So I have aquired 1 light of a traffic light that I salvaged from a local dump. I want to try and connect the light to use it like a lamp, however I am a little worried by it as the connector only has live and netural wires.

Basically I want to know if it is possible to earth the system or is it safe without earthing? I read into double insolation but cannot tell exactly how it works.

Sorry if this is very basic or been answered somewhere else, I wasn't exactly sure of how to find an answer.

  • \$\begingroup\$ Before you invest money into that project, check that the lamp still has a chance of working, by measuring the internal resistance with a multimeter. It should be somewhere between 10–200Ω, depending on wattage (\$R=\frac{U}{I}\$, \$P=UI\$ ⇒ \$I=\frac{P}{U}\$ ⇒ \$R=\frac{U^2}{P}\$, so for e.g. \$U=110\textrm{V}\$ and \$P=1\textrm{kW}\$, you get \$R=\frac{110^2}{1000}=\frac{12100}{1000}=12.1\$) \$\endgroup\$ Feb 23, 2019 at 12:11

1 Answer 1


It's supposed to be inside an enclosure that is earthed, or inside a case made of either two insulating layers or a reinforced insulating layer, so that a single fault will not expose any point on the outside to live current.

Using an earthed case protects you from wiring faults by triggering the GFCI when the live wire connects to the case (e.g. because a connection came loose).

The double insulated case protects you if and because it is unlikely that both layers will break at the same time (i.e. the outer layer protects the inner). Once the outer layer is broken, the device is no longer deemed safe and needs to be disconnected until it is repaired.

The lamp on its own is not a complete product and not safe to operate standalone.

  • \$\begingroup\$ I thought this may be the case, thank you for the help with this. It seems like the answer would be no, but would there be anyway of making it safe? \$\endgroup\$
    – Nathan
    Feb 23, 2019 at 12:48
  • \$\begingroup\$ @Nathan, by building, buying or otherwise obtaining an enclosure that fulfills the requirements. Building something that you won't get shocked by is easy, but "safe" means that if a cat comes in and knocks it down, a toddler looking at it won't get shocked either. You need to avoid the situation where in a few years time a child comes into the room and you need to remember a list of things that aren't childsafe — so everything needs to be safe from the beginning. \$\endgroup\$ Feb 23, 2019 at 15:14

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