Inverter supply to a motorhome

[boltonsparky]

I have been helping my partner's Dad wire up his motorhome. 

He has been supplying kit and I've been fitting it. 

The van is wired for electric hook up so the site feed comes into a 3 way board protected by an RCD then MCBs to the sockets around the van. There is a cable connecting the van body to the earth terminal in the fusebox.

He also would like an inverter to power the sockets when off grid. 

I've fitted a double pole changeover switch between the hook up point on the van and the fusebox so that the inverter if turned on whilst the van is hooked up can't back feed into the site supply. 

The inverter he has provided when powered up shows up as no earth (CPC) when tested.

Readings are as follows

L-N 230v

L-E 0v

N-E 0v

Continuity as follows

L-E open circuit

N-E open circuit

E to ground stud of inverter continuity

We've found some instructions for the inverter and it states that it isn't suitable for our intended use. However there is no mention of this grounding stud on the inverter body nor is it shown on the diagram of the inverter. 

Questions are,

1.is an inverter like we have dangerous when used in this set up?

2.If we were to bond the ground stud of the inverter to the van body would this make it safe to use in this setup no mention of this ground stud at all in the instructions? 

3.Should we only be fitting an inverter that is able to have it's neutral and earth connected, in effect making our own TN-C-S supply from inside the van.

4.I've looked in the blue book under generators and it talks about static converters, is this what they're referring to as an inverter?  

 

[binky]

my van is wired with some 240V sockets and then some 12V outlets, the leisure battery being charged from site mains when connected and supplying the 12v stuff, so effectively I have separate power supplied for different items. EG, on site I use electric kettle, off site I use the gas. I do not have an inverter to use battery to supply mains to anything.

you may find this FB page helpful   The 12V Leisure Electrical Group

 

[boltonsparky]

my van is wired with some 240V sockets and then some 12V outlets, the leisure battery being charged from site mains when connected and supplying the 12v stuff, so effectively I have separate power supplied for different items. EG, on site I use electric kettle, off site I use the gas. I do not have an inverter to use battery to supply mains to anything.

you may find this FB page helpful   The 12V Leisure Electrical Group

Thanks for the link I'll have a look 

I wish there was something definitive on inverters, or if there is I can't find it.

This one has leisure batteries on split charge, mains charge and solar charge. It's got the 12v sockets, 240v sockets USB sockets and gas and satellite tv, microwave and 4g wifi. His view is that if he's going away he wants all the home comforts too. It's a self build job, he's doing a really good job of it, it looks very smart. 

 

[Andy™]

its an IT supply as is. you could always link N-E to make a TNS supply (note TNS, not TNCS), which is what ive done with the inverter in my van

 

[Geoff1946]

My son's home-brew Sprinter conversion has all the gear you list but he's simply connected the invertor output to a separate 13amp socket.

After all you are quite limited as to how much 230 volt gear you can use  from leisure batteries and most invertors are not very efficient for long term running.

It's most efficient to run as much as possible directly from the batteries. For instance he uses a dedicated 12 to 18 volt convertor for a TV.

 

[boltonsparky]

its an IT supply as is. you could always link N-E to make a TNS supply (note TNS, not TNCS), which is what ive done with the inverter in my van

Thanks Andy. I know some inverters don't like the earth and neutral connected together so we will be trying to find one that it is possible on. 

I'll be honest inverters fry my brain and I've been trying to work out potential faults that could arise and then the fault paths to try and get my head round if they are dangerous in certain faults or not. Then there are types that aren't isolated from the negative on the battery side so could potentially send the van body live but if there isn't a connection on the AC side to the body because the earth and neutral aren't linked nothing will trip off, or that's how I understand it.

I've even seen pictures of people earth spiking their inverters into the ground which to me seems totally pointless as there is no reference to the actual earth anyway.

My son's home-brew Sprinter conversion has all the gear you list but he's simply connected the invertor output to a separate 13amp socket.

After all you are quite limited as to how much 230 volt gear you can use  from leisure batteries and most invertors are not very efficient for long term running.

It's most efficient to run as much as possible directly from the batteries. For instance he uses a dedicated 12 to 18 volt convertor for a TV.

In this one most things are 12v, the TV for example is 12v and just connects straight to the battery 12v system. It's only for the microwave and the odd plug in appliance the inverter is used but to just have one socket for the inverter would mean unplugging from the mains sockets, and running an extension across the van to an inverter socket so makes more sense to connect the inverter to the van's existing AC system.   

 

[Andy™]

I've even seen pictures of people earth spiking their inverters into the ground which to me seems totally pointless as there is no reference to the actual earth anyway.

the earth spike is to give the return path from earth to the supply source- same as DNO's install an earth rod at their transformers, large events with generators spike their generators etc. its not to give the installation an earth like a TT supply

 

[boltonsparky]

the earth spike is to give the return path from earth to the supply source- same as DNO's install an earth rod at their transformers, large events with generators spike their generators etc. its not to give the installation an earth like a TT supply

I understand it with generators (or I think I do) when you have cables, FDUs etc. in soggy fields but with a van and inverter setup if the whole van body went live from an inverter inside the van if you stepped out of the van and touched the ground whilst holding the metal bodywork nothing would happen because the van is insulated from the ground by the tyres so there isn't a return path from the outside ground back to the neutral of the inverter so no current could pass through your body. 

Hammer in an earth rod though and there is now a path back to the neutral through your body and the earth rod (via the neutral earth link at the inverter), probably a high resistance one as the earth rod is likely to be poorly installed so an amount of current is likely to pass through your body but with it being a high resistance path would it be enough to trip anything?

 

[Geoff1946]

 

[Andy™]

I understand it with generators (or I think I do) when you have cables, FDUs etc. in soggy fields but with a van and inverter setup if the whole van body went live from an inverter inside the van if you stepped out of the van and touched the ground whilst holding the metal bodywork nothing would happen because the van is insulated from the ground by the tyres so there isn't a return path from the outside ground back to the neutral of the inverter so no current could pass through your body. 

Hammer in an earth rod though and there is now a path back to the neutral through your body and the earth rod (via the neutral earth link at the inverter), probably a high resistance one as the earth rod is likely to be poorly installed so an amount of current is likely to pass through your body but with it being a high resistance path would it be enough to trip anything?

but if the van body was earthed then it woud be at the same potential as the earth rod & ground, therefore no shock. but becaus the vehicle was also earthed then any fault would make ADS do its thing and turn off the power

 

[boltonsparky]

View attachment 10821

I've had generator hire companies turn up and place the earth rod in plastic drains before now  headbang   Another favourite is wedging it under a trailer tyre. 

 

[binky]

Got a lighting project for a stable block and need an inverter around 1.5kW for small appliances, is there a make anyone would recommend?

 

[boltonsparky]

This is about the cheapest one I've found that is suitable for use feeding an AC distribution system (according to the manufacturer) so that the RCDs will function in the event of a fault but as yet haven't had hold of it so can't comment on its quality.

https://www.sunshinesolar.co.uk/Item/VP2500?gclid=Cj0KCQjwupD4BRD4ARIsABJMmZ9O2qlHB7sP2a7b7okhqdapv-HsNZcPrgbS8imTHiP4eoEAK4kR3XIaAku9EALw_wcB

 

[binky]

I'm sure I've seen that at a better price on Amazon? Could be wrong about that as I have been looking at loads! As long as it's a oure sine wave spec it should be ok.

 

[boltonsparky]

I'm sure I've seen that at a better price on Amazon? Could be wrong about that as I have been looking at loads! As long as it's a oure sine wave spec it should be ok.

If you do manage to find the same thing cheaper if you could let me know as a family member is looking to buy it.

I'm going to have a look round myself too.

 

[binky]

If you do manage to find the same thing cheaper if you could let me know as a family member is looking to buy it.

I'm going to have a look round myself too.

think that one has been 'branded', but there are loads on ebay and Amazon, on Amazon I nver buy anything without 4 stars + reviews.

 

[boltonsparky]

think that one has been 'branded', but there are loads on ebay and Amazon, on Amazon I nver buy anything without 4 stars + reviews.

They are plentiful but the ones with the link switch for the RCD seem to be few and far between, I've contacted a few manufacturers of them and they say linking the neutral and earth together manually will make them go bang. I've downloaded quite a few manuals to some of these inverters and they state that it's not suitable for use in a motorhome or feeding an AC distribution system. It's usually a one liner hidden in the manual somewhere. However they may be suitable for your intended use. 

I've also noted from trying to find further information on them that some of the cheaper ones can dump 230v down the battery negative as they aren't isolated from the DC side.