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Eddiesparks
Did a board change today and put in rcbos for mcbs in common areas of a block of flats. Meggered out ok before i started by the way!!
Rcbo for outside lights didnt hold. Mcb was fine before. All others held fine. So neutral to earth fault right? Also disconnected neutral from rcbo no problems til neutral connected, with live connected all good. Connected neutral trip. Connected just neutral - trip. Earth in all the time.
Disconnected that circuit's earth and functional earth to see if it would hold. No joy. Traced earth and it goes nowhere, cut off at contactor! However outside lights gave me a Zs so earth must be taken off another circuit.
Thought about borrowed neutrals - but all other rcbo's held - didnt trip in a pair. Also meggered between neutrals came out ok. Even disconnected all other neutrals except outside lights. No joy.
It's a main board in common areas that feeds that building's power and lights and outside lights plus feeds a few submains. Flats are on separate main incomer individual fuses. Could it be a borrowed neutral from a lighting circuit in one of the flats.
Also, old board had charring round where the main neutral from 100a switch meets neutral bar. Is this probably unrelated and due to bad connection??
What a horrible day. Going back tomorrow to fault find some more. But it's hard to find the ordering of the outside lights there are groups of them all over the place. I suppose get Zs on all of them and lowest is closest to the board.
Wish me luck, but more importantly some highly experienced insight would be great!!
Rcbo for outside lights didnt hold. Mcb was fine before. All others held fine. So neutral to earth fault right? Also disconnected neutral from rcbo no problems til neutral connected, with live connected all good. Connected neutral trip. Connected just neutral - trip. Earth in all the time.
Disconnected that circuit's earth and functional earth to see if it would hold. No joy. Traced earth and it goes nowhere, cut off at contactor! However outside lights gave me a Zs so earth must be taken off another circuit.
Thought about borrowed neutrals - but all other rcbo's held - didnt trip in a pair. Also meggered between neutrals came out ok. Even disconnected all other neutrals except outside lights. No joy.
It's a main board in common areas that feeds that building's power and lights and outside lights plus feeds a few submains. Flats are on separate main incomer individual fuses. Could it be a borrowed neutral from a lighting circuit in one of the flats.
Also, old board had charring round where the main neutral from 100a switch meets neutral bar. Is this probably unrelated and due to bad connection??
What a horrible day. Going back tomorrow to fault find some more. But it's hard to find the ordering of the outside lights there are groups of them all over the place. I suppose get Zs on all of them and lowest is closest to the board.
Wish me luck, but more importantly some highly experienced insight would be great!!