{"id":2247,"date":"2026-10-06T06:14:53","date_gmt":"2026-10-06T06:14:53","guid":{"rendered":"http:\/\/ritoks.com\/"},"modified":"2026-10-06T06:14:53","modified_gmt":"2026-10-06T06:14:53","slug":"current-transformer-ratio-selection","status":"publish","type":"post","link":"https:\/\/ritoks.com\/cs\/current-transformer-ratio-selection\/","title":{"rendered":"Current Transformer Ratio Selection: Primary Current and Secondary Output"},"content":{"rendered":"

Specify a current transformer ratio from the primary circuit, secondary measurement input and exact burden and accuracy evidence. A useful buyer review connects the project requirement to one exact orderable product and preserves the evidence used for approval.<\/p>\n\n\n\n

This guide explains the evidence chain for a current-transformer ratio. It does not calculate a project ratio, declare compatibility with a meter or protection relay, or provide secondary wiring or safety instructions.<\/p>\n\n\n\n

P\u0159ehled podklad\u016f pro rozhodnut\u00ed<\/h2>\n\n\n\n
Pole pro recenzi<\/th>Kupuj\u00edc\u00ed mus\u00ed ur\u010dit<\/th>D\u016fkazy, o kter\u00e9 je t\u0159eba po\u017e\u00e1dat<\/th><\/tr><\/thead>
Primary current<\/td>Normal, maximum and relevant operating range<\/td>Project load study<\/td><\/tr>
Sekund\u00e1rn\u00ed v\u00fdstup<\/td>Exact input required by the receiving meter or relay<\/td>Receiving-device manual<\/td><\/tr>
Pom\u011br<\/td>Declared primary-to-secondary relationship<\/td>Exact CT model row<\/td><\/tr>
Measurement performance<\/td>Accuracy and burden under documented conditions<\/td>Manufacturer data and system calculation<\/td><\/tr>
Mechanick\u00e9 ulo\u017een\u00ed<\/td>Window, conductor, mounting and installation constraints<\/td>Drawing and installation review<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
\"Current
The ratio must connect the real primary circuit to the exact receiving-device input.<\/figcaption><\/figure>\n\n\n\n

Start With the Real Primary Current Range<\/h2>\n\n\n\n

The primary side should be described by the expected operating current, maximum normal condition and any meaningful variation that affects measurement. Selecting from conductor ampacity or protective-device frame size alone can place normal readings in an unsuitable part of the measurement range.<\/p>\n\n\n\n

Record how the current estimate was obtained and whether future operating modes change it. The buyer does not need to force a final ratio before the receiving-device input and measurement objective are known.<\/p>\n\n\n\n

Match the Secondary Output to the Receiving Device<\/h2>\n\n\n\n

A current transformer and a meter form an interface. The CT secondary declaration must match the exact input expected by the meter, transducer or relay. A familiar ratio notation is not enough to establish that relationship. Request both documents and review them together.<\/p>\n\n\n\n

Do not use a product family page to infer input compatibility. Neighboring meter variants may accept different sensors or secondary signals. The approval record must name the exact receiving device and its terminal documentation.<\/p>\n\n\n\n

Understand What the Ratio Expresses<\/h2>\n\n\n\n

The ratio states the declared relationship between primary current and secondary output under the product’s defined conditions. It does not by itself establish accuracy across the required operating range, available burden, saturation behavior or suitability for protection. Those are separate evidence fields.<\/p>\n\n\n\n

When quotations offer different ratios, compare the resulting measurement use rather than treating the values as catalog alternatives. Each proposal should explain how the ratio aligns with the project’s primary-current range and receiving input.<\/p>\n\n\n\n

Review Burden and Accuracy as a System<\/h2>\n\n\n\n

The connected input, lead path and terminals contribute to the secondary circuit seen by the transformer. The responsible engineer should calculate and verify that complete circuit against the exact CT and receiving-device documents. Procurement should preserve the inputs rather than guessing from a headline accuracy class.<\/p>\n\n\n\n

Ask where accuracy is declared, at which conditions and for which order code. Never combine the ratio of one model, burden data from another and dimensions from a third. If the system calculation is missing, mark the proposal incomplete.<\/p>\n\n\n\n

Confirm Frequency, Purpose and Operating Context<\/h2>\n\n\n\n

State whether the measurement supports indication, energy monitoring, control, protection or another purpose. These uses can demand different evidence. Also record the system frequency and waveform context that the manufacturer requires for its declaration.<\/p>\n\n\n\n

This guide deliberately avoids treating a measurement CT as a protection CT or vice versa. The proposed device must be documented for the intended role, and any special behavior must be evaluated by the system designer.<\/p>\n\n\n\n

Verify Window Size and Installation Constraints<\/h2>\n\n\n\n

The primary conductor, bar arrangement, insulation, bending space and access determine whether the CT can be installed. A ratio match does not prove mechanical fit. Request the exact outline drawing and confirm that the window accommodates the real conductor without unsupported modification.<\/p>\n\n\n\n

For retrofit work, a split-core construction may change installation access, but it does not remove the need to review ratio, output, burden, accuracy and environmental conditions. Keep construction choice separate from electrical approval.<\/p>\n\n\n\n

\"Current
Ratio is only one field in a complete CT approval record.<\/figcaption><\/figure>\n\n\n\n

Vytvo\u0159te soubor d\u016fkaz\u016f pro p\u0159esn\u00fd model<\/h2>\n\n\n\n

Create one approval record for the proposed Current Transformer order code. Put each project requirement beside the supplier document that answers it. Preserve the exact datasheet, drawing, table, instruction or selection output used, including its revision or retrieval date. A category page can establish family context, but it cannot prove an exact rating, terminal arrangement or system combination.<\/p>\n\n\n\n

Zkontrolujte, zda ka\u017ed\u00fd schv\u00e1len\u00fd popis odpov\u00edd\u00e1 stejn\u00e9 objedn\u00e1vateln\u00e9 polo\u017ece. Podobn\u00e1 pouzdra mohou obsahovat odli\u0161n\u00e9 obvody, nap\u00e1jec\u00ed zdroje, svorky, p\u0159\u00edslu\u0161enstv\u00ed nebo funkce. Nekombinujte maxim\u00e1ln\u00ed po\u010det kus\u016f z jedn\u00e9 varianty, sch\u00e9ma z jin\u00e9 a volitelnou funkci z t\u0159et\u00ed. Nevypln\u011bn\u00e1 pole v\u00fdslovn\u011b ozna\u010dte, aby z\u016fstala viditeln\u00e1 p\u0159i obchodn\u00ed kontrole.<\/p>\n\n\n\n

Udr\u017eujte vstupy projektu odd\u011blen\u00e9 od d\u016fkaz\u016f o produktu<\/h2>\n\n\n\n

The project team defines the application: source, load, duty, environment, controls, mechanical limits and required functions. The supplier identifies an exact Current Transformer and supports it with exact documents. Neither side should fill a gap by inference from appearance, a shared family name or one matching headline value.<\/p>\n\n\n\n

B\u011bhem porovn\u00e1v\u00e1n\u00ed nab\u00eddek pozastavte platnost z\u00e1znamu o \u017e\u00e1dosti. Dojde-li ke zm\u011bn\u00e1m v topologii, zdroji, zat\u00ed\u017een\u00ed, prost\u0159ed\u00ed, sk\u0159\u00edni nebo po\u017eadovan\u00e9m v\u00fdkonu, vystavte revidovan\u00fd z\u00e1znam a po\u017e\u00e1dejte ka\u017ed\u00e9ho dodavatele o op\u011btovn\u00e9 potvrzen\u00ed vybran\u00e9ho produktu. V opa\u010dn\u00e9m p\u0159\u00edpad\u011b by se mohlo st\u00e1t, \u017ee zd\u00e1nliv\u011b srovnateln\u00e9 nab\u00eddky budou odpov\u00eddat odli\u0161n\u00fdm technick\u00fdm po\u017eadavk\u016fm.<\/p>\n\n\n\n

\u010cast\u00e9 chyby p\u0159i zad\u00e1v\u00e1n\u00ed ve\u0159ejn\u00fdch zak\u00e1zek<\/h2>\n\n\n\n

Avoid selecting a Current Transformer from one headline value while the application context remains incomplete. Do not use a circuit, curve, terminal drawing or performance claim from a neighboring model. A product photograph and a family page can support discovery, but neither is exact technical evidence.<\/p>\n\n\n\n

Tak\u00e9 se vyhn\u011bte p\u0159edpokladu, \u017ee je sou\u010d\u00e1st\u00ed dod\u00e1vky p\u0159\u00edslu\u0161enstv\u00ed, komunika\u010dn\u00ed funkce, ochrann\u00e1 funkce nebo koordinovan\u00fd v\u00fdsledek, pokud to nen\u00ed uvedeno v nab\u00eddce a v dokumentaci k p\u0159esn\u00e9mu modelu. N\u00e1hradn\u00ed d\u00edl mus\u00ed spl\u0148ovat stejn\u00e9 po\u017eadavky na topologii, jmenovit\u00e9 hodnoty, zp\u016fsob mont\u00e1\u017ee a posouzen\u00ed d\u016fkaz\u016f jako p\u016fvodn\u00ed kandid\u00e1t.<\/p>\n\n\n\n

Jak porovnat nab\u00eddky dodavatel\u016f<\/h2>\n\n\n\n

Normalize every Current Transformer offer to the same application record. Keep document revisions, stated conditions, included accessories and open questions beside each value. This makes differences in delivered scope visible and prevents a lower-cost but narrower offer from appearing equivalent to a complete solution.<\/p>\n\n\n\n

P\u0159esta\u0148te s porovn\u00e1v\u00e1n\u00edm, pokud nen\u00ed zn\u00e1m\u00fd kl\u00ed\u010dov\u00fd vstupn\u00ed \u00fadaj aplikace, pokud je uveden\u00fd model nejednozna\u010dn\u00fd, pokud je po\u017eadovan\u00e1 specifikace podlo\u017eena pouze \u00fadajem jin\u00e9ho v\u00fdrobce nebo objednac\u00edm k\u00f3dem, nebo pokud instalace nespad\u00e1 do r\u00e1mce dostupn\u00fdch podklad\u016f. Jedn\u00e1 se o technick\u00e9 mezery, nikoli o redak\u010dn\u00ed detaily.<\/p>\n\n\n\n

Kontrola reviz\u00ed a nahrazen\u00ed<\/h2>\n\n\n\n

Give the approved Current Transformer record a revision identifier and keep it with the project file. If the supplier changes the order code, accessory, firmware, drawing or stated operating condition, identify the change before accepting it. A substitution is a new technical proposal even when its price, housing or product-family name looks familiar.<\/p>\n\n\n\n

Zopakujte pouze dot\u010den\u00e9 kontroly, ale nevynech\u00e1vejte je. Ov\u011b\u0159te, zda revidovan\u00fd kandid\u00e1t st\u00e1le odpov\u00edd\u00e1 zmrazen\u00e9 \u017e\u00e1dosti, zda k n\u00ed pat\u0159\u00ed v\u0161echny uveden\u00e9 dokumenty a zda maj\u00ed v\u0161echny otev\u0159en\u00e9 v\u00fdjimky sv\u00e9ho odpov\u011bdn\u00e9ho pracovn\u00edka. Tento mal\u00fd krok v r\u00e1mci \u0159\u00edzen\u00ed zm\u011bn zabra\u0148uje tomu, aby byl technicky prov\u011b\u0159en\u00fd v\u00fdb\u011br nahrazen neprov\u011b\u0159en\u00fdm komer\u010dn\u00edm ekvivalentem.<\/p>\n\n\n\n

Pracovn\u00ed postup p\u0159i rozhodov\u00e1n\u00ed<\/h2>\n\n\n\n