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How much can a breaker withstand?

post #1 of 37
Thread Starter 
Anyone know just how much a 15 amp breaker can withstand before tripping?

I currently run my Onkyo TX-NR1010
Crown XLS 2000 sub amp
PS3
Cable Box
Def Tech CS-8080 w/ built in amplifier.

Reason I'm asking is I'm concerned about getting Def Tech powered towers and adding another 2 amplifiers to the load.

Granted I wont run the front 3 at full range probably like a 50hz crossover. Just curious if that load will be stressing the breaker?

Thanks for any help!
post #2 of 37
There are some really good articles online that go into detail. IIRC, a breaker will handle very short pulses up to about 100% over the rating, and longer surges of perhaps 20 - 50%. My old tube amp exceeded 15 A at turn-on and did not trip a 15 A breaker -- as long as I cycled it on after the rest of the stuff was on. Running around 15 A constantly will take it out in a few seconds if not sooner.

Chances are unless you listen at insane levels you won't blow anything. I have about 4 kW (~33 A plus bias loss, call it 60 - 80 A theoretical max) of amplifiers plus other components on a 20 A breaker and have never blown it even listening very loudly (think teenage boys) to inefficient 4-ohm speakers. I do use the trigger circuit from my AVR to turn on the amps, through a distribution box, to help provide a little delay before the amps are switched on.
Edited by DonH50 - 9/24/13 at 5:50am
post #3 of 37
The biggest determining factor for when a breaker trips is how long an overcurrent is sustained. A typical 30 qamp breaker will handle it's rating for around three hours before tripping out. Hit it with 3 times rating and it should trip in 30 seconds. Boost to five times and its less than ten seconds. Anything over 7 times should trip immediately. Many factors weigh in to how much current is being delivered to the device and how much is being lost in the connections from the breaker to the outlet being used.
post #4 of 37
Quote:
Originally Posted by TenTonBass View Post

Anyone know just how much a 15 amp breaker can withstand before tripping?

I currently run my Onkyo TX-NR1010
Crown XLS 2000 sub amp
PS3
Cable Box
Def Tech CS-8080 w/ built in amplifier.

Reason I'm asking is I'm concerned about getting Def Tech powered towers and adding another 2 amplifiers to the load.

Granted I wont run the front 3 at full range probably like a 50hz crossover. Just curious if that load will be stressing the breaker?

Thanks for any help!

At least
- An 850W 9" CRT projector
- 4 stereo amplifiers rated at 720VA max , mostly running 6 Ohm loads. 325VA at rated output into 8 Ohms, 550VA into 4 Ohms. 50VA idling.
- 2 stereo amplifiers rated at 1500 VA max, one running 2.5 Ohm loads and the other bridged into 6 Ohms. 675 VA at rated output into 8 Ohms, 1180 into 4 Ohms, 1320 bridged into 8 Ohms. 72VA idling
- Miscellaneous equipment

That's 38A peak rounding up on amplifier loads although I never had any problems.

FTC ratings are with a full-power sine wave, although there's 31dB between dialog and full power on home theater sound tracks so you're usually loafing along at less than a Watt and not going to get anywhere near that.
Edited by Drew Eckhardt - 9/23/13 at 7:58pm
post #5 of 37
This graph explains it:

post #6 of 37
What Don said is right - if you are going to have problems they are going to be at start up. That is why most really big amps now have soft start circuitry. 15 years ago I had a monster Adcom amp with a 15a fuse and it would dim the lights when started and would trip the breaker if several other things on that same branch circuit were running - never had it trip after it was already running. Now I have several amps with a combined "max" power draw much higher, but they all have soft start circuitry and never any problems.
post #7 of 37
Quote:
Originally Posted by TenTonBass View Post

Anyone know just how much a 15 amp breaker can withstand before tripping?

I currently run my Onkyo TX-NR1010
Crown XLS 2000 sub amp
PS3
Cable Box
Def Tech CS-8080 w/ built in amplifier.

Reason I'm asking is I'm concerned about getting Def Tech powered towers and adding another 2 amplifiers to the load.

Granted I wont run the front 3 at full range probably like a 50hz crossover. Just curious if that load will be stressing the breaker?

Thanks for any help!
Being an Electrician I'll give you my answer. As far as the circuit is concerned and the NEC states, for a non-continuous load (3 hours or less) it is 100%, for a continuous load (more than 3 hours) it is 80%. I always like to figure 80% of the breaker rating for a continuous load, a good example would be lighting. So 15 amps x .80 = 12 amps.

The trip curve of the breaker is inverse time, the higher the current the faster it trips. When a motor or transformer (welder) are turned on there can be 6 - 8 times the rated amps drawn in a fraction of a second. The breaker is rated for this inrush...to a point.

Example of a higher load over a longer period of time. That means if the breaker was at ambient temperature of your average home room (70°F) you might be able to load it to 16 amps for a few minutes before it trips. At that point it will be hot, if you reset it and try that again it will trip faster. If this is repeated the breaker will trip instantly until it cools down. Repeated tripping isn't good for the breaker, as it age and how many times it has been tripped. With that said if you want the breaker to perform at its best and it is old, at the very least replace it with a new one. I had a breaker that was 20 years old and started to trip easier when loaded up.

Other example would be starting and stopping a motor constantly or spot welding with a welder. These situations draw 6 - 8 times what the breaker might be rated at, but are for fractions of a second, the breaker has a little time to cool.

Heat here is a big factor along with duty cycle of the amount of current draw and the length of time it is drawn. If you are really that worried about it put it on a dedicated circuit (only it is on the breaker for load). Make sure all your connections are tight and well made from the breaker terminal, wire nuts if any, connection to receptacle in wall, and amp plug to receptacle. Some older houses have worn out receptacles, any thing you plug into them practically falls out. Loose or bad (house) wiring connections are bad, they get hot and can be a fire hazard. They can also prematurely trip a circuit.
post #8 of 37
I could nitpick here in a few places but mostly this anecdotal evidence is how it is without using any electrical theory. Like mtn-tech I have a big Outlaw amp rated at 200w/ch x 7. When it was on the same circuit as a Sunfire True Sub rated at 2700 watts in a medium sized room with the volume no higher than half, it never tripped the 20 amp breaker. In fact prior to purchase of the sub, the salesman allowed me to test it with Aaron Copeland's Fanfare for the Common Man CD. I plugged into an adapter that let me read RMS amps on my Fluke multimeter. With those kettle drums being whacked I saw 16 then 18 and finally 23 amps. Obviously if that was sustained it would have tripped the breaker, but that's the point. Music is mostly in bursts, so while I commend you for providing your data, you'd be better off acquiring something like a Kill a Watt or an amp clamp plugged into a multimeter. Theory has it's place but what do you do with the fact that household circuit breakers are notoriously inaccurate and typically trip higher than their rating. Fuses are more accurate, but.....

Try not to share neutrals and use a dedicated circuit if possible.Remember the circuit breaker protects the whole circuit, not specific pieces of equipment. If you conclude that you're almost maxing out the circuit, you'd be better off with a second dedicated circuit. If a circuit breaker is going to see sustained loads over half of it's rating, you will shorten it's life. The higher, the shorter.
post #9 of 37
I may have been a little redundant as I was probably typing at the same time as Soundtastic. I should mention breakers don't trip on over-current but rather from heat which is caused by over-current for the most part, which gets back to Soundtastic's point about ambient temperature.

Actually "breakers" aren't rated for the inrush of highly inductive loads like a motor and less so for transformes but dual element "motor rated" breakers are. To that poiint large amps, especially old ones without slow start, could benefit from dual element breakers by tolerating the surge at turn on.

Soundtastic's point about loose connections on high current circuits can't be stressed enough.
post #10 of 37
several good answers, but if you feel like your not actually "getting an answer" that is because it is...complicated and there really isn't a way to know for sure.

in theory a 15 amp at 120 volts can only output 15 * 120 watts or 1800 watts.

but, speakers are not purely resistive, their impedance varies with frequency, so depending on which frequency is being played, more or less current will be pulled.

then as mentioned you can overshoot the amp rating of the breaker for short amounts of time. how much time depends on several things.

then there is the content that you are playing. sustained 10hz notes will be pulling a ton of current, while drum hits with big peaks aren't so taxing.

so I know that doesn't help much, but that is part of why there isn't really a yes/no answer to your question.

just calculating on the simple wattage would suggest that your amp, which can output 2000 watts would blow your circuit all by itself, but it does not.

by the way, good to see you.
post #11 of 37
Quote:
Originally Posted by mjd420nova View Post

The biggest determining factor for when a breaker trips is how long an overcurrent is sustained. A typical 30 qamp breaker will handle it's rating for around three hours before tripping out. Hit it with 3 times rating and it should trip in 30 seconds. Boost to five times and its less than ten seconds. Anything over 7 times should trip immediately. Many factors weigh in to how much current is being delivered to the device and how much is being lost in the connections from the breaker to the outlet being used.


A typical molded case circuit breaker (thermal/magnetic) will have two trip elements (long time and instantaneous). The long time elements are typically thermal and rely upon the heating effect of current to determine trip time. The instantaneous element is typically magnetic and relies upon a solenoid type coil to operate the trip mechanism. A typical molded case breaker will have an instantaneous trip rating of 10x-12x rating (15A breaker x 10xn = 150A instantaneous). The long time element trip time is dependent upon the type of bi-metal heating strip used and provides for the inverse time trip characteristic of the long time element. Depending upon the long time trip curve, a breaker may handle a 3x rated overload for a period of seconds to minutes. Residential type breakers we have tested in the past typically trip in less than 20 seconds at 3x rated current.
post #12 of 37
Quote:
Originally Posted by LTD02 View Post

several good answers, but if you feel like your not actually "getting an answer" that is because it is...complicated and there really isn't a way to know for sure.

in theory a 15 amp at 120 volts can only output 15 * 120 watts or 1800 watts.

but, speakers are not purely resistive, their impedance varies with frequency, so depending on which frequency is being played, more or less current will be pulled.

One of two important considerations.

The other consideration is the crest factor of music, which varies from 6 dB to over 20 dB. This may actually be the stronger of the two considerations.

The filter capacitors in the amp tend to average out short term peaks.
Quote:
then as mentioned you can overshoot the amp rating of the breaker for short amounts of time. how much time depends on several things.

Agreed.
Quote:
then there is the content that you are playing. sustained 10hz notes will be pulling a ton of current, while drum hits with big peaks aren't so taxing.

Unless you are playing test tones or pure sine waves you won't be playing pure 10Hz tones. You will be playing sounds that have fundamentals of 10 Hz. Music in general is full of harmonics. Most if not all bass instruments produce sounds that have more energy in harmonics then is in the fundamental. Complex sounds have crest factors > 6 dB even if they are steady tones.
Quote:
just calculating on the simple wattage would suggest that your amp, which can output 2000 watts would blow your circuit all by itself, but it does not.

The fact that the rated impedance of speakers usually describes only a small part of the impedance curve with the rest of it being twice rated or more, is one reason why.

The various ways that music has a crest factor of > 6 dB (that is 25% power) are a very strong reason why.
post #13 of 37
Some one who understands impedance factors, way more than the average non-engineer type could understand but a very real factor in system design. Reactive impedance of speakers is measured with a DC source and expressed in ohms. This is the average reading over the operating range of the speaker. As stated, music is ripe in harmonics and beat notes that can not be captured by digital conversion schemes and once removed from the content, can't be replaced/replicated. The current handling is a complex formula involving all the power comsumption of the device , not just that being delivered to the speakers.
post #14 of 37
Another point, and a few short answes:

1. If you have any quality piece of electrical equipment regardless of what it is, in this case an amplifier, it should/will have a high quality power supply. There should be capacitors in there that can store power to sustain short burst of high current draw, and they quickly (fractions of a second) recharge for another burst. Capacitors can have the dielectric leak or dry out, so something very old can have diminished performance.

2. Like stated above, take a current reading with an amp clamp, Sears sells an adapter to plug into a receptacle, then plug something into it. Then the clamp can be installed around the adapter to take a reading. Depending on the meter you may not see real time peaks/surges, but you will get an idea. A scope would be ideal, but that is overkill.

3. Run the unit at the highest volume and see what happens, see if the breaker can sustain the load.

4. Put it and every other piece of high current draw equipment on its own dedicated 15 amp or if needed 20 amp circuit. If you do this it may be overkill, but will almost guarantee trip free operation.

All theory aside, do some real world testing and trials, then make adjustments/installations as needed.
post #15 of 37
Quote:
Originally Posted by mjd420nova View Post

Some one who understands impedance factors, way more than the average non-engineer type could understand but a very real factor in system design. Reactive impedance of speakers is measured with a DC source and expressed in ohms.

Academic point - I know of no way to measure reactive impedance with steady-state DC. The classic means use AC signals, while some modern techniques use pulses.
Quote:
This is the average reading over the operating range of the speaker.

Which varies with frequency. Impedance magnitude and phase angle a fairly complete characterization of a speaker's demands on the environment. There are some nonlinear effects and strictly speaking speaker impedance might usefully be measured at very low and very high levels and differences would be expected.
post #16 of 37
Ten Ton Bass, you've brought the experts out of the woods. Actually this makes for a good read.
But a good basis in theory can lead to a practical solution or explanation.

So picture cooking dinner on an electrical cooktop. If you started with boiling a pot of water on high, you're going to see that burner go to full current draw until the thermostat kicks in. Then picture cooking four different items on burner 1-4. They're going to have different start times and different temperature settings. Then their thermostats are going to be peaking at different times. Say burners 1&2 are capable of 2 1/2 amps and 3&4 are 5 amps. Unless you're boiling 4 pots of water started at the same time, you're chance of drawing 15 amps is less than hitting the lottery. You're electronics looks like that to the circuit breaker.

Strange analogy, but I hope you get the point. Theory has it's place, but sometimes you need real world testing to come to a conclusion.

About that 15 amp breaker, today's receptacle circuits are typically 20 amps with 15 usually saved for lighting. If you know wire sizes, check to see if it's really 14 gauge. If it is 12 gauge plop a 20 amp breaker in there for a start. Also if that's a standard convenience outlet sharing other loads on a 15 amp circuit, it might be time to consider pulling a new dedicated 20 amp circuit.
post #17 of 37
Many good posts covering the issue, so much is already covered. Again, safety first, that can't be said enough. However, as long as it's helpful to those reading, don't forget about voltage drop and the subtle yet insidious effects from a loaded up circuit like squashing dynamics during demanding material, etc.

Yes a breaker will pass extra-ordinary amounts of current for surprisingly long periods of time. I just shared this in another thread 3 days ago;
"Another pertinent aspect, oversizing branch circuit wiring. I've recommended it for years around here, but amplifier circuits for subwoofers,...upsize the wiring significantly if you want to remove the wiring as a potential choke-point impeding current delivery.

A 20 amp circuit can pass 7-8 times the rated 20amp trip amount, .. for up to a second or more. It will allow up to 3x the rated amount for up to 10sec or so. And most importantly, the same 20amp circuit, can allow up to 1.5-2times the rated amount for a period extending as long as 30 seconds.

* That's over 100amps for around 1-2 seconds, about 60amps for around 10 seconds, and the circuit will allow 30-40amps for as long as 30 seconds! From a 20a breaker."


As stated, assure connections are tight from the breaker lug/screw, all the way to the device. Moderately high (yet within normal range) currents will find a slightly loose connection point, and this will exacerbate the situation even more. Expansion and contraction from thermal effects can easily further loosen connections, so always be mindful of such.

Upsizing a branch circuit (or as many circuits as it takes) primarily to accommodate subwoofer amplification, and to a lesser extent other high wattage amplification, can be a significant performance upgrade if the situation warrants it. It all depends on the distance between the panel and the load, but upsizing at least one trade size can offer benefits eliminating the wiring as a potential limiting factor in low impedance current delivery. So just be mindful of all aspects when examining both the safety and the performance situation.


Good luck
post #18 of 37
Practically speaking, a marginal circuit is better served with another 20 amp circuit, essentially doubling the wattage available. While a one gauge increase has it's place, mostly for long runs and not likely in residential, you're incrementally increasing headroom unless you also up the breaker size to 10 gauge, but then everything else will be rated for 20 amps. Then you've only increased ampacity by a factor of 1/2. Everything 12 gauge or less is so common it makes anything larger seem disproportionately expensive.

If any work is done it might be a good time to tighten all connections in the breaker panel although the line side of the main should be done by an electrician. If you have stab-in breakers, likely for residential, you might want to have someone turning on and off devices in the house, especially your HT, while it's dark, with the panel's dead front off and look for any arcing. There shouldn't be any. You could clean the bus bar links. You can clean the breaker tabs or replace them. With the main turned off the only danger point is the line side of the main breaker.
post #19 of 37
Not sure going from 15 A to 20 A doubles the wattage, math doesn't seem to work out for me... What does "up the breaker size to 10 gauge" mean?

FWIWFM, our house is wired with 14 AWG (15 A circuits) everywhere but the range (10 AWG, I think), sub-service to a shed (8 AWG), and my media room (20 A circuit, 12 AWG).

There are a number of breaker manufacturers and a little variation in their actual curves. I seem to recall an NEC spec for the curves but it has been decades since I took the Journeyman's test...
post #20 of 37
Quote:
Originally Posted by Patrick Collins View Post


...So picture cooking dinner on an electrical cooktop. If you started with boiling a pot of water on high, you're going to see that burner go to full current draw until the thermostat kicks in. Then picture cooking four different items on burner 1-4. They're going to have different start times and different temperature settings. Then their thermostats are going to be peaking at different times. Say burners 1&2 are capable of 2 1/2 amps and 3&4 are 5 amps. Unless you're boiling 4 pots of water started at the same time, you're chance of drawing 15 amps is less than hitting the lottery. You're electronics looks like that to the circuit breaker.

Strange analogy, but I hope you get the point. Theory has it's place, but sometimes you need real world testing to come to a conclusion.

About that 15 amp breaker, today's receptacle circuits are typically 20 amps with 15 usually saved for lighting. If you know wire sizes, check to see if it's really 14 gauge. If it is 12 gauge plop a 20 amp breaker in there for a start. Also if that's a standard convenience outlet sharing other loads on a 15 amp circuit, it might be time to consider pulling a new dedicated 20 amp circuit.
Good analogy, just like the other day when I did a current reading on my AC unit to see if I could run it off my generator during a power outage. Nope, the AC is fed with 20 amp breaker, when the compressor starts inrush is 60 amps for a fraction of a second, the only draws 7 amps while running. The generator would run the AC, but not start it. Also with the cook top analogy, this would be duty cycle, time on vs. time off. Music is dynamic always changing frequency, amplitude, etc. There will never be a constant current draw, well unless you are playing a constant test tone and high volume.

True in a newer house usually the practice out there is to use 15 amp circuits for lighting. Some areas like a kitchen have to have 20 amp receptacle circuits by NEC. Most of the time a 15 amp duplex ( what you normally see in your house) receptacle is installed on a 20 amp circuit, which is code compliant. Each spot to plug in is considered a receptacle, so there is technically (2) 15 amp receptacles on the circuit. What I'm getting at is that the one of the two you plug into is only rated for 15 amps, another bottle neck. Upgrade it to a 20 amp unit.

Quote:
Originally Posted by FOH View Post


Yes a breaker will pass extra-ordinary amounts of current for surprisingly long periods of time. I just shared this in another thread 3 days ago;
"Another pertinent aspect, oversizing branch circuit wiring. I've recommended it for years around here, but amplifier circuits for subwoofers,...upsize the wiring significantly if you want to remove the wiring as a potential choke-point impeding current delivery.

A 20 amp circuit can pass 7-8 times the rated 20amp trip amount, .. for up to a second or more. It will allow up to 3x the rated amount for up to 10sec or so. And most importantly, the same 20amp circuit, can allow up to 1.5-2times the rated amount for a period extending as long as 30 seconds.

* That's over 100amps for around 1-2 seconds, about 60amps for around 10 seconds, and the circuit will allow 30-40amps for as long as 30 seconds! From a 20a breaker."


As stated, assure connections are tight from the breaker lug/screw, all the way to the device. Moderately high (yet within normal range) currents will find a slightly loose connection point, and this will exacerbate the situation even more. Expansion and contraction from thermal effects can easily further loosen connections, so always be mindful of such.

Upsizing a branch circuit (or as many circuits as it takes) primarily to accommodate subwoofer amplification, and to a lesser extent other high wattage amplification, can be a significant performance upgrade if the situation warrants it. It all depends on the distance between the panel and the load, but upsizing at least one trade size can offer benefits eliminating the wiring as a potential limiting factor in low impedance current delivery. So just be mindful of all aspects when examining both the safety and the performance situation.


Good luck
Up sizing wire in your average home for voltage drop isn't really needed, but if you are looking for every edge then go for it. The cost to amount of return is minimal. If you have the extra time and money to do it, go for it. Otherwise save if for something else.

There's that reoccurring theme of making sure you have properly made tight connections. Good point on the thermal effects.

Quote:
Originally Posted by Patrick Collins View Post

Practically speaking, a marginal circuit is better served with another 20 amp circuit, essentially doubling the wattage available. While a one gauge increase has it's place, mostly for long runs and not likely in residential, you're incrementally increasing headroom unless you also up the breaker size to 10 gauge, but then everything else will be rated for 20 amps. Then you've only increased ampacity by a factor of 1/2. Everything 12 gauge or less is so common it makes anything larger seem disproportionately expensive.

If any work is done it might be a good time to tighten all connections in the breaker panel although the line side of the main should be done by an electrician. If you have stab-in breakers, likely for residential, you might want to have someone turning on and off devices in the house, especially your HT, while it's dark, with the panel's dead front off and look for any arcing. There shouldn't be any. You could clean the bus bar links. You can clean the breaker tabs or replace them. With the main turned off the only danger point is the line side of the main breaker.

Be careful working in your panel, it can be done. Electricity has always been potentially dangerous, but you should see how nuts the industry is lately with arc flash and wearing the proper gear. True just the top of the main is "hot" if you shut the main off. Do yourself a favor and work arms length away, keep your body back. Wear some leather gloves if you can work in them. For sure where all cotton and a long sleeve shirt and pants. This betters your odds of not getting burned if something happens.

Another thing to keep in mind with an older home. Say you take the cover off your panel and see a #12 gauge wire, which is good for 20 amps on a 15 amp breaker, this doesn't mean you can put it on a 20 amp breaker. You really need to know what gauge every inch of the wire is on the circuit. All it take is for someone who was handy and added something down stream and used #14 gauge wire between two junction points (boxes). Now anything down stream of this can draw "20" amps and is going through the #14 wire only rated at 15 amps. Before you consider upping the breaker size it is wire to open up every "box" and check the gauge of the wire.

Easier than this and it has been said before, at this point just fish in a dedicated 20 amp circuit with #12 gauge wire (yellow jacketed) and be done with it.
post #21 of 37
"Unless you are playing test tones or pure sine waves you won't be playing pure 10Hz tones."

...or reproducing digital effects that have been created for movies or games which can be very different from music.
post #22 of 37
Quote:
Originally Posted by LTD02 View Post

"Unless you are playing test tones or pure sine waves you won't be playing pure 10Hz tones."

...or reproducing digital effects that have been created for movies or games which can be very different from music.

AFAIK digital FX in movies are generally not pure tones. I hear lots of harmonics in the EFX in the movies I watch.
post #23 of 37
Quote:
Originally Posted by DonH50 View Post

Not sure going from 15 A to 20 A doubles the wattage, math doesn't seem to work out for me...

Its 225 versus 400 which is pretty close to doubling.

Quote:
What does "up the breaker size to 10 gauge" mean?


I looked at the spec sheets for some common breakers and they specify a single 10 gauge wire as the maximum that they will take. A lot of breakers now have plastic shields over the screw terminal that restricts the size of wire that they can take.
Quote:
FWIWFM, our house is wired with 14 AWG (15 A circuits) everywhere but the range (10 AWG, I think), sub-service to a shed (8 AWG), and my media room (20 A circuit, 12 AWG).

It varies with the house. Code allows putting 15 amp breakers on 12 gauge lines. The point that was raised about not upgrading a breaker just because the wire going into it is 12 gauge is a good one.

Doing major home improvements is a good time for upgrading and rationalizing wiring, when the walls are open. I think we added 5 new 12 gauge circuits and upgraded the existing circuit(!!) when we redid my daughter's kitchen. There was a new breaker panel and it had a lot of non-code and code but ugly stuff going on inside which was rationalized.

My house was built in 1933 and is the biggest hodgepodge of wiring I've ever seen. The original house was built using a funny kind of wire that looks like coaxial cable with a stranded hot wire, stranded neutral, and wound with plated steel wire. Just to add spice, there were numerous fuse block/distribuiton points. About a third of the house is new construction which is 14 gauge Romex for the lighting circuits and 12 gauge for the circuits with just outlets. There is a new main breaker panel and several modern subpanels. There is still one of the old fuse block/distribution point mash-ups, unfortunately. Unfortunately 3 out of 4 of the bedrooms are wired with the funny coax passing through a steel frame, so the neutral is bonded to the house frame at many points and arc fault breakers can't work.
Edited by arnyk - 9/27/13 at 3:39am
post #24 of 37
I must be missing something, I thought he was talking line wattage?
15 Arms * 120 Vrms = 1800 W
20 Arms * 120 Vrms = 2400 W (33% higher)

Got it on breaker wire, I always thought they were rated by current. As I said, decades since I really looked at most of this, save a little research when we finished our basement a few years ago.

Our local code specifies min wire gauge, not sure there is any max. I know folk who ran 12 AWG everywhere to reduce IR drop and provide more margin. It does cost more. I would have done it if I had thought about it; decades ago 12 AWG was used everywhere, but copper has gotten a lot more expensive since then. The one thing I did not catch is that the basement sub-service was routed with 10 AWG, I think, and really should have been 8 or 6. Aaarrghhh...

I had to rewire part of my grandparent's house in college (I was living there). It was all wire-and-knob! Two lines about 6" - 12" apart (depending) on litt;e porcelain stand-offs. With some very scary old wires, including some that sound like what you had (have?) as well. With old oily'ish insulation that was flaking off, and some wicked corrosion on some of the wires. At one point I jiggled a wire and the insulation fell off and the porcelain knob just fell into little pieces.

As for arc-fault breakers, they are now code here, and I hate them. A couple work OK, but several would trip if you through a light switch in another room on a different circuit. the worst offender was one in a bedroom that would trip whenever the treadmill was turned on, several rooms away on a dedicated circuit and on the other phase of the service. We went over that one several times, and I finally just replaced it with a regular breaker. I have heard endless horror stories about them... Hopefully they'll improve soon.
post #25 of 37
Quote:
Originally Posted by DonH50 View Post

I must be missing something, I thought he was talking line wattage?
15 Arms * 120 Vrms = 1800 W
20 Arms * 120 Vrms = 2400 W (33% higher)

You are right and I was wrong - I've been working with speaker systems and constant impedance systems so much lately that my mind defaulted to P=I*R, instead of the proper equation for constant voltage systems P=I*V
post #26 of 37
Rewiring can be a big job, replacing aluminum with copper and getting a three phase 440 volt line to a seperate box. A much older home, from the turn of the century (1900) had original pipes for gas lighting and when wired, the pipe was used as nuetral and a single wire pulled through the pipe for the hot. Serious indeed. Pulled romex throughout and added double coax, triple CAT5 and 8 pairs of control lines for automation and sensors. The code changes almost yearly but most only affect manufacturers.
post #27 of 37
^^^ Safety ground? we don't need no stinkin' safety ground! smile.gif

@Arny: NP, at least once a month I post something completey brain-dead and when I look at it later think "how the $@$#@ did I write that?!?!"


For anybody who doesn't have the equations on tap, using P = power, I = current, V = voltage, and R = resistance/impedance:

V = I * R (or I = V / R, or R = V / I)

P = I * V = I^2 * R = V^2 / R

Re-arrange as needed.
post #28 of 37
Ten Ton Bass probably has his house rewired by now while we're just talking to each other.

My reference to "doubling the wattage" was when installing a 20a circuit in addition to, not in lieu of an existing circuit, or in the case of his 15a circuit, event more so.

Question for TTB, when you mentioned adding "two more amps", were you referring to the built in active amps or two additional amps. For the geniuses here, you might want to list all of your wattages or amps, we don't charge much. Just need you to respond. Otherwise there will be a bill sent. FWIW, we know where you live.

Arny it sounds like you have some funky knob and tube wiring. That had it's place in it's day but is woefully inadequate today. If in fact the neutrals are touching metal studs, assuming they are grounded, not only would that present problems for 'arc fault', any bathrooms with GFI would constantly trip. The GFI needs to see identical current on the hot and neutral and with the neutral touching the stud that won't happen. I'm a huge fan of GFIs, arc fault not so much.

BTW there is a case for oversized (never undersized) wires in breakers. The most common is reducing circuit resistance on long runs and if you're ignorant enough to use aluminum wire, that is in cu/al rated breakers, Don't forget the NoLox. In fact you have to use one gauge larger when using aluminum wire because of the extra resistance.
post #29 of 37
Be careful casually substituting impedance for resistance in that equation. Impedance can include capacitive and inductive components and greatly impact the power factor with leading or lagging current. biggrin.gif
post #30 of 37
Quote:
Originally Posted by Patrick Collins View Post


Arny it sounds like you have some funky knob and tube wiring.

Not at all. I know knob and tube wiring, and this ain't it. The cable is like coax except the shield is loosely wrapped around the hot wire instead of braided. And there is the steel wire wrapper. Looks like long springs. Here's a shot of some dead wires:



Oops, this is an example of one of the cables that has 2 hots inside one neutral.

We have houses in the area that were originally wired knob and tube (circa 1915) but my house was built in 1933 and by then knob and tube was out of the picture for new construction in this area.

I have a friend that still has an older house with some knob and tube still in place. Done right it is actually very long lived as long as none of the porcelain breaks and the wires keep their integrity. Insulation on the wire is optional and a lot of the older stuff was wired with bare wire. When copper wire corrodes it is usually caused by water leakage or old style acid solder flux residue.
Quote:
That had it's place in it's day but is woefully inadequate today. If in fact the neutrals are touching metal studs, assuming they are grounded, not only would that present problems for 'arc fault', any bathrooms with GFI would constantly trip. The GFI needs to see identical current on the hot and neutral and with the neutral touching the stud that won't happen. I'm a huge fan of GFIs, arc fault not so much.
Quote:

As good fortune would have it, all of the bathrooms and the kitchen are 100% new Romex wiring. No problems with GFCIs. Besides GFCIs don't care if neutral and safety ground are the same wire on the supply side. Its the delivery side where it matters. Unfortunately 3 out of 4 of the bedrooms that are still wired with the old stuff.
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