Auxiliary Contact Block FAQs: 19 Questions Procurement Teams Ask Us Auxiliary contact blocks are small, inexpensive, and easy to overlook — right up until the wrong one is ordered and a signalling circuit doesn't work. Below are the questions we hear most often from procurement and engineering teams sourcing auxiliary contacts for contactors and circuit breakers, grouped by theme so you can jump straight to the section that matters for your order — specification, sourcing, standards, installation, or pricing. Need help specifying or sourcing an auxiliary contact block for your site? Talk to Our Expert Team Quick-Reference Summary Before the detailed Q&A below, here's the short version for anyone comparing options against the clock: Question Short Answer What does it do? Adds NO/NC signalling contacts to a contactor or breaker for status feedback, interlocking or indication Is it brand-specific? Yes — mechanically matched to a contactor/breaker frame size and mounting position Common contact configs 1NO/1NC, 2NO/2NC, 3NO/1NC, 4NO and other combinations depending on the block Governing standard Tested with the parent contactor (IEC 60947-4-1) or breaker (IEC 60947-2) Typical UK lead time Stock for common configurations; short lead time for less common or obsolete references Brands stocked ABB and Allen-Bradley, matched to the installed contactor or breaker range Specification & Compatibility What is an auxiliary contact block used for? It adds extra signalling contacts (normally open and/or normally closed) to a contactor or circuit breaker, used to feed status information — such as "contactor energised" — back to a PLC, indicator lamp, or interlock circuit. Will any auxiliary contact block fit any contactor? No. Auxiliary contact blocks are mechanically specific to a contactor frame size and mounting position (front, side, bottom) from the same manufacturer's range — always match the block to the exact contactor model. What does "1 NO / 1 NC" mean on a datasheet? It describes the contact configuration: how many normally-open and normally-closed contacts the block provides. A "2NC/2NO" block has two of each. How do I choose between ABB and Allen-Bradley auxiliary contact blocks? The choice is largely dictated by which contactor or breaker range is already installed — auxiliary contacts are brand and frame-size specific, so match to your existing equipment rather than choosing a brand independently. What current rating do auxiliary contacts carry? Auxiliary contacts are signalling contacts, not power contacts — typical ratings are in the range of a few amps at control voltage, well below the main contactor's load current rating. Wiring them into a load circuit by mistake, rather than a control or signalling circuit, will damage the contact and can create a safety issue, so always confirm the rated current on the datasheet before connecting anything beyond a PLC input, relay coil or indicator lamp. Can I fit more than one auxiliary contact block on the same contactor? Many contactor ranges allow a front-mounted block plus a side or bottom-mounted block simultaneously, giving extra contact combinations where a single block doesn't provide enough NO/NC points for the interlocking or signalling scheme required. Check the parent contactor's datasheet for the maximum number of auxiliary positions it supports before specifying more than one. What's the difference between an auxiliary contact block and a miniature circuit breaker (MCB)? They're not interchangeable and don't compete for the same job — an MCB is the primary overcurrent protection device switching the actual load current, while an auxiliary contact block is a low-current signalling accessory fitted to a contactor or breaker purely to report status back to a control system. Confusing the two on a parts list usually means someone has misread a datasheet rather than a genuine specification choice. What's the difference between a snap-on and a screw-fit auxiliary contact block? Snap-on blocks clip directly onto a designated slot on the contactor or breaker body with no tools required, and are the more common format on modern ABB and Allen-Bradley ranges. Screw-fit or bolt-on variants are more common on older or larger frame sizes, and typically need a screwdriver and a touch more care to avoid cross-threading the fixing. Both are equally reliable when fitted correctly — the choice is dictated by the parent device, not by preference. Sourcing & Lead Times Once the correct contact configuration is confirmed, the next question from most procurement teams is availability — here's what to expect on stock, lead time and bulk ordering. Where can I buy auxiliary contact blocks in the UK? ZF Corporation stocks ABB auxiliary contact blocks for UK delivery, and can source Allen-Bradley and other brand equivalents on request. What is the typical lead time for an auxiliary contact block in the UK? Common configurations are typically available from stock; less common mou…