Hi all,
Does anybody know where I can find standards for DC cabling for -48v systems?
I'm looking for general best common practices, cable colouring etc.
Thanks,
[Digging up an older post; I let a couple of thousand NANOG posts pile up in my NANOG folder]
Does anybody know where I can find standards for DC cabling for -48v systems?
Book Resource that anyone dealing with telecom DC power systems should have on their shelf:
'DC Power System Design for Telecommunications" by Whitham D. Reeve, published by Wiley, ISBN (print) 97680471681618 and is available in the Wiley online library.
It is not an inexpensive book, but is written from the point of view of someone with 30 years of practical 'in-the-CO' experience.
The various standards for DC distribution are referenced in this volume. If you have access to the Telcordia standards, the relevant standard is referenced in this volume (I left my copy at home, so can't quote the Telcordia standard right now).
Saying all that, the NEC does have covering articles, and a good rule of thumb is to use black or red (or other normal AC 'HOT' color like blue, brown, orange, or yellow) for the ungrounded conductor, white or gray for the grounded conductor, and green, yellow with a green stripe, or bare for the grounding conductor (using the definitions in the NEC for those conductors).
(In an AC circuit the grounded conductor is commonly referred to as the 'neutral' for center-tapped or wye systems, but grounded phase three-phase systems (corner-grounded) are known that have no neutral.)
In the typical 'protect the outside plant's lead sheathed buried cable' -48VDC system, the battery/rectifier positive is the grounded conductor and should be white or gray per NEC, with the negative ungrounded conductor being black, red, blue, or other approved NEC ungrounded conductor color (basically anything except an approved color for the grounded or grounding conductors) or using other site-specific and posted identifiers per the relevant NEC article(s). I'm citing the 2008 edition of the NEC here, even though the 2011 edition is out, simply because I don't have a 2011 edition handy, and I do have a 2008 edition....and article numbers have been known to change between editions....
You can find the requirements for identifying conductors in NEC (2008) articles 250.119 (grounding conductors), 200.6 (grounded conductors), 210.5(C) (branch circuit ungrounded conductors), and 215.12 (feeder ungrounded conductors). Examples of the colors are found in the Handbook version's exhibit 200.3, and accompanying commentary around that exhibit. (The handbook version of the NEC is worth the extra expense for the exhibits and commentary alone).
Now, having said all that, I have seen common 'in the rack DC rectifiers with no battery' setups with black and red as negative and positive, respectively. And, as long as neither positive nor negative are grounded, that seems to meet NEC. As soon as you ground one conductor, and get into NEC-covered territory, you need to use white or gray (or other 200.6 approved means with the 200.7 exceptions allowed) for the grounded conductor, regardless of polarity.
Hope that helps, and doesn't overwhelm.
'DC Power System Design for Telecommunications" by Whitham D. Reeve,
published by Wiley, ISBN (print) 97680471681618 and is available in
the Wiley online library.
Disappointingly, that book does *not* appear to be in Safari, unless you've
misremembered the title...
Cheers,
-- jra
It wasn't in Safari when I last checked (last year, right before I canceled my subscription, since I didn't really use Safari like I once had). I looked on the Wiley site for the ISBN and double-checked the title prior to the post.
This book is worth its price, even though it's steep. Here's an Amazon link (wraps):
http://www.amazon.com/Power-System-Design-Telecommunications-Handbook/dp/047168161X/
$80.95 lowest new copy found. I paid more than that for my copy in 2007.
What's interesting here is that this is the third book I've seen on Amazon where the used price is higher than the new; last week I ordered a new paperback copy of 'Pierce's Piano Atlas, 12th Edition' for 30-something dollars, but the used price was like a thousand dollars.... odd. Not that high today, just $118 (versus $37.57 new)... But that's still higher than new (and way OT... sorry).
Disappointingly, that book does *not* appear to be in Safari, unless you've
misremembered the title...
It is on Wiley's online library however:
http://onlinelibrary.wiley.com/book/10.1002/0470045035
Alex
I suspect Tim would be very interested to hear that Wiley thinks that.
And I hate to tell Wiley this, but I ain't got $3k laying around right now
to subscribe to their service, though I'm sure it's very handy if you're,
say, Level(3).
Cheers,
-- jra
Off-topic, but this usually happens when the book has a "new" price listed, but
is in fact unavailable/out-of-print. So it would be $34.95 if there were new copies
to be had....
This is correct. I collect certain old books. For a real shocker, take a look at this slim volume on quantitative analysis and the stock market.
The used copies range from a few hundred to a significant amount, and the collectible ones (including a signed first edition) top out at $2,495.00 (anyone who likes is welcome to purchase that signed first edition and send it to me as a gift).
I really wish they would just reissue the book. I'd buy it. It doesn't even need updating (I'd prefer that it wasn't). It could be a celebration of the 35th year since its publication.
Sometimes a paper book is better (the wiring book is another excellent example).