300 mA RCD main switch agricultural (tripping)

[The apprentice]

Hi there thank-you for taking the time to read this! I have a 300mA Rcd in a grain shed on a farm now every time I try reset it won’t stay on there are 3 phases that go into the main switch
And it isolates all 3 bar the neutral so when wen everything is turned off mcb rcbo in the board it still trips iam guessing this is through the neutral if I could some how isolate the neutral and then hopefully it would stay up then turn one on at a time thoughts on fault finding ?

 

[ImpededLoop]

You'll need to disconnect each circuit and insulation resistance test them to identify which one(s) are causing the problem. I'd also test the RCD and you'll need to disconnect the outgoing neutral to be able to do this.

 

[brianmoooore]

It will be an earth neutral fault OR if the testing of the RCD has been neglected, and the thing hasn't been off for years, it could be the mechanism sticking. Been working on farm electrics for 45 years, and have come across this on numerous occasions.
Testing needs to be done with an IR tester, operated by someone who knows how to use it.

 

[SparkySy]

Is this a main switch for the whole installation or a sub board? If you have a 3phase RCD it should have the neutral running through it too i.e. 4pole. If you have single phase loads then the rcd will see an inballence due to current flowing back through the neutrals.
Either that or you have a neutral earth fault as mentioned above.
Have you any pictures?

 

[The apprentice]

You'll need to disconnect each circuit and insulation resistance test them to identify which one(s) are causing the problem. I'd also test the RCD and you'll need to disconnect the outgoing neutral to be able to do this.

I would need to turn every switch off to insulation resistance test it so no lights etc get damaged this is the 2nd rcd main switch I have out in because thought it was faulty put the other one in and tripped straight away wouldnt let me out it on

 

[The apprentice]

It will be an earth neutral fault OR if the testing of the RCD has been neglected, and the thing hasn't been off for years, it could be the mechanism sticking. Been working on farm electrics for 45 years, and have come across this on numerous occasions.
Testing needs to be done with an IR tester, operated by someone who knows how to use it.

The cable feeding the new 3 phase board that a spark done then I took over was working fine then the grain dryer had a borrowed neutral that had to be disconnected now is there anychance he’s got his phases mixed up with it being an armour and the beautiful could be live

 

[The apprentice]

Is this a main switch for the whole installation or a sub board? If you have a 3phase RCD it should have the neutral running through it too i.e. 4pole. If you have single phase loads then the rcd will see an inballence due to current flowing back through the neutrals.
Either that or you have a neutral earth fault as mentioned above.
Have you any pictures?

Main switch is for the whole installation now I have sub boards off this running icleast 20 meters then 4 led strip lights also part of the old lights are wired to in armour nightmare

 

[ImpededLoop]

I would need to turn every switch off to insulation resistance test it so no lights etc get damaged this is the 2nd rcd main switch I have out in because thought it was faulty put the other one in and tripped straight away wouldnt let me out it on

You can test line and neutral together in one Croc clip to earth in the other Croc clip. This prevents any equipment from getting damaged.

 

[The apprentice]

Main switch is for the whole installation now I have sub boards off this running icleast 20 meters then 4 led strip lights also part of the old lights are wired to in armour nightmare

 

[The apprentice]

You can test line and neutral together in one Croc clip to earth in the other Croc clip. This prevents any equipment from getting damaged.

Thanks mate, thing is all socket circuits are 30mA etc all 3 phase stuff isn’t so iam going for the 3 phase stuff

 

[SparkySy]

Have you a picture of it installed?
If it was working and now is not what has changed since it last worked? It could be the weather or rodent damage.
Are the RCBO's single pole? Could still be a neutral earth fault on one of those if they are.

 

[The apprentice]

Have you a picture of it installed?
If it was working and now is not what has changed since it last worked? It could be the weather or rodent damage.
Are the RCBO's single pole? Could still be a neutral earth fault on one of those if they are.

I will get a pic on Friday mate what has changed is the old bud bar system he re routed the cable that fed that to a main switch then the grain dryer was a borrowed neutural then we left it on a normal main switch for time being and when we put it back in I tripped once grain dryer was removed

 

[Sib_elec]

I will get a pic on Friday mate what has changed is the old bud bar system he re routed the cable that fed that to a main switch then the grain dryer was a borrowed neutural then we left it on a normal main switch for time being and when we put it back in I tripped once grain dryer was removed

Have you IR tested the grain dryer wiring?

 

[The apprentice]

Have you IR tested the grain dryer wiring?

Was a borrowed neutral