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Author Topic: Seemingly simple rating question  (Read 9786 times)

Tim McCulloch

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Re: Seemingly simple rating question
« Reply #10 on: July 29, 2014, 12:30:02 PM »

Are you sure? See the Cerrowire ampacity chart below.

They want to peddle copper.

I see TJ beat me to the screen capture...  Yes, I'm really sure.
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Mike Sokol

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Re: Seemingly simple rating question
« Reply #11 on: July 29, 2014, 12:39:35 PM »

Yeah, I see that according to code the breaker has to be derated for multi-conductor wire, and the chart I posted was for single conductors. However, I seem to remember a Hubble applications chart showing #6 to be the largest wire size their CS6364 is rated to accept. Or am I mistaken? 

Going bigger than #6 like a lot of copper for a 50 amp service...  ;D

Tim McCulloch

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Re: Seemingly simple rating question
« Reply #12 on: July 29, 2014, 12:47:26 PM »

Yeah, I see that according to code the breaker has to be derated for multi-conductor wire, and the chart I posted was for single conductors. However, I seem to remember a Hubble applications chart showing #6 to be the largest wire size their CS6364 is rated to accept. Or am I mistaken? 

Going bigger than #6 like a lot of copper for a 50 amp service...  ;D

The greater ampacity shown in the manufacturer's chart is based on maximum conductor temperature.  If someone is comfortable with 75C, load it up, kids.  I'll stick with bigger copper and temperatures that won't burn my hand.
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TJ (Tom) Cornish

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Re: Seemingly simple rating question
« Reply #13 on: July 29, 2014, 12:48:04 PM »

Yeah, I see that according to code the breaker has to be derated for multi-conductor wire, and the chart I posted was for single conductors. However, I seem to remember a Hubble applications chart showing #6 to be the largest wire size their CS6364 is rated to accept. Or am I mistaken? 

Going bigger than #6 like a lot of copper for a 50 amp service...  ;D
#6 is commonly used, but illegal.  Your chart was for different types of cable - THHN and NM.  SOOW has a lot of rubber - an effective insulator of both heat and electricity.
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Jay Barracato

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Re: Seemingly simple rating question
« Reply #14 on: July 29, 2014, 12:50:38 PM »

The greater ampacity shown in the manufacturer's chart is based on maximum conductor temperature.  If someone is comfortable with 75C, load it up, kids.  I'll stick with bigger copper and temperatures that won't burn my hand.

i remember pulling into a festival to see 50 feet of extra feeder cable in a big coil at the back of the stage smoking.

"Hi, I am Jay the band tech for [fill in]. It looks like your main power feed is about to catch on fire. Nice to meet you..."
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Jay Barracato

Ray Aberle

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Re: Seemingly simple rating question
« Reply #15 on: July 29, 2014, 12:54:01 PM »

i remember pulling into a festival to see 50 feet of extra feeder cable in a big coil at the back of the stage smoking.

"Hi, I am Jay the band tech for [fill in]. It looks like your main power feed is about to catch on fire. Nice to meet you..."
Jay, thanks for the laugh! I mean, that would suck for them to suddenly have their electrics go out, but the story was great.

-Ray
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Frank Koenig

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Re: Seemingly simple rating question
« Reply #16 on: July 29, 2014, 01:16:49 PM »

Just to add a little to the noise, NEC 400.5 (B) [second paragraph] says that the neutral (in a balanced system) doesn't count as a current carrying conductor when figuring the ampacity of a portable cord. This makes physical sense, harmonic currents notwithstanding. -F
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Tim McCulloch

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Re: Seemingly simple rating question
« Reply #17 on: July 29, 2014, 01:27:51 PM »

Just to add a little to the noise, NEC 400.5 (B) [second paragraph] says that the neutral (in a balanced system) doesn't count as a current carrying conductor when figuring the ampacity of a portable cord. This makes physical sense, harmonic currents notwithstanding. -F

But special occupancies in NEC 500 & 600 negate, change, or ignore parts of 300 and 400.  And just when you think you understand it.... oy.  Lots of reading involved to eventually discover that you probably have a better grip on *your* occupancy than the guy or gal inspecting it, but that they have the authority and we have none.

"Things are seldom what they seem / skim milk masquerades as cream."  - Gilbert & Sullivan
« Last Edit: July 29, 2014, 01:29:57 PM by Tim McCulloch »
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Mike Sokol

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Re: Seemingly simple rating question
« Reply #18 on: July 29, 2014, 01:40:49 PM »

Just to add a little to the noise, NEC 400.5 (B) [second paragraph] says that the neutral (in a balanced system) doesn't count as a current carrying conductor when figuring the ampacity of a portable cord. This makes physical sense, harmonic currents notwithstanding. -F

Hmmm... So is derating not required because there's only "2" current carrying conductors in this sort of cable? I guess if it was mostly 240-volt loads (heaters) then you could get around it with the less than 50% load diversity factor. But how does one calculate that for 120-volt amplifiers? Stereo loads, perhaps?  :o

Tim McCulloch

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Re: Seemingly simple rating question
« Reply #19 on: July 29, 2014, 01:52:18 PM »

Hmmm... So is derating not required because there's only "2" current carrying conductors in this sort of cable? I guess if it was mostly 240-volt loads (heaters) then you could get around it with the less than 50% load diversity factor. But how does one calculate that for 120-volt amplifiers? Stereo loads, perhaps?  :o

NEC 520 has different de-rating requirements from 400.5, and it depends on the type of load, proximity to heat-producing fixtures, and a couple other things.  This is where the Code gets messy and can lead to confrontations with the Authority Having Jurisdiction.
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"If you're passing on your way, from Palm Springs to L.A., Give a wave to good ol' Dave, Say hello to progress and goodbye to the Moonlight Motor Inn." - Steve Spurgin, Moonlight Motor Inn

ProSoundWeb Community

Re: Seemingly simple rating question
« Reply #19 on: July 29, 2014, 01:52:18 PM »


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