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Discussion Starter · #1 ·
The National Electric Code allows a service conductor and feeder conductor to be rated at only 83% of the service rating and feeder rating, respectively, as shown in Section 310.15(B)(7) in the 2017 Edition and 310.12 in 2020.

So, the service panels would be rated at 100%. According to the trip curves, the breakers would only trip within the tolerance band, which is roughly 115% to 145% of the rated load for infinite-duration loads, with the nominal trip amount being roughly 125%. Those numbers are a whopping 138.55%, 174.7%, and 150.6% of the service/feeder conductors' ratings.

So, in a rare event where all loads add up to exceed the service/feeder conductor ampacity ratings but are not high enough to trip the breaker, who will be liable? For example, a service/feeder conductor burns out and causes a fire before the breaker trips at 138.55%, 150.6%, or 174.7% of the service/feeder conductor rated ampacity.
 

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Discussion Starter · #4 ·
I'm asking about the exact intent (for clarity purposes when the NEC's wording is unclear or contradictory) of the NEC by its creator (NFPA) or buildings department, and I thought there would be some people here that are part of those administrative boards. So, that is why I asked. If it is only electricians who are not part of permit-approving boards here, then of course it is pointless to ask here. However, one first needs to try on order to know. That is why I'm posting here to see if I can try to get any insider information from the authors of the NEC and electrical permit issuers.

So, is it normally only electricians here, or are there also a substantial amount of posts from NFPA staff and electrical permit issuers here?
 

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This allowance is only for dwellings. Just by their very nature, they have smaller supplies. Plus your talking overloads on multiple breakers when having a catastrophic failure. You’re now going to have faults phase to phase or phase to ground. Those aren’t going to wait for a trip curve.
 

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Discussion Starter · #6 ·
Just by their very nature, they have smaller supplies. Plus your talking overloads on multiple breakers when having a catastrophic failure. You’re now going to have faults phase to phase or phase to ground. Those aren’t going to wait for a trip curve.
Not necessarily. It can just be normal types of loads, just at a hugely abnormal amount of load. This is why I said rare. Such a specific type of overload may be so rare that it has never happened, not even once, in all of the 125+ years of the National Electric Code. I'm just wondering who will be liable if (not necessarily when, because it might take 1,000 years for one to finally happen, and the NEC would likely not exist by then) such an event happens due entirely by fault of the coverage hole in the code.
 

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Everyone meets Code, which is theoretically a consensus safety opinion by industry experts. Even if you sue NGPA itself you hav to show that somehow the code making process is defective. This would be easier to show with AFCIs but not 331.

Among other issues you’d hav to show actual damages to change the Code or claim liability or there is no tort. So from a legal point of view this is all a nonstarter.

Plus your technical argument does not hold water. The handle ratjng is the “pickup” rating. The breaker should never trip under any temperature or X/R below that rating in open air. In a panel it decreases to 80% of that value owing to elevated temperatures in a panel unless it is 100% duty rated. The breaker curve should be compared to a damage curve for the wiring that you are protecting. If it is below that curve (including tolerance) out to 3 hours, we are good. We do not consider or use “infinite” conditions. The handle value is a “size”..

As to arguing about diversity factors if you have a “typical” load it won’t go above this. I challenge you to find a non-contrived case where it does. If you are doing commercial/industrial work you can’t go by recommended diversity. If I have a process where I know I have 3 motors that have to run at all times and the controls tweak a valve to control amps, diversity goes out the window. Similarly when designing for motor loads (article 430 or 440) I really don’t care what the handle value is because a circuit breaker nominal value is grossly oversized: I’m just sizing for short circuits.

This myth that NEC does not provide adequate protection is simply not true. This has been around for a while.
 

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We are suppose to size the feeders for the calculated load. Yes someone could start to overload the circuits in the house and eventually it could affect the feeders. But it is the homeowner violating the rules. They could convert the bedrooms into rental rooms with hot plates or start a grow room with high intensity lights. We could use 3/0 and a 200 amp service but then they could keep adding loads. Circuit breakers work on heat and they probably will trip before it causes bigger problems. If it keeps tripping and the homeowner keeps re-setting it, then that is on him.
I kind of agree on allowing a de-rating on the service feeder and a lot of towns also question some things. #4 for a 100 amp service with gas cooking and dryer is fine. But with an electric dryer and electric stove I use #2 copper.
 

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Not necessarily. It can just be normal types of loads, just at a hugely abnormal amount of load. This is why I said rare. Such a specific type of overload may be so rare that it has never happened, not even once, in all of the 125+ years of the National Electric Code. I'm just wondering who will be liable if (not necessarily when, because it might take 1,000 years for one to finally happen, and the NEC would likely not exist by then) such an event happens due entirely by fault of the coverage hole in the code.
In a law suit, everybody gets sued. The low man takes the rap and the deeper pockets might take the hit.
 

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Not necessarily. It can just be normal types of loads, just at a hugely abnormal amount of load. This is why I said rare. Such a specific type of overload may be so rare that it has never happened, not even once, in all of the 125+ years of the National Electric Code. I'm just wondering who will be liable if (not necessarily when, because it might take 1,000 years for one to finally happen, and the NEC would likely not exist by then) such an event happens due entirely by fault of the coverage hole in the code.
People have and do overload their services all the time. On Long Island I did tons of service upgrades, most were because their existing 100 amp service from the 1960's when the mass-developing started, all the way to homes that just wanted a bigger panel and ran out of slots, planning on expanding, gonna sell etc... But for those who ever actually tripped their main breaker were usually already experiencing other issues like 1/2 the house flickering or always tripping even the smaller breakers anyway and it gets very played if you're service isn't adequate.

Homes wired with 100a if not gas appliances often bought and added them anyway, lots of finished basements with 2nd electric ranges, or it was "cheaper" to buy an electric dryer than the 20-30 dollar more expensive gas model... over the years people added central a/c and that's a tough enough nut to swallow to also have to change to a bigger service. People added built in pools, and hot tubs, and a lot of window unit A/C's if there wasn't a central unit. Over time the normal expected loads add up to outpace the supply you've got and then you know ya gotta upgrade.

Only once have I seen a service entrance cable that actually shorted, of course it was a Federal Pacific Split Buss and they put a 60 amp apartment subpanel in the slot not protected by any main, And the total load of this 1 family home illegally converted into at least 3 seperate units each with electric ranges was way more than that poor #4 alumiun SEU cable between the meter and the panel melted right up, over time the bare copper #6 which was routed through the same bored holes for the SEU cable probably got very hot as well since the outdoor SEU between meter and weatherhead was perfectly intact.

This was a house On Pond Path or Farm-To-Market Rd if I remember correctly.
 

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Discussion Starter · #12 · (Edited)
But it is the homeowner violating the rules.
Here, I am assuming that the homeowner is not violating the rules. For example, electrical codes prohibit people from installing wiring that does not have sufficient ampacities for the expected loads or hard-wiring devices that have loads exceeding the ampacity of the supply circuit. However, it does not prohibit people from plugging into existing receptacle outlets for multiple appliances collectively have a current draw that exceeds the ampacity of the supply. In the last case, it is only the job of the circuit breaker to prevent overload.

For example, a house may have a main breaker rated at 100A and 10 individual breakers that have a combined rating of 150A, but the service conductor is only rated for 83A. In a large party, many people may decide to bring their own countertop appliances and plug into multiple outlets throughout the home to prepare for food. Each circuit is loaded to 13A, which is well within the limit, so none of their breakers trip. However, the main breaker and service conductor now each have a load of 130A, which is above theor ratings. Given that breakers trip within 115% to 145% of their ratings for long-duration loads, that breaker if manufactured peroperly doesn't have to trip at 130A. That main breaker happens to be one that is less sensitive but still passes quality control, so it doesn't trip despite not being defective. Now, the service conductor is at 156.6% of its rated load and causes a fire from being overloaded. Now who is liable?
 

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These are not even realistic scenarios. I have never been to a party where people bring their own appliances. That is just trolling imo. Also a breaker will trip over the ampacity of the breaker but it may take a few minutes or so which is not enough time to cause damage to the conductor.
 

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... the service conductor is at 156.6% of its rated load and causes a fire from being overloaded. Now who is liable?
I'd like to see the setup where a conductor "causes a fire from being overloaded" at 156.6% of its (NEC) rated load.
 

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These are not even realistic scenarios. I have never been to a party where people bring their own appliances. That is just trolling imo. Also a breaker will trip over the ampacity of the breaker but it may take a few minutes or so which is not enough time to cause damage to the conductor.
People might not bring their own appliances to a party but there are a lot of foreigners in my area that buy houses and rent out bedrooms complete with a hot plate and small refrigerator. I am doing a fire job right now where the lady had a ranch house split into 4 illegal apartments. She wants it restored the way it was before the fire but she is not going to rent it out. Right. Is there an emoji for me being sarcastic?
 

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People might not bring their own appliances to a party but there are a lot of foreigners in my area that buy houses and rent out bedrooms complete with a hot plate and small refrigerator. I am doing a fire job right now where the lady had a ranch house split into 4 illegal apartments. She wants it restored the way it was before the fire but she is not going to rent it out. Right. Is there an emoji for me being sarcastic?

So I bet it wasn't the main that caused the fire.
 

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Here, I am assuming that the homeowner is not violating the rules. For example, electrical codes prohibit people from installing wiring that does not have sufficient ampacities for the expected loads or hard-wiring devices that have loads exceeding the ampacity of the supply circuit. However, it does not prohibit people from plugging into existing receptacle outlets for multiple appliances collectively have a current draw that exceeds the ampacity of the supply. In the last case, it is only the job of the circuit breaker to prevent overload.

For example, a house may have a main breaker rated at 100A and 10 individual breakers that have a combined rating of 150A, but the service conductor is only rated for 83A. In a large party, many people may decide to bring their own countertop appliances and plug into multiple outlets throughout the home to prepare for food. Each circuit is loaded to 13A, which is well within the limit, so none of their breakers trip. However, the main breaker and service conductor now each have a load of 130A, which is above theor ratings. Given that breakers trip within 115% to 145% of their ratings for long-duration loads, that breaker if manufactured peroperly doesn't have to trip at 130A. That main breaker happens to be one that is less sensitive but still passes quality control, so it doesn't trip despite not being defective. Now, the service conductor is at 156.6% of its rated load and causes a fire from being overloaded. Now who is liable?
The NEC does dictate the amount of load one can plug in. The problem is the homeowners do not know the codes. I see many homeowners who were apartment dwellers and now they are home owners. In my opinion they should not be a homeowner. They have no idea where the electric panel or main shut off are. No idea where the main water shut off is. What type of heat they have. etc....
There are many things in life where there is no hard and fast rule or mandate. SMEs look at years of examples and come up with a general principle. It is up to the guy in the field or the engineer to see if more is needed.
You are asking many "what if" situations that we really don't waste our time on thinking. If you really want answers I suggest you buy the IAEI book on one and two family houses. It is well written and has diagrams.
 
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