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 gp_wa 09-09-2008 02:58 PM

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?

 chris75 09-09-2008 03:03 PM

Quote:
 Originally Posted by gp_wa (Post 156547) 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?

 gp_wa 09-09-2008 03:16 PM

Quote:
 Originally Posted by chris75 (Post 156549) 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.

 YerDugliness 09-09-2008 05:10 PM

Quote:
 Originally Posted by gp_wa (Post 156547) 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 :jester:???

Dugly :cool:

 220/221 09-09-2008 05:28 PM

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". :thumbup:

Give John Lennon a heads up too.

 gp_wa 09-09-2008 05:39 PM

Quote:
 Originally Posted by 220/221 (Post 156596) 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?

 gp_wa 09-09-2008 06:06 PM

Quote:
 Originally Posted by YerDugliness (Post 156591) I suppose it would depend on the vertical rebound index of the flux capacitor, wouldn't it :jester:???
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.

 Mightyidi 09-09-2008 07:01 PM

Use awg #6 fused at 60 amps

 220/221 09-09-2008 07:04 PM

Quote:
 Do the math on which number? 52 or 60?

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

 Speedy Petey 09-09-2008 07:18 PM

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.

 gp_wa 09-09-2008 08:18 PM

Quote:
 Originally Posted by 220/221 (Post 156631) 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...

 gp_wa 09-09-2008 08:21 PM

Quote:
 Originally Posted by Speedy Petey (Post 156643) 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.

 Speedy Petey 09-09-2008 08:30 PM

In your case, 52MCA & 60 Max OCPD, the answer is still 60A and #6.

 gp_wa 09-09-2008 08:32 PM

Quote:
 Originally Posted by Speedy Petey (Post 156683) 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?

 Stubbie 09-09-2008 08:40 PM

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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