a bulb which uses 75 W at 120 V, dumping 40 W of waste heat into the plastic and ceramic bits.

But the wiring is going to run hotter from the doubled current.
posted by sebastienbailard at 12:25 AM on July 2, 2012


That kind of backs up how I first spotted the issue. Plugged one of the 110-240v IKEA table lamps in (after checking the rating on the base) and found the bulb only glowed a little rather than being fully effective. Took the bulb out and found it was a 220-240v rated 60w. It's an incandescent bulb so it's true for them as well as filament bulbs from the looks of it.

I'm off to buy a 30w bulb, test it in the IKEA lamp and if all good, go with that. If we find it's not enough light, I'll have to look at rewiring the lamps with new bulb mount wires. That's a better solution than chancing it and risking a fire.

Thanks for the advice guys.
posted by arcticseal at 7:18 AM on July 2, 2012


Follow-up: I'm going to take them to my neighbourhood lighting store for rewiring as the bulb mounts also look to be uncommon in N. America so best to get them looked at rather than burn the house down cutting corners.
posted by arcticseal at 1:13 PM on August 1, 2012


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