# Max Zs Values — Zs Values 18th Edition BS 7671 > Calculates and looks up maximum permitted Zs values for electrical safety. (iPhone/iPad app by Pro Certs Software Ltd.) - Source: https://appshunter.io/ios/app/max-zs-values/id498838137 (this page in markdown: same URL + `.md`) - Developer: [Pro Certs Software Ltd](https://appshunter.io/developer/444429696) - Category: Reference, Productivity - Price: $9.99 - Age rating: 4+ - Requires: iOS 11.0 · 15 MB - Languages: American English - Released: 2012-02-12 - Data updated: 2026-08-28 - Monetization: paid - User reviews in markdown: https://appshunter.io/ios/app/max-zs-values/id498838137/reviews.md ## What is Max Zs Values? Calculate and look up the maximum permitted Zs value ( earth loop impedance ). Max Zs Values also includes the 80% temperature adjusted values and a some MCCB 60947-2 manufacture Zs charts. - 100% BS 7671 Zs Values - 80% On Site Guide Zs Values - 0.4 (s) second disconnection times - 0.2 (s) second disconnection times - 5 (s) second disconnection times - Common BS EN Devices: Scroll through the list of protective devices and select the device rating to calculate the maximum permitted Zs value for your selected protective device and rating combination. - 60947-2 MCCB's Zs Tables: Look up the maximum permitted Zs tables for a selection of MCCB manufacture devices (some). - Maximum Zs Features: + Maximum Disconnection Times + BS 7671 18th Edition Zs Tables + Fuse's + MCB's + RCBO's + RCD's in TT earthing systems + Max REC Ze values + 100% values + 80% values + 0.4 second disconnection times + 0.2 second disconnection times + 5 second disconnection times + Uo 55v (U 110v) single phase and Uo 63.5v (three phase) Zs values + BS EN 60947-2 MCCB manufacture device charts (some) There is now a new "Zs Converter" to convert old Zs values to the new 18th edition 230v Cmin Zs values. Check out our collection of electrical apps such as the "Pro Certs" Electrical Certification App for iPad. ## Key features - 100% BS 7671 Zs Values - 80% On Site Guide Zs Values - Adjustable disconnection times (0.4s, 0.2s, 5s) - BS EN Device Zs calculation - MCCB 60947-2 Zs charts - Zs Converter for 18th edition ## Recent user reviews (10 of 29) All indexed reviews: https://appshunter.io/ios/app/max-zs-values/id498838137/reviews.md ### 1/5 — Unhappy long standing customer *2023-07-11, version 3.1.12* Really unhappy that I have purchased this app previously at nearly £10 - had it for years, used it often. Purchased a new phone and I’ve had to repurchase it. Even though I’ve used the same email address to repurchase. I feel like that is unfair. ### 1/5 — Rip off *2023-06-14, version 3.1.12* Really poor app ### 5/5 — Essential for commissioning. *2023-04-19, version 3.1.12* I have had this app for a few years and the update is amazing!!!! Everything is always up to date, easy to use l. has many variety of MCB, fuses and MCCBs values available. Well done to whoever made it. ### 4/5 — Insightful *2021-08-18, version 3.1.6* No, not Mccb’s but type 4 3871. Seeing that you had the Mccb’s gave me hope for the 3871’s Other than that it’s a great app. Bad mood, sorry for the gut reaction. ### 5/5 — Cert Time Saver *2021-07-15, version 3.1.6* Brilliant app. Saves valuable time when fillling out certs especially for MCCB max zs. Awesome. ### 5/5 — Give it a go *2021-07-07, version 3.1.6* I couldn’t find a Zs reading for a breaker so I brought this app and I’m very impressed by it. Will be very handy on site for doing periodic’s ### 5/5 — Review *2021-06-15, version 3.1.6* Excellent app and easy to use ### 5/5 — Excellent *2021-01-20, version 3.1.4* I downloaded this app last year and it was great very handy, There was an issue with the software but the developers was extremely helpful and went out of their way to fix this issue, I’ve recently downloaded the updated version and can honestly say it’s gold excellent stuff ### 4/5 — Great app but... *2020-12-02, version 3.1.3* Love this app very handy when needing to remember figures,values etc. However since iOS 14 sadly does no longer display correctly on my iPhone xs which deems some of the functions unusable atm - hopefully a fix for this is in the pipeline?. ### 5/5 — Electrician *2020-10-23, version 3.1.3* Constantly improving and adding more information to the app ## Frequently asked questions about Max Zs Values ### What does the Max Zs Values app do? The app calculates and allows you to look up the maximum permitted Zs value (earth loop impedance) for electrical installations. It is based on the 18th Edition of BS 7671 and includes important adjustments and data for accurate safety assessments. ### What are the key features of this app? Key features include 100% BS 7671 Zs values, 80% On Site Guide Zs values, support for various disconnection times (0.4s, 0.2s, 5s), calculation for common BS EN devices (fuses, MCBs, RCBOs, RCDs), and MCCB manufacturer Zs charts. It also includes a Zs converter for older values. ### How much does the Max Zs Values app cost? Based on the provided information, the app is a paid application. There are no mentions of in-app purchases or advertisements, indicating a one-time purchase model. ### Who is the target audience for this app? This app is designed for electricians, electrical engineers, and anyone involved in electrical installations who needs to ensure compliance with BS 7671 safety standards. It's particularly useful for calculating and verifying earth loop impedance values. ### What are the common use cases for this app? Common use cases include calculating the maximum permitted Zs value for specific protective devices and ratings, checking compliance with different disconnection times, looking up manufacturer-specific Zs data for MCCBs, and converting older Zs values to the current 18th edition standards. ## Version history (last 5 releases) ### 3.1.18 — 2025-07-29 29/07/2025 v3.1.18 - UI improvements. - In-app optimisations. ### 3.1.16 — 2024-02-09 - Added Schneider TeSys MCCB max Zs table. - New PDF viewer to fix the pinch/zoom/scroll bug when viewing PDF tables. - A few UI improvements. ### 3.1.12 — 2022-08-24 A few UI improvements and minor optimisations. ### 3.1.11 — 2022-08-11 - Added a new "Zs Converter" to convert old Zs values to the 18th edition 230v Cmin Zs values. - Added Wylex NHG MCCB Zs table. ### 3.1.10 — 2022-04-05 Minor bug fixes. ## Apps similar to Max Zs Values | App | Rating | Price | Category | | --- | --- | --- | --- | | [PASMA](https://appshunter.io/ios/app/pasma/id535470547) | — | Free | Reference | | [CEF TechTalks](https://appshunter.io/ios/app/cef-techtalks/id6760725844) | — | Free | Reference | ## More apps by Pro Certs Software Ltd - [Watts Amps Volts Calculator](https://appshunter.io/ios/app/watts-amps-volts-calculator/id450813841) - [kVA Calculator](https://appshunter.io/ios/app/kva-calculator/id467407057) - [Electrical Tools and Reference](https://appshunter.io/ios/app/electrical-tools-and-reference/id564264558) - [R1+R2 Zs Ze Calculator](https://appshunter.io/ios/app/r1-plus-r2-zs-ze-calculator/id572416784) - [Fault Current Calculator (PFC)](https://appshunter.io/ios/app/fault-current-calculator-pfc/id577611194) All apps by Pro Certs Software Ltd: https://appshunter.io/developer/444429696 --- *Data collected daily from the US App Store and indexed by [AppsHunter](https://appshunter.io/). User reviews are verbatim App Store reviews. Ratings, prices and chart positions refresh continuously; this snapshot is from 2026-08-28.*