Announcement

Collapse
No announcement yet.

Question of a Different Stripe

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

    Question of a Different Stripe

    Howdy!

    I am new here; so please be gentle

    I am also a "low voltage guy" who, for a variety of reasons, gets heavily involved in designing the power distribution systems that support our Data Centers and our Communication Closets. As a part of this work, I have yet another "Neutral Marking" question. I have searched the Mike Holt Forum and found numerous articles about "white wires." The problem is, I am not seeing anything that answers my specific question (clarification actually); and, thus far, the threads that come the closest are all closed. This means I cannot pick one of those and chime in with a "what about this?" query.


    The basic scenario is this: We have an area that will be served by three (3) 120 Volt branch circuits. For the purposes intended, there will be three (3) "hot" wires, and three "neutral" (grounded) conductors -- all pulled into a common raceway (conduit). It would be nice if there were a simple way to "match up" each neutral with its associated hot wire. A "colored stripe" would, from a visual point of view, be ideal.


    Looking through the code, I find, "Wires that have their outer covering finished to show a white or gray color but have colored tracer threads in the braid identifying the source of manufacture shall be considered as meeting the provisions of this section..."

    From reading this, it is unclear [to me] whether they are saying that the stripe must not only be "in the braid" but must also be the component that actually *identifies* the source of manufacture; or if the stripe may simply be "co-resident with" the printing that identifies the source of manufacture. To put it another way: May I use as the grounded conductor a white wire, on which the manufacturer's markings are printed in black, that also has a colored (non-green) stripe embedded in the same layer of the covering as said black printing?


    I apologize if this seems like a trivial question or concern. It's just that I have established a good working relationship with our electricians. My Dad used to tell me, "It's often better to keep your mouth shut and be thought a fool, than to open it and remove all doubt."

    In keeping with Dad's advice, I'd just like to be sure my suggestion is not foolish before I make it to the folks with whom I have to work!

    Thanks!!
    -- 101 --

    #2
    You can purchase white conductors with colored stripes. Also if you use a quote in the thread from the NEC kindly give us the section so we can look at the context.

    Looking through the code, I find, "Wires that have their outer covering finished to show a white or gray color but have colored tracer threads in the braid identifying the source of manufacture shall be considered as meeting the provisions of this section..."
    Rob

    Moderator

    All responses based on the 2014 NEC unless otherwise noted

    Comment


      #3
      Welcome to The Forum. The easiest way to keep track of which neutral goes to which hot is, when pulling the wire in the Raceway, alternate black and white spools on the wire stand, or have a top middle bottom setup. Staggering your wire pairs will also help keep track of them.

      As a fellow electrician who also got his start in Communications, I've been able to pull up to two dozen cables at one time without marking them on either end. I simply take a sharpie to the rabbit-pull boxes, or to a piece of masking tape applied to the reals. I keep track of the lead ends by how they are taped and staggered.

      To keep track of them in the panel, I put a small zip tie around the wires before I cut them loose of the spools. and I believe that multiwire Branch circuits (n/a to your install) must be tied together in the panel as of maybe the 2014 NEC.
      Electricians do it until it Hertz!

      Comment


        #4
        Speaking of multiwire Branch circuits, if you have a 3 phase panel, you could just pull one neutral with your three hots and not have to worry about which neutral goes with which hot.
        Electricians do it until it Hertz!

        Comment


          #5
          There is no requirement that you identify the grounded conductors in any special way. Tieing them to the hot wire it goes with at each end works and is a cheap solution.
          Bob

          Comment


            #6
            In a data center, it's likely that the load will have a high harmonic current. The "neutral" conductor in a 3-phase multi-wire branch circuit needs to have √3 as much ampacity as the ungrounded (hot) conductors.
            http://www.ecmweb.com/content/fundamentals-harmonics

            Comment


              #7
              Originally posted by petersonra View Post
              There is no requirement that you identify the grounded conductors in any special way. Tieing them to the hot wire it goes with at each end works and is a cheap solution.
              Gentle correction...200.4(B) requires grouping or marking to clearly show which neutral goes with each circuit in a conduit run such as the OP described. On a big job it would be worthwhile to order grounded conductor with a colored tracer for each phase as it saves a lot of labor. For everyday small work you can just tape them together in groups.

              Comment


                #8
                Originally posted by texie View Post
                Gentle correction...200.4(B) requires grouping or marking to clearly show which neutral goes with each circuit in a conduit run such as the OP described. On a big job it would be worthwhile to order grounded conductor with a colored tracer for each phase as it saves a lot of labor. For everyday small work you can just tape them together in groups.
                He did say to tie them to the hot conductor.
                Rob

                Moderator

                All responses based on the 2014 NEC unless otherwise noted

                Comment


                  #9
                  Originally posted by infinity View Post
                  He did say to tie them to the hot conductor.
                  You may be right, but I was not certain. Just a clarification.

                  Comment


                    #10
                    Originally posted by texie View Post
                    You may be right, but I was not certain. Just a clarification.
                    the code does not require them to be color coded. for just three sets of them it seems like a lot of extra effort to buy 3 rolls of white wire with different tracers on them.
                    Bob

                    Comment


                      #11
                      Originally posted by drcampbell View Post
                      In a data center, it's likely that the load will have a high harmonic current. The "neutral" conductor in a 3-phase multi-wire branch circuit needs to have √3 as much ampacity as the ungrounded (hot) conductors.
                      http://www.ecmweb.com/content/fundamentals-harmonics
                      Interesting article. Is it as relevant today as when it was written in 1999?

                      In a perfectly balanced three-phase system where the load on the neutral is 0, what would be the amperage from the harmonics assuming worst case scenario?
                      Electricians do it until it Hertz!

                      Comment


                        #12
                        Originally posted by JFletcher View Post
                        Interesting article. Is it as relevant today as when it was written in 1999?

                        In a perfectly balanced three-phase system where the load on the neutral is 0, what would be the amperage from the harmonics assuming worst case scenario?
                        Worst case scenario would be if the load current was 100% third harmonic (not credible, but you asked for the worst case). In that circumstance the neutral current would be three times the balanced current in each of the hots.

                        Comment


                          #13
                          Originally posted by JFletcher View Post
                          Interesting article. Is it as relevant today as when it was written in 1999? ...
                          It's less relevant, because some manufacturers install power-factor-correcting front ends in their switch-mode power supplies, which eliminate harmonic currents.
                          But how much less relevant, I can't say. The EU has enacted power-factor correction regulations, but the USA has not. Much of the equipment in the USA will include it because so much equipment is designed for a global market, but it's always possible that a manufacturer will take the cheap way out and design a USA-only version.

                          But as an American installer, the question's probably irrelevant. Until the USA enacts power-factor-correction regulations and the old equipment is taken out of service, you have to assume that a data center will have significant third harmonics and upsize the shared "neutral" accordingly. If not, you risk overheated neutrals, open neutrals and neutral-to-ground faults.

                          If poor-power-factor electronic devices are a significant fraction of the building's total load, this problem also exists in the conductors between the transformer and the main panel, and between the main panel and the sub panel(s).

                          The same possibility exists in LED lighting.

                          More than you ever wanted to know: https://www.fairchildsemi.com/applic...N/AN-42047.pdf

                          Comment


                            #14
                            We often refer to a 120/208 multiwire branch circuit (MWBC) as a full boat, 3 hots and a neutral. Any MWBC has to have a common trip circuit breaker. meaning you have to turn off all circuits to work on one.
                            Using 3 hots and 3 neutrals is a better way to go. I buy striped wire from my wholesale house all the time for control wire. While you don't need striped wire, the panel make up will be much faster. Also mentioned is the need to use cable ties on the hots/neutral, you also need to do this in a junction box, again the striped wire will be faster.
                            I would get black/orange stripe, white/black stripe: the orange means a computer circuit
                            Moderator-Washington State
                            Ancora Imparo

                            Comment


                              #15
                              Originally posted by JFletcher View Post
                              Interesting article. Is it as relevant today as when it was written in 1999?

                              In a perfectly balanced three-phase system where the load on the neutral is 0, what would be the amperage from the harmonics assuming worst case scenario?
                              I engineer broadcast and data facilities. I never allow shared neutrals on technical circuits. I also specify 200% neutral oversize for panel feeders unless using an OEM delta/wye PDU, which in most cases have beefed up neutral busses.

                              As noted above power factor correction on newer power supplies has relaxed the risk and with most broadcast systems being digital today, "average" technical center neutral current has no ill effects in signal integrity. But I still stick to 1980s methods just to be safe.

                              Comment

                              Working...
                              X