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> But a 10 amp plug can still fit and sit snugly in a 15 or 20 amp socket, and a 15 amp can still fit into a 20 amp socket with no problems. It’s pretty clever.

by terom 3y ago

> But a 10 amp plug can still fit and sit snugly in a 15 or 20 amp socket, and a 15 amp can still fit into a 20 amp socket with no problems. It’s pretty clever. That sound dangerous. The larger fuse sized for the 20A socket will not protect the smaller conductors in the cable sized for the 10A plug, they can get overloaded. The three-phase / industrial CEE plugs and sockets used in the EU are sized for 16A/32A/63A/125A. It's perfectly legal and safe to make a passive adapter that lets you plug a 32A appliance or distribution box into a 16A socket, you just can't load it higher than the 16A fuses on the socket. Going the other way around (16A plug into a 32A socket) you MUST have a circuit breaker in between to provide the required overload protection.

Tyrannosaur 3y ago
That doesn't make sense though. The fuses aren't to protect the load; they are to protect the circuit. It's up to whatever device you are plugging in to not draw more current than it can handle. If I have a 3 Watt doohickey, I don't go looking around to find a 0.025A socket, I plug it in to my 15A wall socket and everything works great.
- terom 3y ago
  Yeah, the risks mainly come with extension cords, like plugging a bunch of 10A appliances into a single 20A outlet via a 10A rated extension cord with multiple 10A outlets. Appliances themselves with their own input fuses and captive cables are less risky, although some kind of internal wiring short could still get all melty. It's true that sizing the plugs that way does prevent you from plugging a 20A appliance into a 10A extension cord, which makes sense.
bdavbdav 3y ago
Each individual socket isn’t fused though. The entire circuit is. The fuse(breaker) is going to be significantly bigger than any of those amperages. The breaker is there to protect the wiring in the building, nothing more. It’s spec’d to the gauge of the cable in the wall typically.
HalcyonCowboy 3y ago
It's not dangerous in practice. Reading through NEC in the US, there's plenty of leeway for mixing ampacity ratings on circuits, within certain limits. For example, it's fine to have 10x 15A duplex on a 20A circuit. It results in less wiring, and allows for logical grouping of circuits. Electrical code starts from the the most common causes of electrical failures, and tries to design down from there. The ampacity ratings on devices and various components of the circuit are designed to reject the common causes of failure, and conductor failure at the device isn't one of them (appliance manufacturers are more likely to get their devices certified, so if there's a failure in the appliance, some other part of the appliance's electrical system will fail before the conductors do). So the ampacity of the connector (duplex and plug) is meant to reject certain combinations (plugging a 30amp appliance into a 15amp duplex/circuit). It's obviously very easy to get around that by just wiring things together wrong (18AWG wire on a 30Amp circuit), but by design, a 30amp appliance with the proper plug cannot be plugged into a 15amp outlet. Of course, this is informed by the electrical code in my home country, so I understand that other places and people have different experiences, but electrical accidents have been on a steady downward trend since the 80's, so the NFPA NEC has to be doing at least some things right.
- unwind 3y ago
  Is "ampacity" really a better word than "current"? And the unit symbol is just "A", like "30 A". I realize I'm nitty but this is a technical-minded forum after all.
  - jcrawfordor 3y ago
    "ampacity" means "capacity in amperes" or more literally "ampere capacity." You could say current capacity too but it takes longer. Ampacity is the language used in the electrical code. "amp" also seems to be more common to write than "A" for electricians. Remember that the SI standardization of unit abbreviations is actually a pretty modern thing, so lots of fields existed before unit abbreviations were standardized and continue to use existing practices.
    - 3y ago

by terom 3y ago

Tyrannosaur 3y ago

That doesn't make sense though. The fuses aren't to protect the load; they are to protect the circuit. It's up to whatever device you are plugging in to not draw more current than it can handle. If I have a 3 Watt doohickey, I don't go looking around to find a 0.025A socket, I plug it in to my 15A wall socket and everything works great.

terom 3y ago
Yeah, the risks mainly come with extension cords, like plugging a bunch of 10A appliances into a single 20A outlet via a 10A rated extension cord with multiple 10A outlets. Appliances themselves with their own input fuses and captive cables are less risky, although some kind of internal wiring short could still get all melty. It's true that sizing the plugs that way does prevent you from plugging a 20A appliance into a 10A extension cord, which makes sense.

bdavbdav 3y ago

Each individual socket isn’t fused though. The entire circuit is. The fuse(breaker) is going to be significantly bigger than any of those amperages. The breaker is there to protect the wiring in the building, nothing more. It’s spec’d to the gauge of the cable in the wall typically.

HalcyonCowboy 3y ago

It's not dangerous in practice. Reading through NEC in the US, there's plenty of leeway for mixing ampacity ratings on circuits, within certain limits. For example, it's fine to have 10x 15A duplex on a 20A circuit. It results in less wiring, and allows for logical grouping of circuits. Electrical code starts from the the most common causes of electrical failures, and tries to design down from there. The ampacity ratings on devices and various components of the circuit are designed to reject the common causes of failure, and conductor failure at the device isn't one of them (appliance manufacturers are more likely to get their devices certified, so if there's a failure in the appliance, some other part of the appliance's electrical system will fail before the conductors do). So the ampacity of the connector (duplex and plug) is meant to reject certain combinations (plugging a 30amp appliance into a 15amp duplex/circuit). It's obviously very easy to get around that by just wiring things together wrong (18AWG wire on a 30Amp circuit), but by design, a 30amp appliance with the proper plug cannot be plugged into a 15amp outlet. Of course, this is informed by the electrical code in my home country, so I understand that other places and people have different experiences, but electrical accidents have been on a steady downward trend since the 80's, so the NFPA NEC has to be doing at least some things right.

unwind 3y ago
Is "ampacity" really a better word than "current"? And the unit symbol is just "A", like "30 A". I realize I'm nitty but this is a technical-minded forum after all.
- jcrawfordor 3y ago
  "ampacity" means "capacity in amperes" or more literally "ampere capacity." You could say current capacity too but it takes longer. Ampacity is the language used in the electrical code. "amp" also seems to be more common to write than "A" for electricians. Remember that the SI standardization of unit abbreviations is actually a pretty modern thing, so lots of fields existed before unit abbreviations were standardized and continue to use existing practices.
  - 3y ago