how many watts is a 'brown'

junkhound

junkhound

Senior Member
Location
Renton, WA
Occupation
EE, power electronics specialty
new one on me, an internet friend asked me tht question:
My response follows, any others?

ans:
'brown' typically a current indicator, not watts.

as in: How do you know a 3 phase system has high harmonics? ans: "the white wire has turned brown"

Probably not what you were asking, so what was the context you saw the term 'brown' used in?

Resistor code: brown = x10 or value of 1 , black is zero, the other colors are per Roy G Biv, the famous naming specialist, one of Newton's consultants on light.



Or did you see the term in regards to an arc flash event, as in a 'brown pants' event?

then there is the obvious 'brownout', meaning the watts capability of the utility is lacking, so distribution voltage dropped to lessen overall load., but assume you knew that one.
 
as in: How do you know a 3 phase system has high harmonics? ans: "the white wire has turned brown"

Third harmonics add in the neutral. The reference to the white wire turning brown was a humorous attempt to say the neutral was so overloaded it was burning.
 
ptonsparky said:
Or the white wire wasn’t terminated properly.

Brown, Orange, Yellow. BOY
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That's how I learned it in Cleveland for all 480/277, then when I worked in Columbus for a couple of years, come to find out they used orange specifically for the high/wild leg in a delta, while violet was their color of choice for B-phase in a wye.
 
ModbusMan said:
while violet was their color of choice for B-phase in a wye.
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We switched to that color scheme in the Baltimore Washington area for the same reason even though we have very little high leg delta used in this area. I don't remember when that happened though but when it did there was no code rule forcing us to. The change was very fast and I don't know what pushed it into existence.
 
Hv&Lv said:
as in: How do you know a 3 phase system has high harmonics? ans: "the white wire has turned brown"

Third harmonics add in the neutral. The reference to the white wire turning brown was a humorous attempt to say the neutral was so overloaded it was burning.
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If you use gray instead of white it may take longer before this indicator is as visible.
 
junkhound said:
ans:
'brown' typically a current indicator, not watts.
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Surface temperature rise is going to depend on watts dissipated in the wire per unit surface area, along with a factor for how well the wire can dissipate heat in the given installed environment. So suppose a wire of diameter d is carry a current I. The resistance per unit length will vary as 1/d2, so the power dissipated per unit length will vary as I2/d2. The surface area will vary as d, so the power dissipated per unit area will vary as I2/d3.

So it's watts dissipated (edit: per unit length) / diameter. Which means watts is closer to the right answer than current is.

Cheers, Wayne
 
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wwhitney said:
Surface temperature rise is going to depend on watts dissipated in the wire per unit surface area, along with a factor for how well the wire can dissipate heat in the given installed environment. So suppose a wire of diameter d is carry a current I. The resistance per unit length will vary as 1/d2, so the power dissipated per unit length will vary as I2/d2. The surface area will vary as d, so the power dissipated per unit area will vary as I2/d3.

So it's watts dissipated / diameter. Which means watts is closer to the right answer than current is.

Cheers, Wayne
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Current and resistance per foot, both directly determine the Watts per foot of heating power that causes the damage.
 
Carultch said:
Current and resistance per foot, both directly determine the Watts per foot of heating power that causes the damage.
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I think you may be disagreeing with what I wrote, so let me just ask this: let's say I double the conductor diameter and double the current. What will happen to the conductor surface temperature rise?

The "watts per foot" is the same, but the surface area has doubled, so I believe the surface temperature rise will halve. Yes?

Hence I2/d3.

Cheers, Wayne
 
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hornetd said:
We switched to that color scheme in the Baltimore Washington area for the same reason even though we have very little high leg delta used in this area. I don't remember when that happened though but when it did there was no code rule forcing us to.
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No NEC rule on colors used for certain voltages. Just when TWO or more are in the same facility there should be a difference between them and noted at the service, or some such wording.
 
junkhound said:
Resistor code: brown = x10 or value of 1 , black is zero, the other colors are per Roy G Biv, the famous naming specialist, one of Newton's consultants on light.
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Close, no Indigo and Violet, but Violet Gray and White at the end, 8 and 9. Because Violet g.... never mind. I will not write the rest. Ha!
 
wwhitney said:
Hence I2/d3.
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So if for conductor sizes #10 to 1000 kcmil, I take the 90C Cu ampacity as I (in amps), and I take the THWN-2 diameter including insulation (in mm), and compute I2/d3, I get values that vary from 42 to 30 and generally decrease with diameter. While the diameters vary from 4.2 to 33.3 mm, and ampacities vary from 55 to 1055. Obviously the I2/d3 values are not constant, as this model is a bit simplistic, but their (multiplicative) range is much less than the range of either I or d.

Just doing the same computation with the copper diameter gives a range of 408 to 98, not nearly as tight. Which makes sense, as the insulation is playing a role here. I didn't check other insulation types to see if there is one whose standard thickness gives an even tighter range for I2/d3.

Cheers, Wayne

P.S. I threw out #14 and #12 as outliers where the rounding to multiples of 5 would be very significant (55 and 44 are the results), and Chapter 9 didn't have diameters for THWN-2 in sizes above 1000 kcmil.
 
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