50 ohms continuity between Line & CPC

[m4tty]

Hi,

If a lighting circuit has got 50 ohms continuity between Line & CPC why would a 5a fuse not blow.

Think I may be missing the obvious so feel free to flame lol

 

[ProDave]

well at 230V and 50 ohms, then by ohms law the current flow will be 4.6A so a 5A MCB will not trip.

My bet is you have a neutral to earth short, and the 50 ohms you are reading is the resistance of a light bulb, in which case that 50 ohms will increase a lot when the light is on, and hot, so the actual current will be even less.

EDIT:

As Doc says in the post below, it might not even be a fault at all if it's TNC-S

 

[Doc Hudson]

And if it is only the live breaker you have switched off and it is a TN-C-S the Neutral and Earth will be shorted at the incoming head. So it could easily be a forgotten lamp. Its not a landing or hall lamp making its path to neutral back through another light circuit is it?

Doc H.

 

[Technician]

If you carefully disconnect each conductor in that circuit

(I am assuming you are doing a R1 + R2 test) and use a long

lead to measure the continuity of each one, you should soon

identify the fault. I would also recommend that you prove

the value of Rn by the same method.

Use the long lead to do the R2 test as well. R2 test value will

be less than the R1 + R2 test value by as much as 50%.

Are you referring to a "borrowed neutral" Doc? Good point.

 

[Andy™]

could even be something wired wrong - if its wired L-E, you will get readings like that, and L-N will have no continuity

 

[SPECIAL LOCATION]

Well....

I shall just say I agree with my esteemed colleagues here...

nowt more worth saying I think!

Just that gut instincts suggest that 50ohms is a strange value to have as a fault...

i.e. damp bridging some joint, or insulation break down, more likely to be dead short or higher than 50ohms i think!?