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Calculator · Access control · BS EN 60228 cable data

Access control lock cable calculator

Enter the power supply voltage, the lock's rated voltage and current, and the cable. You see the voltage at the lock, whether it is within the tolerance you choose, and the longest cable for that lock. Low voltage at a lock can mean a magnetic lock holds with less force, or a strike fails to release.

Your figures

V
V
Enter the current in
mA

At the lock's rated voltage, from its data sheet.

Copper, per conductor. Resistance is the maximum BS EN 60228 allows, so real cable is usually a little better.

m

One way, from the power supply to the lock.

Check the lock's data sheet.

Result

Enter the supply, the lock and the cable to see the result.

Working

V_lock = V_supply − I × R, where R = r × 2 × L × k

  • V_supply is the voltage at the power supply output. V_rated is the voltage printed on the lock.
  • I is the current the lock draws. Use the figure for the lock's rated voltage from its data sheet.
  • r is the resistance of one conductor per metre (BS EN 60228, plain copper, at 20 °C), L the run length and k the hot-cable factor (1.20 at 70 °C).
  • The lock needs at least V_rated × (1 − tolerance). Lock makers give a tolerance in their installation guides, commonly 5%, 10% or 15%.

There is no UK standard figure for this. 5% is the voltage drop that lock makers such as Securitron and SDC tell installers to design the wiring to. The locks themselves often accept 10 to 15%, and Abloy UK gives plus or minus 10% for its 8037 series electric strikes. Use the figure on your lock's data sheet.

Measure the voltage at the lock with the lock energised once it is installed. Longer runs are easier at 24 V than at 12 V, because the same current drops the same volts, which is a smaller share of the supply.

For guidance only. Always check against the current edition of the standard and the manufacturer's data.

Built by the engineer behind Kerova, certificate software for fire and security firms.