Earth cable in caravan

[petrK]

Hi,

NewB question. I got old caravan - there is green-yellow cable attached to chassis from water taps and also it was from fridge(that i removed due to caravan rebuild), I suppose current coming for water-pump connected to taps wont be likely very high(there is 10 Amp fuse for this). But i want to install new system where max current flow can go very high ( say 200A). I dont understand how grounding works in the caravan. What i know cable is attached to chassis, but how chasiss is connected to physical ground - throught corner steadies? Have hard time to get this, appriciate any light on this

 

[RogerL]

Hi,

NewB question. I got old caravan - there is green-yellow cable attached to chassis from water taps and also it was from fridge(that i removed due to caravan rebuild), I suppose current coming for water-pump connected to taps wont be likely very high(there is 10 Amp fuse for this). But i want to install new system where max current flow can go very high ( say 200A). I dont understand how grounding works in the caravan. What i know cable is attached to chassis, but how chasiss is connected to physical ground - throught corner steadies? Have hard time to get this, appriciate any light on this

If you want a system with 200A, you need a qualified electrician to design and install it as you clearly don't understand enough about it - probably not the advice you were looking for!

 

[otherclive]

Hi,

NewB question. I got old caravan - there is green-yellow cable attached to chassis from water taps and also it was from fridge(that i removed due to caravan rebuild), I suppose current coming for water-pump connected to taps wont be likely very high(there is 10 Amp fuse for this). But i want to install new system where max current flow can go very high ( say 200A). I dont understand how grounding works in the caravan. What i know cable is attached to chassis, but how chasiss is connected to physical ground - throught corner steadies? Have hard time to get this, appriciate any light on this

What on Earth do you plan to do with 200 amps?

 

[ProfJohnL]

The Green & Yellow wire is a UK continuous protection circuit also informally known as the earth, and its to comply with the UK wiring codes that all exposed metallic parts should be wired back to the earth in the consumer unit. The cable is safety system and should not be deliberately used to carry any current for any appliance.

Nothing in a caravan is safe to use with 200A! .

Get advice from a local professional electrician who can advise you and ensure you are safe and in accordance with your local electrical regulations

 

[petrK]

What on Earth do you plan to do with 200 amps?

I actually see that my question makes no sense. 200amps is maximum discharge of battery, 200A i mentioned is actually too much, even in case of maximum load - 1,5kw 12v inverter with other DC appliances.

Yet i still dont understand earthing in caravan - if i understand it correctly its protection if current gets to the metalic cover where shouldnt be so it gets back to the ground and wont get to human touch. Just cannot make much sense how this works in chassis.

 

[Hutch]

I take it Petrk , English is not you First language, so we have to translate what's you problem is. Give us time please.

 

[ProfJohnL]

Earthing in caravans relies on the earth conductor in the Electric Hook Up Cable. It does not use the caravans contact with the ground, becasue the caravan manufacturer does not know what surface the caravan might be used on. But to protect the humans from any part of the caravan becoming live caused by a fault, all exposed metal components are required to be connected back to the earth strip in the caravans consumer unit to provide a low resistance path for any fault current to use rather than anybody who might touch it.

The earthing system is designed to work for the mains system which is limited to 16A. 230V ac

The 12Vdc system must not rely on the caravans metal structure to complete the 12V circuits. Each 12V appliance must have a 12V and 0V wire that returns to the caravan's 12V control panel.

You tell us you want a 1.5kW inverter. You would not be able to use it at full power for very long becasue if it were delivering 1.5kW it would need at least 125A of 12V power from the battery. The battery simply could not supply that much current for very long (about 1 hour) A 120Ah battery in good condition only stores about 1440 Watt Hours of energy. Its possible a 1.5kW inverter could exceed the the batteries constant current discharge rate.

 

[Woodentop]

Agreed with the Prof - in the main. Users should not forget that leisure batteries are rated at 20hrs, not 10 hrs like a car battery. So a 120Ah car battery should - in theory at least - provide 12A for 10 hours but a leisure battery of the same current rating will only provide 6A for 20 hours. If you draw current above that rate the battery will run down significantly more quickly.

Also don't assume invertors are 100% efficient - they ain't. A decent quality unit will probably be around 80-85% efficient. That means that if you draw 100W from the invertor, at 80% efficiency it will draw 125W from the battery. Remember as well that unless you get a specific pure sinewave invertor the unit output will be a series of steps that attempt to replicate a sinewave but because the steps are very steep (one level to the next may be only microseconds) many equipment don't like them. Pure sinewave however replicates the mains exactly but they cost twice the price.

The one certain thing is that watts is watts no matter at what supply voltage. A 20W lamp will draw 20W whether it is a 12V lamp or a 240V lamp. The current will be different but not the power. BUT a 1500W invertor is the maximum load it can handle - you can still put a 20W mains light on it that will work perfectly well!

 

[SteveW]

Hi,

NewB question. I got old caravan - there is green-yellow cable attached to chassis from water taps and also it was from fridge(that i removed due to caravan rebuild), I suppose current coming for water-pump connected to taps wont be likely very high(there is 10 Amp fuse for this). But i want to install new system where max current flow can go very high ( say 200A). I dont understand how grounding works in the caravan. What i know cable is attached to chassis, but how chasiss is connected to physical ground - throught corner steadies? Have hard time to get this, appriciate any light on this

Hi, the common use of the word “earth” to describe what is actually the “protective conductor” is causing confusion here. The caravan protective conductors (green/yellow) wires are connected to the caravan chassis rather than earth. There is a link back to actual earth via the EHU lead but the system does not rely on this for protection. You are in a metal box that may or may not be linked to earth via the steadies etc, it’s earthing status is unknown. The caravan protective conductors ARE connected to the caravan chassis. So if an occupant touches a live wire a shock current might flow, but to the caravan chassis rather than earth. The caravan supply board has an RCD cutout , hence this leakage current is detected and it trips provided the chassis is linked as described. Earth need not be involved at all in a separate leisure vehicle installation.

None of this has anything to do with the 12V circuits.

Steve