Sub Mains

[wreck-it-steve]

Hi,

In our current setup we have a three phase service head with 25mm tails feeding a 3 phase 125a distribution board. This is used as a sub mains board Nd MCBs (single pole and three phase) feed sub consumer units both inside and out side the property.

My question is really about if this is the correct way to do it and if MCBs are ok as the isolation for the sub boards. Each sub board or panel has its own isolator.

We are having renovation work done and would get it all changed if it sounds wrong.

Thanks[/url]

 

[RF Lighting]

Yes it's fine for a standard 100A TP type supply with BS1361 fuses.

If the supply is larger, the fault currents may require you to use a panel board with MCCBs or HRC fuses, but this is only normally a problem in large commercial and industrial properties.

 

[wreck-it-steve]

Yes it's fine for a standard 100A TP type supply with BS1361 fuses.

If the supply is larger, the fault currents may require you to use a panel board with MCCBs or HRC fuses, but this is only normally a problem in large commercial and industrial properties.

Thanks for your reply. It is a commercial property but the supply is a no bigger than 100a. so the mcbs are ok for isolation of each sub main? One or two of the sub mains are converted to TT at their point and have double pole mcbs supplying them from a third party panel.

 

[RF Lighting]

Yes the MCBs are fine.

 

[Risteard]

Selectivity/discrimination will be a problem with MCBs.