Few fauls come accross today...

[SafetyEICR]

Few faults that got alarm bells ringing today.

3P+N MCCB Panel fed directly from busbar chamber wired in 3 x single 120mm s.w.a cables with 25mm pvc/pvc neutral conductor. MCCB Panel feeds plant equipment, no submains.

I'm right in thinking neutral conductor should be equal phase c.s.a unless particular conditions are met?

Do harmonics come into the equaltion?

Also main switch for MCCB rated to 250a. OCP for MCCB panel is 400a 88.2 in the busbar main switch, Would you warrant this a code?

 

[Guest55]

main panel switch only has to be capable of handling the total load from the panel , not the upstream device rating so ok.
as for neutral csa smaller than phases , was common years ago but compared against todays standards should be equal so worth a mention in the report , code wise tough to gauge , probably a C3 , but thats only my opinion.

 

[Darkwood]

You are saying the neutral and 3ph are to a specific plant equipment... assuming this is a designed calculated load it can be possible to reduce the Neutral conductor size, has the neutral been added at a later date as this would suggest its just been put in alterations ect or additions that require a neutral.

Old installations were common to see the neutral sized for the job that they did but like large lathes where 3phase supplies exceeded 100amp were needed and a neutral was on required for the control system ...it can save alot of pennies if the calcs are done correctly.

Reg 523 section covers this so yes thermal effects, harmonics etc need to be taken into account, but nothing wrong if done correctly. I suspect been 100mm shy of the phase conductors it would surely show signs of overheating if not designed.

You may be confusing Earth cable regs.... with regards to live conductor CSA

 

[Engineer54]

Reduced neutral cables and singles were generally half sized. So i would imagine this small neutral conductor has been provided for specific requirement such as controls and/or some other small power requirement within the equipment...

 

[Guest111]

As E54 says reduced neutrals were very common at one time,the danger today comes from changes of use,unbalanced loads and harmonics people very often change the use of a circuit without fully understandin the implications.