Type 2 Mcb and 17th Regs

[Steve3948]

Hi All,

I see that Type 2 Mcbs are no longer mentioned in tables under Maximum permitted Zs in the new 17th Regs.

The new values are based on 230V instead of 240V, so I imagine it's just a case of doing the equation to find maximum permissible Zs when carrying out a PIR and finding type 2 in use.

 

[Spark123]

Yep, don't think they were in the 16th ed after 2001 either?? 230 / (value x 7) for a type 2.

There are some max measured figures in the back of the new GN3, not 100% sure how they arrive at them though. Doesn't look like they are using the 0.8 correction factor anymore.

 

[Steve3948]

You are probably right about 16th, I had a print off, on all max zs values stuck on the wall above the PC, whenever my Amtech Software did show a value I just checked my print off.

Just looked in the back of the GN3 and again you are right, how I missed that I don't know, I did fumble through a few times honest

The values shown as you say do not work out with the X7 ? but at least I know where they are now.

Many thanks.

 

[Spark123]

The values in GN3 are maximum measured values for cables with a particular K value.
The ones you need for your forms are maximum permissable values, i.e. when the cable is at its maximum operating temperature.
In the 16th edition, if you multiplied the max permissable figures by 0.8 then the result was the max measured value.
Using the 230 / (size x 7) will give you a maximum permissable value for a type 2 MCB.