Look up the maximum Zs values for MCB's, Fuses, MCCB's and ACB's with 100% values and the temperature adjusted values all in one place.

Calculate and look up the maximum permitted Zs value ( earth loop impedance ) to BS 7671. 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
- Printable 60947-2 MCCB Zs Tables

- 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
+ Ze + R1+R2 = Zs calculator
+ 100% values (BBB)
+ 80% values (OSG)
+ 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

A maximum Zs calculator for iPhone and iPad.

Check out our collection of electrical apps such as the "Pro Certs" Electrical Testing & Certification App or visit for more info.

What’s New

Version 3.1.7

Added manufacture BS 3871 Type 4 max Zs values.

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