Advice on 461.2 needed

[tomlonsborough]

Hi folks,

Just need a bit of advice regarding whether or not neutrals require switching.

- 3 phase board, 3 pole main switch, neutral is un-switched. 416.2 (ii) states that switching of the neutral is not required if the conductor is reliably connected to earth by a low resistance to meet the disconnection time requirements of Ch41. How might I conclude that the resistance is low enough, and therefore the reg has been adhered to?

Couple of extra details regarding the above if required:

• TN-C-S
• Zs @ DB is about 0.08 Ohms
• Continuity measurement between N-Earth about 0.07 Ohms
• BS88-2 63A fuses

- 3 phase dishwasher, 4 pole rotary isolator requires replacement. Similar situation to above, I'm trying to work out if I can fit a 3 pole and leave the neutral un-switched.

Many thanks in advance!

Tom.

 

[Risteard]

In a TN system it's not really desirable to switch the neutral as any failure in this regard will start a fireworks display. The neutral is reliably connected to Earth by a suitably low impedance in a TN system.

 

[telectrix]

as above. 4 pole switching generally only required on a TT earthing system.

 

[davesparks]

How might I conclude that the resistance is low enough, and therefore the reg has been adhered to?

If its a TN system it is low enough.

 

[Strima]

As above, no need to switch the neutral in a TN.