Maximum Zs Values
BS 7671 Max Zs Values
Max Zs values for Over-current Protective Devices (OPD) and Residual Current Devices (RCDs) are laid out in BS 7671. The max zs values for Moulded Case Circuit Breakers (MCCB) and Air Circuit Breakers (ACB) differ between manufactures and again between specific part numbers. We have sourced as many of the MCCB and ACB max zs tables as we can and included them within our Max Zs Values mobile app.
BS 7671 Max Zs Values = 100% Zs values, On-Site Guide = 80% Zs values.
Trying to locate the correct maximum Zs value for a specific protective device can be very time consuming, sometimes you may find yourself needing the Zs value for a specific device and can't find it or don't have the Zs table to hand, introducing the Max Zs Values app, all your Zs values in one place.
Download Max Zs Values for iOS or Max Zs Values for Android.
Maximum Zs tables, charts and calculators right at your fingertips!
Features
- Common Devices Zs Calculator
- RCDs and RCBOs
- RCDs in TT Earthing Systems
- MCCBs and ACBs
- Fuses (Cartridge and Wire)
- MCCBs Settings Symbols
- 100% Zs Values
- 80% Zs Values
- 0.2, 0.4 and 5s
- Max Disconnection Times
- DNO Ze Values
- Uo 55v (110v) & 63.5v Zs Values
Reviews
Don’t take our word for it – here’s what other users say:
Great app!!! I have been using this app for a few years now and I can not fault it, it’s easy and convenient to use and rather than having to overthink and take you away from the everyday job it saves time.
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.
Handy app just made better thank you. The Mccb max zs sheets are so useful.
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.
60947-2 Zs Tables
MCCB EARTH FAULT LOOP IMPEDANCE
This Max Zs Values app contains many manufacture BS EN 60947-2 MCCB Zs tables, select 60947-2 MCCB Devices option to see the full list of manufactures, select a manufacture to view the MCCB Zs tables.
Menu:
- Common BS EN Devices
- 60947-2 MCCB Devices
- MCCB Setting (symbol meanings)
- DNO / DSO Ze Values
- Uo 55v and 63.5v Zs Values (110v single phase and three phase)
- Zs – Ze = R1+R2 Calculator
- Maximum Disconnection Times
MCB Max Zs Values
FUSES | MCBs | RCBOs
Under the Common BS EN Devices menu item you can scroll through a comprehensive list of all common BS and BS EN fuses, MCBs and RCBOs.
- MCB Miniature Circuit Breaker
- MCCB Moulded Case Circuit Breaker
- ACB Air Circuit Breaker
- RCD Residual Current Device
- RCBO Residual current operated Circuit Breaker with Over-current protection
Once you have selected a protective device use the Rating column to select your device rating and hit the “Get Results” button to calculate the maximum permitted Zs value for your selected protective device and rating combination.
- 100% Zs Values
- 80% Zs Values
- 0.2s & 0.4s
- 5s
Max Ze Values
EXTERNAL ZE | DNO MAX ZE VALUES
The maximum permitted Ze depends on the earthing system type, be that TN-C-S, TN-S, TN-C, TT or IT earthing systems.
DSO = Distribution System Operator (previously known as DNO).
DNO = Distribution Network Operator (previously known as REC).
REC = Regional Electric Company.
TT Max Ze
RCD MAX ZS FOR TT EARTHING SYSTEMS
Satisfying the maximum permitted earth fault loop impedance values in a TT earthing system may not be possible due the the higher Ze readings in a TT system.
BS 7671 table 41.5 offers alternative maximum permitted Zs values for TT earthing systems, other regulations may also apply.
RCD OPERATING CURRENTS
- 30 mA
- 100 mA
- 300 mA
- 500 mA
NOMINAL VOLTAGES
- 50V > 120V
- 121V > 230V
- 231V > 400V
- 400V and over
Demo video may show an older version of the app
Max Zs Values
- MCCBs and ACBs
- Fuses (Wire and Cartridge)
- MCBs and Circuit Breakers
- RCDs and RCBOs
