Max Zs Values18th Edition Max Zs values.
✔ BS 7671 100% Values
✔ On Site Guide 80% Values
✔ 0.2s Disconnection Times
✔ 0.4s Disconnection Times
✔ 5s Disconnection Times
+ Extra Zs Calculators and Tables
Max Zs Values App for iOS & Android
Max Zs Values is an easy to use Zs calculator for looking up and calculating the maximum permitted Zs value for RCBO’s, RCD’s, MCB’s, fuses and some manufacture MCCB’s. Earth loop impedance (Zs) is measured in ohms.
Spending hours hunting for max Zs tables and Zs values is now thing of the past with this Max Zs Values app.
Max Zs Tables
- Table 41.1 – Maximum Disconnection Times
- Table 41.2 – Maximum Zs Values for Fuses at 0.4s
- Table 41.3 – BS EN 60898 and 61009-1 Zs Values
- Table 41.4 – Maximum Zs Values for Fuses at 5s
- Table 41.5 – Zs Values for 61009-1 & 61008-1 in TT Systems
- Table 41.6 – Zs Values for Uo 55v (single phase) and 63.5v (three phase)
- DNO (DSO) Ze Values & Earthing System Types Diagram
- 0.2 seconds (s)
- 0.4 seconds (s)
- 5 seconds (s)
Max Zs Calculators
- Common BS EN Devices
- Manufacture 60947-2 MCCB Tables
- MCCB Explanation of Settings Symbols
- RCD’s in TT Earthing Systems
- REC Ze Values
- Uo 55v and 63.5v Max Zs Calculator
- Zs – Ze = R1+R2 Calculator
Max Zs Charts
- BS7671 18th Edition Zs Values (100% Values)
- BS7671 On Site Guide Zs Values (80% Values)
- Maximum Disconnection Times Table for TN & TT Earthing Systems
- Print the 60947-2 MCCB Zs Tables
- Request New Manufacture Zs Tables
- Fully Supported
- Well Maintained
Date: August 2021 - Added BS 3871 Type 4 max Zs values (various manufacturers) - Added a news feed from our blog Date: February 2021 - Some layout improvements - Corrected a spelling typo Date: September 2020 - Added: MCCB Explanation of Setting Symbols - Added: DNO Ze Values & Earthing System Types Diagram - Changed: Re-worded reference from REC to DNO / DSO Date: May 2020 - Improved UI - Added a custom document viewer to view the MCCB Zs tables Date: September 2019 - Added the ability to print the MCCB Zs tables - Added more BS EN 60947-2 MCCB manufacture Zs tables - Reduced app download size Date: 2019 - Complete new redesign - Complete new UI - Back-end improvements - Added a few new calculators Date: 2018 - BS 7671 18th edition update - Zs values updated Date: 2015 - BS 7671 17th edition amd 1 update - Zs values updated Date: 2013 - Maintenance update Date: 2013 - iOS 6 update Date: 2013 - Fixed BS88 bug Date: 2012 - New protective devices added - Zs database updated Date: 2012 - Sharing function improved Date: 2012 - 1st release
Max Zs Values
BS7671 18th Edition Zs Values
Max Zs Values | DemoWatch the app in action!
App ReviewsRead what Our Happy Customers Are Saying
All your applications are very useful, quick to operate.
Keep up the great work,
Max Zs Values.
Excellent straight forward app
with rule of thumb calculation populated
Handy app just made better.
The Mccb max zs sheets are so useful.
Very convenient app.
Really helps to get an idea of the
loop impedance quickly.
FAQ's & How To
How to calculate max Zs
In order to calculate the maximum permissible Zs value we need to know the following data:
- la = The amount of current required to trip the MCB within the given time.
- In = The rating of the protective device in amps.
- Uo = Voltage to earth
Calculate Zs Formula:
Uo x 0.95 (Cmin) / la = Max Zs (100% value) x 0.8 = Max Zs (80% value)
Example: BS EN 60898 Type B 32 Amp
Ia: 5×32(A) = 160(A)
Uo: 230v x 0.95 = 218.5v
218.5(Uo) / 160 (la) = 1.36525, 100% Zs value rounded to 1.37 Ω.
1.37 (100% Zs Value) x 0.8 = 1.096, 80% Zs value rounded to 1.1 Ω.
Which Zs values should I use, 100% or 80% values?
It is generally recommended that the 100% max Zs values should be recorded on an electrical installation certificate or condition report.
However the actual measured Zs values obtained should be compared to the 80% temperature adjust values, this is to allow for the rise in cable temperature in fault conditions.
Should a measured Zs value exceed the 80% temperature adjusted Zs value then this would be considered a C2 observation.
- 100% Max Zs values = Record on paperwork.
- 80% Max Zs values = Compare to actual measured Zs values.
How to calculate Zs
To calculate Zs for an existing circuit is a simple calculation using the known Ze and R1+R2 values, however we have added a Zs calculator anyway for convenience.
How to calculate R1+R2
To calculate R1+R2 is a simple calculation using the known Ze and Zs or Zdb values, however we have added an R1+R2 calculator to the app anyway as it can be very handy if you have multiple R1+R2 calculations to make.
Get the AppAn extensive database of maximum Zs values.
✔ Calculate Max Zs
✔ Calculate Zs
✔ Calculate R1+R2
✔ 100% and 80% Zs Values
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