Question about Zs Values in BS7671

Hello there,

Sorry bit of a trivial question but it is bugging me!

I have a question about the Zs values in table 41B1 of BS7671:2001 Requirements For Electrical Installations.

I wanted to check I could manually calculate the values, so that I know I understand where they come from.

So I calculated 230 divided by the current needed to cause disconenction in 0.4 seconds, looked up from appendix 3.

The results I got differed from the table, but only slightly.

There are two explanations I can think of:

1. The table uses 240 volts for it's calculations (even though the text says it uses a U0 of 230V)
2. Temparature is taken into account. A factor of 1.04 (which I have seen somewhere in the onsite guide) would do the trick.

Does anyone have a definitive answer?

Thanks

Martin