Installation Query: Campervan Powering Workshop Off-grid

[Iveavan]

The simple question.
If I wanted to power my workshop (which is currently connected to the grid, under TN-C-S arrangement ) from my campervan (TN-S arrangement), how would you install this? And do I need an "Earth Rod"?

Now for the more "in-depth" long question" and explanation of the proposed off-grid system.

With the help/ advice from Gromett (so I will tag him within this question), we've been trying to plan / work out a safe solution on how to do/go around this.
We both feel and agree this needs an 'experts eye going over the proposed way, in which I plan to install this'.

So if they are any experts who solely install 'off-grid applications', your advice/input would be greatly welcomed & appreciated .
To be fair, my experience has really been with 'three phase industrial charging systems and industrial three phase busbars over the past 30 years' (MHE Engineering), and Gromett is a former electrician. So, as you can appreciate, this is not something we have done before, as it is an 'unusual bespoke setup / application'.

However! I think I should start with my proposed setup first, as this is neither a permanent installation nor a mobile installation but more of a mixture of the both ( probably the best way to describe and simplify the below installation is -

" a generator supply with TN-S arrangement connected to the workshop, but transfering and isolating the grids TN-C-S arrangement").

My workshop is connected to the grid, however! The grid supply is an TN-C-S arrangement which is coming into the property that it is currently connected to, I don't particularly want to change it to a TT arrangement nor add an TT arrangement for the workshop due to the implications of the grid supply (TN-C-S arrangement), nor can I share/connect to the grid TN-C-S earth arrangement with the off-grids TN-S arrangement.

Over the past 3 years, I've suffered with a lot of power outages to the property ( around 8 so far ), so I want an off-grid solution to deal with this involving the campervan as a battery bank.

My campervan setup.
Within my campervan, I have one 'Victron Multiplus ii, 24v 5000va. The DC power supply for the Multiplus is two Lifepo4 24v 280a Fogstar Drift batteries, ground to its own ground point upon the chassis ladder of the van.

Whilst the Multiplus is in off-grid mode ( island mode ), it is in the state of "an N-E bond arrangement (TN-S)".

How I propose to install this?

From the Multiplus (witthin the campervan), or from the AC-1- out to the CU (using 6mm2, 3-core H07RN-F cable). Within the CU, the circuit is fed through a ('ALL' RCDs & MCBs mentioned below and throughout are 'double pole Schneider RCDs & MCBs') 40a 30ma RCD and a 16a type b MCB.

(The Multiplus, the CU, and the off-grid output socket are all bonded to the chassis ladder of the van (using 10mm2 Earth wire), and any exposed metal surfaces have equipotential bonding).

From the CU and before entering the off-grid output socket, they will be another 40a 30ma RCD *(a backup RCD if the one in the van's CU should fail to trip).

From the second RCD onto the van's off-grid output socket , this is a 32amp isolated socket in order to plug the workshop into the van. Connecting the two will be a 6mm2 3-core H07RN-F cable with 32a plugs on both ends (van plug end male, workshop plug end female).

The cable above will be connected from the output socket of the van and the wall mounted 32a input socket.
From that wall mounted input socket is a 6mm2 twin and earth SWA cable routed away from it and clipped onto the wall of the house ( around a 5mt run ), where it will terminate at the automatic transfer switch.

The automatic transfer switch will disconnect the grid supply. So, thats the Live, Neutral & Earth (grid "TN-C-S" arrangement will disconnected / isolated) will be isolated from the cable run going from the transfer switch and onto the workshop CU, but only once the off-grid cable from the van is plugged into the wall socket and the isolator switch is turned on, (which is on the vans off-grid 32a output socket). Then, the vans off-grid feed supply (16a maximum, Live, Neutral & earth, TN-S arrangement) will be supplying the power supply over onto the cable run going from the transfer switch onto the workshop CU, powering the workshop.

On the grid input feed and the off-grid input feed on the transfer switch, they will be an individual 40a 30ma RCD and a 6a type b MCB dedicated to each feed before going through the relays and then onto the workshop cable run ( two Schneider iCT 25A 2NO 2NC 220...240V 50Hz contactor - A9C20838)

I hope I have explained the above well and in detail in trying to share with you and what Im trying to achieve here?

So my questions are.

Can anyone see any issues over my proposed way of installing this?

Because the off- grid power supply is coming from my campervan into the workshop, which doesn't have a earth rod (due to the N-E bond arrangement (TN-S) ) and supplying my workshop under a TN-S earth arrangement, do I need to install an 'Earth Rod' for the campervan ( the source ) ?

Any help, advice, or input would be greatly appreciated. Many thanks, Mark C.

 

[Gromett]

I suggested he needed to discuss this Raul and perhaps others on here such as autorouter etc? Sorry If I missed anyone with expertise in this?

It's an oddball one :/

 

[Raul]

I can see few things wrong in here, but mostly you are on the right track. If you still in the industry, 3 phase or one phase, makes no difference, just pick one line and a neutral instead of 3 lines. What you are doing is a dual power supply in a dwelling, covered in the bs7671 part8 chapter 82.
The earthing arrangement in your van does not have a earth point, (IT) but a return path for fault current(PE), back to source(inverter). Even if you bond the N-E, does not make it a TN-S, this is a earthing arrangement type that has the characteristics of a grid supply: N-E separated at transformer, but the E is still bonded to a ground rod, that makes it TN-S. It enters your property as 3 wires, or 2 wires and the outer sheathing as 3rd wire, for PE.

Now, when you isolate the garage from PME TN-C-S supply, from you own van supply it HAS to be TT: this is explained in regulation 826.1.1.2. of bs7671. You become an individual PEI, reg 824.3. Each supply has to provide its own PE return path, you probably know that already. But, you can't take the power outside the van without a TT PE protection, and preferably under 100ohms.
What's the point in running a 6mm2 PE from inverter (supply) to garage CU, if you don't provide a equipotential 0v to earth you standing on? This has to be TT 100%, and preferably under 100ohms, 16mm2 main earth from rod to MET in CU. And rcd with TT is a MUST, this you covered already, but I would go 32A b curve instead of the 40A mentioned. Your Inverter will not be able to give enough kA fault current to trip a 40A. Also, if you have any main bonding entering the garage CU, they have to be isolated, when you operate in islading mode, (van supply). Any existing main bonding has to stay on the PME side, under no circumstances this should have NO continuity to your TT rod.
Let me know if something is not clear.

 

[Iveavan]

I can see few things wrong in here, but mostly you are on the right track. If you still in the industry, 3 phase or one phase, makes no difference, just pick one line and a neutral instead of 3 lines. What you are doing is a dual power supply in a dwelling, covered in the bs7671 part8 chapter 82.
The earthing arrangement in your van does not have a earth point, (IT) but a return path for fault current(PE), back to source(inverter). Even if you bond the N-E, does not make it a TN-S, this is a earthing arrangement type that has the characteristics of a grid supply: N-E separated at transformer, but the E is still bonded to a ground rod, that makes it TN-S. It enters your property as 3 wires, or 2 wires and the outer sheathing as 3rd wire, for PE.

Now, when you isolate the garage from PME TN-C-S supply, from you own van supply it HAS to be TT: this is explained in regulation 826.1.1.2. of bs7671. You become an individual PEI, reg 824.3. Each supply has to provide its own PE return path, you probably know that already. But, you can't take the power outside the van without a TT PE protection, and preferably under 100ohms.
What's the point in running a 6mm2 PE from inverter (supply) to garage CU, if you don't provide a equipotential 0v to earth you standing on? This has to be TT 100%, and preferably under 100ohms, 16mm2 main earth from rod to MET in CU. And rcd with TT is a MUST, this you covered already, but I would go 32A b curve instead of the 40A mentioned. Your Inverter will not be able to give enough kA fault current to trip a 40A. Also, if you have any main bonding entering the garage CU, they have to be isolated, when you operate in islading mode, (van supply). Any existing main bonding has to stay on the PME side, under no circumstances this should have NO continuity to your TT rod.
Let me know if something is not clear.

Thank you, Raul.
No, I haven't been in the MHE industry for some time now, in all honesty. But this is a great help! And the answer I needed and in great understandable depth too .

My apologies, Raul. you are absolutely right! Within its current state, the van is currently 'Isolation Terre' as it is not directly grounded. For some reason, this did not compute within my mind at the time of writing. "".

So, yes! Definitely, a TT arrangement is needed and testing going forwards, with 16mm2 earth cable from the Earth rod terminating upon the MET within the CU within the van, and RCDs needs to be 32a. .
Many thanks for your help/advice with this one, Raul . All the best to you, mate. Mark.

 

[Gromett]

I can see few things wrong in here, but mostly you are on the right track. If you still in the industry, 3 phase or one phase, makes no difference, just pick one line and a neutral instead of 3 lines. What you are doing is a dual power supply in a dwelling, covered in the bs7671 part8 chapter 82.
The earthing arrangement in your van does not have a earth point, (IT) but a return path for fault current(PE), back to source(inverter). Even if you bond the N-E, does not make it a TN-S, this is a earthing arrangement type that has the characteristics of a grid supply: N-E separated at transformer, but the E is still bonded to a ground rod, that makes it TN-S. It enters your property as 3 wires, or 2 wires and the outer sheathing as 3rd wire, for PE.

Now, when you isolate the garage from PME TN-C-S supply, from you own van supply it HAS to be TT: this is explained in regulation 826.1.1.2. of bs7671. You become an individual PEI, reg 824.3. Each supply has to provide its own PE return path, you probably know that already. But, you can't take the power outside the van without a TT PE protection, and preferably under 100ohms.
What's the point in running a 6mm2 PE from inverter (supply) to garage CU, if you don't provide a equipotential 0v to earth you standing on? This has to be TT 100%, and preferably under 100ohms, 16mm2 main earth from rod to MET in CU. And rcd with TT is a MUST, this you covered already, but I would go 32A b curve instead of the 40A mentioned. Your Inverter will not be able to give enough kA fault current to trip a 40A. Also, if you have any main bonding entering the garage CU, they have to be isolated, when you operate in islading mode, (van supply). Any existing main bonding has to stay on the PME side, under no circumstances this should have NO continuity to your TT rod.
Let me know if something is not clear.

Thanks Raul much appreciated. When Iveavan mentioned I was a former electrician it was decades ago, and I was on the 15th edition and didn't deal with any of this stuff from memory. Late 80s early 90s.
I knew you were the guy to speak to Thanks.

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[Raul]

16mm2 earth cable from the Earth rod terminating upon the MET within the CU within the van,

The 16mm2 main earth conductor its only needed from rod to garage DB, or CU. Not into the van, from the van to garage DB, you have the 3x 6mm2 feed that is more than enough, and PE is same size as phase, on that feed.
Again, that 16mm2 it is swapped with your PME in islading mode, and when on grid mode, PME is back on and the 16mm2 disconnected.

 

[Iveavan]

The 16mm2 main earth conductor its only needed from rod to garage DB, or CU. Not into the van, from the van to garage DB, you have the 3x 6mm2 feed that is more than enough, and PE is same size as phase, on that feed.
Again, that 16mm2 it is swapped with your PME in islading mode, and when on grid mode, PME is back on and the 16mm2 disconnected.

Ha, Right! Yes, I understand that! As this, is what was 'originally' confusing to myself "do I need an 'Earth Rod" at the source ? (the van). This makes far more sense being an permanent installation to the workshop ( with a transfer switch to isolate the PME when in use, on the TT arrangement and vice versa when on PME grid use ) rather than a semi permanent installation, unplugging earth from a mobile source (van), as and when I needed to use the van .

and just reverting back to this for the above "And rcd with TT is a MUST, this you covered already, but I would go 32A b curve" . So an 32a 'RCBO curve-b ' to be installed in the workshop consumer unit (which I have got to change for a larger on to be fair) due to it's duel use, which makes sense now, as from the Vans output 32a isolated socket is already covered in the van's CU via a 40a 30ma RCD and a 16a MBC curve - b.
Cheers, Raul .