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Old 02-26-2010, 09:31 AM   #16
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Originally Posted by joseph2293 View Post
Of course you could run the breaker at 100% capacity but think about the consequences...if your running at 100% capacity how much margin do you have before the breaker will trip on an overcurrent? The answer is close to none...thats why the "general rule" for CONTINUOUS LOADS is to not load the breaker more than 80% so your not tripping your breakers constantly
Get serious...how many homeowners calculate what they are running on any one circuit ?

Answer....almost none....if the breaker trips they move something to another circuit
No-one tests to run at 80%
I have the tools to test all my appliances & devices & I never bother to check myself
I had a washing machine (7a?), 7a dehumidifer, 7a sump pump & 3a mini-fridge all on the same 20a circuit
It tripped the circuit once (Spring) when my wife was doing laundry, dehumdifier came on & the sump pump
I ran another circuit for a new freezer & the mini-fridge
But that setup existed for years
And how many continous loads are there in a residential house that are not already on a dedicated citrcuit ?

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Old 02-26-2010, 12:35 PM   #17
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i thought that part of the 3hr, 80% calculation was giving the wire a break so it wouldn't overheat. a 12 gauge wire is designed to take 20 amps, but 20 amps for 12 hours a day seems like you're pushing it to overheat at that point. if you're running new wire i wouldn't worry about it so much, but if it's k&t then i certainly would.
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Old 02-26-2010, 01:03 PM   #18
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Actually K&T can carry more since the 2 wires are seperated & can cool off faster
The problem usually w/K&T is the insulation fails, or its been patched/modified incorrectly
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Old 02-26-2010, 03:08 PM   #19
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Originally Posted by Scuba_Dave View Post
Get serious...how many homeowners calculate what they are running on any one circuit ?

Answer....almost none....if the breaker trips they move something to another circuit
No-one tests to run at 80%
I have the tools to test all my appliances & devices & I never bother to check myself
I had a washing machine (7a?), 7a dehumidifer, 7a sump pump & 3a mini-fridge all on the same 20a circuit
It tripped the circuit once (Spring) when my wife was doing laundry, dehumdifier came on & the sump pump
I ran another circuit for a new freezer & the mini-fridge
But that setup existed for years
And how many continous loads are there in a residential house that are not already on a dedicated citrcuit ?
get serious?!?! this is industry practice...obviously someone with a non-technical background would say it doesn't matter...who in the hell would load there breaker to 100% capacity...NO ONE...except for you of course
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Old 02-26-2010, 03:39 PM   #20
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Originally Posted by joseph2293 View Post
get serious?!?! this is industry practice...obviously someone with a non-technical background would say it doesn't matter...who in the hell would load there breaker to 100% capacity...NO ONE...except for you of course
Industry practice ??
We are talking residential - DIY
And you know nothing of my background

I don't know a single person besides myself that even owns a meter
People load a breaker until the breaker goes off
My wife has done this most of her life....she plugs her 12a vac/1650w hair dryer in anywhere...if it trips the breaker she plugs it in somewhere else
You think people run around & test devices for power draw before they plug something else in ?

Do you even think most homeowners have even heard of any 80% continous load NEC code ??
For that matter how many would even know what NEC stood for ?

How many continous load items are in a residential setting that do not have a dedicated circuit ?
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Old 02-26-2010, 03:55 PM   #21
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Quote:
Originally Posted by Scuba_Dave View Post
Industry practice ??
We are talking residential - DIY
And you know nothing of my background

I don't know a single person besides myself that even owns a meter
People load a breaker until the breaker goes off
My wife has done this most of her life....she plugs her 12a vac/1650w hair dryer in anywhere...if it trips the breaker she plugs it in somewhere else
You think people run around & test devices for power draw before they plug something else in ?

Do you even think most homeowners have even heard of any 80% continous load NEC code ??
For that matter how many would even know what NEC stood for ?

How many continous load items are in a residential setting that do not have a dedicated circuit ?
Its only in the NEC...but who follows that...this all started with you by the way...i said it was a GENERAL RULE...i didn't say HE HAD TO DO IT...i think you just need to chill out and stop trying to tell everyone what YOU THINK IS RIGHT...i personally would never just load up one breaker until it trips and then just take some receptacles off that circuit...its sounds more funny than anything
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Old 02-26-2010, 03:57 PM   #22
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Quote:
Originally Posted by joseph2293 View Post
Its only in the NEC...but who follows that...this all started with you by the way...i said it was a GENERAL RULE..
Yes for continous loads
And for the 3rd time answer my question....

How many continous loads are there in a residential setting that do not already have a dedicated circuit ?

Started by me ?
You were the one telling people they can only load a circuit to 80 %

Quote:
Originally Posted by joseph2293 View Post
generally you should not exceed 80% of the rated full load of a breaker...for instance a 15 amp breaker shouldn't be loaded more than 1440 watts...15 A x 120 V * 0.8 = 1440 watts
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Old 02-26-2010, 04:05 PM   #23
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Originally Posted by Scuba_Dave View Post
Yes for continous loads
And for the 3rd time answer my question....

How many continous loads are there in a residential setting that do not already have a dedicated circuit ?

Started by me ?
You were the one telling people they can only load a circuit to 80 %
note the "GENERALLY"....and how about lighting circuits??? if continuous is determined by over 3 hours...i would think many people have continuous loads on their breakers...how about electric heaters??

now please go away
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Old 02-26-2010, 04:05 PM   #24
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Originally Posted by Scuba_Dave View Post
....she plugs her 12a vac/1650w hair dryer in anywhere...
Can you explain where you are getting 12a for a 1650w hair dryer? Doing so might help explain something that has bugged me for years.

It seems that the typical modern hair dryer is rated at 1875 watts. But for a 120 volt circuit, that would require 15.6 amps. Since the amperage is greater than 15 amps, it would seem that they would require a 20 amp outlet and therefore they should have 20 amp plugs (where one blade is shaped like a sideways 'T'). But I've never seen a hair dryer with anything but a standard 15 amp plug.

This has been a bit of a pet peevie of mine because our house was built (12 years ago) with only a 15 amp circuit, and we get nusiance breaker tips just because we'd to be able to have some lights on when we use a hair dryer.

(I've included in my building permit for basement renovations to run an additional 20 circuit to the bathrooms so I can simply run a hair dryer without the nusiance breaker trips.)
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Old 02-26-2010, 04:09 PM   #25
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Quote:
Originally Posted by HooKooDooKu View Post
Can you explain where you are getting 12a for a 1650w hair dryer? Doing so might help explain something that has bugged me for years.

It seems that the typical modern hair dryer is rated at 1875 watts. But for a 120 volt circuit, that would require 15.6 amps. Since the amperage is greater than 15 amps, it would seem that they would require a 20 amp outlet and therefore they should have 20 amp plugs (where one blade is shaped like a sideways 'T'). But I've never seen a hair dryer with anything but a standard 15 amp plug.

This has been a bit of a pet peevie of mine because our house was built (12 years ago) with only a 15 amp circuit, and we get nusiance breaker tips just because we'd to be able to have some lights on when we use a hair dryer.

(I've included in my building permit for basement renovations to run an additional 20 circuit to the bathrooms so I can simply run a hair dryer without the nusiance breaker trips.)
The bathroom should have its own dedicated 20 amp circuit with a GFCI protecting the outlets near sinks
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Old 02-26-2010, 04:10 PM   #26
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Quote:
Originally Posted by joseph2293 View Post
note the "GENERALLY....and how about lighting circuits??? if continuous is determined by over 3 hours...i would think many people have continuous loads on their breakers...how about electric heaters??
I'm not going anywhere

NO NOT generally...only when the load is continous
Residential lighting is NOT considered a continous load under NEC
Every electric heater I have ever had installed has had a dedicated circuit
Plug ins are usually rated at 1500w or less = 83.3% of a 15a circuit
Do you think homeowners DO NOT plug these into a 15a circuit?
Do you think they run around & unplug everything else from a 20a circuit to make sure they do not exceed 80% ??
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Old 02-26-2010, 04:13 PM   #27
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Quote:
Originally Posted by Scuba_Dave View Post
My wife has done this most of her life....she plugs her 12a vac/1650w hair dryer in anywhere...if it trips the breaker she plugs it in somewhere else
Quote:
Originally Posted by HooKooDooKu View Post
Can you explain where you are getting 12a for a 1650w hair dryer? Doing so might help explain something that has bugged me for years.

It seems that the typical modern hair dryer is rated at 1875 watts. But for a 120 volt circuit, that would require 15.6 amps. Since the amperage is greater than 15 amps, it would seem that they would require a 20 amp outlet and therefore they should have 20 amp plugs (where one blade is shaped like a sideways 'T'). But I've never seen a hair dryer with anything but a standard 15 amp plug.
I've never seen a hair dryer rated at 1875w, but I guess you must have one
Usually Mfg's have items that use less then a 15a circuit so that they can be used in older houses with only 15a circuits

I'm not sure when the 20a bath circuit went into effect
12 years ago would be 1997/8 being built ? So...1995 code maybe ?
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Old 02-26-2010, 04:31 PM   #28
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Quote:
Originally Posted by joseph2293 View Post
generally you should not exceed 80% of the rated full load of a breaker...for instance a 15 amp breaker shouldn't be loaded more than 1440 watts...15 A x 120 V * 0.8 = 1440 watts
Quote:
Originally Posted by Scuba_Dave View Post
This is false, breakers are rated to run at 100% capacity
Quote:
Originally Posted by HooKooDooKu View Post
Sure, a breaker is rated to run at 100% capacity, but doesn't the NEC dictate that a circuit be designed to not exceed 80% of rated capacity?
http://ecmweb.com/mag/electric_sizing_circuit_breaker/
Quote:
Originally Posted by jbfan View Post
Only on loads designed to run more than 3 hours at a time!

OK, can anyone start sighting code references to backup any of their claims?


What I can find is NEC 210.23(A)(1)&(2)
(1) seems to say that any single portable plug-in appliance can not exceed 80% of the circuit rating, and
(2) seems to say that any single non-portable device (excluding lights) can not exceed 50% of the circuit rating if other devices (lights or recepticals) are on the same circuit.

I can also find where "3 hours" is used to DEFINE a "continuous load".

I can also find where NEC 210.19(A)(1) and 210.20(A) says that a branch-circuit must be sized by a combination of 100% of noncontinuous loads plus 125% of continuous loads.
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Old 02-26-2010, 04:33 PM   #29
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This has been beaten to death a number of times
So much so that most electricians that come on here refuse to look-up & cite the code reference again

From what I can find a 20a bath circuit was required in 1999
Not sure about before that...possibly the 15a was code when your house was built

non-portable - like a dishwasher

Are you ignoring the rest of 210.23 ??
Re-read the very 1st paragraph
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Old 02-26-2010, 04:48 PM   #30
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Quote:
Originally Posted by Scuba_Dave View Post
I've never seen a hair dryer rated at 1875w, but I guess you must have one
Usually Mfg's have items that use less then a 15a circuit so that they can be used in older houses with only 15a circuits

I'm not sure when the 20a bath circuit went into effect
12 years ago would be 1997/8 being built ? So...1995 code maybe ?
Check out www.walmart.com, they have several 1875w and even 1900w hair dryers. That's why I'm adding a 20 amp circuit to each bathroom, just so I can have a 20 amp outlet dedicated to just hair dryers.

Mater of fact, it looks like when I do the math, it looks like the 1900w hair dryers just about max out a 20 amp circuit based on NEC's 125% rule (1920w would exactly max it out). But yet these hair dryers are still designed to plug into a 15 amp circuit. I don't get it.

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