{"id":43,"date":"2016-04-07T13:47:52","date_gmt":"2016-04-07T05:47:52","guid":{"rendered":"http:\/\/www.cnbonet.com\/blog\/?p=43"},"modified":"2016-12-23T11:59:02","modified_gmt":"2016-12-23T03:59:02","slug":"43-2","status":"publish","type":"post","link":"https:\/\/www.cnbonet.com\/blog\/43-2\/","title":{"rendered":"4 Practical Approaches To Minimize Voltage Drop Problems"},"content":{"rendered":"
\"wire
4 Practical Approaches To Minimize Voltage Drop Problems (photo credit: lhcb-elec.web.cern.ch)<\/figcaption><\/figure>\n
<\/div>\n

<\/a>What NEC states for max. voltage drop?<\/h2>\n

The NEC states in an Informational Note that a maximum voltage drop of 3% for branch circuit conductors<\/strong>, and 5% for feeder and branch circuit conductors together<\/strong>, will provide reasonable efficiency of operation for general use circuits.<\/p>\n

For sensitive electronic loads, circuits should be designed for a maximum of 1.5% voltage drop for branch circuits at full load, and 2.5% voltage drop for feeder and branch circuits combined at full load.<\/p>\n

\n

Four practical approaches can be used to minimize voltage drop problems:<\/strong><\/p>\n

    \n
  1. Increasing the number or size of conductors<\/li>\n
  2. Reducing the load current on the circuit<\/li>\n
  3. Decreasing conductor length, and<\/li>\n
  4. Decreasing conductor temperature<\/li>\n<\/ol>\n<\/div>\n
    <\/div>\n

    <\/a>1. Increase the Number or Size of Conductors<\/h3>\n

    Parallel or oversized conductors<\/strong> have\u00a0lower resistance per unit length than the Code-required minimum-sized conductors, reducing voltage drop and increasing energy efficiency with lower losses than using the Code-required\u00a0minimum-sized conductor.<\/p>\n

    In data centers and other sensitive installations, it is not uncommon to\u00a0find conductor gauges for phase, neutral, and ground exceeding Code minimums, and a separate\u00a0branch circuit installed for each large or sensitive load.<\/div>\n

    To limit neutral-to-ground voltage drop,\u00a0install a separate, full-sized neutral conductor for each phase conductor in single-phase branch circuit applications.<\/p>\n

    For three-phase feeder circuits, do not downsize the grounded conductor or\u00a0neutral<\/strong>. For three-phase circuits where significant non-linear loads are anticipated, it is\u00a0recommended to install grounded or neutral conductors with at least double the ampacity of each\u00a0phase conductor.<\/p><\/blockquote>\n

     <\/p>\n

    <\/a>2. Decrease Load Current<\/h3>\n

    Limiting the amount of equipment that can be connected to a\u00a0single circuit will limit the load current on the circuit. Limit the number of receptacles on each\u00a0branch circuit to three to six<\/strong>.<\/p>\n

    Install individual branch circuits to sensitive electronic loads<\/strong>or\u00a0loads with a high inrush current.<\/div>\n

    For residential applications, install outdoor receptacles not to\u00a0exceed 50 linear feet between receptacles, with a minimum of one outdoor receptacle on each\u00a0side of the house, and with individual branch circuits with a minimum of 12 AWG to each\u00a0receptacle<\/strong>.<\/p>\n

     <\/p>\n

    <\/a>3. Decrease Conductor Length<\/h3>\n

    Decreasing conductor length<\/strong> reduces the resistance of the\u00a0conductor, which reduces voltage drop. Circuit lengths are usually fixed, but some control can be\u00a0exercised at the design stage if panels or subpanels are located as close as possible to the loads,\u00a0especially for sensitive electronic equipment.<\/p>\n

     <\/p>\n

    <\/a>4. Adjust Conductor Temperature<\/h3>\n

    The conductor temperature is in turn dependent on each\u00a0of the three factors above, since more heavily loaded circuits will run hotter.<\/p>\n

    \n

    Conductor\u00a0temperature is a major factor in conductor resistance, and therefore in voltage drop. The\u00a0temperature coefficient of electrical resistance for copper, \u03b1, is 0.00323\/\u00b0C<\/strong>, or a resistance\u00a0change of about 0.3%<\/strong> for each \u00b0C of temperature change. The effect of temperature can be\u00a0determined by the following equation:R2<\/sub> = R1<\/sub> [1 + \u03b1 \u00b7 (T2<\/sub> \u2013 T1<\/sub>)]<\/span><\/p>\n

    Where R1<\/sub><\/strong> is the resistance (\u03a9) at temperature T1<\/sub><\/strong> and R2<\/strong> is the resistance at temperature T2<\/sub><\/strong>.<\/p>\n<\/div>\n

    Temperature T1<\/sub><\/strong> is often referenced at 75\u00b0C<\/strong>. As noted, voltage drop is a particular concern at high conductor loadings, where conductor temperatures will also be high.<\/p>\n

     <\/p>\n

    Examples \/\/<\/h2>\n

    The interactions between conductor sizes, load currents, and conductor lengths\u00a0at various supply voltages are shown in Table 1 below.<\/p>\n

    The combinations of various load currents<\/strong> \u2013 from 8 to 30 amperes \u2013 andsupply voltages<\/strong> \u2013 from\u00a0120 to 480 volts \u2013 are shown in the left two columns of the table. The next four columns show\u00a0the maximum circuit lengths<\/strong>(one-way) for four different conductor sizes to attain a 3% voltage\u00a0drop<\/strong>.\u00a0The last four columns are maximum lengths for an allowable 1.5% voltage drop<\/strong>.<\/p>\n

    \n

    For example, a 12 ampere load<\/strong> in a 120 volt circuit<\/strong> on a 14 AWG conductor<\/strong> will exceed a 3%\u00a0voltage drop<\/strong> (3.6 volts) if the circuit is longer than 49 feet<\/strong> from source to load.If the conductor\u00a0is upsized to 12 AWG the allowable distance increases significantly to 78 feet each way<\/strong> (an\u00a0increase of 59%). If the load is increased to an allowable maximum of 15 amps for 14 AWG\u00a0conductor, the allowable length is only 39 feet, and moving to a 12 AWG conductor would\u00a0increase this to 62 feet (also an increase in length of 59%).<\/p>\n<\/div>\n

    The 1.5% data values<\/strong> are given for situations when it is necessary to comply with NEC\u00a0647.4(D).<\/p>\n

    Verify the equipment\u2019s actual requirements whenever possible. The much tighter 1.5%\u00a0voltage drop allowance<\/strong> on the right side of Table 1 cuts the allowable lengths to only 1\/2 of\u00a0their values at 3% voltage drop<\/strong>. Conductor upsizing is often mandated for the protection of sensitive electronic equipment. Voltage drop can be minimized if the panel or subpanel can be\u00a0located as close as possible to the point of use.<\/p>\n

    Another measure is to install sufficient circuits to avoid high current levels on any one circuit<\/strong>.\u00a0Where loads can be split onto separate circuits, the reduced load per circuit will enhance quality\u00a0and reliability.<\/div>\n

    Perusal of Table 1 inevitably leads to the conclusionthat voltage drop is too often ignored<\/strong>.<\/p>\n

    For example, the lengths of many branch circuits in 14 AWG wire exceed even the 3% voltage\u00a0drop of 39 feet, not to mention the tighter 1.5% drop of 20 feet. When this happens, the integrity\u00a0of both the wiring and of many loads is put in jeopardy.<\/strong><\/p><\/blockquote>\n

    Table 1 \u2013 Maximum Recommended Lengths of Single-Phase Branch Circuits, as a Function of Load Current, Supply Voltage, and Conductor Size, for Both 3% and 1.5% Voltage Drops.<\/strong><\/p>\n

    \"voltage-drop-maximum-recommended-lengths\"<\/a>
    Maximum Recommended Lengths of Single-Phase Branch Circuits, as a Function of Load Current, Supply Voltage, and Conductor Size, for Both 3% and 1.5% Voltage Drops<\/figcaption><\/figure>\n
    <\/div>\n

    Notes regarding above table \/\/<\/h4>\n
      \n
    • Branch circuit lengths shown in the table are half the calculated distance from the V = IR Ohm\u2019s Law formula<\/strong>, rounded to the\u00a0nearest 1-foot increment. For example, the calculated value for 14 AWG at a load current of 15 amps and a supplied voltage of\u00a0120 volts using the value of 3.07 \u03a9\/1,000 feet for a 3% drop (or 3.6 volts) is 78 feet. Since the conductors must carry the current\u00a0over and back, the allowable one-way distance from source to load is 39 feet.\n
      <\/div>\n<\/li>\n
    • For convenient use of the NEC tables, loads are assumed to be purely resistive, direct-current loads<\/strong>. Alternating current values\u00a0differ only slightly. Harmonics or inductive loads may accentuate voltage drop, and decrease recommended circuit lengths.\n
      <\/div>\n<\/li>\n
    • Calculations are based on resistance values found in NEC Chapter 9, Table 8 for solid, uncoated copper conductors<\/strong>. For 14\u00a0AWG, the resistance is 3.07 \u03a9\/1,000 feet, for 12 AWG it is 1.93 \u03a9\/1,000 feet, for 10 AWG it is 1.21 \u03a9\/1,000 feet, and for 8\u00a0AWG (stranded) it is 0.778 \u03a9\/1,000 feet. Conductor temperatures higher than 75\u00b0C (167\u00b0F) will increase these resistances, and\u00a0vice versa.<\/li>\n<\/ul>\n

      Reference:<\/strong> Recommended Practices for Designing and Installing Copper Building Wire Systems \u2013 Copper Development Association Inc.<\/em><\/p>\n","protected":false},"excerpt":{"rendered":"

      4 Practical Approaches To Minimize Voltage Drop Problems (photo credit: lhcb-elec.web.cern.ch) What NEC states for max. voltage drop? The NEC states in an Informational Note that a maximum voltage drop of 3% for branch circuit conductors, and 5% for feeder and branch circuit conductors together, will provide reasonable efficiency of operation for general use circuits. […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[11],"tags":[14,13],"_links":{"self":[{"href":"https:\/\/www.cnbonet.com\/blog\/wp-json\/wp\/v2\/posts\/43"}],"collection":[{"href":"https:\/\/www.cnbonet.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.cnbonet.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.cnbonet.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.cnbonet.com\/blog\/wp-json\/wp\/v2\/comments?post=43"}],"version-history":[{"count":6,"href":"https:\/\/www.cnbonet.com\/blog\/wp-json\/wp\/v2\/posts\/43\/revisions"}],"predecessor-version":[{"id":138,"href":"https:\/\/www.cnbonet.com\/blog\/wp-json\/wp\/v2\/posts\/43\/revisions\/138"}],"wp:attachment":[{"href":"https:\/\/www.cnbonet.com\/blog\/wp-json\/wp\/v2\/media?parent=43"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.cnbonet.com\/blog\/wp-json\/wp\/v2\/categories?post=43"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.cnbonet.com\/blog\/wp-json\/wp\/v2\/tags?post=43"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}