ECN Forum Forums General Topics of the Trade General Discussion Area troubleshooting a short

Why not just use a test lamp wired in series with the breaker?

Dereck,

Because:

1) the test lamp does not draw enough current to cause a large enough voltage drop on the cable that allows reliable detection

2) the short my well be to Earth, and the cable could become "hot" should the fault be intermittent

3) any induction on the cable from others in the vicinity could cause the fault to appear in another area (by using DC, the meters become insensitive to any AC influence on the cable)

4) the high current source must be fully isolated so as to not influence the readings - the mains input is not isolated (one leg, at least, is taken to Earth - well it should be!).

M.

They already have something like that...

www.mtadistributors.com/products/IN2-CT

I knew I'd seen that before!

as long as the globe drags about 5 to 10 amps, then that is perfect (on 3V, that would be about 15 to 30W - have a feeling torches are a little lower than that - lantern style with screw type batteries have huge globes hence the suggestion).

M.