Recent testing question

mrtweaver

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May 2007
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Recently I took a test for a tech position. There is one question to which I feel I could have answered better. I am taking a poll here to see how others would have answer it.

THe question was: Design a 24Vdc power supply.

My answer: I am sorry there is not enough information here to properly design a power supply. I require the following information to design it properly:

a. The incomming supply voltage
b. The load type and rating
c. How clean/filtered the dc's requirments are

Then at the bottom of my answer i drew a simple power supply with step down transformer, full wave rectifier and filter caps with the notation that the above information would make the drawing and specification of part more accurate.
---------------------------

I think there was a better way to answer this that would have been shorter but just dont know. Maybe I put to much thought behind the question and answer. SO how would the rest of the skill professionals answer such a question??

Thanks and have a great day.
 
question

One question I was asked during an interview was:
If you see a yellow wire in an enclosure, what would that tell you?
I had to ask what the answer was, had never heard of it. I am a Master electrician, with fifteen years experience, but it was new to me.
Any takers on this one?
 
The yellow wire should indicate that the power source for that wire is from another source separate from the panel. In other words turning off the disconnect on that panel will not remove the existing voltage on the yellow wire.
 
The yellow wire should indicate that the power source for that wire is from another source separate from the panel. In other words turning off the disconnect on that panel will not remove the existing voltage on the yellow wire.

Shouldn't this be orange wirring? Yellow or green is forbidden to use i think scince this can be confussed with Earth Yellow/green
 
The yellow wire should indicate that the power source for that wire is from another source separate from the panel. In other words turning off the disconnect on that panel will not remove the existing voltage on the yellow wire.
That is what the person testing me said. I assume this is fairly common, then. I would like to hear how many had heard of it, just to see it was only me in the dark.
Thanks
 
That is what the person testing me said. I assume this is fairly common, then. I would like to hear how many had heard of it, just to see it was only me in the dark.
Thanks

Yep, Yellow indicates remotely powered or intra-panel interlock/interconnect. Uniformly accepted, I believe. To the other OP, never heard of an orange wire for this purpose. Always, Yellow, Yellow/White or Yellow/Black, in my experience.
 
I think you answered it well.

I might add:
d) If standard off-the-shelf equipment is available, buy it instead.

That's funny. That is the first thing that came to my mind and probably how I would have answered it period. In 1/10th the time you design one, I could buy one from Siemens, Sola or AB and have the problem solved.
 
Agree with yellow wire. Very common to denote that voltage on wire would not be isolated by turning off the disconnect in the panel. I usually bring these to a seperate terminal strip at the bottom of the cabinet and label which panel feeds them.
 
It might be common but the code stipulates orange.

NFPA 79-30 13.2.4.1 The Color ORANGE shall be used to identify ungrounded conductors that remain energized when the main supply circuit desconnecting means is in the off position. This color identification shall be strictly reserved for this application.
 
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Some of my automotive customers have begun to change their interlocking wire colors from yellow to orange. But, regardless of color, I always put a lamacoid tag on the panel door indicating that the selected color wire is remotely powered.
 
It might be common but the code stipulates orange.

NFPA 79-30 13.2.4.1 The Color ORANGE shall be used to identify ungrounded conductors that remain energized when the main supply circuit desconnecting means is in the off position. This color identification shall be strictly reserved for this application.

What year is your code? I have all the NFPA codes upto 2002 (and the proposed 2005 changes) via our subscription service. Here is a passage from NFPA 79 2002 edition Chapter 14:

14.2.4 Identification by Color for Other Conductors.
14.2.4.1* Ungrounded circuit conductors that remain energized when the supply disconnecting means is in the off position shall be consistently applied as either ORANGE or YELLOW. These color identifications shall be strictly reserved for this application only.
Exception No. 1: Internal wiring on individual devices purchased completely wired.
Exception No. 2: Where the insulation used is not available in the colors required (e.g., high temperature insulation, chemically resistant insulation).

Now the discussion begins on if you should actually be following this section (or many other sections of the NFPA). Many states are way way behind in adopting the national concensus standards. I personally like them and follow them as much as I can. It pretty hard keeping up to date on all the codes if your company won't send you to the classes or buy the updated versions (the reason I only have 2002).

So by my interpretation of the NFPA code, yellow is acceptable for the wire color.
 
OK, very interesting.

Up until 2002, the color yellow was allowed (along with orange). Starting in the 2005, the color yellow was omitted.

There are several proposals to reinstate the color yellow for this section.

Even more interesting is that I can't find the "free" version you talk about. Everything wants me to add my membership ID. Another big problem with all this codes is why keep them secret unless you pay a fee. I understand that there are some costs in doing this business, but for the average person or small business, these cost rival the AB software costs.

I'm not sure why the NFPA board would do something stupid like this. To allow yellow as a color for years then all of a sudden to change it knowing the installation base of that section would cause confusion for generations of industrial technicians and engineers is a bad move. This sounds like a good reason not to adopt some of the national consensus standards.
 
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