What was the fault?

[Lectrician]

We replaced some lighting in a warehouse when they re-racked and altered it around. We utilised many of the the same feeds, but installed new lighting trunking and fluorescents.

8 rows of trunking, 12 6ft twin fittings on each row, each wired alternately so if there is a fault only 50% die in the aisle, and just 50% can be switched on during the day as the warehouse is pretty light from the skylights.

Only a few months old, and two circuits tripped, 50% in one aisle and 50% in another aisle. Both circuits meggared absolutely fine to earth, could not feesably check L to N.

Both circuits re-energised and lasted for a good week until we got the next call, again, the same two circuits out. They couldn't tell us when they had failed.

Meggared both again, to earth both fine. Decided to split the circuits in half to prove which half was causing issues. The fittings are high frequency T8's.

Any guesses at the final outcome?

 

[JohnD]

was it raining?

or lots of condensation on the roof?

 

[wotan]

Flying ants nesting inside of light fittings?

Wotan

 

[DetlefSchmitz]

EDIT: No, I'm talking nonsense.

 

[sparkwright]

Some sort of weird 'borrowed' neutral?

 

[Lectrician]

Both circuits constantly meggered out fine L to E and N to E in their entirety.

The feeds from the TP DB, via the grid switch to the first fittings meggered out fine L to E, N to E and L to N.

The trunking was fed fed centrally, so three cables in the first fitting which worked out well to isolate half and half. Isolated half of each circuit and left for a couple days, both circuits tripped in that time. Reconnected the isolated half and isolated the other half. Again, both circuits tripped fairly quickly. This kind of points to the cable from the TP DB, via the grid switch to the first fittings being faulty. Odd that two should be. Meggering them both when isolated from the lights returned with perfectly clear readings L-N, L-E, N-E.

We installed the cables in the trunking but did not install the cables from the trunking to the TP DB, via the grid switch (but did replace the grid switch).

 

[WabbitPoo]

You do know this is a DIY site, don't you? That implies "in the home" I believe...

 

[333rocky333]

Were they Double pole gridswitches by any chance,

 

[Lectrician]

You do know this is a DIY site, don't you? That implies "in the home" I believe...

If it stretches your brain too much, you can easily pass this topic by (Pressing the back button is quickest I believe). You do know you can click "ignore" too if you would prefer.

Were they Double pole gridswitches by any chance,

Nope, all 20amp single pole.

 

[bernardgreen]

Was it something like an extractor fan(s) ( a big industrial one ) with remote / automatic switching taking supply from the lighting ciruit.

 

[Lectrician]

Both circuits tripping wasn't a coincidence....

 

[333rocky333]

Were they two different phases

 

[RF Lighting]

That's what I'm thinking

Two different phases and somehow the wiring has got damaged in the trunking causing the phases to short together.

 

[WabbitPoo]

You do know this is a DIY site, don't you? That implies "in the home" I believe...

If it stretches your brain too much, you can easily pass this topic by (Pressing the back button is quickest I believe). You do know you can click "ignore" too if you would prefer.

Were they Double pole gridswitches by any chance,

Nope, all 20amp single pole.

You miss the point - the forum is already clogged with stuff the DIYer doesnt need to know, and you have added to that.

Just my 2p

 

[bernardgreen]

You miss the point - the forum is already clogged with stuff the DIYer doesnt need to know, and you have added to that.

But this none DIY chatter does ( hopefully ) let the average DIYer see there is more to electrical safety and reliability than just buying bits and connecting them together in a way that works.