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Old 12-21-2007, 03:12 PM   #16
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Gauge Wire and Breaker Discrepancy


I'm still confused because the people I talked to at the hardware store and such say you don't go up on the breaker. As in your example below,

Quote:
Originally Posted by HouseHelper View Post
Since there are no 55A breakers, you are allowed to use a 60A.
I have been told that you want the breaker to be rated slightly lower than the amperage of the wire so that a breaker will open before the wire reaches its maximum amperage, thus protecting the wire on the circuit. Have I been misinformed? What is the correct analogy here in order to select the right wire/breaker combination?

Stubbie did mention the temperature rating, indicating that not all wires, panels, and subpanels are created equal so this may be adding to my confusion. In Stubbie's example,
Quote:
Originally Posted by Stubbie View Post
In a nutshell #2 copper will be either 95 amps or 115 amps depending on some factors....those being type of wire insulation and is the feeder between panels a certain type of cable like UF-B or SER cable or individual wires in conduit like thhn/thwn. Most likely #2 copper will be individual wires in conduit and likely to be thhn/thwn rated temperature insulation but could be other types of wire or cables.
If I am following this correctly, it is possible that there is a # 6 AWG that is rated higher than 60 Amps and therefore a 60 Amp breaker would make sense to me in that case. However, a # 6 AWG that is rated at 55 Amps and paired with a 60 Amp circuit breaker just seems like it would run very close to hot if given the chance. Wouldn't it be safer to use a 50 Amp breaker in this case? I think I'm about to lose my marbles here. Please explain. I'm sure I will understand this soon with the right analogy being the key factor here as I am obviously not an electrician.

Thanks,
Mac

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Old 12-21-2007, 03:39 PM   #17
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Gauge Wire and Breaker Discrepancy


You should not listen to the people at the hardware store, but listien to stubbie and the others.
The code allows going to the next size, if the size you need is not made.
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Old 12-21-2007, 03:43 PM   #18
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This is a great thread. The great thing about the NEC is, as far as ampacity goes, it takes all the guess work away.

#6 AWG NM/b (Romex) is rated 55A under the 60deg column. #6AWG THHN/THWN is rated 65A under the 75deg column. The 90deg column rates #6AWG at 75A.

The writers of the NEC took the entire table under consideration when they allowed us to go up in breaker size. Your job, and mine as well , is to take the rules as gospel and not wonder why...but just do.

Andy
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Old 12-21-2007, 06:08 PM   #19
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Gauge Wire and Breaker Discrepancy


Terminals for equipment rated 100 amps or less must have the conductor sized under the 60 degree column, UNLESS you know for certain that the terminal ratings and the insulation rating of the conductor are above that, without that information the safest bet is to use the 60 degree column which will give you 95 amps for 2 awg. The 75 degree column will allow you 115 amps.

For terminals over 100 amps you will need to use the 75 degree column. You can still use conductors that are listed in the 90 degree column such as thhn, but you can only use the ampacities of those conductors that correspond with the 75 degree column, because the 90 degree column ampacities is only used for derating conductors.

And as far as the next higher breaker goes if you have a code book check out 240.4 there is some good info there.
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Old 12-21-2007, 06:27 PM   #20
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Gauge Wire and Breaker Discrepancy


Scout

Quote:
I have been told that you want the breaker to be rated slightly lower than the amperage of the wire so that a breaker will open before the wire reaches its maximum amperage, thus protecting the wire on the circuit. Have I been misinformed? What is the correct analogy here in order to select the right wire/breaker combination?
You have been misinformed but in a conservative manner most likely because these people are not sure themselves so they are playing it safe.

I told you there is no easy answer......

First let me explain why I told you what to use for breaker and wire size. You were not able to determine if the GE panel you have is rated for 75C terminations therefore I only considered 60C ampacities for 6 awg copper thwn in conduit since that is the wiring method you said you preferred. That ampacity is 55 amps. NEC 240.4 (B)(1)(2)(3) allows the next size breaker above an ampacity that doesn't fall on a standard breaker size in your situation. 55 amps is not a standard breaker size so 60 amp breaker is allowed ( see Speedy's post #3). This is very conservative considering I would bet that the GE panel is rated for 75C terminations. The sub-panel will be rated 75C since it is a modern panel. If you could have proved 75 C terminations in the GE panel then the #6 awg copper thwn in conduit would be good for 65 amps and you could place that on a 70 amp breaker using 240.4(B). So you see we are derating the #6 thwn ampacity because we can't prove termination temperature to be 75C at the GE panel. The wire is capable of much higher ampacity than 55 amps. But we are having to play it safe due to the unknown termination rating of the GE panel. Also understand that the 60 amp breaker is on a wire that can handle more than 60 amps....soooo you don't have any issues with getting the wire too hot. The temperature rating of a wire is the result of the maximum ampacity it can safely operate at continuously before any other factors are considered with out failure. The odds of you running that thwn continuously at 65 amps is pretty slim if not impossible and it will not happen on a 60 amp breaker. Hope this makes sense.

As an added note any under ground conduit run is considered a wet loaction and therefore only wire insulations rated for wet location can be used the 'W' in THWN stands for wet rated.

Stubbie

Last edited by Stubbie; 12-21-2007 at 09:24 PM.
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Old 12-21-2007, 07:29 PM   #21
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Quote:
1. I have read 4 electrical books on adding a sub-panel while visiting the hardware store and they all recommend pairing up # 6-3 wire with a 50 amp breaker not a 60 amp breaker. Help me get past this discrepancy!
Because the 6-3 G they are talking about is UF-b cable and it is only rated at 55 amps no other amperages regardless of temperature terminations for the equipment. They are saying 50 amp breaker to cover there behinds in the event you are a crazed homeowner wanting to operate something in excess of 55 amps continuously 24/7.

Quote:
2. # 6 wire is a good starting point for a sub-panel also according to what I've read. However, after 55 feet there will be a certain percentage voltage drop for every foot thereafter. My panels will need 65 feet of wire between them leaving me at 10 feet over the 55 feet voltage drop zone. If I understand this correctly, I will experience an approximately 5% - 30% voltage drop depending on several factors.
Go here and plug in your info and see for yourself. You will use 240 volts for the voltage, copper, 65 feet one way, 60 amps load.....vary the amperage and see how it effects the voltage drop. Anything less than 3% drop on the feeder is super.

http://www.electrician2.com/calculat...r_initial.html

Quote:
After reading these findings, I decided, with the help of one electrician, 2 hardware employees, and one wholesale electrical supply company employee, that I should try for some over-kill and go with something I could safely add more circuit to in the future. I was advised to use the # 2 AWG wire, 125 Amp sub-panel, and 1 100 Amp double pole breaker from the service panel (following the advice caused me to find the 100 Amp breaker discrepancy that I originally posted here).
Sorry but that makes no sense to me whatsoever . You would be sizing your shop for a 2 man cabinet making business. If over kill is what they call that then that is certainly overkill. From the description of what you said you were going to operate in your shop this is way more than you need. I would suggest putting in conduit big enough to pull a 100 amp feeder in someday if you would ever need it. I doubt you will. If you did have a demand load for the shop that required a 125 amp panel you likely will be exceeding the capabilities of the house main panel to support it .
Quote:
However, before I started any research at all, I originally was going to use the existing 50 Amp double pole breaker from my service panel. From there, connect the #6-3 wire rated for direct bury (no conduit!) Run that to a 100 Amp indoor sub-panel and run all my circuits from there. Isn't it funny how things can evolve and get out of hand with a difference of opinion and tons of mis-information? If you guys can clarify the two hurdles I have, it would be greatly appreciated.
50 amps on 6/3 G uf-b will probably be just fine if you want to keep that plan.

Quote:
Finally the 30" bury was relayed to me by a local electrician in my area as well as the folks at the wholesale electrical supply store. I will call the city permit office to confirm.
I've never heard of 30" bury for a sub-panel feeder in pvc this is almost twice as deep as code requires. Direct bury is only 24 ".

If your sources of information continue to give you this erroneous information refer them here and they can discuss it on this thread.

Last edited by Stubbie; 12-22-2007 at 11:03 PM.
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Old 12-21-2007, 10:26 PM   #22
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Gauge Wire and Breaker Discrepancy


I can't thank all of you enough for providing such terrific advice. I am feeling much more knowledgable now about setting up my circuits appropriately. If I have anymore wiring questions, I know I can count on you guys to set me straight. I kind of wish I have some more questions to ask as I really enjoyed this thread. It has been a fantastic learning experience.

Happy Holidays everyone!
Mac
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Old 12-21-2007, 11:47 PM   #23
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Gauge Wire and Breaker Discrepancy


Would 'broken scout' be referring to an international scout ?
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Old 12-22-2007, 12:48 AM   #24
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Gauge Wire and Breaker Discrepancy


Actually yes, how did you guess? In case you are wondering why broken_scout? Like most folks who work on old trucks, I spend more time tinkering on mine than I do driving them. They are actually quite reliable. I should learn to ease up on the tinkering and just enjoy driving them. I just picked up a 1976 Traveler that is going to have some rust repaired hopefully next month. It is a 2 wheel drive at the moment but plan to convert it to a 4 wheel drive this summer.

I noticed you are a Ford guy. A few of my top 10 favorite all time vehicles are Fords and/or Mercurys, namely 1978 or 1979 Ford Broncos with a 400m motor and C6 tranny and 1970 Mercury Cougar with a 351 Cleveland motor, which is the first car I have ever owned that was handed down to me from my Grandmother. Can you tell I like old cars, trucks, and tractors? Shoot - I like anything that is old and useful!

Mac
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Old 12-22-2007, 12:25 PM   #25
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That's cool you like older vehicles and tractors. One of my very good friends builds custom stainless steel exhaust systems for people rebuilding international scouts. He has a couple that are pretty impressive that he drives on an everyday basis and a few that he takes to shows all over the USA. I too love to rebuild older lawn tractors and use them. I'm not much for the show stuff... I like to get em running again and sell and/or give them away to friends or family that are less fortunate than I and could use a good mower. Nothing makes me fell better than to have my 40 year old lawn tractor purring along while my neighbors ponder how in the heck to work on their new JD's or Cubs or whatever. I always laugh when people say it costs too much to repair them might just as well buy a new one. Heck... it aint about money.

Last edited by Stubbie; 12-22-2007 at 01:09 PM.
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Old 12-22-2007, 10:34 PM   #26
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Stainless steel exhaust sounds perfect, considering these trucks run through the mud alot. Your friend has the scout bug pretty bad. I go to scout club meetings once a month and we all have at least two or three trucks or more. lol!

Lawn mowers and go carts were some of my first hobbies. I donít tinker on go carts anymore, but for the last two years, I have been trying to learn about old Dixon zero turn mowers. They are, in my opinion, one of the neatest riding lawn mowers around. They are fast and turn on a dime. I started out with a 1984 Dixon 311 with a 30 inch deck, and later found a 1979 Dixon 424 with 42 inch deck that came with a snow plow and an extra wide seat which is kind of rare. But Iím kind of partial to my Dadís 1965 International tractor too! Itís like a Swiss Army knife, you can attach anything to it and get the job done. Isnít it funny how so many of the lawn mowers out there that are being tossed out, frequently only need maybe $15 or $20 in parts or just a little elbow grease only and no money, and they are up and running great again. I get the same feeling too when my neighbors buy a new mower and have to send it back several times for same problem. The old stuff isnít perfect, but like you said ďHeckÖit aint about money.Ē

Thanks to you and everyone else who chimed in on this thread. Iíll be able to tinker on my projects in a well lit shop soon, and use my extension cord for other things.

Thanks again and Merry Christmas,
Mac
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Old 12-22-2007, 11:07 PM   #27
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Gauge Wire and Breaker Discrepancy


Keep that scout running and Merry Xmas to you.

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