Caravan RCD's

[agmason]

Has anybody had any experience with the RCD devices on caravan systems tripping when there is a thunderstorm. It's happenend a couple of times but not being present when this happens makes it hard to solve

 

[ruston]

If it is the same caravan it could just be the van taking in water  if there is a deluge. Caravans are known for the odd leak , and condensation.

 

[Rob_the_rich]

Just been reading about SPDs downstream of RCD (eg on telephone supply) causing RCDs to trip

 

[binky]

Has anybody had any experience with the RCD devices on caravan systems tripping when there is a thunderstorm. It's happenend a couple of times but not being present when this happens makes it hard to solve

I'm thinking tin box, and induced voltages - we have to consider these issues on Solar PV, but I've not known a thunderstorm to trip RCDs. I have known lighting strikes to induce surge currents that wipe out an inverter.

 

[agmason]

Just been reading about SPDs downstream of RCD (eg on telephone supply) causing RCDs to trip

No SPD's in the system

If it is the same caravan it could just be the van taking in water  if there is a deluge. Caravans are known for the odd leak , and condensation.

No leaks & it's not necessarily when it's raining

 

[agmason]

Has anybody had any experience with the RCD devices on caravan systems tripping when there is a thunderstorm. It's happenend a couple of times but not being present when this happens makes it hard to solve

I'm considering installing an SPD in the caravans consumer unit to deal with any induced voltages 

 

[Blue Duck]

Better earthing? where's the tranny?have you tested the arseydee?

I thought SPD's were a one shot deal??

questions questions....

 

[Tony S]

I’d concentrate on the earthing before SPD’s.

I used MOV’s on the OH supply and transorb GDT's on the OH phone line when I lived in the wilds of Derbyshire. Both rely on a good earth.

They stopped the phones, fax, television, etc. blowing up every time there was thunder in them there hills.

 

[roys]

Tony why did need a "motor operated valve" on an overhead supply?

 

[Rob_the_rich]

Have been reading a bit more about common mode currents due to lightning strikes causing RCDs to trip in TT systems. It can happen apparently, this from Marc's tech pages http://www.marcspages.co.uk/pq/3342.htm

Nuisance tripping (as shown above) is not just limited to serious faults where there are large changes in voltage. If there is sufficient unbalanced noise on the Live and Neutral i.e. the Live and Neutral do not have noise superimposed in an equal but opposing phase, then this will be 'seen' by the RCD as an imbalance especially if high amounts of leakage is 'biasing' the RCD.

What sure does not give the RCD a fighting chance is when such imbalance in the Neutral is created with the use of TNC-S style systems and especially where the Neutral is bonded to Earth at the entrance to the premises. Any noise on the Neutral is transferred to the Earth thus giving the Earth a similar potential to Neutral (the local Earth usually has a higher impedance than Neutral and easily takes on this potential).

The differential mode noise (simply the turning on of a significant load in an adjacent property), which would usually cause equal but opposing disturbances in the Live and Neutral and therefore cancel, is now found as equal and opposing disturbance across the Live and Earth.

This, therefore, presents a case where the Live and Neutral currents flowing through the RCD to Earth (via the filter capacitors) are not equal and opposing, and will be again be interpreted by the RCD as an earth leakage event. In this case the simplest cure is to employ an RCD that ensures the leakage is sustained before activating a trip (please note we do not state removing the RCD!).

This situation can be exacerbated with T-T, Z-T and I-T systems (see here) as the weaker earth systems can easily introduce noise and voltages into the RCD core in the form of unbalanced or common mode currents, especially in the presence of ground gradients (voltages that exist as a result of current flowing through the ground).

Such systems are extremely prone to RCD trips during lightning storms as a result of ground gradients even with cloud-to-could strikes (there is this weird thinking that only cloud-to-ground strikes cause ground voltages!).

But, it does not need a lightning storm; It could well be a neighbour with a problem causing an RCD to trip. If the neighbour has some Live-Earth fault causes voltage gradients in the surrounding earth mass, this is picked up by the T-T system's earth rod and transferred into the RCD as common-mode currents.

A word about 'Electronic' RCDs; These devices, as opposed to the electro-magnetic-mechanical types, are extremely prone to nuisance tripping because they are designed to not only trip during imbalance but also trip if a fault is detected with the incoming supply. Unfortunately, being electronic, these devices have very fast reaction times and will trip even on extremely sharp events such as switching transients. Many a case of nuisance tripping has been resolved by replacing the RCD with the more basic type.

Would using an AC type RCD help here? since it doesn't "see" DC currents.

 

[ruston]

Thanks for posting that.

 

[Tony S]

Tony why did need a "motor operated valve" on an overhead supply?

MOV Metal Oxide Varistor

GDT Gas Discharge Tube

 

[phil d]

MOV Metal Oxide Varistor

GDT Gas Discharge Tube

you need2 GDT's on a phone line,in a strike usually both lines rise to  the same potential,connect a GDT from A leg to earth and another from B leg to earth and that can prevent it.commonly they are connected across the A and B legs to prevent some idiot shoving 240 up the line,yes it does happen.

 

[Tony S]

When BT ran a new line in, they in their infinite wisdom removed the original carbon surge arrestors. Several ruined answer phones and FAX machines later I decided to fit the 120V GDT’s to both legs to earth, end of problem.

Living at 1000Ft above MSL, we got more than our fair share of thunder storms.

 

[OnOff]

Have been reading a bit more about common mode currents due to lightning strikes causing RCDs to trip in TT systems. It can happen apparently, this from Marc's tech pages http://www.marcspages.co.uk/pq/3342.htm

Would using an AC type RCD help here? since it doesn't "see" DC currents.

So glad to read this. Have exactly this problem when there's localised lighting strikes and I'm TT. 

EDIT: Often wondered if it's a factor we're in a deep sided valley with everything tall and/or metallic like trees, houses, barns plus all the scrap and farming equipment concentrated in a line of sorts along the bottom of the valley. The valley sides are clear. Might seem fanciful but it feels like when a storm's overhead we get more strikes in a line along the valley floor.