Calculate / look up the maximum permitted Zs values ( earth loop impedance ) as per BS 7671 2018. Also includes 80% temperature adjusted values and a some MCCB 60947-2 Zs charts.

> 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 device.

> Manufacture 60947-2 MCCB's:
Now includes many manufacture Zs charts for 60947-2 MCCB's.

+ BS 7671 18th Edition 2018
+ BS EN protective devices
+ Fuse's
+ MCB's
+ RCBO's
+ RCD's in TT earthing systems
+ Max REC Ze values
+ Ze + R1+R2 = Zs calculator
+ 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

Check out our other electrical apps such as the "Pro Certs" Electrical Testing & Certification App, visit >> for more info.

What’s New

Version 3.1.1

V: 3.1.1 - 02/09/2019
> Added a print function to PDF charts.
> Added some more manufacture 60947-2 MCCB Zs charts.
> Reduced app size so it runs faster and takes up less storage space.

Ratings and Reviews

5.0 out of 5
2 Ratings

2 Ratings

Astect Gibbo ,


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

Developer Response ,

Thank you for your feedback.

comedy explorer ,

Very handy

Works well for me.

Developer Response ,

Thank you for your feedback.

Cavemanflynn ,


I have the whole Pro-Certs range of iPhone software. If they keep producing quality items like this I can throw away my onsite guide! Keep up the good work!! ( can wait to see if you can make software to bill my customers as well!! Lol)


Pro Certs Software Ltd
8.7 MB

Requires iOS 10.0 or later. Compatible with iPhone, iPad and iPod touch.



Age Rating


  • Family Sharing

    Up to six family members will be able to use this app with Family Sharing enabled.

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