3 phase question

[PompeySparks]

'Unbalanced 3 phase loads induce a current in the neutral making the problem worse'

However unbalanced the phases are, the current in the neutral will not exceed the current in the highest loaded phase (unless under very exceptional conditions!). Therefore the current in a neutral of a three-phase system will not usually be as high as in any of the phases.

In a single phase system, the Neutral current is ALWAYS as high as the phase current meaning you will generally get a higher amount of current in the neutral of a 100A single phase installation than the neutral of a 3x100A three-phase installation!.

'When I was an apprentice an Electrician pulled the fuse on a lighting circuit I was working on. It was in a wet area. I touched the neutral and got a zap.'

Was the fuse in when you started working on it!?. As others have previously said, as long as the neutral is tied down at the PME service head then the neutral current will always return to the transformer via the cable itself and not through a person touching the neutral as this is a much higher resistance path!

This is why it is so common for people to only isolate the phase and work on a circuit with the neutral still connected.

 

[Lectrician]

Like the last reply - it is clear - no need to recap!


There can be a small potential between neutral and "mother earth". In a PME install, there can also be a potential between the installation earth and "mother earth".

This potential is caused by the network voltage drop and circulating network currents (caused by parallel paths in common bonding etc).

This is the reason PME is not to be used in swimming pools, communal shower blocks, petrol stations etc. For swimming pools and showers, you can recieve a 'percieved electrical shock' from the potential of an earthed pipe to wet tiles for example, and in petrol stations, the circulating currents could enter bonded pipework/tanks/pumps, and cause a spark...

 

[Pensdown]

Thanks guys, now I can cancel my order for DP MCB's

 

[Adam_151]

Thanks guys, now I can cancel my order for DP

This is an electrical forum

 

[Pensdown]

LOL.. I'm now with BAS...apprentices* SHOULD be used as circuit testers

*replaceable young person who think they know everything