Maximum extension lead lengths
The two charts directly below summaries the maximum extension lead length as per the PAT test code-of-practice
& calculated maximum permitted Volt-drop ( power loss ). All our leads comply with these guidelines.
Plugging 1.5mm,2.5mm,4.0mm csa only leads into a circuit protected by a RCD does allow the user
to extend these max limits slightly further but volt drop & cable csa still has to be factored in.
Note: If you exceed these maximum lengths when joining "multiple leads" some electrical equipment
will not function correctly (especially electronic equipment) & the protection device
in some cases will not function within the wiring regulations maximum disconnection times.
Every extension lead requires to be fully uncoiled before use otherwise due to the tightly packed cable any heat cant escape, the cable will initially start to warm which starts a cycle of overheating , as the lead gets warmer the cable resistance increases,volt drop increases and the core temp continues to rise.
4.1 BEAB document 40, Test parameters for appliances covered by the BS EN 60335 series of standards
The factory applied limit for appliances with a supply cord is not to exceed 0.2ohm , see table below for reference
The csa & maximum quoted lengths of all our leads allows secure tripping of the overcurrent device provided the actual installation complies with BS7671.
How volt drop effects extension leads
110volt temporary installations are effected mostly by volt drop. That’s why on unplanned 110volt
temporary installations lights are dimming, power saws are failing in operation, drills are slow to get up to speed etc
which in turn will reduce the efficiency of the work in hand and the service life of the equipment
For example we will calculate the voltdrop on a handheld 1760watt drill being used 30metres away from a 110volt source.
The formula for volt drop is
1.5mm cable (32mv*16a*30m) = (0.032v*16a*30m) = 15.36volt drop
2.5mm cable (19mv*16a*30m) =(0.016v*16a*30m) = 7.68volt drop
4.0mm cable (12mv*16*30m) = (0.012v*16a*30m) =5.76volt drop
- The 30metre 1.5mm csa extension lead will have 94volts at the 1760watt drill under load, the drill performance will be very poor & the total resistance of the lead should register as a PAT test fail.
- The 30metre 2.5mm csa extension lead will have 102volts at the 1760watt drill under load, the drill performance should be adequate but the total resistance of the lead should register as a PAT test fail
- The 30metre 4.0mm csa extension lead will have 104volts at the 1760watt drill under load, the drill performance will be excellent & the lead is fit for purpose.
overheating of cables reduicng the service life of voltage sensitve electrical equipment so choosing the correct extension lead for the task is very important.
All our extension leads comply the IET guidelines for maximum volt-drop.