testing a B&B without disconnecting bonding

[shedhopper]

Hi This is my first post. I'm trying to test a working hotel / B&B at the moment and even though I'm Insulation resistance testing live AND neutral to earth on the lighting circuit as an agreed limitation; I'm still getting a zero reading. I suspect it might be something to do with 16th Ed bonding but I can't disconnect the bonding conductors at the board as there are people in the property at all times. Has anyone had an experience like this? Any suggestions how I could proceed or should I just tell the owner that a working hotel is an un-testable hotel?
Thanks a lot

 

[somersetsparks]

If its a 3 phase DB with a triple pole switch, then unless you switch off and disconnect the neutral link you will always have N-E continuity (PME). If its single pahse with main switch off then it sounds like you have a fault?

 

[Adam]

I presume this is with the neutral disconnected from the Neutral bar?

If so, it will most likely be due to a borrowed neutral, that will still be connected to neutral bar.

Are most of the insulation resistance readings high?

 

[tony mc]

It will have nothing to do with the bonding connected !

Are you disconnecting the neutral ?

Whats the reading when you switch to low ohms from Meg ohms on your meter!

 

[shedhopper]

Hi yes it's single phase with the main switch off. You're right it could always be a fault, I just thought I'd post in case anything obvious I'd missed came up. Thanks a lot

 

[shedhopper]

Yes neutral disconnected, most other IR readings are nice and high. There are still a couple of untested circuits in the DB so I'll look out for that. Thanks

 

[somersetsparks]

Hi yes it's single phase with the main switch off. You're right it could always be a fault, I just thought I'd post in case anything obvious I'd missed came up. Thanks a lot

Fault it is then! as has been suggested the borrowed neutral could be a likely candidate for a 0.00 or very low reading, try it on the low ohm's scale. Good luck!

 

[shedhopper]

Good to know its not the bonding then, thanks. Yes the neutral is disconnected, I'm testing the circuit on its own, not the entire DB at once. Whe I go from Low Ohms to Meg Ohms the reading is clear, waiting for me to hit test (meger 1720)

 

[shedhopper]

Will do. Cheers

 

[tony mc]

Try the test again then switch the landing light to the opposite position (off) and see if that changes the reading !

 

[Adam]

Will you be disconnecting every circuit in the DB to test?

If so, you may find another circuit with very low reading. If this happens, disconnect both circuits neutrals (with circuits isolated, of course) and try the test again. If the test is clear with both removed, it is most certainly a borrowed neutral.