{"id":4134,"date":"2026-10-27T06:00:00","date_gmt":"2026-10-27T06:00:00","guid":{"rendered":"https:\/\/cnsuton.com\/?p=4134"},"modified":"2026-10-27T06:00:00","modified_gmt":"2026-10-27T06:00:00","slug":"switch-disconnector-ith-vs-ie","status":"publish","type":"post","link":"https:\/\/cnsuton.com\/id\/blog\/switch-disconnector-ith-vs-ie\/","title":{"rendered":"Switch Disconnector Ith vs Ie: Which Current Governs Selection?"},"content":{"rendered":"

When comparing Ith vs Ie for a switch disconnector, use the rated operational current Ie for the actual switching duty and review the thermal characteristic Ith under its declared conditions. Ith is a conventional free-air thermal current reference; it is not independent approval to make or break that current under every load condition. Ie belongs with the operational voltage, utilization category and other manufacturer conditions. A correct purchase therefore checks both characteristics, together with the enclosure and isolation function. Selecting the largest amperage on a catalogue page can miss the very duty the switch must perform.<\/p>\n

Describe the load before choosing a current<\/h2>\n

Start with the circuit function. Is the device required to isolate equipment after another device has interrupted the load, or must it make and break the load itself? Then identify the load type, operating voltage, normal current and expected switching pattern. A resistive circuit, a mixed distribution load and a motor-related duty do not automatically impose the same switching demand. The electrical designer should identify the applicable category rather than allowing a purchasing shorthand to decide it.<\/p>\n

Record whether the load information is a design value, an actual measurement or an estimate. Also identify future expansion that is part of the approved design. Do not increase the chosen rating merely because some load details are missing. Unknown current, voltage or duty should be a documented question. Oversizing a nominal device does not establish an approved switching function, correct conductor connections or coordination with upstream protection.<\/p>\n

What Ith establishes and what it leaves open<\/h2>\n

Ith is associated with the thermal assessment under specified free-air conditions. It helps describe current-carrying capability in that reference context, but the actual installation can differ. An enclosed assembly introduces its own temperature-rise and arrangement questions. Nearby heat sources, conductor routing and the approved connection arrangement can matter to the final selection. A free-air reference value should therefore stay attached to its stated conditions throughout the review.<\/p>\n

Do not use Ith as a substitute for a declared operational rating. A switch may carry a current under one condition while having a different operational duty under another. Equally, the relationship between two current values should not be assumed from another manufacturer's device. Use the exact product data and the assembly designer's verification. Where an enclosed thermal characteristic or a correction is required, request it for the offered arrangement rather than inventing a percentage deduction.<\/p>\n

\"HGL(ETGL)
Reference-based illustration of the actual SUTON HGL(ETGL) series Load disconnector exterior. The image does not independently establish ratings, wiring, certification or a safe operating condition.<\/figcaption><\/figure>\n

What Ie adds to the selection<\/h2>\n

Ie is the rated operational current for the declared conditions. For a switching decision, it must be read with operational voltage and utilization category. Those conditions define the application in which the manufacturer makes the operational declaration. An amperage without them is incomplete evidence. Check the applicable category row, current size and pole configuration, including any stated limits on the isolation or switching function.<\/p>\n

Keep the supporting voltage symbols separate. A large insulation-voltage figure does not raise an operational-current declaration or approve a new duty. The Ue, Ui and Uimp guide<\/a> explains those voltage questions. This article addresses the current-selection decision: which current belongs to the proposed operation, which thermal conditions still need verification, and what evidence the supplier must provide before a purchase is accepted.<\/p>\n

Read HGL current rows without losing their limits<\/h2>\n

The SUTON HGL\/ETGL product page<\/a> includes a conventional heating-current row and separate operational-current rows associated with AC-21B, AC-22B and AC-23B. Their presence supports a structured comparison rather than a one-number selection. The online presentation contains several current sizes and grouped headings, so request a clearly aligned model-specific data sheet where a particular column is uncertain.<\/p>\n

The page also describes the family as intended for infrequent switching and isolation, and states that models rated 1000 A and above are suitable for electrical isolation only. Preserve that restriction. A value in a current table must not override an explicit function limit in the product declaration. Ask SUTON to confirm the exact configuration, permitted duty and applicable supporting documents instead of interpreting a family table as blanket load-switching approval.<\/p>\n

The exterior photograph cannot prove a current rating. It helps identify the product family and physical form only. Nameplate information, the exact ordering code and the approved technical documents must agree with the delivered unit. Where any of these conflict, resolve the discrepancy before energization through the responsible engineer and supplier. Do not assume that a visually similar switch has the same thermal or operational declaration.<\/p>\n

Compare current characteristics in a single review sheet<\/h2>\n
\n\n\n\n\n\n\n\n\n\n\n
Characteristic<\/th>\nEvidence needed<\/th>\nIncorrect shortcut<\/th>\n<\/tr>\n<\/thead>\n
Ith<\/td>\nExact thermal reference conditions<\/td>\nTreating it as universal load-breaking current<\/td>\n<\/tr>\n
Ie<\/td>\nCurrent with voltage and utilization category<\/td>\nSelecting from amperes alone<\/td>\n<\/tr>\n
Enclosed installation<\/td>\nApplicable manufacturer and assembly evidence<\/td>\nAssuming free-air conditions inside a cabinet<\/td>\n<\/tr>\n
Function<\/td>\nExact switching or isolation declaration<\/td>\nOverriding restrictions with a larger frame<\/td>\n<\/tr>\n
Fault conditions<\/td>\nWithstand or protective combination evidence<\/td>\nTreating normal current as fault protection<\/td>\n<\/tr>\n
Delivered identity<\/td>\nModel code, nameplate and approved documents<\/td>\nAccepting visual similarity as equivalence<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

The table is a qualitative review aid based on the product's separate current declarations and the IEC 60947-3 product scope<\/a>. It intentionally supplies no universal reduction factor or pass current. Complete the evidence fields using the exact offered configuration. If the category or enclosure information remains open, the selection remains open even when the nominal amperage seems generous.<\/p>\n

Example: the larger thermal value does not settle the choice<\/h2>\n

Consider a hypothetical enquiry for a switch carrying a stated design load and occasionally interrupting it during normal operation. The supplier provides a high thermal-current reference but no operational current for the required voltage and category. That evidence is incomplete. The correct next step is to request the missing operational declaration, not to assume that the thermal figure is a safe switching limit or choose an arbitrary margin below it.<\/p>\n

If a second offer supplies a suitable operational declaration, the enclosure and assembly questions still remain. A complete selection has to satisfy all applicable conditions together. Conversely, when the required function is isolation after another device interrupts the current, the exact isolation declaration and system arrangement must be checked. That does not turn an isolating device into a load-breaking switch. The utilization-category guide<\/a> supports the duty discussion without replacing model-level approval.<\/p>\n

Enclosure temperature is an assembly question<\/h2>\n

The temperature surrounding the installed device can differ from room temperature. Internal heat sources, ventilation arrangements and the conductor system influence the assembly's thermal conditions. Record the intended installation and maximum expected conditions in the enquiry. Then ask for the applicable manufacturer's instructions and the assembly builder's verification. Do not import a correction factor from a circuit breaker or another disconnector family simply because both are rated in amperes.<\/p>\n

Likewise, a bigger enclosure or a fan is not an automatic engineering solution. Changes to ventilation can affect ingress protection, contamination and maintenance requirements. The responsible designer must evaluate the complete arrangement. Follow HSE guidance on electrical equipment<\/a> for competent planning and maintenance, while obtaining product-specific limits from the supplier. This guide provides a selection framework, not a procedure for testing a live panel's thermal limits.<\/p>\n

\"HGL(ETGL)
Reference-based illustration of the actual SUTON HGL(ETGL) series Load disconnector exterior. The image does not independently establish ratings, wiring, certification or a safe operating condition.<\/figcaption><\/figure>\n

Do not confuse current carrying with fault protection<\/h2>\n

Ith and Ie do not by themselves establish short-circuit protection or coordination. A disconnector's thermal and operational current characteristics are distinct from the protective functions provided elsewhere in the circuit. The design must also address prospective fault conditions, the relevant withstand or conditional rating and the specified protective combination. These checks belong to the complete design and should not be replaced by selecting a larger current frame.<\/p>\n

For that separate question, use the Icw and conditional short-circuit rating guide<\/a>. Keep its evidence alongside the current-selection sheet without combining unlike quantities. Amperes of normal operational current, a declared short-time withstand condition and a conditional fault rating answer different questions. Each should retain its own units, conditions and approved configuration in the purchase record.<\/p>\n

Build a clear supplier enquiry<\/h2>\n

Provide the system voltage, frequency, load description, design current, operating pattern, installation conditions and required pole arrangement. Ask for the exact Ie declaration at that voltage and category, the applicable thermal characteristics and any enclosure conditions. Include the intended conductor arrangement and approved operating accessories. Request explicit confirmation where the device is used only for isolation or where a family description restricts loaded switching.<\/p>\n

The final acceptance record should connect the selected model code to the approved documents and delivered nameplate. Record any exceptions and keep substitutions subject to the same checks. A replacement with a larger headline current is not automatically equivalent if the category, installation or isolation function changes. For the wider purchase sequence, return to the isolator switch guide<\/a> and keep the current decision as a traceable part of the complete selection.<\/p>\n

Frequently asked questions<\/h2>\n

Should I select a load switch using Ith or Ie?<\/h3>\n

Use Ie for the required operational duty at the stated voltage and utilization category, while also verifying the relevant thermal and installation conditions. Ith alone does not approve making and breaking the load. Both values require the exact manufacturer's definitions and supporting documents.<\/p>\n

Can I apply a fixed percentage to Ith to estimate Ie?<\/h3>\n

No universal conversion is established here. The relationship depends on the product and declared duty. Obtain the actual operational rating rather than making a percentage assumption. A numerical margin cannot replace missing voltage, category or configuration evidence.<\/p>\n

Does a suitable Ie mean the enclosed panel is approved?<\/h3>\n

No. It is a device-selection input. The enclosure, conductors, ambient conditions and complete assembly still require their applicable verification. Keep the manufacturer's device declaration and the assembly designer's evidence together before accepting the installation.<\/p>\n

Educational video<\/h2>\n

Ohms Law Explained – The basics circuit theory by The Engineering Mindset. This independent educational explanation introduces the current, voltage and resistance quantities used when reviewing electrical loads. It does not define a SUTON operational current or replace the exact product declaration.<\/p>\n