Solar panel systems earthing

[RayS]

Seeing so many others on site in Spain using solar panels plus inverters instead of site EHU but not having investigated such things myself I it occurred to me that they may not or do not have an earth connection as provided by the EHU cable. The same may be true for portable generators. The vehivles are standing on insulators, tyres and probably steady pads so not likely to be providing any earth connection path.
Does this mean that the safety trips an effectively disabled ? I refer to those protecting against fault rather than overload conditions.
Earthing requirements have always been a bit of a blind spot to me, so a clear simple explanation would be of great interest to me and doubtless others

 

[Grey13]

Does this mean that the safety trips an effectively disabled ? I refer to those protecting against fault rather than overload conditions.

I guess you are referring to the Residual Current / Earth leakage unit. This works by detecting a less than 30 mA leak from the mains to the neutral & applies to the 240 vac circuit. It will have no affect on the 12 V circuit / solar panel.

It will however work for a leak from a live wire to the caravan earth and or the ground outside. So if your van chassis had a live potential and you were bare foot on a wet patch and touched the van it would trip.

 

[ProfJohnL]

Hello Ray

As others have pointed out, the solar array will almost certainly be notionally a 12V dc system, and as such doe not need to earthed, but the more detailed issue is with inverters - should the 230V side be earthed?

I have thought about this and the answer is yes becasue the use of low voltage (Ironically that is how the industry describe mains 230V ac) but the method is not entirely clear, but there is a similar issue with running portable generators including those with inverters.

This may be of some help:

https://www.caravantalk.co.uk/library/files/Beginners-Guide-To-Generators.pdf

 

[Dodger524]

The RCD protective device work by measuring the current flowing into the circuit and comparing it to the current flowing out. If this becomes unbalanced by a leak greater than the rating of the RCD, it trips.

 

[ProfJohnL]

Hello Dodger

Your point is correct, but it only addresses part of the problem of a faulty appliance and the risk of shock in the context of a caravan using an independent (i.e. Not grid mains) 230Vac supply.

An RCD as you say compares the current flowing in both the Live and neutral legs, and if there is a difference of sufficient magnitude the RCD should operate and in the case of caravans to isolate both live an Neutral legs. The operation of the RCD relies on the presumption that an imbalance of current is due to a fault that carries some of the current to ground, and where a caravan uses an EHU, that would be ok becasue the Earth wire in the EHU will be connected to true ground through the sites wiring. and at some point in the supply system the ground and neutral will be linked.

The problem with many small generators and inverters used for caravanning is the construction regulations do not require the generator manufacture to link Earth to Neutral. This means that depending on how the caravan is connected to the generator/inverter there is every possibility the earthing system is not properly connected by the neutral side of the supply and is in fact left floating with respect to the supply.

If this is the situation, then there is every possibility that if a fault arises on the caravan wiring or appliances such that the live came into contact with metal part of the caravan or appliance, with no fault route back to the supply there will be no current flow to imbalance an RCD, and the caravan metal work or appliance casing would be at live potential.

The risk is that the combined surface area of the caravan and all the metal appliances will introduce a significant capacitance to the system such that under the fault condition the metal work could not only assume the supply voltage but also build up a significant charge. If a human or animal were to touch the metal work and some how make the link back to the supply neutral at the same time, the charge build up on the surface of the caravan may sufficient to be discharge through their body and electrocute them.

The added difficulty arises becasue some inverters may have a split rail output, and others have a single sided output which may prevent the earth and neutral lines being tied together to allow RCD's to operate.

A plug in s Neon light socket tester should tell you if there is a floating earth problem or not.

 

[RayS]

Thanks Prof. I didn't express my question too clearly. I should have explained it is the output from the inverter or generator I am concerned with not the dc output from the solar panel. With inverters / generator outputs now available at a nominal 2Kw tihis eqauls or perhaps exceeds the power you can take from many campsite EHUs and so presumably offers the same risk of shock and damage in the event of fault.

Could you elaborate on what a three light neon tester can tell about a floatinf earth. From the display it seems to differentiate only between earth connection or no earth connection.

 

[ProfJohnL]

Hello Ray
I'm sorry i didn't make my reference clear. A floating earth is an earthing system that is not properly connected to there is no earth.

 

[Fred460]

I think what is being referred to with regard to the neon light tester is an MK plug on the front of which are three neon lights. So when electricity is being supplied to your unit and the plug is switched on, then depending on what lights come on will give you an indication of the state of play with regard to what's happening with the current supplied. All three lights on means everything is OK but only one or two lights coming on will give you an indication of whatever the problem might be. I use one of these plugs all the time - particularly on continental sites where reverse polarity is still a problem. I always carry a short lead with the negative/positive cables reversed to easily overcome the problem of reversed polarity. The plugs are readily available in Halfords.