{"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\/de\/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

Entscheidungsgrundlagen auf einen Blick<\/h2>\n\n\n\n
Bewertungsfeld<\/th>Der K\u00e4ufer muss festlegen<\/th>Anzufordernde Nachweise<\/th><\/tr><\/thead>
Primary current<\/td>Normal, maximum and relevant operating range<\/td>Project load study<\/td><\/tr>
Sekund\u00e4rausgang<\/td>Exact input required by the receiving meter or relay<\/td>Receiving-device manual<\/td><\/tr>
Verh\u00e4ltnis<\/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>
Formschluss<\/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

Erstellen Sie eine Beweisdatei nach dem Exaktmodell<\/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

Stellen Sie sicher, dass jede akzeptierte Angabe denselben bestellbaren Artikel beschreibt. \u00c4hnliche Geh\u00e4use k\u00f6nnen unterschiedliche Schaltungen, Stromversorgungen, Anschl\u00fcsse, Zubeh\u00f6rteile oder Funktionen enthalten. Kombinieren Sie nicht das maximale Familienkontingent einer Variante, ein Schaltbild einer anderen und eine optionale Ausstattung einer dritten. Markieren Sie ungekl\u00e4rte Felder ausdr\u00fccklich, damit sie bei der kaufm\u00e4nnischen Pr\u00fcfung sichtbar bleiben.<\/p>\n\n\n\n

Projektdaten von Produktnachweisen trennen<\/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

Sperren Sie den Angebotsdatensatz, w\u00e4hrend die Angebote verglichen werden. Sollten sich die Topologie, die Quelle, die Last, die Umgebung, das Geh\u00e4use oder die erforderliche Leistung \u00e4ndern, erstellen Sie einen \u00fcberarbeiteten Datensatz und bitten Sie jeden Anbieter, das Angebot erneut zu best\u00e4tigen. Andernfalls k\u00f6nnten scheinbar vergleichbare Angebote unterschiedliche technische Anforderungen erf\u00fcllen.<\/p>\n\n\n\n

H\u00e4ufige Fehler bei der Beschaffung<\/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

Gehen Sie au\u00dferdem nicht davon aus, dass ein Zubeh\u00f6rteil, eine Kommunikationsfunktion, eine Schutzfunktion oder ein koordiniertes Ergebnis enthalten ist, es sei denn, dies geht aus dem Angebot und den Unterlagen zum genauen Modell hervor. Ein Ersatzteil erfordert dieselbe Topologie, Nennleistung, Montageart und \u00dcberpr\u00fcfung der Nachweise wie das urspr\u00fcnglich vorgeschlagene Produkt.<\/p>\n\n\n\n

So vergleichen Sie Angebote von Lieferanten<\/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

Unterlassen Sie den Vergleich, wenn eine entscheidende Anwendungsvorgabe unbekannt ist, das angef\u00fchrte Modell mehrdeutig ist, eine erforderliche Angabe nur durch einen anderen Hersteller oder eine andere Bestellnummer gest\u00fctzt wird oder die Installation au\u00dferhalb der verf\u00fcgbaren Nachweise liegt. Hierbei handelt es sich um technische L\u00fccken und nicht um redaktionelle Details.<\/p>\n\n\n\n

\u00c4nderungen und Ersetzungen kontrollieren<\/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

Wiederholen Sie nur die betroffenen Pr\u00fcfungen, verzichten Sie jedoch nicht auf diese. Vergewissern Sie sich, dass der \u00fcberarbeitete Kandidat weiterhin der festgelegten Anwendung entspricht, dass alle referenzierten Dokumente dazu geh\u00f6ren und dass alle offenen Ausnahmen einem Verantwortlichen zugeordnet sind. Dieser kleine Schritt der \u00c4nderungskontrolle verhindert, dass eine technisch gepr\u00fcfte Auswahl durch ein ungepr\u00fcftes kommerzielles \u00c4quivalent ersetzt wird.<\/p>\n\n\n\n

Entscheidungsablauf<\/h2>\n\n\n\n