I doubt that harmonics are a problem on relatively small and single phase loads.

I also doubt that a distribution system fault is to blame, no common or likely fault would increase the supply current, but not trip the overload protection.

Probably poor connections leading to simple ohmic heating. Either poor workmanship by the installers, or poor manufacture of devices resulting in poor internal connections. Possibly not helped by frequent overloading and repeated re-setting. Damp may have corroded connections and resulted in heating.

Are the RCDs indoors or out doors?  If outdoors could you supply a picture of the enclosure?  Who has changed the RCDs in the past and are they using a Torque driver to the correct Nm as specified by the manufacturer?  A lot of RCDs have different Torque setting for the terminal at the top and bottom. 

We have mused this sort of thing before, and wondered last time for water heaters I think.. Unless the supply loops through the incoming terminals onto the next it is hard to see how more heat would be created in live than neutral - presumably they are within 30mA of each other...
So we have to conclude the heating curretn is similar but cooling is not as good, either because the layout of the cables in the box is assymetric, or because inside the device that terminal has less metal attached to it to act as heatsink.  I do expect the two sides to be different, as in the RCBO, the live connects to the current sensing part with its heater and coil, the neutral has a contact and passes the sensing coil.
It may be an age thing, but I preferred traditional terminals with round cable tunnels and double grub screws - a rectangular cage only sort of hits where it touches, and that is not really an all-round contact.

M

Why is the RCD dirty?  Could there be enviromental factors

Is the cable split-con , so the cable construction of the incoming phase and neutral are quite different ? (we assume SWA but maybe not. ) If so cooling will be uneven.

Mike

Hi,

answer to various queries.

Pictured device is dirty due to storage in barn AFTER removal due to fault.

Devices are installed in a manufacturer designed IP rated enclosure specifically for caravan hook ups

All work carried out by a registered electrician and why only the neutral terminals on the supply side if it a torque issue ?

Re the unbalancing of heat dissipation this could be something and I will be asking the manufacturer for their comments on the evidence. Will take one apart when I get home just to see if there is an internal difference/issue.

Regarding overload/reset we have a 16A Type C device serving one caravan and the owner does not have users saying the devices have tripped and need resetting.

I am intrigued with this fault as having done a fair number of surveys of all types of building it’s something I have not seen before. 

I am not sure on the IP and IK rating for that enclosure but I wonder what the designed operating temp range for the RCD is.

At 30 degrees C what is the actual trip current?

at minus 5 degrees C  what is the actual trip current?

and the owner does not have users saying the devices have tripped and need resetting.

site owner wouldn't necessarily be aware - most caravanners will be happy to just reset it themselves (on some club sites there's an electrical interlock with the socket, so the RCBO needs to be switched on manually after plugging in - so most are familiar with lifting the flap).

   - Andy.

Hi,

walk around site again and all enclosure are same manufacturer with IP 65 enclosure and IP44 socket connections. Temperature rating from data sheet is -25 to +60C. 

Re cable type the standard 3core,PVC/SWA/XLPE is very much what it looks like and a 16mm separate CPC to ground electrode at each position.

Problem ha been ongoing for a couple of years minimum so still has me intrigued ?

Keep try guys, must be a reason ? Why aren’t other sites having same issue ?

cheers

Dave

Why aren’t other sites having same issue ?

Do we know that they aren't? On most sites I've been to the boxes seem to contain a mish mash of brands (some with even a mix of RCCB+MCBs and RCBOs so definitely look like they've gone through a fair bit of on-site revision). Seems to me that some of the box manufacturers don't always pick the most "reassuringly expensive" devices either (and their choice of components may vary over time anyway).

   - Andy.