TT supply for static caravans

[TJC1]

Need some advice, I have 7 static caravans to connect which need to be connected via TT

1. All the vans have a 30ma RCD main switch internally

2. All the vans come with a 2.5mm artic flex ready for connection

3. All vans will be connected through an double pole isolator switch

4. There is a new 100a 3phase PME supply ready

Here are my two options;

A - Convert the mains into TT, install a 100ma time delayed RCD and connect vans

B - Leave the PME supply up to the caravans and install an earth rod for each van

Thoughts?

 

[pc1966]

I would go with (A) but obviously check you main earth rod is good enough and not close to any PME buried stuff (bonded water pipes, etc)

 

[pc1966]

Might be useful:

https://tinyurl.com/5c5w3zyr

 

[TJC1]

I would go with (A) but obviously check you main earth rod is good enough and not close to any PME buried stuff (bonded water pipes, etc)

It’s definitely my preferred option, I just worry that somehow to 30ma internally may cause the 100ma to trip

 

[pc1966]

It’s definitely my preferred option, I just worry that somehow to 30ma internally may cause the 100ma to trip

With 100mA delay it should be fine. Of course if you have 7 * 9mA max on all it is over In/2 = 50mA but unlikely.

300mA delay is an option for more margin, but then looking at under 167 ohm Ra value to meet disconnection.

 

[buzzlightyear]

B - Leave the PME supply up to the caravans and install an earth rod for each van

That's what I would do.

 

[pc1966]

That's what I would do.

It is six of one and half dozen of the other.

PME to the supply RCD is easy and allows OCPD disconnection so simpler DB to feed it all. But then you need to meet 5s disconnection on those feeds and depending on cable length, etc, that might be a problem.

Going up-front RCD makes that aspect simpler as sub-main R1+R2 no longer a real issue and potentially higher OCPD for a bit of over-current selectivity with feed point OCPD, but easier for one fault to take out the lot. And you still need 30mA MCB/RCD or DP RCBO at each point.