Number of outlets

[kwired]

Haven't wired many new homes recently, but even before AFCI requirements increased around here I may still have put 4 bedrooms on one circuit. Usually the receptacles on a 20 amp circuit and lighting on a 15 amp circuit- which may also have some additional lighting then just the 4 bedrooms (maybe adjacent hallway, closets, or bath lights)so I guess depending on how you look at it those four rooms plus some extras are on two circuits.

 

[JFletcher]

Ok the problem lies with adding more resistance for every outlet that you may add . More resistance more vd
Get over a 0.5 ohm now you start to exceed the 3% recommended by the code
The bigger problem is the available fault current drops way down Read over an 1 ohm
The slows clearing time for the breaker causing wires to heat up and possibly melt , cause damage , or a fire The NEC needs to address this problem..We are way behind the rest other nations when it come to this problem a big design problem!

Huh? How much resistance does a proper termination add, 0.002ohms maybe? If you're sticking to 3% VD, distance is going to affect it much more than the number of devices on a circuit. 1 ohms still gives 120A on a 120V circuit, which is plenty to trip OCPD before the wires melt.

The NEC is not a design manual. If you are that concerned about it, upsize your longer homeruns one wire size, or limit yourself to 10-12 receptacles/15A circuit. Your points, while theoretically possible, dont pan out in practice: as others have mentioned, the millions of residences and businesses not catching fire is proof enough for me that current practices are fine. The fires that are caused by electrical problems, I surmise very few of them are caused by too many outlets (i.e. termination resistance) on a circuit.

 

[Ingenieur]

The reason is because it doesn't matter
5,10 or 15 no difference

even if you have a 1 ohm loop R (unlikely) that is still 120 A fault (ideally)
600% of a 20 A CB, will trip at its limit <5 sec

even if people keep plugging crap in and exceed 20 A the time over-current protection will trip

nuisance tripping may be the biggest issue and even it is a small one

 

[sparks1]

Huh? How much resistance does a proper termination add, 0.002ohms maybe? If you're sticking to 3% VD, distance is going to affect it much more than the number of devices on a circuit. 1 ohms still gives 120A on a 120V circuit, which is plenty to trip OCPD before the wires melt.

The NEC is not a design manual. If you are that concerned about it, upsize your longer homeruns one wire size, or limit yourself to 10-12 receptacles/15A circuit. Your points, while theoretically possible, dont pan out in practice: as others have mentioned, the millions of residences and businesses not catching fire is proof enough for me that current practices are fine. The fires that are caused by electrical problems, I surmise very few of them are caused by too many outlets (i.e. termination resistance) on a circuit.

I do agree with some of the points you make here. A longer run would add much more resistance combined this with each additional outlet that is added to the circuit.It all adds up to lower the available fault current. Not possible to stay with in guidelines of 3% vd in most cases if you wore four bedroom on a circuit . You do the math. The availablebe fault current should be at least 10 times at every outlet to have a 15 amp breaker clear a fault safely in about 30 ms in Mose case it too low and the breaker does not react fast enough to clear the fault of it even trip it at all due to too much resistance. This is a design problem that been ignored for years.
Manufacturer came out with AFCI breakers and call them arc fault circuit interrupters
What they really are is an Available Fault Current Interrupter they sense the Avail fault current if it is to low and trip masking the real problem , so if you have a number 14/2 circuit run over 56 feet is where the problems begin

 

[kwired]

nuisance tripping may be the biggest issue and even it is a small one

Exactly why NEC shouldn't specify how many outlets on a circuit or assign a load to them if there is no designated load, dwelling or non dwelling. Overcurrent protection still protects the circuit from overload. Beyond that how many outlets not dedicated to a specific load are on a circuit is pretty much a design issue.

 

[Ingenieur]

Most residential faults aren't bolted low Z faults
they are intermittent arcing
over current protection is more important
and most will trip at < 5 sec at 500%
even at 1000% 1 sec range
well within the conductor limitations

#14
2 16x16 bedrooms + run from basement pnl
4 receptacles/room
perhaps 400' loop 1.5 ohm max
your bolted fault current 80A or ~500%
even this limited ckt is on the time curve not instantaneous

this practice has been fine for decades and imo does not need regulation
the circuit is protected for short circuit and overload

 

[sparks1]

The reason is because it doesn't matter
5,10 or 15 no difference

even if you have a 1 ohm loop R (unlikely) that is still 120 A fault (ideally)
600% of a 20 A CB, will trip at its limit <5 sec

even if people keep plugging crap in and exceed 20 A the time over-current protection will trip

nuisance tripping may be the biggest issue and even it is a small one

Next time you wire a couple of bedrooms take out you ohm meter and measure the resistance of the circuit from the breaker to the furthest outlet with 12 outlets on the circuit . Let start out at the 1st outlet located in the basement near the panel and put an outlet every 12 feet to include bedroom total distance 144feet for testing purposes and continue down the line checking the resistance at every outlet
located entire run is
Remove all light bulbs . Check the continuity and I'll bet you are way over 1 ohm .

 

[George Stolz]

Next time you wire a couple of bedrooms take out you ohm meter and measure the resistance of the circuit from the breaker to the furthest outlet with 12 outlets on the circuit . Let start out at the 1st outlet located in the basement near the panel and put an outlet every 12 feet to include bedroom total distance 144feet for testing purposes and continue down the line checking the resistance at every outlet
located entire run is
Remove all light bulbs . Check the continuity and I'll bet you are way over 1 ohm .

If you're so concerned about it: put down the Doritos, step away from your computer, set up your experiment yourself and get a fire started for yourself. We'll look forward to hearing from you when you have your results.

 

[sparks1]

Most residential faults aren't bolted low Z faults
they are intermittent arcing
over current protection is more important
and most will trip at < 5 sec at 500%
even at 1000% 1 sec range
well within the conductor limitations

#14
2 16x16 bedrooms + run from basement pnl
4 receptacles/room
perhaps 400' loop 1.5 ohm max
your bolted fault current 80A or ~500%
even this limited ckt is on the time curve not instantaneous

this practice has been fine for decades and imo does not need regulation
the circuit is protected for short circuit and overload

I have a 14/2 circuit with two bedrooms on the the 2nd FLr
The total distance is about 150' with 15 points
The reading at the first outlets reads .63 ohms, PEFC 197 amps, PSC 194 amp
Middle of the loop outlet reads 1.39 ohms 89 amps PEFC ,PSC 86 amps
Last outlet 1.86 ohms 67amps PEFC , PSC 65 amps

So this is clearly a big problem in my opinion
No way to stay within 3% VD here .
vd starts at from the time we leave the xtrm not the panel anther issue entirely

Don't need NEC to design something but they set standards for our industry

 

[sparks1]

If you're so concerned about it: put down the Doritos, step away from your computer, set up your experiment yourself and get a fire started for yourself. We'll look forward to hearing from you when you have your results.

Your too funny!

 

[kwired]

I have a 14/2 circuit with two bedrooms on the the 2nd FLr
The total distance is about 150' with 15 points
The reading at the first outlets reads .63 ohms, PEFC 197 amps, PSC 194 amp
Middle of the loop outlet reads 1.39 ohms 89 amps PEFC ,PSC 86 amps
Last outlet 1.86 ohms 67amps PEFC , PSC 65 amps

So this is clearly a big problem in my opinion
No way to stay within 3% VD here .
vd starts at from the time we leave the xtrm not the panel anther issue entirely

Don't need NEC to design something but they set standards for our industry

What does PEFC and PSC mean here?

 

[sparks1]

Your too funny!

So the bottom line here is ...that some would suggest it is better to do nothing at all and everthing is fine
I believe we need s safer standard to reduce the number of electrical fires . Talk to you local fire chiefs for stats on the number fire caused by electrical wiring problems. We do needto have alimit on the number of outlets .you can't just assume nothing is going to happenyou can't just keep on adding outlet s and not take into account that the additional distance and resistance may cause the breaker to fail to open
Let get it right!

 

[roger]

So the bottom line here is ...that some would suggest it is better to do nothing at all and everthing is fine

That would be me

I believe we need s safer standard to reduce the number of electrical fires . Talk to you local fire chiefs for stats on the number fire caused by electrical wiring problems.

That would be your job, you are going to have to have something along this line to include with your PI or the CMP will simply reject it for lack of substantiation.

Roger

 

[George Stolz]

So the bottom line here is ...that some would suggest it is better to do nothing at all and everthing is fine
I believe we need s safer standard to reduce the number of electrical fires . Talk to you local fire chiefs for stats on the number fire caused by electrical wiring problems. We do needto have alimit on the number of outlets .you can't just assume nothing is going to happenyou can't just keep on adding outlet s and not take into account that the additional distance and resistance may cause the breaker to fail to open
Let get it right!

No, you're looking at the number of car washes in the nation and then using that number to conclude that car washes cause accidents because everyone knows that reduced visibility contributes to crashes.

It is nonsense, and the code is just fine as it sits, as per its scope.

 

[Ingenieur]

I have a 14/2 circuit with two bedrooms on the the 2nd FLr
The total distance is about 150' with 15 points
The reading at the first outlets reads .63 ohms, PEFC 197 amps, PSC 194 amp
Middle of the loop outlet reads 1.39 ohms 89 amps PEFC ,PSC 86 amps
Last outlet 1.86 ohms 67amps PEFC , PSC 65 amps

So this is clearly a big problem in my opinion
No way to stay within 3% VD here .
vd starts at from the time we leave the xtrm not the panel anther issue entirely

Don't need NEC to design something but they set standards for our industry

why is it a 'big problem'?

I assume you measured total loop R and by points you mean receptacles
since 1000' of 14 is only 2.7 ohm Z
your wire for the loop is 300/1000 x 2.7 ~8
you have 1 ohm in the connections, sounds like bad termination(s)

15 A ckt loaded to 12 at last receptacle
loop drop is 1.86 ohm or 20 V
wire is only 10 V

the issue is not the number of receptacles but poor design ( perhaps installation)
use #12 with a 20/1

worse case 400% of cb frame
should trip in 5-7 sec well within the cable rating
it can take >100 A for longer than that

iirc it's 5% from service to last load?
from ECM
Contrary to common belief, the NEC generally doesn't require you to size conductors to accommodate voltage drop. It merely suggests in the Fine Print Notes to 210.19(A), 215.2(A)(4), 230.31(C), and 310.15(A)(1) that you adjust for voltage drop when sizing conductors. It's important for you to remember that Fine Print Notes are recommendations, not requirements [90.5(C)].

The NEC recommends that the maximum combined voltage drop for both the feeder and branch circuit shouldn't exceed 5%, and the maximum on the feeder or branch circuit shouldn't exceed 3% (Fig. 1). This recommendation is a performance issue, not a safety issue.

 

[K8MHZ]

I have a 14/2 circuit with two bedrooms on the the 2nd FLr
The total distance is about 150' with 15 points
The reading at the first outlets reads .63 ohms, PEFC 197 amps, PSC 194 amp
Middle of the loop outlet reads 1.39 ohms 89 amps PEFC ,PSC 86 amps
Last outlet 1.86 ohms 67amps PEFC , PSC 65 amps

So this is clearly a big problem in my opinion
No way to stay within 3% VD here .
vd starts at from the time we leave the xtrm not the panel anther issue entirely

Don't need NEC to design something but they set standards for our industry

You left out the fact that the conductor alone accounts for about 1 ohm. 14AWG is about 3 ohms per 1000 feet. Even with only one outlet and set of connections, you will have .9 ohms, or 9 volts of drop at the end of a 150' run of 14AWG at 10 amps. The problem with the VD is not the number of outlets, it's the length of the circuit.

 

[tom baker]

Ok the problem lies with adding more resistance for every outlet that you may add . More resistance more vd
Get over a 0.5 ohm now you start to exceed the 3% recommended by the code
The bigger problem is the available fault current drops way down Read over an 1 ohm
The slows clearing time for the breaker causing wires to heat up and possibly melt , cause damage , or a fire The NEC needs to address this problem..We are way behind the rest other nations when it come to this problem a big design problem!

The "NEC" is us. Changes have to be started by the users, please submit a change for the 2020 NEC. You'll need some very good technical substantiation.

 

[Ingenieur]

So the bottom line here is ...that some would suggest it is better to do nothing at all and everthing is fine
I believe we need s safer standard to reduce the number of electrical fires . Talk to you local fire chiefs for stats on the number fire caused by electrical wiring problems. We do needto have alimit on the number of outlets .you can't just assume nothing is going to happenyou can't just keep on adding outlet s and not take into account that the additional distance and resistance may cause the breaker to fail to open
Let get it right!

fires are started by 'problems'
this is not a problem

on a 15 A 14 awg circuit you woulld need >6 ohms to not trip
By your numers a 500' run (1000' loop) with 50 devices on it

Your are being condescending and speaking to us as if we are clueless or callous or both

like you see something 1000's of others do not and ingnoring all the education and experience of those who write the Code
we are 't morons (I except myself lol)

 

[peter d]

I might be going out on a limb but I think we're being trolled. Not necessarily by someone with malicious intent to troll, just someone grossly misinformed.

 

[JFletcher]

So the bottom line here is ...that some would suggest it is better to do nothing at all and everthing is fine
I believe we need s safer standard to reduce the number of electrical fires . Talk to you local fire chiefs for stats on the number fire caused by electrical wiring problems. We do needto have alimit on the number of outlets .you can't just assume nothing is going to happenyou can't just keep on adding outlet s and not take into account that the additional distance and resistance may cause the breaker to fail to open
Let get it right!

How many electrical fires/year are acceptable to you? If that number isnt zero, then you are accepting a compromise of systems. If zero was your answer, sure, it's possible to build a bulletproof (fireproof) electrical system, but at what cost? Even RMC piping, metal boxes, fire annunciation, compartmentalization, and suppression can still catch fire if the right chain of events occurs. You could build the building out of concrete, metal stud, and durarock; the building would be basically fireproof, but then you go and put mattresses, couchs, carpets, drapes, etc. i.e. things that are very flammable and produce toxic smoke in it, and all bets are off.

NFPA results already show that small things, like interconnected smoke detectors, raise survivability of a fire substantially. Personally, I think having sprinklers in houses would do more for all fires than anything an electrician could do even with a blank check. Not all fires are electrical in nature, and many electrical fires are extinguished by de-energizing the equipment, something we simply dont have available on a residential scale (e.g., something that would automatically throw the disconnect from the xfmr upon a fire alarm).