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Comment by theamk | Hacker News Reader

Really, worrying about 20 amp in a 15 amp circuit?

If one likes to worry about such things, there are much scarier things: unswitched extension cords [0]. One 15 amp plug in input, three 15-amp outlets on outputs. Sold in most stores and used very widely. Nothing illegal about it. Plugs into 15 amp rated outlet, wire itself is rated for just 13 amps, and you can pull up to 45 amps in the worst case (like if you plug in three electric kettles).

[0] https://www.homedepot.com/p/GE-12-ft-2-Wire-16-Gauge-Polariz...

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At 15 amp circuit breaker will trip in 3-10 seconds if confronted with a 45 amp load.

The number of sockets on an extension cord is immaterial to the available current just as is the number of receptacles on a circuit.

Putting 12 two-socket receptacles on a 15 amp circuit does not mean you can get 360 amps, after all.

The risk with 13 amp extension cords is the gap between the extension cord's safe capacity and the trip point of the circuit breaker. If you plug a 13 amp cord into a 20 amp T-slot receptacle, the breaker will happily supply 20 amps indefinitely even as the cord melts and ignites.

God I wish more people using electrical lawn equipment paid attention to the rating of their extensions cords. Nothing like seeing somebody buy the cheapest super-long cord they can for their electric pole saw and wondering how long before it melts.

I’m going to blame the manufacturers for this one as well, they don’t usually provide current limits meaning you have to grab a table giving safe loads based on AWG and length.

I’m pretty sure I could tow a car with my outdoor power cord/reel.

Or for that matter, with my jumper cables. I paid around $5 more for these monsters than the option next to them, which was flimsy, ridiculously short, and barely had claws. $5. It took me two seconds to make that decision and another 30 to stand there making sure I didn’t misread the prices and then trying to figure out why the others even existed.

I wish UL and other regulatory bodies would take a page from UK electrical standards and require cords that aren't capable of carrying the full amperage available at the socket to have fuses. Voltage drop protection wouldn't be a bad idea, either.

No one should be expected to look up ampacity and voltage drop tables just to avoid starting a fire.

Yes, but if all the wires are rated 15A, and the breaker is 15A or less, there's no issue.

The problem case is putting equipment onto a 20A breaker using 15A wires and plugs.

Or putting 20A equipment on a 15A breaker and wiring. The breaker won't trip immediately. Things will heat up slowly until the breaker trips, and you will have damage.

If you follow the link I showed, you'd see that the wires are actually rated 13 amperes, less than maximum capacity of the outlet.

So it is not that uncommon to have unsafe wiring combinations -- be it 20A equipment on 15A wiring, or 15A equipment on 13A wiring.

Neither is illegal, for better of for worse. Know the specs of your equipment if you deal with non-trivial electrical power.

Wires are generally not rated for any specific current - the insulation is rated for a certain thermal load, and then electricians have a bunch of look up tables for the environment, run length and current to determine what gauge to use.

I see nothing worrying here, this is pretty standard to me. You have a single 15A input and multiple 15A output, but you cannot use all the outputs at 15A at the same time.

As long as you use it on regular domestic outlets you will be limited by the 15A of your breaker anyway.

This is the same as all the USB hubs chargers. They often have 5 outputs rated 2A each, but the whole hub limits you to 2A total.

Wouldn’t the breaker trip if you try to suck 45 amps through a 15 or 20 amp breaker?

After a minute, I think. Depends on your breaker rating.

20 amps on a 15 amp breaker will take a while to trip. You will have wiring damage.

Over here in Germany we call the breakers Leitungsschutzschalter, which translates to wiring protection switch. They're specifically sized to protect the wiring in an overload situation, both gradual overloads and short circuits.

The main issue is actually with the slightly-less trigger-happy breakers (class D) needing a sufficiently low resistance on the output to ensure that the magnetic trigger is both reliably triggered if you short the outlet, yet reliably not triggered by the current spike allowed from it's class. They trigger between 10 and 20 times the nominal rating, and 16 A is the typical circuit choice here. Ensuring that you reliably hit 320 A through a long circuit isn't the easiest/cheapest thing.

Class B should be used for home use, and all domestic appliances should not trigger it.

C/D are more appropriate for industrial use, where wiring and devices are designed beforehand, and people (ideally) won't just join together extension cords, and put multiple electric motors on it.

C is quite typical for new installations due to the abundance of SMPS's, which can easily cause issues after a power loss due to the combined inrush current.

But yeah, D is indeed rare, and not typically found in domestic installations.

Laymans simply say "Sicherung".

15 amp Schneider QO breakers are rated to trip in between 3 and 9 seconds in response to a 45 amp load. They are rated to trip a 20 amp load within 50-300 seconds.[0]

[0] https://schneider-electric.app.box.com/s/cgxddrh26v9tpd48d2k...

Unless your wiring was damaged or sketchy, it will have no issue taking 20 amps for a while. Problem is a (small) chance it could in fact cause issues, possibly fires, possibly at a later date.

People don't usually count consumption of their devices, so plugging in pretty much anything that the circuit breaker will take is a fairly common occurrence.

If that were true, wouldn't UL refuse to certify them?

And if quantity and type of receptacles are intended to be a form of overcurrent protection, wouldn't the UL refuse to certify a duplex 5-15R receptacle for use on a 15 A circuit?

The fact that they do not leads (non-electrician) me to believe that outlet types differ to prevent unintentionally plugging devices into inappropriate circuits, not to prevent intentional abuse.

The present example is just a band-aid fix for cases where lower-current devices are connected in through some intermediate wiring (UPS, extension cord, RV power system, etc.) with a plug consistent with its own, higher ampacity, and in this application, seems no more prone to abuse than a garden-variety 15 A duplex receptacle on a 15 A circuit.

How many of the things with UL stamped/moulded into them that are available for sale on AliExpress do you suppose UL have ever even seen, never mind certified?

Isn't the breaker supposed to protect the damage? If it doesn't, why not just make the breaker more sensitive?

Depending on the age and quality of wiring there may be “hot spots” that can start a fire before there’s enough draw to trip the breaker. Old residential aluminum wiring is terribly dangerous for this reason. Corroded wire splices can do it too. That’s why I always solder my romex junctions!

https://en.wikipedia.org/wiki/Aluminum_building_wiring#Older...

Relative lost his whole house to old wiring in the attic. Staples, aging plastic, and thermal cycling. Roof was engulfed before the smoke alarms went off.

soldering electrical wiring is really not a good idea. just use wagos

Agree, Wago’s Lever Nuts especially are a game changer.

Those DIYers who reject the “licensed electrician and I need a permit” model could benefit most from them - they’re almost foolproof.

Instead they’re expensive, hard to find as Lowe’s/Home Depot don’t sell them, and not too many average people are familiar with them.

I won’t ever buy plain wire nuts again unless it’s to cap a single wire.

>> ...expensive

What do you expect? It's German engineering :-)

Soldering those is forbidden here nowadays. Has to be crimped with a metal jacket around the ends.

If everything is working correctly, yes.

If things aren't working correctly, you get an electrical fire.

I think the worst is plugging surge protectors into surge protectors. Or plugging a surge protectors into ups. (not all, but most)

It's confusing to people because dumb power strips can be daisy chained with no problem.

Our fire guy didn't like the unfused kind of extension cords much. One can understand why, you overload the electric lead and hope that the breaker is thrown before the insulation burns through.

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