Understanding How To Size A Circuit Conductor - Electrical - DIY Chatroom Home Improvement Forum

 DIY Chatroom Home Improvement Forum Understanding how to size a circuit conductor
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09-09-2008, 02:58 PM   #1
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## Understanding how to size a circuit conductor

Let's say I have a device, a time machine perhaps, that I will be hard wiring into my panel with it's own breaker. On the label, next to where it says "1.21 gigawatts", it says that minimum ampacity is 52 amps and maximum circuit breaker size is 60 amps.

Per the NEC, which of those numbers (beside 1.21 gigwatts ) should I use to determine conductor gauge, and why?

09-09-2008, 03:03 PM   #2
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Quote:
 Originally Posted by gp_wa Let's say I have a device, a time machine perhaps, that I will be hard wiring into my panel with it's own breaker. On the label, next to where it says "1.21 gigawatts", it says that minimum ampacity is 52 amps and maximum circuit breaker size is 60 amps. Per the NEC, which of those numbers (beside 1.21 gigwatts ) should I use to determine conductor gauge, and why?

Is this really just an AC unit?

09-09-2008, 03:16 PM   #3
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Quote:
 Originally Posted by chris75 Is this really just an AC unit?
No it's a time machine :D

I'm trying to keep it general by not actually telling you what it is. If it matters, then I'm hoping that will just be part of the answer.

09-09-2008, 05:10 PM   #4
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Quote:
 Originally Posted by gp_wa Let's say I have a device, a time machine perhaps, that I will be hard wiring into my panel with it's own breaker. On the label, next to where it says "1.21 gigawatts", it says that minimum ampacity is 52 amps and maximum circuit breaker size is 60 amps. Per the NEC, which of those numbers (beside 1.21 gigwatts ) should I use to determine conductor gauge, and why?
I suppose it would depend on the vertical rebound index of the flux capacitor, wouldn't it ???

Dugly

 09-09-2008, 05:28 PM #5 Member   Join Date: Oct 2007 Posts: 2,294 Rewards Points: 1,000 Circuit/breaker sizes go from 50 to 60 amps. 52 is greater than 50 so do the math. #6 When you get it up and running, find me when I'm about 10 years old and tell me to move to Seattle and befriend a "Mr Bill Gates". Give John Lennon a heads up too.
09-09-2008, 05:39 PM   #6
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Quote:
 Originally Posted by 220/221 Circuit/breaker sizes go from 50 to 60 amps. 52 is greater than 50 so do the math. #6
Do the math on which number? 52 or 60?

09-09-2008, 06:06 PM   #7
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Quote:
 Originally Posted by YerDugliness I suppose it would depend on the vertical rebound index of the flux capacitor, wouldn't it ???
No, this is a newer model, well actually an older model, it gets confusing with these things. Anyway, they switched to a linear dual axis rebound index after (I mean before) some guy got turned into a newt. It'll be in the news twelve years ago.

 09-09-2008, 07:01 PM #8 Newbie   Join Date: Aug 2008 Posts: 19 Rewards Points: 10 Use awg #6 fused at 60 amps
09-09-2008, 07:04 PM   #9
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Quote:
 Do the math on which number? 52 or 60?

Edited:
Quote:
 Circuit/breaker sizes go directly from 50 to 60 amps

 09-09-2008, 07:18 PM #10 Licensed Electrical Cont.     Join Date: Feb 2004 Location: NY State Posts: 7,821 Rewards Points: 1,992 It certainly DOES matter what it is. A/C's, motors and welders all have dedicated sections in the code and follow certain rules. Time machines do not have this luxury. __________________ Sometimes I feel like if I answer any more questions it is like someone trying to climb over a fence to jump off a bridge and me giving them a boost.
09-09-2008, 08:18 PM   #11
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Quote:
 Originally Posted by 220/221 Edited:
You're missing my question. I am asking which number is of relevance to this calculation, 52 (minimum ampacity), or 60 (maximum protection).

I understand why you'd use a 60 amp breaker as apposed to a 52 amp one...

09-09-2008, 08:21 PM   #12
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Quote:
 Originally Posted by Speedy Petey It certainly DOES matter what it is. A/C's, motors and welders all have dedicated sections in the code and follow certain rules. Time machines do not have this luxury.
If it has a motor, does that have a bearing on which of the two numbers I've asked about are relevant?

I thought that the difference was between continuous and intermittent rating, and that a continuous rating changes the wire gauge needed for a particular amp rating.

In other words, a heat coil drawing 50 amps might require #6 wire, while a motor drawing 50 amps might require #5.

 09-09-2008, 08:30 PM #13 Licensed Electrical Cont.     Join Date: Feb 2004 Location: NY State Posts: 7,821 Rewards Points: 1,992 In your case, 52MCA & 60 Max OCPD, the answer is still 60A and #6. __________________ Sometimes I feel like if I answer any more questions it is like someone trying to climb over a fence to jump off a bridge and me giving them a boost.
09-09-2008, 08:32 PM   #14
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Quote:
 Originally Posted by Speedy Petey In your case, 52MCA & 60 Max OCPD, the answer is still 60A and #6.
My case, assuming what? (sorry) A/C, motor, welder, none of the above?

09-09-2008, 08:40 PM   #15

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If your time machines factory nameplate says minimum ampacity 52 amps then you need to size the conductor based on that amperage. Which would be a #6 awg copper conductor or one with a higher ampacity. The max breaker is just that 60 amps maximum. You can't use a 50 because it is not sufficient for the load served. As said several times there is not a 55 amp breaker so next protection size after 52 amps is 60. Motors are 1.25 times the largest plus the sum of the rest, if a single motor then 1.25 times the flc of that motor. If the equipment is a continuous load (will be operating for 3 hours or more) then it is 1.25 times the rated ampacity of that equipment. If however a nameplate states minimum ampacity then continuous or whatever has already been factored in and the equipment must be served with conductors that have at least that minimum ampacity.

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