# Hot!



## running dummy (Mar 19, 2009)

I had an odd service call the other day, at least odd to me. The customer was complaining of his main breaker tripping repeatingly. When I arrived and started inspecting I found that 4 breakers (2,3,4,5 ckts) were extremely hot!!! You could not even touch the top of the breakers! Circuits 3,5 was a 2 pole 100 A breaker for an electric furnace. This ultimately seemed to be the root cause of the situation. I took current and voltage readings and everything came up NORMAL. The 100A breakers was drawing 83 amps at full load but was heating up very quickly! (It was so bad when I pulled the breaker out it crumbled in my hand!) I pull the 4 breakers and noticed a dark build up on the aluminum buss. I took my flat head screwdriver and carefully scraped away the majority of the build up (of course live, with bare hands). Then I installed new breakers and with a small amount of dielectric grease on the breaker. This seemed to be a quick fix but told him he should have this inspected more closely VERY soon! (this was on thanksgiving day and I was here to basically put a band-aid on this) I then turned on the breaker and metered the circuit in question as it cycled through its full load amps. Everything checked out and there was little heat involved. (it was barely warmer than the breakers next to it, sorry no fancy IR gun ha ha)

My question is: Why was the breaker getting so hot when voltage readings and currents were all within normal operating parameters? I believe the build up on the buss was creating a high resistance connection point, but wouldn't this cause higher currents? Also is there some sort of thermal overload on most residential Main Breakers? (This panel was a Cutler Hammer panel) I am not well experianced in the service side of this business so any insight would be welcome. 

By the way, I believe the HO opted for a panel upgrade. Another guy from my shop went over to his house that following week.


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## running dummy (Mar 19, 2009)

also, VD was only 2-3 V when the furnace cycled


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## RePhase277 (Feb 5, 2008)

Well, was the 3 V drop only across the breaker, or was the 3 V measured at the breaker and the main? If it was dropped across the breaker, then at 83 A it would dissipate 249 watts. Think about how hot a 250 W light bulb is. You couldn't put your hand on it either.

And yes, the heating caused by continuous high load, coupled with the additional heating caused by a poor bus connection, could trip a weak main. I've seen sunlight do it to outdoor mains.


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## running dummy (Mar 19, 2009)

InPhase277 said:


> Well, was the 3 V drop only across the breaker, or was the 3 V measured at the breaker and the main? If it was dropped across the breaker, then at 83 A it would dissipate 249 watts. Think about how hot a 250 W light bulb is. You couldn't put your hand on it either.
> 
> And yes, the heating caused by continuous high load, coupled with the additional heating caused by a poor bus connection, could trip a weak main. I've seen sunlight do it to outdoor mains.


I see where you are coming from and your logic. The VD was measured acrsoss the mains also. And the heat generated melted the frame of the breaker.


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## DipsyDoodleDandy (Dec 21, 2009)

*meltdown*

I see that alot. In my case its usually from people not tightening the conductor down on breaker and less often the springs get loose over time and arc. Either way it will just heat everything up til it builds up and sometimes kicks off the breaker and sometimes not. I've never heard of a thermal overload in panel other than in breakers. It's amazing how hot they get sometimes and still don't kick. Saw Factory lights once drawing 29 amps continuous (18hrs day) on 20 amp breaker and still didn't kick out. 

Watch this http://electronics.howstuffworks.com/circuit-breaker.htm

Anyone notice anything interesting in that video in basement?


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## goose134 (Nov 12, 2007)

> Anyone notice anything interesting in that video in basement?


All EMT? Looks like all the basements around here.


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## DipsyDoodleDandy (Dec 21, 2009)

*Emt*

you got it. I never see that here at all. Literally, in 10yrs around here I've never seen that in residential other than old jobs I was on. Where are you?


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## running dummy (Mar 19, 2009)

all emt here too. both in the chicagoland area


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## brian john (Mar 11, 2007)

DipsyDoodleDandy said:


> ISaw Factory lights once drawing 29 amps continuous (18hrs day) on 20 amp breaker and still didn't kick out.


 
A 20 amp breaker will carry 29 amps for a long time BY DESIGN and not trip.

To the OP you need to do a FOP (VD test) test across the CBs


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## DipsyDoodleDandy (Dec 21, 2009)

*News*

that's news to me. Are you serious? Your telling me all these years the 80% overload theory was wrong?


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## running dummy (Mar 19, 2009)

well most breakers are inverse time correct? I wouldnt think it would hold that long but I knew that was built in to them.


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## JayH (Nov 13, 2009)

Here is a GE Time Current curve for a 20A ground fault breaker.

http://www.geindustrial.com/publibrary/checkout/Time%20Current%20Curves%7CGES-9882%7Cgeneric

The breaker has many other variables that would allow it to hold 29 amps for a long period including temperature and age.


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## user4818 (Jan 15, 2009)

DipsyDoodleDandy said:


> that's news to me. Are you serious? Your telling me all these years the 80% overload theory was wrong?


Yes, completely wrong.


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## brian john (Mar 11, 2007)

JayH said:


> Here is a GE Time Current curve for a 20A ground fault breaker.
> 
> http://www.geindustrial.com/publibrary/checkout/Time%20Current%20Curves%7CGES-9882%7Cgeneric
> 
> The breaker has many other variables that would allow it to hold 29 amps for a long period including temperature and age.



Ambient, load of the adjacent CB's, panel cover off, panel cover on, fan blowing on it and on and on......


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## Speedy Petey (Jan 10, 2007)

DipsyDoodleDandy said:


> that's news to me. Are you serious? Your telling me all these years the 80% overload theory was wrong?


What theory is this?


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## DipsyDoodleDandy (Dec 21, 2009)

*Breakers*

So how many amps can run through a main on a 200 amp Breaker all day without tripping it?


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## DipsyDoodleDandy (Dec 21, 2009)

*amp*

Ok. So the ampacity of 12 gauge thhn is 20 amps, then why would you put a 20 amp breaker that let 29 amps flow continuous?? I must be missing something?


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## DipsyDoodleDandy (Dec 21, 2009)

*This Theory*

This Theory

Sizing a circuit breaker.
Share This Article 

(11) 
May 1, 1996 12:00 PM, Pauley, Jim; Young, Sandi

Circuit breakers are designed to carry 100% of their rated current while the NEC dictates an 80% application. Why the difference?

One of the most often asked questions is, "How do I size a circuit breaker?" A commonly misunderstood fact about circuit breakers (CBs) is related to the percentage of loading permitted by the NEC and the CB design, and why the two may be different. Let's investigate both aspects.

CB design

A CB is designed and evaluated to carry 100% of its rated current for an indefinite period of time under standard test conditions. These conditions, per UL 489, Underwriters Laboratories Standard for Safety for Molded-Case Circuit Breakers and Circuit Breaker Enclosures, include mounting the CB in free air (i.e.: with no enclosure) where the ambient temperature is held at 40 [degrees] C (approximately 104 [degrees] F). Under these conditions, molded-case CBs are required not to trip at rated current.

However, a CB most frequently is applied in equipment at 80% of its rated current under NEC Sec. 384-16(c). If you understand why this requirement is in place, you'll be able to apply CBs correctly.

CB characteristic trip curves

CB characteristic trip curves document how long it takes for specific CBs to trip depending upon the level of current. Fig. 1 shows a typical curve for a thermal-magnetic CB. The curved portion at the top represents the time it takes for the CB to trip on overload. An overload condition will cause heat buildup around the current path, within the CB as well as along the power conductors. This heat, which is generated by the current flow, is actually what causes the CB to trip in this region not simply the magnitude of the current flow. This portion of the curve is said to have an inverse time characteristic, which means that the CB will trip in less time at higher levels of current flow.

Since the current path (including both the CB and the conductor) reacts to heat, the overall operating temperature of the equipment becomes a factor in sizing a CB in an enclosure.

Other factors that may affect this equipment operating temperature include:

* Size and location of the enclosure;

* More than one current carrying device housed in the same enclosure;

* Level of current each device is carrying; and

* Environmental conditions in the area of the equipment.

Consequently, simply designing a CB to hold 100% of its rated current only addresses a portion of the concern. The equipment must be able to safely sustain the heat generated by all sources without exceeding the temperature limits in the product test standard. Both of these factors are accounted for by the sizing rules imposed by the NEC.

1996 NEC

The 1996 NEC recognizes that overcurrent protective devices will be affected by heat in the system. As such, it defines the concept of continuous loads and the 80% rule to try and offset the effects of heat in the system when sizing a CB.

Continuous loads. To better understand the sizing aspects of a CB, you must first clearly understand the concept of continuous loads. In Art. 100, the NEC defines a continuous load as "a load where the maximum current is expected to continue for three hours or more." It's critical for you to understand that this is a load at its maximum current uninterrupted for at least three hours. Office lighting typically meets this qualification.

NEC sizing rules. Secs. 210-22(c), 220-3(a), 220-10(b), and 384-16(c) all relate to the sizing rules for overcurrent protective devices (OCPDs). The first three all specify the same requirement:

OCPD size = 100% of noncontinuous load + 125% of continuous load.

Sec. 384-16(c) has the same requirement, except that it's stated in terms of the loading of the OCPD. This rule states that an OCPD can be loaded to only 80% of its rating for continuous loads. Remember that 80% is the inverse of 125% (0.80 = 1 [divided by] 1.25) and, as such, the rules are indeed identical in their end requirement.

Read the rule closely; the 125% sizing of the OCPD (or 80% loading) is only applicable when continuous loads are involved. CBs and other OCPDs can be sized at 100% of their rating for noncontinuous load applications.

100%-rated devices. The NEC does recognize complete assemblies (including the OCPDs) that are listed for operation at 100% of their rating for continuous loads. This means that the equipment has undergone additional testing to verify that it can handle the additional heat rise associated with this level of operation.

A 100%-rated CB and the end use equipment have been tested to verify that the additional heat generated by the 100% continuous loading conditions is safely dissipated. Other equipment specifications also are driven by the need to dissipate the heat associated with the level of heat rise achieved during 100% rated testing. In cases where the temperature at the CB wiring terminals exceeds 50 [degrees] C during 100% rated testing, UL 489 requires the use of 90 [degrees] C insulated wire (sized at the 75 [degrees] C ampacity) with these CBs, and the CB must be marked as such by the manufacturer. UL 489 also specifies minimum enclosure size and venting requirements if needed for heat dissipation. A CB that successfully has passed these additional tests is still not listed for application at 100% of its rating for continuous loading unless it's marked as such by the manufacturer.

In summary, a CB either carries a standard rating (80%) or a 100% rating. The standard rating is subject to the NEC sizing rules we've just discussed. CBs that are 100%-rated are permitted to be loaded continuously at their full rating as long as the assembly is listed and conductors are properly connected.

CB sizing examples

The following are examples of sizing rules.

Example 1: 50A continuous load and 125A noncontinuous load.

OCPD = 100% noncontinuous load + 125% continuous load = (1.00 x 125A) + (1.25 x 50A) = 187.5A

Therefore, a 200A OCPD is needed. If a 100%-rated CB is chosen, a 175A rating (125A + 50A) is acceptable.

Example 2: 300A noncontinuous load.

A 300A device is acceptable; a 100%-rated device is not needed since the load is noncontinuous.

Example 3: 200A continuous load.

OCPD = 100% noncontinuous load + 125% continuous load = (1.00 x 0A) + (1.25 x 200A) = 250A

Therefore, a 250A device is needed. If a 100%-rated CB is selected, a 200A rating is permitted.

Example 4: 16A continuous and 30A noncontinuous.

OCPD = 100% noncontinuous load + 125% continuous load = (1.00 x 30A) + (1.25 x 16A) = 50A

Therefore, a 50A device can be selected. Although 100%-rated devices typically are not available in sizes this small, the permitted rating would still be 50A (16A + 30A = 46A; rounded up to 50A).

Jim Pauley is Manager, Industry Standards, and Sandi Young is Circuit Breaker Product Specialist with Square D Co., Lexington, Ky. and Cedar Rapids, Iowa respectively.


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## 480sparky (Sep 20, 2007)

DipsyDoodleDandy said:


> Ok. So the ampacity of 12 gauge thhn is 20 amps, then why would you put a 20 amp breaker that let 29 amps flow continuous?? I must be missing something?


The ampacity of 12 THHN is 30 amps, not 20.


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## DipsyDoodleDandy (Dec 21, 2009)

*...*

not when it's next to 15 others in a 1/2" conduit


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## DipsyDoodleDandy (Dec 21, 2009)

*....*

and I knew about all this

The ampacity of 12 gage THHN is 30 amps, per 310.16, but 

240.4(D) Small Conductors. Unless specifically permitted in 240.4(E) or (G), the overcurrent protection shall not exceed that required by (D)(1) through (D)(7) after any correction factors for ambient temperature and number of conductors have been applied.
(3) 14 AWG Copper. 15 amperes
(5) 12 AWG Copper. 20 amperes
(7) 10 AWG Copper. 30 amperes

Most electricans then state the ampacity of 12 AWG THHN is 20 amperes, when its actually 30.


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## 480sparky (Sep 20, 2007)

DipsyDoodleDandy said:


> not when it's next to 15 others in a 1/2" conduit


 
Then the ampacity would be.......... what?

Quickly, now... this is a test!


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## 480sparky (Sep 20, 2007)

DipsyDoodleDandy said:


> ............Most electricans then state the ampacity of 12 AWG THHN is 20 amperes, when its actually 30.


 
Most electricians would state the ampacity of 12 THHN as 30.

Those who are either new to the trade or don't bother to open a code book will say it's 20.


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## DipsyDoodleDandy (Dec 21, 2009)

*and this...*

Example: The ampacity of each 12 THHW conductor in a dry location is 30A, based on the values listed in the 90°C column of Table 310.16. If we bundle nine current-carrying 12 THHN conductors, the ampacity for each conductor (30A at 90°C, Table 310.16) needs to be adjusted by a 70% adjustment factor [Table 310.15(B)(2)(a)].

Adjusted conductor ampacity = 30A × 0.70 = 21A


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## 480sparky (Sep 20, 2007)

DipsyDoodleDandy said:


> Example: The ampacity of each 12 THHW conductor in a dry location is 30A, based on the values listed in the 90°C column of Table 310.16. If we bundle nine current-carrying 12 THHN conductors, the ampacity for each conductor (30A at 90°C, Table 310.16) needs to be adjusted by a 70% adjustment factor [Table 310.15(B)(2)(a)].
> 
> Adjusted conductor ampacity = 30A × 0.70 = 21A


So are you going to give us the entire ampacity lecture, including ambient temperatures and rooftop installations as well?


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## DipsyDoodleDandy (Dec 21, 2009)

*...*

no...I'm done


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## 480sparky (Sep 20, 2007)

DipsyDoodleDandy said:


> no...I'm done


 
But you haven't answered the question posed in post 22.......


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## DipsyDoodleDandy (Dec 21, 2009)

*...*

don't know exactly..feet up in air, no code book near but i would guess roughly 18.5 as as crude guess


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## 480sparky (Sep 20, 2007)

DipsyDoodleDandy said:


> don't know exactly..feet up in air,...


Huh?



DipsyDoodleDandy said:


> .....no code book near but i would guess roughly 18.5 as as crude guess


Not even close.

Here, let me help:

Number of 
Current-Carrying 
Conductors 
Percent of Values in Tables 310.16 through 310.19 as Adjusted for Ambient Temperature if Necessary
4–6 80
7–9 70
10–20 50
21–30 45
31–40 40
41 and above 35


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## DipsyDoodleDandy (Dec 21, 2009)

*huh*

what is your question? I was getting ampacity for 12 gauge thhn in a 1/2" conduit with 15 current carry conductors and you made me google a chart giving me 50% derating making it 15 amps...so I was off by 3.5amps. but that's what beer can do to you


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## 480sparky (Sep 20, 2007)

DipsyDoodleDandy said:


> what is your question?.....


What does how many feet in the air have to do with it.



DipsyDoodleDandy said:


> .....I was getting ampacity for 12 gauge thhn in a 1/2" conduit with 15 current carry conductors and you made me google a chart giving me 50% derating making it 15 amps...so I was off by 3.5amps. .......


 
Wrong. Try again.



DipsyDoodleDandy said:


> ......but that's what beer can do to you


I don't imbibe, so I wouldn't know.


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## DipsyDoodleDandy (Dec 21, 2009)

*ok*

ok...uncle..what's the answer then


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## 480sparky (Sep 20, 2007)

dipsydoodledandy said:


> ok...uncle..what's the answer then


 
0. .............


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## DipsyDoodleDandy (Dec 21, 2009)

*well*

sure....of coarse it's over the limit and is not legal since the max is 10 or so


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## 480sparky (Sep 20, 2007)

DipsyDoodleDandy said:


> sure....of coarse it's over the limit and is not legal since the max is 10 or so


9. 13 if it's a nipple.


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## DipsyDoodleDandy (Dec 21, 2009)

*...*

it was in imc

I'm crying uncle for tonight...I can't open an more windows or look at anymore charts tonight...

be back tomorrow


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## Magnettica (Jan 23, 2007)

Dude buy a code book.


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## RIVETER (Sep 26, 2009)

*Hot*



running dummy said:


> I had an odd service call the other day, at least odd to me. The customer was complaining of his main breaker tripping repeatingly. When I arrived and started inspecting I found that 4 breakers (2,3,4,5 ckts) were extremely hot!!! You could not even touch the top of the breakers! Circuits 3,5 was a 2 pole 100 A breaker for an electric furnace. This ultimately seemed to be the root cause of the situation. I took current and voltage readings and everything came up NORMAL. The 100A breakers was drawing 83 amps at full load but was heating up very quickly! (It was so bad when I pulled the breaker out it crumbled in my hand!) I pull the 4 breakers and noticed a dark build up on the aluminum buss. I took my flat head screwdriver and carefully scraped away the majority of the build up (of course live, with bare hands). Then I installed new breakers and with a small amount of dielectric grease on the breaker. This seemed to be a quick fix but told him he should have this inspected more closely VERY soon! (this was on thanksgiving day and I was here to basically put a band-aid on this) I then turned on the breaker and metered the circuit in question as it cycled through its full load amps. Everything checked out and there was little heat involved. (it was barely warmer than the breakers next to it, sorry no fancy IR gun ha ha)
> 
> My question is: Why was the breaker getting so hot when voltage readings and currents were all within normal operating parameters? I believe the build up on the buss was creating a high resistance connection point, but wouldn't this cause higher currents? Also is there some sort of thermal overload on most residential Main Breakers? (This panel was a Cutler Hammer panel) I am not well experianced in the service side of this business so any insight would be welcome.
> 
> By the way, I believe the HO opted for a panel upgrade. Another guy from my shop went over to his house that following week.


 You said that you told the customer that he needed it checked out really soon. If you were there for the call why wasn't it your job to do that? And if it was Thanksgiving where did you find a store with the exact main breaker that you needed?


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## DipsyDoodleDandy (Dec 21, 2009)

*Great Tip*

That was an awesome tip Mag. First thing Monday I"m going to go buy one of those things. Where can I find one?


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## 480sparky (Sep 20, 2007)

DipsyDoodleDandy said:


> That was an awesome tip Mag. First thing Monday I"m going to go buy one of those things. Where can I find one?


 
Try WalMart.


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## Mastertorturer (Jan 28, 2009)

brian john said:


> A 20 amp breaker will carry 29 amps for a long time BY DESIGN and not trip.
> 
> To the OP you need to do a FOP (VD test) test across the CBs


Could you source that please.


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## JohnJ0906 (Jan 22, 2007)

Mastertorturer said:


> Could you source that please.


Check the trip curves on any brand of circuit breaker.


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## JohnJ0906 (Jan 22, 2007)

JohnJ0906 said:


> Check the trip curves on any brand of circuit breaker.


http://ecatalog.squared.com/pubs/Ci...rs/QO-QOB Circuit Breakers/0730CT9801R108.pdf

There is Square D - the trip curve charts start on page 19


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## brian john (Mar 11, 2007)

480sparky said:


> Try WalMart.


 
I was looking for a better link for explanation but start here.

http://www.geindustrial.com/products/applications/DER-019.pdf

Molded case circuit breakers are inverse time current devices, higher the current the faster to operate.


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## Mastertorturer (Jan 28, 2009)

JohnJ0906 said:


> http://ecatalog.squared.com/pubs/Circuit%20Protection/Miniature%20Circuit%20Breakers/QO-QOB%20Circuit%20Breakers/0730CT9801R108.pdf
> 
> There is Square D - the trip curve charts start on page 19


Could you circle where it shows 29 continuous Amperes without tripping?

_Ontario Electrical Safety Code 14-104_

_The rating or setting of overcurrent devices shall not exceed the allowable ampacity of the conductors they protect._

_Ontario Electrical Safety Code 4-004_

_The Maximum current that a copper conductor of a given size and insulation may carry shall be as follows:_

_(b) one, two, or three conductors in a run of raceway, or 2- or 3-conductor cable, except as indicated in subrule (1)(d), as specified in Table 2;_

_Table 2 _

_#14 AWG NMD-90 (85-90 degrees celsuis)_
_15 Amperes_

_#12 AWG NMD-90 (85-90 degrees celsuis)_
_20 Amperes_

Maybe electricity works differantly where you're from but where I'm from 29 continuous Amperes on a 20 Ampere breaker is a direct code violation and a defective breaker. 

_Ontario Electrical Safety Code 2-300_
_General Requirements for maintenance and opperation_

_(1)All operating electrical equipment shall be kept in safe and proper_
_working condtion._
_(4)Defective equipment shall either be put in good order or permenently_
_disconnected._


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## sparky105 (Sep 29, 2009)

they have some interesting rules in thier nec book


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## user4818 (Jan 15, 2009)

When I saw the title of this thread, I immediately thought that it was about me.


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## 480sparky (Sep 20, 2007)

Peter D said:


> When I saw the title of this thread, I immediately thought that it was about me.


Are you so dyslexic you read it as "Hack!"? :laughing:


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## Mastertorturer (Jan 28, 2009)

sparky105 said:


> they have some interesting rules in thier nec book


I can't tell if that's sarcasm. :confused1:


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## DipsyDoodleDandy (Dec 21, 2009)

*decipher*

It's hard to tell anything on here. I'm calling siemans to get to the bottom of this 29 amp thing tomorrow


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## nolabama (Oct 3, 2007)

I am new to this site - Scribed - but they have some great reads

This one that I am sharing has some great info on Inverse time overloads - with charts.

Pages about 28-33

http://www.scribd.com/doc/6358171/Basics-Of-Circuit-Breakers


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## running dummy (Mar 19, 2009)

RIVETER said:


> You said that you told the customer that he needed it checked out really soon. If you were there for the call why wasn't it your job to do that? And if it was Thanksgiving where did you find a store with the exact main breaker that you needed?


First of all get off my ****. second of all read the post. I didn't replace the main breaker, it was a 100 amp breaker that Home Depot sold. And I wasn't going to charge the guy emergency rates to rip his panel apart when replacing the breaker fixed the immediate problem.


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## RIVETER (Sep 26, 2009)

*Hot*



DipsyDoodleDandy said:


> not when it's next to 15 others in a 1/2" conduit


Can you get 16 #12s in a 1/2 in conduit?


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## sparky105 (Sep 29, 2009)

Mastertorturer said:


> I can't tell if that's sarcasm. :confused1:


 not sarcasm just some times the difference makes me shake my head


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## 480sparky (Sep 20, 2007)

RIVETER said:


> Can you get 16 #12s in a 1/2 in conduit?


 
I know I could. Very easily.


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## brian john (Mar 11, 2007)

Mastertorturer;


I suggest you do some web searching, read the links provided, check the curves provided and read the AMERICAN Electrician's Handbook.
 it is all there for the reading and understanding. Or put 24 amps on a CB and see for yourself, I find self experimentation works best for self education or come to my shop and I'll put 5000 amps on a 4000 amp CB for you and watch it all day long.

Better yet I'll put 29 amps on a 20 amp cb tomorrow and time it for you.


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## DipsyDoodleDandy (Dec 21, 2009)

*Ocd*

I'm not arguing with you. It's just a hard concept to grasp. It's counterintuitive but, I'm going to hook up 29 amps on a 20 amp breaker tomorrow and time it and report back. I saw the spec's...I'll see what reality says. I'm sure I could be wrong and if so, no problemo. That's what I'm here for.


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## JohnJ0906 (Jan 22, 2007)

Mastertorturer said:


> Could you circle where it shows 29 continuous Amperes without tripping?
> 
> _Ontario Electrical Safety Code 14-104_
> 
> ...


I don't think that 29 amps will hold indefinitely, BUT, what did you learn from the trip curves? Up to 135% of the breaker rating will probably never trip, or if it does, will take quite a long time.
Remember, these are *inverse time* breakers. They are designed not to trip instantaneously at 20.01 amps. The higher the current, the faster it will trip. A short term overload won't damage a conductor or it's insulation. The higher the overload, the faster the breaker will trip. A short circuit will trip within cycles.

By your interpretation of those articles you posted, you must install instant trip breakers.


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## Mastertorturer (Jan 28, 2009)

Well I give people the opportunity to double check their work before mentioning they're wrong a second time.

29 Amperes is 1.45 times or (145%) greater than 20A which is the rating of the breaker. 

First off the Curve is wide to account for the variable quality and characteristics between breakers and possible differances in ambient temperature. Use the furthest edge of the curve on the graph as it's the maximum possible Rated Current/Time before the breaker trips.























A breaker will infact trip at 29A. Also notice on the graph that it's technically possible for the breaker to trip at 20.01 under ideal conditions as you can see by the line running straight down the 1x multiplyer for Rated Current.

Once the amperage increases by as little as 1 it will take between 400-500 seconds to trip. In my opinion an increase of 1 amp on the conductors and 8 minutes maximum of overcurrent at the breaker is not a long time nor is it enough to cause damage to the breaker.

I'd be interested in your own experiments to prove otherwise as it would conflict with this graph from the manufacturer.

:laughing: Don't take it personally.


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## DipsyDoodleDandy (Dec 21, 2009)

*ok*

Nice :thumbup: Ok...now let me go find 2x1800 watt hairdryers, timer, and see what happens. That should do it. I'll be back.......


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## DipsyDoodleDandy (Dec 21, 2009)

*ok....*

Drum Roll....2 Hairdryers

1-SuperIonicCurlMaster 2000W
1-BionicWomanHairstyler 1600W

Voltage at Recep. 124V

Actual Reading during test 29.03 amps

Kicked out at 7 min 29 secs


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## Mastertorturer (Jan 28, 2009)

DipsyDoodleDandy said:


> Drum Roll....2 Hairdryers
> 
> 1-SuperIonicCurlMaster 2000W
> 1-BionicWomanHairstyler 1600W
> ...


You just happened to have the two correct wattage appliances to produce 29 Amps and you actually measured to within .01 Amperes of the mathmatical outcome? Give or take line loss (Not really applicable) ambient temperature and the possibility that there is a margin of error in the manufacturers wattage (probably rounded up).

2000w + 1600w = 3600w

3600 = 29.032258064516129032258064516129
124v

Then it comes between the 1x - 1.5x Rated current section of the graph which is roughly 400-500 seconds or 8 minutes. 

If you're not lying then that is hilarious. Although I can't help but think this is false unless you take pictures of the two hair dryers, the 20A receptacle, the 20A breaker with your clamp meter showing that amperage. 

I will trust the trip time if you can show me that. I'd like this all to be true as it proves the curve correct but it seems too perfect.

PS: You also found those two appliances between 12:52 & 1:11 subtracting your test time of 7 min. 29 sec. leaving you with exactly 11 min 31 sec. To find the appliances + timer, open your panel, plug them in, run back to your panel, measure then post back here. 

And those are funny names for appliances. This is a place of science sir! not of games!


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## brian john (Mar 11, 2007)

Mastertorturer said:


> You just happened to have the two correct wattage appliances to produce 29 Amps and you actually measured to within .01 Amperes of the mathmatical outcome? Give or take line loss (Not really applicable) ambient temperature and the possibility that there is a margin of error in the manufacturers wattage (probably rounded up).
> 
> 2000w + 1600w = 3600w
> 
> ...


I have to think you know nothing or care to know nothing or too lazy to learn anything about the operation of molded case circuit breakers. Links have been posted by several forum members to try and guide you in the right direction, but it seems you are afraid to admit you have not known the truth about how molded case circuit breakers work or do not care about how a major protection device in your chosen profession works. Which means you may want to start all over in the apprenticeship, because it appears you missed a major lesson in school.

I have in my office 10's of 1000's of circuit breaker test reports, all the ones with CBs in the acceptable range for time/current operation are either wrong which means there are 1000's of defective components out there or you are wrong.

If you would like I will video tape a high current test of a CB, but maybe not because you will most likely accuse me of shopping the video.

GO back and study a few links that were posted for you.


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## DipsyDoodleDandy (Dec 21, 2009)

*It was real*



Mastertorturer said:


> You just happened to have the two correct wattage appliances to produce 29 Amps and you actually measured to within .01 Amperes of the mathmatical outcome? Give or take line loss (Not really applicable) ambient temperature and the possibility that there is a margin of error in the manufacturers wattage (probably rounded up).
> 
> 2000w + 1600w = 3600w
> 
> ...


Actually, it was all real, well, I might of embellished a bit on the names of the hairdryer's, but there were two females here wanting them back to dry their heads. I was going to videotube it but did'nt feel like it. Those were the actual numbers. The receptacles were within 10 ft of panel and it was about 75F in the basement on a 6 yr old breaker near the bottom. Maybe someone else want's to youtube it but I'm not too worried about it.


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## prldrp1 (Jun 1, 2009)

480sparky said:


> The ampacity of 12 THHN is 30 amps, not 20.


 


What code book is that in????.....don't look at the 100% column


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## Speedy Petey (Jan 10, 2007)

prldrp1 said:


> What code book is that in????.....don't look at the 100% column


WHAT??? Why not? 
And what is the "100% column" anyway?


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## DipsyDoodleDandy (Dec 21, 2009)

*here*

Here are the hair dryers and links. The wigo I used was 1600 on label.

http://www.amazon.com/Conair-Thermal-Ceramic-2000-Dryer/dp/B000JI4X6U

http://hotcurlingirons.stores.yahoo.net/wg5124.html

I really ran straight down, did it, and back up.


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## 480sparky (Sep 20, 2007)

prldrp1 said:


> What code book is that in????.....


I like to use a real obscure book. It's called the National Electrical Code, published by the National Fire Protection Agency, One Battery March Park, Quincy, Massachusetts 02169-7471.

Publication #70.

Table 310.16.


I'd think they would know what they're doing...... they've published NFPA #70 since 1911.


What Code are you using?




prldrp1 said:


> .....don't look at the 100% column


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## DipsyDoodleDandy (Dec 21, 2009)

*thread*

yeah. I see it. What is not making sense to me if you look at chart attached and manipulate it you will see that using #12 NM-B has an ampacity of 30 amps, 25 Max OCPD, and 16amps max continous load rating. So, why would you put a 20 amp breaker on a conductor with a max continuous load rated at 16 amps if it's not going to kick til maaaybe 29 amps after a long time????? 

That's all I'm saying?


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## brian john (Mar 11, 2007)

DipsyDoodleDandy said:


> yeah. I see it. What is not making sense to me if you look at chart attached and manipulate it you will see that using #12 NM-B has an ampacity of 30 amps, 25 Max OCPD, and 16amps max continuous load rating. So, why would you put a 20 amp breaker on a conductor with a max continuous load rated at 16 amps if it's not going to kick til maybe 29 amps after a long time?????
> 
> That's all I'm saying?


 
AS I understand it, all the manufactures work together (sort of) through NEMA, IEEE, UL, ANSI and a host of other organizations. They know the tripping characteristics of a 20 amp CB they also know the temperature limitations of standard conductors utilized for electrical wiring and, this is what they have arrived at. Conductor insulation and the NEC tables allow for a large margin of safety. Which covers two issues discussed here recently maximum allowable megger voltage and tripping curves of CBs.

Heck I have put 4000 amps on 4/0, not for very long damn insulation was dripping in a minute. Seriously we load 4/0 to 400 amps for hours and 4/0 to 1600 amps regularly for short durations in testing and parallel 500 kcmils to 10,000 amps for several minutes.


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## electricalperson (Jan 11, 2008)

Mastertorturer said:


> You just happened to have the two correct wattage appliances to produce 29 Amps and you actually measured to within .01 Amperes of the mathmatical outcome? Give or take line loss (Not really applicable) ambient temperature and the possibility that there is a margin of error in the manufacturers wattage (probably rounded up).
> 
> 2000w + 1600w = 3600w
> 
> ...


 
you have a lot to learn before you can argue with anybody about this. ive seen 20 amp breakers hold over 20 amps many many times. higher the current faster they trip.

you must be an apprentice. probably a very cocky one


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## Mastertorturer (Jan 28, 2009)

electricalperson said:


> you have a lot to learn before you can argue with anybody about this. ive seen 20 amp breakers hold over 20 amps many many times. higher the current faster they trip.
> 
> you must be an apprentice. probably a very cocky one


You're an incorrect know-it-all journeyman. Yeah; now we're both 8 year old name calling idiots together. We can rules these forums with impunity.


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## electricalperson (Jan 11, 2008)

Mastertorturer said:


> You're an incorrect know-it-all journeyman. Yeah; now we're both 8 year old name calling idiots together. We can rules these forums with impunity.


what am i incorrect about? teach me master apprentice.


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