Ze and earthing of static caravan

[Tom420]

I'm doing an EICR on a static caravan after being called on to fix to a couple of problems due to loose connections.

It's all fine now within the installation in question but the earthing arrangement on the site is bothering me as it is relying on many multiple connections in steel armour around the site and I would have expected an installation like this to have its own earth rod. Has anyone else come across this, should I flag it up as a FI for the site supply or just sign the condition report for this installation as adequate and cut?

The supply is via a looped 16sq.mm. 2core SWA cable to a plug and socket connection box outside the caravan, the supply earth is the armour. Within the connection box is a 16A MCB, 30mA RCD and kWh meter. A 3c 2.5sq.mm. flex is wired from the plug to the DB within the caravan, the earth terminal within the CU (fed from the 2.5sq.mm. flex) is bonded to the caravan chassis, internal water and gas pipes. The gas is bottled and the incoming water pipe is plastic so there are no fortuitious earth paths.

I've not examined any other caravans or the site earthing but from driving around I have seen what looks like a DB next to the connection box of one caravan (about six caravans away from this one and next to the site office) with what looks like a single 5/8" earth rod. The other caravans (there's about a hundred and I've only glanced at them whilst driving around) appear to have the connection box with loop in/loop out SWA.

The Ze at "my" caravan is 58.3 ohms and my Zs readings are 59.something. The RCDs in the connection box and internal consumer unit trip together at 39.6ms, 21mA ramp. So it's all fine relying on the RCD for the disconnection times and the good old "1667 ohms max but less than 200ohms".

But there appears to me to be a high likelihood of someone standing barefoot on wet grass touching a metal caravan relying on many steel armour connections to an single earth rod and a high likelhood of breaks or degredation in the earth loop which could go unnoticed.

The only existing paperwork is a factory cert for dead tests.

Thank you in advance for your thoughts,

 

[westward10]

You need to need to find the origin and evaluate the earthing system, 58.3 ohm at the caravan suggests TT, if not then something is amiss. It is a tricky one as strictly speaking the socket outlet for the caravan is a separate installation.

 

[davesparks]

the earthing arrangement on the site is bothering me as it is relying on many multiple connections in steel armour around the site and I would have expected an installation like this to have its own earth rod.

Can you explain this a bit further as it doenst really make sense to me?

All installations have multiple connections in protective conductors, as long as the connections are properly made then what's the problem?

Why would you expect it to have its own earth rod? It wouldn't change anything about the number of connections in the protective conductors.

 

[buzzlightyear]

Delete

 

[Tom420]

Thanks for the replies, unfortunately I can't check the site earthing, I would expect the site to be a TT private distribution system.

I've checked through the regs and I can't find anything wrong, the high ze and lack of local earth rod were my original concerns.

The caravan earth is through the incoming swa and the extent of my inspection is the caravan so I'll put TNS on the report, list the Ze as 58 ohms, the max Zs as 1667 ohms and sign the report as satisfactory.
In the past, 16sq.mm. SWA was inadequate as a CPC (unless shown to be permitted by the adiabatic equation) but the disconnection times are met by the RCD.