[pyro214]

I'm familiar with the smallest breaker/ cable requirements for a load. Example, a 10A continuous load would require a 10A * 1.25 = 12.5A rated breaker or "the next standard size up". Unfortunately, "the next standard size up" is ambiguous and I'm wondering how large a breaker/cable can be for the load application.

14-104 states that the breaker must be rated equal to or less than the cable; we're primary protecting our cables, but what about the load?

If I have a 5A breaker on a 10A cable, what is the smallest continuous load that can be connected to a 120VAC Power-Supply Unit?

 

[AlbertaBeef]

I'm familiar with the smallest breaker/ cable requirements for a load. Example, a 10A continuous load would require a 10A * 1.25 = 12.5A rated breaker or "the next standard size up". Unfortunately, "the next standard size up" is ambiguous and I'm wondering how large a breaker/cable can be for the load application.

14-104 states that the breaker must be rated equal to or less than the cable; we're primary protecting our cables, but what about the load?

If I have a 5A breaker on a 10A cable, what is the smallest continuous load that can be connected to a 120VAC Power-Supply Unit?

You are only quoting the portion of 14-104 up until the infamous work 'except]. Here is the rest of the rule that applies to your question:

14-104 Rating of overcurrent devices (see Appendix B)
(1) The rating or setting of overcurrent devices shall not exceed the allowable ampacity of the conductors that
they protect, except
(a) where a fuse or circuit breaker having a rating orsetting of the same value as the ampacity of the
conductor is not available, the ratings or settings given in Table 13 shall be permitted to be used
within the maximum value of 600 A;

Do any of these scenarios violate the CEC:

1. A 0.2A continuous load connected to a 120VAC input using a 10A rated cable protected by a 5A rated breaker
2. A 7A continuous load connected to a 120VAC input using a 100A rated cable protected by a 15A rated breaker
3. The above scenario however the equipment has an internal fuse

Are these serious questions, or are we helping with your homework?

 

[pyro214]

Are these serious questions, or are we helping with your homework?

I've Googled for ~2 hours with no results. I've stumbled across this set up in person and am curious as to the physics/ codes behind it as I feel it will come up frequently in my future: "when is the cable/breaker too large for the load".

I've looked at 14-104(a) and Table 13 and it still doesn't answer my question about the cable/circuit breaker vs. the low load.

 

[mr_electrician]

I've Googled for ~2 hours with no results. I've stumbled across this set up in person and am curious as to the physics/ codes behind it as I feel it will come up frequently in my future: "when is the cable/breaker too large for the load".

I've looked at 14-104(a) and Table 13 and it still doesn't answer my question about the cable/circuit breaker vs. the low load.

Well what about voltage drop. There is a perfect example of having a larger wire on a smaller rated breaker. :whistling2:

 

[pyro214]

Well what about voltage drop. There is a perfect example of having a larger wire on a smaller rated breaker. :whistling2:

By larger I mean diameter, length is a constant. Voltage drop will be not a concern

 

[FrunkSlammer]

"when is the cable/breaker too large for the load".

We size the over current protection for the conductor, but sometimes we can overrate the over current for special loads.

So the breaker can never be too large for the load, but the only time the breaker can be too large for the conductor is when we've exceeded the limits of the electrical code.

My answer is bizarre, but only because your question is bizarre. Just remember, breaker is for the conductor.

 

[pyro214]

We size the over current protection for the conductor, but sometimes we can overrate the over current for special loads.

So the breaker can never be too large for the load, but the only time the breaker can be too large for the conductor is when we've exceeded the limits of the electrical code.

My answer is bizarre, but only because your question is bizarre. Just remember, breaker is for the conductor.

Thank you for some insight.

 

[FrunkSlammer]

Well if the installation is done properly, a failure in the load should either cause an open or a short of the circuit. Open is a fine failure situation and a short should hopefully be handled by the breaker.

It's rare a load should fail in between, but it does happen! That's why we get goofy things like AFCI breakers put into code.

 

[pyro214]

Well if the installation is done properly, a failure in the load should either cause an open or a short of the circuit. Open is a fine failure situation and a short should hopefully be handled by the breaker.

It's rare a load should fail in between, but it does happen! That's why we get goofy things like AFCI breakers put into code.

Thank you for helping me wrap my head around this... it's been bugging me for a while now.

What about situations that would cause 4A to be delivered to a 0.2A load where a 5A breaker has been installed onto the cable? The breaker wouldn't pop and the equipment would eventually be severely damaged.

 

[FrunkSlammer]

What about situations that would cause 4A to be delivered to a 0.2A load where a 5A breaker has been installed onto the cable? The breaker wouldn't pop and the equipment would eventually be severely damaged.

Amps can't get delivered.. it's just a flaw in your perception of how electricity and circuits work.

There's no such thing as a 0.2A load.. there's a load that has Xohms of impedance. That impedance relative to the voltage is what sets the demand for the amount of current drawn.

Now if something had the ability to over current and it would be catastrophic of some nature, the manufacturer would put something like a fuse in the device. If it over currents, the fuse opens and the day is saved.

We're making progress and it's not stupid questions. Took me forever to get a handle on it… but one day it just clicked, thanks to a good professor.

Think about this.. the power lines outside your house have the capacity to provide thousands of amps to your home, but what is protecting your home from getting overjuiced with all that power? A tiny little 100A (or 200A) breaker in your main panel. That tiny little 100A over current device is the same as some tiny little 0.2A fuse in a dvd player. If a failure happens on the load side, the over current operates and opens the circuit, preventing catastrophic failure.

 

[pyro214]

Amps can't get delivered.. it's just a flaw in your perception of how electricity and circuits work.

There's no such thing as a 0.2A load.. there's a load that has Xohms of impedance. That impedance relative to the voltage is what sets the demand for the amount of current drawn.

Now if something had the ability to over current and it would be catastrophic of some nature, the manufacturer would put something like a fuse in the device. If it over currents, the fuse opens and the day is saved.

We're making progress and it's not stupid questions. Took me forever to get a handle on it… but one day it just clicked, thanks to a good professor.

Think about this.. the power lines outside your house have the capacity to provide thousands of amps to your home, but what is protecting your home from getting overjuiced with all that power? A tiny little 100A (or 200A) breaker in your main panel. That tiny little 100A over current device is the same as some tiny little 0.2A fuse in a dvd player. If a failure happens on the load side, the over current operates and opens the circuit, preventing catastrophic failure.

To clarify for the "4 amps being delivered"; would a short circuit in the equipment be able to cause 4A to be drawn even though its operating full-load current is 0.2A @120VAC? If true, based on what you're saying is we would rely on the equipment's internal fuses to 'defuse' the situation.

 

[FrunkSlammer]

Yeah a short could cause 4amps of draw, overheating the load, melting something, and opening the circuit… be that a fuse or not a fuse. That sort of stuff is all part of the UL/CSA certification. Equipment needs to fail safely.

Imagine if all blenders and toasters and tv's and chargers just caught on fire when they failed? Things fail all the time and we just chuck them in the trash and buy a new one.

 

[pyro214]

Yeah a short could cause 4amps of draw, overheating the load, melting something, and opening the circuit… be that a fuse or not a fuse. That sort of stuff is all part of the UL/CSA certification. Equipment needs to fail safely.

Imagine if all blenders and toasters and tv's and chargers just caught on fire when they failed? Things fail all the time and we just chuck them in the trash and buy a new one.

That clears up everything. Thank you very much FrunkSlammer!

 

[FrunkSlammer]

No problem bud. Please ask more questions, they're good ones!

It's a nice change from the usual "Kan i du dis?" threads. :laughing:

 

[l0sts0ul]

To throw in my 2 cents,

The only loads we usually care about trying to protect are motors and transformers.

To be honest , we care about protecting conductors. Part2 of the CEC Deals with oc protection of equipment.

If you want examples of what your thinking of, you have a tv. Mostly likely it draws between 2-4 amps. But you have a 15 amp breaker on #14 wire rated for 15amp.

 

[oliquir]

almost all small loads equipment have inside fuses to respect UL CSA certifications

 

[Wirenuting]

You can, if you like to waste, place any oversized conductor on a breaker..
But you can not place a conductor on a breaker that is beyond the designed limits of the breaker to except the conductor. (It's listing)

ie:: a #2 wire on a 15 amp single pole breaker. No trimming of conductor strands allowed.