Caravan site readings on TT system

[Bradley6969]

Hi, have a distribution unit which feeds some caravan boxes TT system, it has upfront 300mA RCD and double pole 60898, now I’ve been sent to re gland as the disconnect times wasn’t met, but I’m getting readings of 0.30 ohms when max is either TT 167 ohms or if you go by MCB then 0.59? But the boxes have there own RCD/MCB Maybe last persons tester wasn’t calibrated? Very low but paralel paths?

 

[Wilko]

Hi - mystery...maybe the RCD just didn't trip fast enough when tested?

 

[Deleted member 26818]

Where in the site are you getting readings of 0.3 Ohms?

 

[Bradley6969]

Where in the site are you getting readings of 0.3 Ohms?

The panel which feeds the panel I’m getting 3.15 ohms and the 1st panel is 4 meters from ground mounted transformer

 

[Bradley6969]

So Ze on panel next to transformer is 0.3 and this goes 30/40 meters to panel I’m getting 3.15 ohms

 

[Deleted member 26818]

Is the supply TN-S or TN-C-S?

 

[Bradley6969]

It’s TNS

 

[Deleted member 26818]

Suggests that the SWA is rusted.

 

[Bradley6969]

Suggests that the SWA is rusted.

I’m thinking tighten up the gland and see what I get and yes it’s 4 core 120mm

 

[Deleted member 26818]

If you can’t get the Zs down, you’ll have to TT the other end.

 

[Bradley6969]

If you can’t get the Zs down, you’ll have to TT the other end.

Thanks but what is max Zs for the 400amp Switch?

 

[westward10]

Assuming this is the 400A 60947-2 device you mention in your other thread the 0.30 Ze at source is too high without needing to know the Zs. Aside from needing to know the manufacturer and other details it will be too high.

 

[bigspark17]

I’m thinking tighten up the gland and see what I get and yes it’s 4 core 120mm

Cant you test the swa braiding with shroud removed? This will eliminate the gland being the problem if still high reading.
I would not be happy having the site on TNS as there is no way of guaranting the supply its pme at transformer or may be in the future. TT it.