Home charging question

[Dan123]

I should have said “one doesn’t have to make calculations” but didn’t want to sound pretentious
My argument is that if a circuit can handle a 32A load then it should be called a 32A circuit, not a 40A circuit. The buffer should be built intrinsically into the code, rather than having to be recalculated again and again and again for every new installation.

If the road can accommodate 40 cars per second typically, but only 20 cars when it snows, and it doesn't snow more than 20 days per year, how would you rate the road? 20 cars or 40 cars per second?

There is a very obvious reason for this, though. If you were to do this, requiring everything to be built to 100% continuous use, then you are requiring extra cost of thicker wire size in that 90% of cases where it is just useless and unused. And that is 90% of every circuit in every building in the country. That is a gigantic waste of money.

Besides wasting money, it creates a safety issue. If you have a 32A circuit, and you put a 32A breaker there, then then the breaker will periodically falsely trip when exposed to a continuous 32A current. If you oversize the breaker, then it will fail to immediately trip when higher current flows through, creating a dangerous situation.

 

[Rocky_H]

I can't tag two ratings on this, so I'll have to use comments:

If the road can accommodate 40 cars per second typically, but only 20 cars when it snows, and it doesn't snow more than 20 days per year, how would you rate the road? 20 cars or 40 cars per second?

Agree.

Besides wasting money, it creates a safety issue. If you have a 32A circuit, and you put a 32A breaker there, then then the breaker will periodically falsely trip when exposed to a continuous 32A current. If you oversize the breaker, then it will fail to immediately trip when higher current flows through, creating a dangerous situation.

Disagree. You're not understanding his proposal at all, so your answer is incorrect. There would never be any nuisance trips. You're thinking of things as they are rated now. He is saying that he thinks things should be rated and overbuilt so that they can run at 100% all the time without tripping.

 

[miimura]

Disagree. You're not understanding his proposal at all, so your answer is incorrect. There would never be any nuisance trips. You're thinking of things as they are rated now. He is saying that he thinks things should be rated and overbuilt so that they can run at 100% all the time without tripping.

Exactly. If you install a European industrial IEC 60309 Blue socket rated for 32 amps, the plug, socket, breaker and wire size will all be sized for 100% duty cycle. This is normal for their codes and component sizing and labeling. The North American electrical system is just not done that way, so we have special rules for continuous loads.

 

[Shock-On-T]

If the road can accommodate 40 cars per second typically, but only 20 cars when it snows, and it doesn't snow more than 20 days per year, how would you rate the road? 20 cars or 40 cars per second?

20 cars per second.
If the road can't take 20 cars/sec in all scenarios, then it's not a 20 car/sec road.

Besides wasting money, it creates a safety issue. If you have a 32A circuit, and you put a 32A breaker there, then then the breaker will periodically falsely trip when exposed to a continuous 32A current. If you oversize the breaker, then it will fail to immediately trip when higher current flows through, creating a dangerous situation.

A circuit that periodically trips when exposed to 32 amps continuous current should not be called a 32A circuit.
It should be rated at whatever amperage can be safely used in all scenarios.

 

[Shock-On-T]

There is a very obvious reason for this, though. If you were to do this, requiring everything to be built to 100% continuous use, then you are requiring extra cost of thicker wire size in that 90% of cases where it is just useless and unused. And that is 90% of every circuit in every building in the country. That is a gigantic waste of money.

But you have to spec every circuit 20% bigger anyway, so there's no cost saving.
If you expect a 40A load you need to add a 50A circuit. Why not just call that 50A circuit a 40A circuit, since it's the circuit you need for a 40A load.

 

[Tz00]

Amps are a unit of measurement. The breaker trips at or about 50 Amps, not 40 Amps, that is why it is labeled 50 Amps.

 

[Dan123]

Disagree. You're not understanding his proposal at all, so your answer is incorrect. There would never be any nuisance trips. You're thinking of things as they are rated now. He is saying that he thinks things should be rated and overbuilt so that they can run at 100% all the time without tripping.

You are misunderstanding how circuit breakers work. They are not precise in when they trip. They have a time-current curve.

In order to have a circuit breaker that never trips at 32 amps, the same circuit breaker will not (immediately) trip at 40 amps.

 

[Dan123]

20 cars per second.
If the road can't take 20 cars/sec in all scenarios, then it's not a 20 car/sec road.


A circuit that periodically trips when exposed to 32 amps continuous current should not be called a 32A circuit.
It should be rated at whatever amperage can be safely used in all scenarios.

Ok, your opinion is noted. It's just a little out of touch with practical realities of electrical systems.

 

[Rocky_H]

Sheesh.

But you have to spec every circuit 20% bigger anyway, so there's no cost saving.

No, that's not true. For intermittent loads (which is almost everything), they do not need to be overbuilt. 30A = 30A 50A = 50A. They use 100% of the circuit on and off, and they are fine. It is only for permanent constant loads (which are very few) that they need the overspec requirement.

If you expect a 40A load you need to add a 50A circuit. Why not just call that 50A circuit a 40A circuit, since it's the circuit you need for a 40A load.

You're referring to "a 40A load". Is that a normal intermittent 40A load, or a rare constant 40A load? Intermittent 40A loads are the norm, so they can use 40A = 40A.

You are misunderstanding how circuit breakers work. They are not precise in when they trip. They have a time-current curve.

Yes, I am well aware of that.

In order to have a circuit breaker that never trips at 32 amps, the same circuit breaker will not (immediately) trip at 40 amps.

You still don't seem to get what he was talking about. He's talking about like the European standards, where how they are built versus their naming convention is like "moved up". So a U.S. spec breaker that is labeled as a "40A" is made to run constantly at 32, but could run 40 for some period of time, but might eventually heat up enough to flip at max load like that for a long period.
The European code is to spec everything for constant use, so what they call a "40A" breaker would not be the same and is like up-sized. It would be made to run 40A continuous, so it's probably more like what the U.S. would refer to as a "50A" one.
Does that make sense now? He's just saying he thinks the European way is better.

 

[Shock-On-T]

No, that's not true. For intermittent loads (which is almost everything), they do not need to be overbuilt. 30A = 30A 50A = 50A. They use 100% of the circuit on and off, and they are fine. It is only for permanent constant loads (which are very few) that they need the overspec requirement.

Can't any outlet potentially have a consistent load applied? For example a fan heater could run for hours at max amps, and it could be plugged intro any outlet.
I would have thought that all circuits would have to be spec'd to handle consistent loads.

 

[miimura]

Can't any outlet potentially have a consistent load applied? For example a fan heater could run for hours at max amps, and it could be plugged intro any outlet.
I would have thought that all circuits would have to be spec'd to handle consistent loads.

In American houses, household outlets are usually strung together with several outlets on the same circuit and breaker. A 20A circuit might have 6 or so 15 amp outlets. So, any one plug-in device that runs continuously will not overload the circuit. However, if you run a powerful vacuum and a hair dryer at the same time on the same circuit, it will overload and trip the breaker. Bringing this back around to EV charging, this is the main reason that you don't want to use a shared circuit for EV charging, especially 120V household outlets, because they're very easy to overload. The main point for this discussion is that the wire size and the breaker have to be properly matched, regardless of whether the code in the region labels components with continuous loads or intermittent loads.

 

[eprosenx]

Can't any outlet potentially have a consistent load applied? For example a fan heater could run for hours at max amps, and it could be plugged intro any outlet.
I would have thought that all circuits would have to be spec'd to handle consistent loads.

So generally things that plug in to random wall outlets are not supposed to be really high current and constant loads.

One of the protections in the code I believe is that a given plug connected load (at least that is not connected to a dedicated circuit) is only allowed to draw 80% of the circuit capacity (I need to go look at the details in the code about this). So that is why if you go search on Walmart's site for a plug in wall heater, they are all 1500 watt (12a times their assumption is 125v which is totally marketing math btw...).

In American houses, household outlets are usually strung together with several outlets on the same circuit and breaker. A 20A circuit might have 6 or so 15 amp outlets. So, any one plug-in device that runs continuously will not overload the circuit. However, if you run a powerful vacuum and a hair dryer at the same time on the same circuit, it will overload and trip the breaker. Bringing this back around to EV charging, this is the main reason that you don't want to use a shared circuit for EV charging, especially 120V household outlets, because they're very easy to overload. The main point for this discussion is that the wire size and the breaker have to be properly matched, regardless of whether the code in the region labels components with continuous loads or intermittent loads.

Yeah, any one device is not supposed to be more than 80% of a given circuit, so even if they are constant load devices they should not overload the circuit by themselves. Clearly though, multiple could overload it (though I should also mention that many household circuits are 20a circuits while a heater may only draw 12a, so that leaves yet more capacity).

I violently agree with you that charging EV's off 120v non-dedicated circuits is riskier because of that daisy chain issue. Great callout.