Anyone know about wiring UK wall switches in the US?

[iej]

I'm not trying to be rude, but your master electrician is just plain wrong.

You are confusing current (Amps) with power (Watts)

The current carrying capacity of the device is a constant. You cannot change it, it's down to the physical design of the device.

If you increase the voltage, the amperage goes down for a given wattage (power)
If you decrease the voltage, the amperage goes up for a given wattage (power)

Lower voltage circuits require larger currents to deliver the same amount of Watts. So, 120V wiring is heavier duty than 230V to deliver the same amount of power.

The ability of a particular device to carry a current (measured in amps) only changes if you put in different sized conductors. Increasing the voltage just means you can transmit more power for that number of amps.

Basically, the British 10amp switch on a 120V US circuit can only deliver roughly 1/2 the number of Watts it would deliver in the UK.
The amperage remains absolutely constant as it's basically a description of what size current the device can safely switch and carry.

 

[kb0nes]

Reducing the supply voltage DOESN'T increase the safe current handling of the switch contacts!

This is easily explained by Ohms law, Power = Current^2 x Resistance. In this case the power is in the form of heat dissipated into the contacts based on current flow across the contact resistance.

The contacts are rated for a certain current based on their typical contact resistance and how much heat they can safely dissipate without degradation. Unless you can reduce the contact resistance, or increase the cooling of the contacts it is not wise to run the switch at higher then rated current. You may get away with it for a while, but contact resistance will climb with use and switch actuations and eventually it could fail.

I'm sure the 10 amp rating has a considerable safety margin in it. Also in most cases it is rare to use a typical household wall switch to switch more then a few amps of continuous current. I am reasonably certain that this switch would work perfectly at US supply voltages. I'm not sure I'd ever suggest someone do this though, although I might do it myself as then _I_ accept the liabilities for my own actions.

I think I'm with cadman though, I'd buy that cool looking Leviton triple switch and mount the box sideways.

 

[artcurus]

Again, just saying what he said, and YMMV. (Your Milage May Vary)

If it were me, I wouldn't try it and stick with American switch, which there are similar ones available.

 

[cadman]

This is why I'm a Despard fan ; )

 

[travis]

If the current handling capabilities remain constant, then why do switches have specs listed for either 120 or 250 volts?

http://www.essentialhardware.com/ga...bber&utm_medium=cpc&utm_campaign=pricegrabber

 

[cadman]

In the case of that toggle, they're referring to a motor load in which case they're derating current due to the device's inductive nature. A motor or coil without suppression can generate quite a nasty high voltage arc well above the source voltage which can destory contacts in short order. I think the assumption is made with residential switches that most loads will be resistive. -C

 

[artcurus]

@cadman,

THAT's the brand I was thinking about. Those things were crazy. I've seen them with 4 plugs per unit.

 

[kb0nes]

Switch voltage ratings

The reason a switch voltage rating matters is for insulation value with the switch in both open or closed positions (and to some degree as it transitions). The voltage has no influence on the the current that the switch can safely handle. Of course it is important that the switch not arc across its contacts or have leakage to the mounting etc.

With the exception of arcing, switch contacts fail due to heat which is generated by current flow across the contact resistance. It could be 5 volts or 500, but at 10 amps the heating of the contacts is the same.

Now all the above applies to to steady state operation with non-inductive loads. The switches that show reduced current for higher voltages are being derating due to arc over on break when switching reactive loads. This would be important for switching motors and transformers but not so much for switching lighting loads etc like the typical wall switch would.

 

[tolivac]

Lighting load----not all of these are resistive.Lighting of the incandescent family is--but when the cold lamp is first started---high start current until the filament heats.Other forms of light Flourescent-reactive load becuase of the ballast.Same with HID lighting family-and their start current depends on the type ballast used.If the HID lamp has a Constant Wattage autoformer or isolated constant wattage transformer ballast-then the start current is low when the light is first turned on.As it reaches rated wattage the current increases.Now for the other HID ballast types-reactor(choke coil type)or autotranforfmer reactor types--the start current is HIGH when the light is first turned on-the wiring,switch,and breakers must withstand the start currents.This could last for several minutes.Then as the HID light gets to wattage on these types of ballast-the current than goes DOWN.
It has been found for large LED lights their start current is high,as well-but the start current is only momentary.Usual switches and wiring can handle it.
Light switches can be used on 120V,208-240V and lastly 277V(480V phase to neutral)There are all kinds of light fixtures-flourescent,HID and even LED that can run on 277V.The new LED yard lights installed at our site can run on 120-277V-no tap changing required.(Note 277V boxes are generally marked as such by codes)
Switching DC-this is normally done with DOUBLE pole switches to prevent arcing.You get more arcing on DC when it is interrrupted.I encountered this problem with the tool repair shop-there were many tools turned in with bad switches-these were used by--welder folks who were trying to use the tools on the 120V output of their genset welders-----This 120V is DC or crude AC.So the switches in the tools-grinders mainly had to be double pole.The double pole switch can be used AC or DC.Single pole on tools AC only.For the problem noted--I would use the American style switches-then you are safe--and keep code inspectors happy.They would frown on the foreign switches even though they may work OK.

 

[sudsmaster]

Thanks to those who reinforced the concept that as voltage decreases, amperage must increase to deliver the same amount of power (watts). And more importantly, for clearing up the confusion that switches and wiring are rated for wattage and not amps. It is the amperage that is important in terms of circuit loading... And using a switch rated at 10 amps on 220 volts does NOT mean that it can handle twice the amperage on 110 volts... It can still handle only 10 amps... and on a 110 volt circuit it can support only 1/2 the total wattage that it would on a 220 volt circuit!

 

As for 10 amps being the maximum one might expect on a lighting circuit... well, that assuming the switch isn't also controlling a wall outlet, which is not uncommon at least at one time, where the wall outlet is intended to support plug in lamps. When I bought this place, it had two such circuits, one in the original living room, and another in the master bedroom addition. Fine and dandy, except I didn't know there might be limitations. I refinished the floors and at some point plugged in the floor sander into the switched outlet in the living room. It worked for a while and then stopped. I wound up taking apart the wall switch to find out why. It was a mercury switch and the load had caused the mercury bulb to overheat and leak out all its mercury. Yeah, I know, not a great thing to have, but I figured most of it went down inside the wall so it was pointless to worry about it. In any case, no guarantee that a wall switch will never handle more than the "expected" load. It's a hard and fast rule that every switch on a fused/breaker circuit must be rated at or above the breaker rating. So the breaker will open BEFORE the switch burns out.

 

Maybe someone will install a ceiling fan on the circuit. Maybe they decide they want a bank of heat lamps on it. Maybe that ceiling fan motor seizes up and starts to draw a lot more amps. Maybe they splice into the lighting circuit to support more wall plugs. Who knows?  That breaker on the circuit should then trigger before anything else burns out. Anything else is a disaster waiting to happen.

 

 

Oh, and I replaced that wall switch with a mechanical one rated at 15 amps... the same as the breaker for that circuit.

 

 

[davey7]

Great Formica, btw, Cadman! That application looks perfect for low voltage.