I bought from TLC Electrical 6 Knightsbridge GU10SPIKEBK IP65 garden spike lights at £13.25 each and got some odd insulation resistance readings when testing, John Ward and Thomas Nagy (YouTube influencers), have also commented on the problem, so I thought I’d share what I found.
A cable which carries 230v AC is tested at twice its voltage using an insulation resistance tester, this injects 500v DC into the conductors, any issues with conductor insulation will be displayed as a digital reading.
The ideal reading would be >500 Meg Ohms in my meters case, effectively their is no leakage between the conductors under test, BS7671 allow for a pass at 1 Meg Ohm, however, further investigation is recommended if the reading is 20 Meg Ohms or less.
As I knew the age of the garden cabling, its route and connections, I was surprised at finding a less than expected insulation resistance reading which turned out to be the actual cable cable supplied with the spike fitting.
The cable is a 3 core rubberised insulated ands sheathed cable with the identification H05RN-F 3C 1.00mm2 Ningbo Huashun Electronics printed throughout its length.
This image above shows a length of the faulty cable under test, the meter should show >500 not 185.6 Meg Ohms, (this resistance, when connected in parallel with further faulty cables, which also act as resistors, has the effect of significantly reducing the overall resistance/integrity of the circuit).
Ironically, not every fittings cable was affected, but I had lost confidence in the existing cables and replaced all spike light cables with 3 Core Pond Flexible Cable 0.75mm² 3183P Black, £22 for 25m from Wickes, after which all tested >500.
