Max Zs Values

Pro Certs Software Ltd

About this app

Max Zs values for Android, look up the maximum permitted Zs value (earth fault loop impedance) in accordance with BS 7671 amendment 4 2026.

Max Zs values include 100% (BS 7671) and 80% (On-site guide) temperature adjusted values.

Select from the list of protective devices (fuse's, MCB's, RCBO's) and device ratings to calculate the maximum permitted Zs value for your selected protective device.

Also look up some manufacture BS EN 60947-2 Zs value PDF charts and tables, all printable from within the Max Zs values app.

This Maximum Zs Values app contains Zs tables, charts and calculators all relating to the maximum permitted Zs values of BS 7671.

FEATURES:
- BS 7671 maximum Zs values
- Common BS EN MCB's, RCBO's and fuses maximum Zs calculator
- BS EN 60947-2 MCCB manufacture device charts / tables (some)
- RCD max Zs for TT earthing systems calculator
- DNO max Ze (by enquiry) values
- Uo 55v and 63.5v Zs values (110v single & three phase) calculator
- Ze + R1+R2 = Zs calculator
- Zs - Ze = R1+R2 calculator
- TN & TT maximum disconnection times chart

Pro Certs Software: Trusted by UK electricians since 2011.

What’s new

28/07/2026 v3.1.19
- Android 36 update