Max Zs measurement allowed

[cliffed]

Any ideas on the Max Zs on a 3871 Type 3 13 amp MCB

 

[westward10]

I know you can or could get 13A mcbs but is that a typo?

 

[cliffed]

Here’s a pic from the lighting CP

 

[nicebutdim]

Good to see @westward10 being educated about protective devices

 

[pc1966]

According to this table they don't exist!

https://www.electricalsafetyfirst.org.uk/media/1627/master_earthfaultlooptable.pdf

However, interpolating/scaling between 10A and 15A Type 3 breakers to 13A results in 1.42 ohms.

 

[westward10]

They do exist but are an oddity, Memshield 2 had 13A devices but are rare as hens teeth.

 

[cliffed]

According to this table they don't exist!

https://www.electricalsafetyfirst.org.uk/media/1627/master_earthfaultlooptable.pdf

However, interpolating/scaling between 10A and 15A Type 3 breakers to 13A results in 1.42 ohms.

Yea still trying to find them… will have to calculate using the BS time curve tables

 

[loz2754]

The breakers shown in the (blurry) picture seem to be these - ABB 60898 S271 type C, not BS3871 type 3.
There are datasheets for these that include the time/current charts.
I don't know if this helps at all...

 

[pc1966]

The breakers shown in the (blurry) picture seem to be these - ABB 60898 S271 type C, not BS3871 type 3.
There are datasheets for these that include the time/current charts.
I don't know if this helps at all...

If they are usual type C (instant trip point = 5-10 * In) then you can calculate Zs for cold testing (assuming ~70C operating, etc) as:

Zs = 80% * Umin / Imax = 0.8 * (230 * 0.95) / (13 * 10) = 1.34 ohms

 

[cliffed]

Thanks guys think someone got the details wrong….. happy now

 

[davesparks]

They do exist but are an oddity, Memshield 2 had 13A devices but are rare as hens teeth.

I've never seen the MEM ones but I see a few different brands of 13A MCB used in various stage lighting dimmers.