{"id":49493,"date":"2025-12-07T15:30:20","date_gmt":"2025-12-07T12:30:20","guid":{"rendered":"https:\/\/yilkomer.com\/faz-toprak-ve-faz-faz-arasi-gerilim-seviyesi-hesabi\/"},"modified":"2026-08-25T13:10:47","modified_gmt":"2026-08-25T10:10:47","slug":"phase-to-ground-and-phase-to-phase-voltage-level-calculation","status":"publish","type":"post","link":"https:\/\/yilkomer.com\/en\/phase-to-ground-and-phase-to-phase-voltage-level-calculation\/","title":{"rendered":"Phase-to-Ground and Phase-to-Phase Voltage Level Calculation"},"content":{"rendered":"
\n

Phase\u2013Phase Voltage and SPD Selection | Square Root of 3 (\u221a3) Rule<\/h2>\n
Summary:<\/strong> In electrical installations, surge protective device (SPD) selection is not made solely by looking at the panel voltage.
\nSelections made without considering phase\u2013phase and phase\u2013ground voltage values, the square root of 3 (\u221a3) rule, and the Uc continuous operating voltage level;
\nmay cause the SPD to be exposed to long-term high voltage, leading to burnout and the situation of \u201cthere is protection, but actually there isn\u2019t.\u201d<\/div>\n

YILKOMER does not treat the SPD as a \u201cplug and forget\u201d product,
\nbut as a properly calculated engineering component<\/strong>.
\nIn this article, we explain the square root of 3 (\u221a3) rule, the difference between phase\u2013phase and phase\u2013ground voltage, and the effect of this difference on SPD selection in a practical manner.<\/p>\n

\n

What Are Phase\u2013Phase and Phase\u2013Ground Voltage?<\/h2>\n

In three-phase electrical systems, there are two basic types of voltage.
\nThis difference is not only in terms of measurement,
\nbut is also the main criterion that determines where and at which value the SPD will be used<\/strong>.<\/p>\n\n\n\n\n\n\n
Voltage Type<\/th>\nDescription<\/th>\nCommon Value in T\u00fcrkiye<\/th>\n<\/tr>\n<\/thead>\n
Phase\u2013Ground (L\u2013PE \/ L\u2013N)<\/strong><\/td>\nPotential of a single-phase line relative to ground<\/td>\n230 V<\/td>\n<\/tr>\n
Phase\u2013Phase (L\u2013L)<\/strong><\/td>\nVoltage between two different phases<\/td>\n400 V<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

The Uc continuous operating voltage level<\/strong> written on SPDs
\nrefers to the phase\u2013ground voltage value<\/strong>.
\nPhase\u2013phase voltage is \u221a3 times this value, and there is a 120\u00b0 phase difference between phases.<\/p>\n

\"Y\u0131lkomer<\/p>\n

Note:<\/strong> Selecting an SPD by looking only at the \u201c400 V panel\u201d statement on the installation
\nposes a serious risk because it ignores the reality of phase\u2013ground voltage.<\/div>\n

Square Root of 3 (\u221a3) Formula and Meaning<\/h2>\n

In three-phase systems, phase\u2013phase voltage is \u221a3 times phase\u2013ground voltage:<\/p>\n

Uphase\u2013phase<\/sub> = Uphase\u2013ground<\/sub> \u00d7 \u221a3
\n230 V \u00d7 \u221a3 \u2248 400 V<\/div>\n

This mathematical fact makes the following principle mandatory in SPD selection:<\/p>\n

    \n
  • SPD selection should be made not according to phase\u2013phase voltage, but according to phase\u2013ground voltage<\/strong>.<\/li>\n
  • The Uc value must be able to safely withstand the phase\u2013ground voltage to which the system is continuously exposed.<\/li>\n<\/ul>\n

    The Most Common Mistake in SPD Selection<\/h2>\n
    Wrong approach:<\/strong> \u201cThe panel is 400 V, so a 400 V SPD should be used.\u201d<\/div>\n

    This approach is technically incorrect. Because:<\/p>\n

      \n
    • The majority of SPDs are connected to the phase\u2013ground line<\/strong>.<\/li>\n
    • Lightning impulses and transient overvoltage impulses are directed to ground.<\/li>\n
    • The SPD should act according to 230 V phase\u2013ground voltage<\/strong>, not 400 V phase\u2013phase voltage.<\/li>\n<\/ul>\n

      How to Select the Correct SPD Voltage Level?<\/h2>\n

      Typical recommended voltage levels for TN and TT systems are as follows:<\/p>\n\n\n\n\n\n\n
      Connection Point<\/th>\nSPD Voltage Level (Uc)<\/th>\n<\/tr>\n<\/thead>\n
      L \u2192 PE<\/td>\n275 V<\/td>\n<\/tr>\n
      N \u2192 PE<\/td>\nSpecial N-PE SPD<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

      Using an SPD with a 400 V Uc value may cause protection to activate later<\/strong> and equipment
      \nto be exposed to surges for a longer time.<\/p>\n

      Conclusion:<\/strong> The wrong SPD gives the impression that \u201cthere is surge protection\u201d in the installation, but in reality it does not provide effective protection.<\/div>\n

      Technical Risks of Incorrect SPD Selection<\/h2>\n
        \n
      • It detects the surge late and activates protection late.<\/li>\n
      • Invisible damage may occur in sensitive devices.<\/li>\n
      • An SPD exposed to long-term high voltage may eventually self-destruct<\/strong>.<\/li>\n
      • Even if the system appears to be operating, it may actually remain unprotected.<\/li>\n<\/ul>\n

        A sentence that summarizes this situation:<\/p>\n

        \u201cThere is an SPD, but there is no protection.\u201d<\/strong><\/div>\n

        Protection Levels According to SPD Types<\/h2>\n\n\n\n\n\n\n\n\n
        Area<\/th>\nSPD Type<\/th>\n<\/tr>\n<\/thead>\n
        Main distribution panel<\/td>\nType 1 + Type 2<\/td>\n<\/tr>\n
        Floor panel<\/td>\nType 2<\/td>\n<\/tr>\n
        Device front<\/td>\nType 3<\/td>\n<\/tr>\n
        UPS, data systems<\/td>\nCombined SPD<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

        YILKOMER Engineering Approach<\/h2>\n

        For YILKOMER, an SPD is
        \nnot a \u201cplug and forget\u201d product, but an engineering component positioned through risk analysis.<\/strong><\/p>\n

        Main criteria evaluated in projects:<\/p>\n

          \n
        • Grounding impedance<\/li>\n
        • Neutral structure<\/li>\n
        • System type (TN, TT, etc.)<\/li>\n
        • Building class and purpose of use<\/li>\n
        • Lightning risk and regional conditions<\/li>\n
        • Device sensitivity<\/li>\n
        • Energy level and supply scenarios<\/li>\n<\/ul>\n

          For each project, a custom SPD configuration<\/strong> is applied;
          \ninstead of randomly selecting a product from the catalog, the system is first analyzed and then the SPD is determined.<\/p>\n

          You Cannot Select an SPD Without Knowing the Voltage<\/h2>\n

          The correct approach in order:<\/p>\n

            \n
          1. First define<\/strong> the system<\/li>\n
          2. Then correctly calculate<\/strong> the voltage levels<\/li>\n
          3. As the final step, select<\/strong> the SPD<\/li>\n<\/ol>\n

            Every SPD selection made without knowing the square root of 3 (\u221a3) rule creates invisible but serious risks.
            \nYILKOMER manages this process not by guesswork, but by calculation<\/strong>.<\/p>\n

            \n

            Frequently Asked Questions (FAQ)<\/h2>\n

            Why is phase\u2013phase voltage not taken as the basis for an SPD?<\/h3>\n

            Because SPDs discharge the surge to ground and operate according to phase\u2013ground voltage<\/strong>.
            \nThe protection level is defined on the phase\u2013ground line.<\/p>\n

            Is the same SPD sufficient for every panel?<\/h3>\n

            No. For the main distribution panel, floor panel, device front, or data line,
            \ndifferent SPD types and voltage levels<\/strong> must be used.<\/p>\n

            How can an incorrectly selected SPD damage the installation?<\/h3>\n

            An incorrect Uc value may cause late surge detection, invisible damage in sensitive devices,
            \nand, in the long term, the SPD may self-destruct.<\/p>\n

            \n
            \n

            Get a Quote Now<\/h2>\n

            To learn the correct SPD configuration for your electrical system and
            \nto work with the YILKOMER engineering team, contact us.<\/p>\n

              \n
            • Proper SPD selection and sizing<\/li>\n
            • Risk analysis and site inspection<\/li>\n
            • Detailed reporting<\/li>\n
            • Design consultancy<\/li>\n<\/ul>\n


              \n<\/p>\n<\/div>\n<\/div>\n

              <\/p>\n","protected":false},"excerpt":{"rendered":"

              Phase\u2013Phase Voltage and SPD Selection | Square Root of 3 (\u221a3) Rule Summary: In electrical installations, surge protective device (SPD) selection is not made solely by looking at the panel voltage. Selections made without considering phase\u2013phase and phase\u2013ground voltage values, the square root of 3 (\u221a3) rule, and the Uc continuous operating voltage level; may…<\/p>\n","protected":false},"author":1,"featured_media":992871,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[5],"tags":[],"class_list":["post-49493","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-general"],"_links":{"self":[{"href":"https:\/\/yilkomer.com\/en\/wp-json\/wp\/v2\/posts\/49493","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/yilkomer.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/yilkomer.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/yilkomer.com\/en\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/yilkomer.com\/en\/wp-json\/wp\/v2\/comments?post=49493"}],"version-history":[{"count":1,"href":"https:\/\/yilkomer.com\/en\/wp-json\/wp\/v2\/posts\/49493\/revisions"}],"predecessor-version":[{"id":992872,"href":"https:\/\/yilkomer.com\/en\/wp-json\/wp\/v2\/posts\/49493\/revisions\/992872"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/yilkomer.com\/en\/wp-json\/wp\/v2\/media\/992871"}],"wp:attachment":[{"href":"https:\/\/yilkomer.com\/en\/wp-json\/wp\/v2\/media?parent=49493"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/yilkomer.com\/en\/wp-json\/wp\/v2\/categories?post=49493"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/yilkomer.com\/en\/wp-json\/wp\/v2\/tags?post=49493"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}