NEC Changes For #14 Ampacity

[mbrooke]

UL study



~RJ~

No doubt short circuits are being re-labelled arc faults that just dont happen to trip a breaker magnetically.


Its openly admitted a series arc fault is 100 amps and over. Even if this is a peak value, the RMS equivalent would still be way over the trip curve of a 15 or 20amp breaker. I cant see a short lasting a few seconds tops as apposed to a few cycles setting wood ablaze. I can hold a lighter (which I have out of experimental curiosity) for a few seconds to a 2x4 and while it does leave a local char it does not set the wood a blaze. This of course is assuming an over driven staple. Such a worse case short circuit inside a box would have no effect to begin with.

 

[romex jockey]

terminology

terminology

Ok Mr. MBooke,

I understand short circuit as existing between phases, and a ground fault to go to earth.

Semantics yes, but if we are to describe 'arc' as a different electrical phenomenon, we need to clear this up first.

Let's focus on Ground faults , as it seems the repackaged residential terror , at least to the electrical marketing world....

What is a Gfault? , How does it occur, how is duration vs. impedance a factor?

~RJ~

 

[mbrooke]

Ok Mr. MBooke,

I understand short circuit as existing between phases, and a ground fault to go to earth.

Almost, they go back to the source. That would be the utility transformer via the incoming service neutral.

Semantics yes, but if we are to describe 'arc' as a different electrical phenomenon, we need to clear this up first.

I think so.

Let's focus on Ground faults , as it seems the repackaged residential terror , at least to the electrical marketing world....

That it is unfortunately.

What is a Gfault? , How does it occur, how is duration vs. impedance a factor?

~RJ~

For the sake of this conversation a ground fault is a short circuit between the line (phase) to the equipment grounding conductor or any piece of metal bonded to the equipment grounding conductor.


It works like this. When a short circuit occurs whether a breaker trips thermally or magnetically determines the duration of said fault. When a short circuit magnetically trips its breaker the fault rarely lasts longer then 3 cycles. Magnetic trip has no delay. Now, when a short circuit current is below a breaker's magnetic trip the time it takes to clear a short circuit is a bit longer. It will take over 3 cycles because the bi-metal must heat up first before any action takes place. If the arc sputters this also increases the time a bit. The reason being that when a short circuit sputters the fault current is not fully sinusoidal, it varies in the sine wave. Thus the sputtering fault adds more time to the bi-metals unlatching time.

What determines if a short circuit trips a breaker magnetically or not are two things:

1. The impedance of the circuit. This is further broken in two parts:

a. the impedance of the wire from the panel to the fault. (length and gauge determine this impedance).

b. Fault current from the utility, which basically boils down to the transformer's impedance and that of the service conductors.

2. The magnetic trip threshold of the breaker itself.

 

[romex jockey]

Thank you very much Mr MBrooke

I must say, this incomplete sinusoidal sputtering arc is interesting.

I don't understand the physics , but imagine magnetic qualities somewhat cumulative , not as detectable when broken up?

~RJ~

 

[mbrooke]

Thank you very much Mr MBrooke

I must say, this incomplete sinusoidal sputtering arc is interesting.

I don't understand the physics , but imagine magnetic qualities somewhat cumulative , not as detectable when broken up?

~RJ~

Not as quickly detectable when relying on RMS heating (bi-metal)

But in any case that none perfect current draw is being re-branded as "arcing".

 

[romex jockey]

I fear this is going to be rather a task to quantify Mr MBrooke....~RJ~

 

[mbrooke]

I fear this is going to be rather a task to quantify Mr MBrooke....~RJ~

Give me time and I will explain it. But let me just pitch this: a high current parallel arc is nothing but a marketing play on words for a short circuit which doesn't clear a breaker within a few cycles.

 

[mbrooke]

Anyway getting back on track, the roof top temperature adder was mentioned at some point. Here are some research papers that go with that concept along with demonstrating ways conductor temperature can be measured:


http://www.copper.org/applications/electrical/building/pdf/FactFindingReportAmbientTemperature.pdf

http://www.copper.org/applications/electrical/building/pdf/FactFindingReportAmbientTemperature2.pdf

http://www.iaeisnv.com/yahoo_site_a...Report_on_Conduit_Test_10-14-14.186172755.pdf

 

[iwire]

Anyway getting back on track,

Nothing this weekend, the wife had ideas that where a lot more fun than playing with electricity.

 

[mbrooke]

Nothing this weekend, the wife had ideas that where a lot more fun than playing with electricity.

Its ok, dont sweat it. That time will eventually come :thumbsup: You cant keep a lid on curiosity

 

[FionaZuppa]

so this turned into a OCPD discussion?

when will OCPD technology be advanced into digital control vs old temp/mag control? i mean, i can fit a boat load of electronics into a single pole breaker housing. i could program a picaxe to click the breaker off at any current level (with some additional components).

will all this OCPD talk are we saying that OCPD's are a metric in the ampacity #'s ??

 

[mbrooke]

so this turned into a OCPD discussion?

We (me mostly lol) got carried away :ashamed: But its still your thread, it can go either and any way you want.

when will OCPD technology be advanced into digital control vs old temp/mag control? i mean, i can fit a boat load of electronics into a single pole breaker housing. i could program a picaxe to click the breaker off at any current level (with some additional components).

Well, its already happened with larger breakers:

https://stevenengineering.com/tech_support/PDFs/45CBEIIC.pdf

http://static.schneider-electric.us...Voltage Power Circuit Breakers/0600DB1104.pdf

http://static.schneider-electric.us...uit Breakers and Accessories/48040-495-07.pdf

Already has happened with nearly all new Meduim and high voltage breakers:

https://www.selinc.com/SEL-501/


Electronic units have the advantage of being incredibly precise and can be programmed to do anything with everything. In theory we could even eliminate all moving parts by going to triac/mosfet/IGBT switching however that is still in the R&D phase to my knowledge but doable none the less.

However being me, I would still stick to a mechanical system like we have today for small 200 amp and under 120-480 volt breakers. While one can argue electronics are more reliable having no or few moving parts, they have an Achilles heal involving transients. Repeated surges can render them inoperative. Older GFCIs are a perfect example which have been studied to reveal a high failure rate.

will all this OCPD talk are we saying that OCPD's are a metric in the ampacity #'s ??

Explain. What do you mean by metric?

 

[ActionDave]

Nothing this weekend, the wife had ideas that where a lot more fun than playing with electricity.

If it is anything like my house those ideas involve yard work or painting, or even worse...... shopping.

 

[iwire]

If it is anything like my house those ideas involve yard work or painting, or even worse...... shopping.

Not even close. LMAO.

Overnight getaway without kids. :thumbsup:

 

[FionaZuppa]

We (me mostly lol) got carried away :ashamed: But its still your thread, it can go either and any way you want.


Explain. What do you mean by metric?

i dont mind the ocpd discussion.
metric, as in used as a significant factor in determining the ampacity.

and what i mean about electronic breakers, we landed on the moon ~50yrs ago.

 

[mbrooke]

i dont mind the ocpd discussion.
metric, as in used as a significant factor in determining the ampacity.

At the moment I am trying to see if short circuit clearing time plays a role in our tables. I have a theory that they might, but then again the 250% motor rule tells me otherwise. (Im starting to get tempted on shorting out 150 feet of NM on a 40 amp breaker :angel

and what i mean about electronic breakers, we landed on the moon ~50yrs ago.

I agree, but if I may... Why try and fix what is already been perfected or near perfected? I will take a thermal magnetic breaker any day over an electronic version and a fuse wouldnt bother me in the least over a today's breakers. (heck I actually would take the fuse over the breaker )

 

[FionaZuppa]

At the moment I am trying to see if short circuit clearing time plays a role in our tables. I have a theory that they might, but then again the 250% motor rule tells me otherwise. (Im starting to get tempted on shorting out 150 feet of NM on a 40 amp breaker :angel




I agree, but if I may... Why try and fix what is already been perfected or near perfected? I will take a thermal magnetic breaker any day over an electronic version and a fuse wouldnt bother me in the least over a today's breakers. (heck I actually would take the fuse over the breaker )

150ft of #14 = 0.37875 ohms with little capacitance and little inductance, so lets say @60Hz the Z=0.4ohms, @120v A=300, @240v A=600A
i suspect a 40A breaker would trip almost instantly. what are you expecting?

and, 50yrs to perfect an electronic version is enough time, but seems like they stuck with 50yrs of old technology.

 

[mbrooke]

150ft of #14 = 0.37875 ohms with little capacitance and little inductance, so lets say @60Hz the Z=0.4ohms, @120v A=300, @240v A=600A
i suspect a 40A breaker would trip almost instantly. what are you expecting?

Assuming a magnetic pick up of 40x12=480amps, 300 amps will rely entirelly on the thermal trip. The question is, what will be the final conductor temperature after that trip?

and, 50yrs to perfect an electronic version is enough time, but seems like they stuck with 50yrs of old technology.

IMO I wouldn't say stuck, simply perfected for its intended function at the lowest possible capitol cost.

I still have reservation about electronics in something like this.

 

[FionaZuppa]

150ft of #14 = 0.37875 ohms with little capacitance and little inductance, so lets say @60Hz the Z=0.4ohms, @120v A=300, @240v A=600A
i suspect a 40A breaker would trip almost instantly. what are you expecting?

and, 50yrs to perfect an electronic version is enough time, but seems like they stuck with 50yrs of old technology.

this 150ft of #14 @ 300A in 120v short, thats really 75ft of #14 (two CCC's), etc
i am calculating temp rise of the wire, a 75ft run of 2CCC #14 @300A gets up around 265F during a 3sec ocpd trip
i'll also do 300ft (150ft with two CCC's).

 

[mbrooke]

this 150ft of #14 @ 300A in 120v short, thats really 75ft of #14 (two CCC's), etc
i am calculating temp rise of the wire, a 75ft run of 2CCC #14 @300A gets up around 265F during a 3sec ocpd trip
i'll also do 300ft (150ft with two CCC's).

Hopefully the OCPD will trip before then. The part that I dont know is how fast the bi-metal will respond. Id imagine at 300 amps it would be about 15 to 20 cycles but have no way of knowing.