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 BS7671 IEE wiring regulations maximum disconnection times.

All extension leads must also be uncoiled before use.

110 volt maximum length table

230v/400v extension lead max length

IEE code-of-practice


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.



cable resistance ohms chart table


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
“milli-volts(tabulated value)*amps(load)*length(metres)”

(1760watt/110volts)=16amp load

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

To summaries

Note: excessive volt drop will also increase the current demand the equipment will use which can cause continued nuisance tripping & the
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 IEE guidelines for maximum volt-drop.


volt drop chart 110volt extension leads

volt drop 230v 3 phase extension leads

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