UK we have 32A / 6A (e.g. lighting) circuit breakers, but our individual devices are fused at the plug at 1A / 3A / 6A depending on load. A single house has maybe 10 fuses max at the consumer unit.
US they have more circuit breakers, with breakers at 3A / 6A (?) without any fuses on their device plugs, so they have to routinely change the the tiny circuit breaker at the consumer unit, but because of this limitation, they typically have double the number of circuit breakers at the unit ?
In the above example, the short circuit would still happen through the plug and not before it, so in the UK we would just chuck the plug fuse
Circuit breakers are not one time use like fuses. You can think of them as reusable fuses. An in device fuse only protects if the fault is in the device. If you were to put metal in the outlet, to stop current, you need a fuse in the outlet or somewhere else between the outlet and makns, which is what US has. Circuit breakers are typically 20A (or 15A) and multiple outlets are connected to the same circuit breaker.
No, we don’t have an actual fuse in the outlet or plug. Some devices have an internal fuse, but not like the UK where almost everything has a fuse in the plug.
No. Our appliance wiring standards basically require every appliance to be able to tolerate a fault current high enough to trip a breaker. We put a 20A cord on a 500mA clock radio. If we get a short inside the appliance, it will draw enough current to trip the breaker.
The UK allows appliances to have much much lower fault current requirements than their household wiring. They can get away with this by including a current limiter (a fuse) in their plugs.
We do have provisions for fuses in plugs, but they are typically only used where we would use a lot of very low current wiring: Christmas lighting typically has a tiny fuse in the plug protecting very small wiring.
It depends on where the fault is. Starting at the input power from the cord, the first component on the circuit board is going to be a factory installed fuse. It’s probably the same on circuit boards made for UK and EU devices because it makes good engineering sense to do it that way, even if the plug is equipped with a fuse. So if the fault is somewhere on the board, it blows the appliance fuse. If it’s somewhere before the appliance fuse, it blows either the plug fuse (if equipped), or the breaker.
I was pretty sure you guys on that side of the pond could draw a lot more… AFAIK, you have kettles that draw 3000W, which is 12.5A @ 240V.
(Technically, we can install an outlet capable of doing that, but they are not typical in residential use. Outside of commercial-grade appliances and dedicated circuits, we’re pretty much limited to 1500-1800 watt portable appliances here. Fixed appliances like ranges, water heaters, pools, spas, are effectively unlimited, of course.)
I’ve seen a 16A fuse on a power cable for a 1000W PSU. I don’t know the fuse for my kettle, but do know it runs off a 20A circuit breaker, so that’s it’s upper bound likely
so they have to routinely change the the tiny circuit breaker at the consumer unit,
If I understand the nomenclature correctly, your “consumer unit” is our “load panel” or “breaker box”. We use 15A or 20A breakers for our typical outlets.
If you used unfused plugs, your lower-rated cords could potentially reach fire temperatures without drawing enough current to trip the breaker in the consumer unit. Which is why you use fused plugs: to protect the lower-rated wiring from higher current.
The US uses a different approach. If we used power cords rated to 5A for a 5A appliance, and we plugged them into a 20A circuit, we could have the same problem: A 15A fault current through this cord wouldn’t trip the breaker, but could start a fire. So we don’t do that. Even on our lowest current, corded appliances, we use a cord that is rated to carry a 20A fault current capable of tripping the breaker.
(You will occasionally find cords rated for 7A. This is 7A duty current, and the limitation is because of the specific appliance socket, which has a fuse immediately inside the casing, and other restrictions. The 7A rating is not on the wire itself. On these cords, the wiring is still required to have a fault current rating of 20A)
It’s about the current though no?
UK we have 32A / 6A (e.g. lighting) circuit breakers, but our individual devices are fused at the plug at 1A / 3A / 6A depending on load. A single house has maybe 10 fuses max at the consumer unit.
US they have more circuit breakers, with breakers at 3A / 6A (?) without any fuses on their device plugs, so they have to routinely change the the tiny circuit breaker at the consumer unit, but because of this limitation, they typically have double the number of circuit breakers at the unit ?
In the above example, the short circuit would still happen through the plug and not before it, so in the UK we would just chuck the plug fuse
(Asking, because I genuinely don’t know)
Circuit breakers are not one time use like fuses. You can think of them as reusable fuses. An in device fuse only protects if the fault is in the device. If you were to put metal in the outlet, to stop current, you need a fuse in the outlet or somewhere else between the outlet and makns, which is what US has. Circuit breakers are typically 20A (or 15A) and multiple outlets are connected to the same circuit breaker.
Oh right, thanks for that. So fuses in the outlet are pretty typical in the US?
No, we don’t have an actual fuse in the outlet or plug. Some devices have an internal fuse, but not like the UK where almost everything has a fuse in the plug.
No. Our appliance wiring standards basically require every appliance to be able to tolerate a fault current high enough to trip a breaker. We put a 20A cord on a 500mA clock radio. If we get a short inside the appliance, it will draw enough current to trip the breaker.
The UK allows appliances to have much much lower fault current requirements than their household wiring. They can get away with this by including a current limiter (a fuse) in their plugs.
We do have provisions for fuses in plugs, but they are typically only used where we would use a lot of very low current wiring: Christmas lighting typically has a tiny fuse in the plug protecting very small wiring.
oh, very interesting – for the clock radio example, wouldn’t the radio fry the circuit board before it tripped the breaker?
It depends on where the fault is. Starting at the input power from the cord, the first component on the circuit board is going to be a factory installed fuse. It’s probably the same on circuit boards made for UK and EU devices because it makes good engineering sense to do it that way, even if the plug is equipped with a fuse. So if the fault is somewhere on the board, it blows the appliance fuse. If it’s somewhere before the appliance fuse, it blows either the plug fuse (if equipped), or the breaker.
true!
Depends on where the short was. If it was a frayed lead in the PSU contacting the neutral, that short might not even hit the board.
US breakers are usually 16 A.
15
oh wow. So when a device shorts out, it can do some real damage…
Only about 1500 watts worth
15A @ 120V. Basically, 7.5A @ 240V.
That’s a lot!
Depends. In my kitchen it’s all 32A/230-240volt lines, enough to boil stuff or heat stuff. In the rest of the house a single 16A is for a whole room.
I was pretty sure you guys on that side of the pond could draw a lot more… AFAIK, you have kettles that draw 3000W, which is 12.5A @ 240V.
(Technically, we can install an outlet capable of doing that, but they are not typical in residential use. Outside of commercial-grade appliances and dedicated circuits, we’re pretty much limited to 1500-1800 watt portable appliances here. Fixed appliances like ranges, water heaters, pools, spas, are effectively unlimited, of course.)
I’ve seen a 16A fuse on a power cable for a 1000W PSU. I don’t know the fuse for my kettle, but do know it runs off a 20A circuit breaker, so that’s it’s upper bound likely
If I understand the nomenclature correctly, your “consumer unit” is our “load panel” or “breaker box”. We use 15A or 20A breakers for our typical outlets.
If you used unfused plugs, your lower-rated cords could potentially reach fire temperatures without drawing enough current to trip the breaker in the consumer unit. Which is why you use fused plugs: to protect the lower-rated wiring from higher current.
The US uses a different approach. If we used power cords rated to 5A for a 5A appliance, and we plugged them into a 20A circuit, we could have the same problem: A 15A fault current through this cord wouldn’t trip the breaker, but could start a fire. So we don’t do that. Even on our lowest current, corded appliances, we use a cord that is rated to carry a 20A fault current capable of tripping the breaker.
(You will occasionally find cords rated for 7A. This is 7A duty current, and the limitation is because of the specific appliance socket, which has a fuse immediately inside the casing, and other restrictions. The 7A rating is not on the wire itself. On these cords, the wiring is still required to have a fault current rating of 20A)
Oh that’s an angle I never thought of – protection via thicker wires designed to trip but not to heat. Very clever!