half sized neutral

[bigpaul]

Hi,

Brand new to this. My question is about supply conductors. (LUL) london underground used to have their own supply generated, which came in at platfrom level. This supply has a SWA cable with a 185mm2 3 phase with a 95mm2 neutral (cable must have been specially made). This TNS service is before the main switch. Just wondering if its worth mentioning this on the periodic inspection report and if this breaks any regulations as the majority of the services on the underground station are 240vac supplies, so i would assume there is a large neutral current.(still need to check). Any thoughts?

 

[brizospark]

very good point but most 3 phase eqipment does not require a neutral so lets say 50% of the equipment is single phase requires a neutral the 95mm would be enough?

just a thought?

 

[johnboy6083]

its more to do with balanced loads imo. even with 1ph loads, they will mostly balance out, so your neutral current will be very small in comparison to the phase currents.

 

[IQ Electrical]

The reg's state that where a reduction in CSA of Neutral (compared to Line conductors) occurs (e.g. in 3 phase circuits with closely balanced loads) it is necessary to provide overcurrent protection of the Neutral, which must cause disconnection of the associated Line conductors.

This is assuming that the neutral in question belongs to your client as opposed to the DNO.

 

[ian.settle1]

Used a similar cable many years ago I asked are estimator how come it was like that he replied as stated in other postings as the load was mainly motors and thus balanced the reduced size neutral was for the single phase control circuits only.