disconnection times v voltage bands

[silver surfer]

Guys
BS 7671 table 41.1 shows that a disconnection time of 0.4 secs for 120<volts to <inc 230 volts, and a disconnection time of 0.2 at 230< to < inc 400v. (TN systems).
My query is with a 10%+/- tolerance which could possibly increase 230 volts to 253 volts hence taking your 230v 0.4s disc design into a 0.2 disconnection time scenario.

A bit confused!

 

[JUD]

It's 0.4s for 120V < Uo ≤ 230V.

Uo being the nominal voltage to earth. The tolerance is +10% / -6% (216V - 253V)

 

[IQ Electrical]

It's 0.4s for 120V < Uo ≤ 230V.

Uo being the nominal voltage to earth. The tolerance is +10% / -6% (216V - 253V)

Precisely.

 

[silver surfer]

It's 0.4s for 120V < Uo ≤ 230V.

Uo being the nominal voltage to earth. The tolerance is +10% / -6% (216V - 253V)

What does NOMINAL mean exactly?

 

[IQ Electrical]

What does NOMINAL mean exactly?

It's a value (constant) that we use rather than using the constantly changing supply voltage-235V one minute, 249V the next.