navitron
 
Renewable Energy and Sustainability Forum
Welcome, Guest. Please login or register.

Login with username, password and session length
News: Anyone wishing to register as a new member on the forum is strongly recommended to use a "proper" email address - following recent spam/hack attempts on the forum, all security is set to "high", and "disposable" email addresses like Gmail, Yahoo and Hotmail tend to be viewed with suspicion, and the application rejected if there is any doubt whatsoever
 
Recent Articles: Navitron Partners With Solax to Help Create A More Sustainable Future | Navitron Calls for Increased Carbon Footprint Reduction In Light of Earth Overshoot Day | A plea from The David School - Issue 18
   Home   Help Search Login Register  
Pages: [1]   Go Down
  Print  
Author Topic: Sofar ME3000SP EPS and RCD Query  (Read 666 times)
book_woorm
Full Member
***
Offline Offline

Posts: 114


« on: May 18, 2019, 09:10:26 PM »

I've just had a Sofar ME3000SP installed with a standard RCD protected socket wired to the EPS output. No change over contactor for critical circuits, just a place to plug in a lamp or two when the mains goes off. Everything seems to work fine but the RCD is behaving strangely. This is what I've tried so far.

Mains on Self consumption unit working, PV generating, batteries charging.
Lamp plugged into the socket on the eps green button pressed. Not in EPS mode so lamp does not light. OK so far.
Now what happens when the Sofar looses the mains.

Test 1: Turn of mains at main breaker. Sofar goes into EPS mode and the lamp comes on as expected. Turn mains back on and after a second or two the lamp goes out.
 
Test 2: Turn of the MCB supplying the Sofar unit. Sofar goes into EPS mode and the lamp comes on as expected. Turn MCB back on and after a second or two the lamp goes out.

Test 3: Turn off the Rotary isolator supplying the Sofar unit off. Sofar goes into EPS mode and the lamp flashes on and off immediately as the RCD trips!

Test 4: With the Rotary isolator still off, Unplug the lamp, reset the RCD, RCD trips immediately!

Test 5: Reset the system and Repeat test3 but without the lamp so there is no load on the socket.  RCD trips immediately!

I thought at first this was something to do with Neutral/Earth bonding as the rotary isolator breaks both Line and Neutral to the Sofar but so does the main breaker in the consumer unit but we get two different results. Also without any load there can be no imbalance of currents on the RCD so it should do nothing. All earth bonds have been checked.


Any suggestions as to what might be going on would be welcome.





Logged

2.4 Kw Kyocera Panels (west facing) Feronius inverter; Sonenkraft Solar Thermal with Twin 180Lt & 280 Lt Thermal Stores; SAP 'A' rated property with UFH & wood burner. Full weather compensation on the UFH buffer temperature & differential controller decides where the heat from the wood burner goes.
rogeriko
Hero Member
*****
Online Online

Posts: 1409



WWW
« Reply #1 on: May 18, 2019, 11:33:42 PM »

Definately sounds like neutral earth shorting somehow. Rewire the rotary disconnect just to break the live not the neutral just for an experiment.
Logged

RIT
Hero Member
*****
Offline Offline

Posts: 2044


« Reply #2 on: May 19, 2019, 01:07:38 AM »

Quote
Test 3: Turn off the Rotary isolator supplying the Sofar unit off. Sofar goes into EPS mode and the lamp flashes on and off immediately as the RCD trips!

If wired correctly that should not happen. The lamp should be wired to the EPS side of the ME3000SP which should remain on regardless of the state of the RCD as you have just disconnected the ME3000SP from the CU/RCD via the Rotary isolator. The fact that the lamp goes out means that the ME3000SP has stopped supplying EPS (maybe causing an error code) or the tripping of the RCD has interrupted the EPS circuit in some way, such as the EPS earth being dependent on the neutral path that has been disconnected due to the RCD tripping. This would not show up if you were throwing a single pole MCB, but should if you have a dual pole MCB installed.


One thing that comes to mind when looking at the diagram on page 10 in this document

     https://midsummerwholesale.co.uk/pdfs/sofar-me3000sp-install-manual-2017.pdf

You will see that the EPS module's earth goes to true ground and so does the critical load's earth. I'm wondering if in your configuration the EPS earth has just been connected to the load with the live and neutral outputs - should be easy to tell as you most likely have twin and earth going from the ME3000SP to the dual socket and little else. To be certain you would have to remove the LOAD cable gland to see what has been connected where.

Another question/idea - how many ways is the Rotary isolator, is it switching live and neutral or live, neutral and earth? The diagram indicates that the AC side earth should remain connected.
« Last Edit: May 19, 2019, 01:19:07 AM by RIT » Logged

2.4kW PV system, output can be seen at  - https://pvoutput.org/list.jsp?userid=49083

Why bother? - well, there is no planet B
book_woorm
Full Member
***
Offline Offline

Posts: 114


« Reply #3 on: May 19, 2019, 09:21:29 PM »

Just for clarity the RCD that is tripping is between the EPS output and the socket the lamp is plugged into. Youv'e got to have some protection downstream of any generator.

I've also run another test

Test 6: Rotary isolator on, PV generating, Battery charging. Lamp plugged into the RCD socket wired to the EPS output. Turn off MCB in the consumer unit for the sofar. Lamp comes on and stays on. If I now turn off the Rotary isolator the RCD trips!

i take the point about the rotary isolator may also be braeking the earth, I'll have to have the lid off and check the installers handywork.


Logged

2.4 Kw Kyocera Panels (west facing) Feronius inverter; Sonenkraft Solar Thermal with Twin 180Lt & 280 Lt Thermal Stores; SAP 'A' rated property with UFH & wood burner. Full weather compensation on the UFH buffer temperature & differential controller decides where the heat from the wood burner goes.
book_woorm
Full Member
***
Offline Offline

Posts: 114


« Reply #4 on: May 19, 2019, 09:24:16 PM »

I should also have said the EPS earth output is bonded to the MET.
Logged

2.4 Kw Kyocera Panels (west facing) Feronius inverter; Sonenkraft Solar Thermal with Twin 180Lt & 280 Lt Thermal Stores; SAP 'A' rated property with UFH & wood burner. Full weather compensation on the UFH buffer temperature & differential controller decides where the heat from the wood burner goes.
RIT
Hero Member
*****
Offline Offline

Posts: 2044


« Reply #5 on: May 19, 2019, 10:37:55 PM »

Just for clarity the RCD that is tripping is between the EPS output and the socket the lamp is plugged into. Youv'e got to have some protection downstream of any generator.

LOL, now that is a rather key point - My first question is - who told you that?  

It is possible that the following is being quoted

Quote
BS7671:2018 Section 411.3.3 states that RCDs are necessary on all socket outlets under 32A

BUT the detail states the following

Quote
Subclause 4.11.3.3 entitled “Additional requirements for socket outlets and for the supply of mobile equipment for use outdoors

As always the issue with the regs is that no one outside the trade purchases the document as its not cheap. I have come across this due to the deployment of UPSs and the following is the latest write up on the subject I have referenced.

      https://www.powerinspired.com/residual-current-devices-rcd-and-isolated-ups-systems/

If all outputs from UPS based devices had to be configured with RCD's you end up in the situation that all UPSs on sale to consumers are currently unusable as just about all have 13A/IEC sockets, with no provision for an RCD or MCB.


It would be worth you trying to track down a contact at the manufacture of the ME3000SP to see if it can even support the needs of a standard RCD as it's EPS output may not be clean enough or earth and N may even be joined. You have a device that has been in the market place for some time, but while the latest edition of the regs came in on 1st January 2019, only installations after 31st December 2019 have to comply with the new rules - this leaves a lot of manufacturers to sell equipment that does not conform to the new regs.

      https://legislationupdateservice.co.uk/news/bs-76712018-requirements-for-electrical-installations-iet-wiring-regulations-published/


What is true is that an RCD may be required on the grid AC side of the ME3000SP. This is dependent on the design of the ME3000SP and the type of cabling used. The common practice is to just install an RCD, with the slight complication that the regs cause the RCD to end up at logically the wrong end of the cable - the regs seem to class an inverter as a load, not a source.
« Last Edit: May 20, 2019, 11:05:00 AM by RIT » Logged

2.4kW PV system, output can be seen at  - https://pvoutput.org/list.jsp?userid=49083

Why bother? - well, there is no planet B
rogeriko
Hero Member
*****
Online Online

Posts: 1409



WWW
« Reply #6 on: May 19, 2019, 11:03:50 PM »

If you disconnect the live wire in the CU on any circuit, say on a socket, and you then short the neutral and earth wires together the rcd will trip on that circuit even though there is no voltage present on the live. I believe this is whats happening here.
The only reason you get a shock off the mains is because to save money the National Grid use an earth return to their generators. If they used a wired return and did not ground any of their circuits then you would not get a shock. This is why they use isolating transformers in swimming pools and outdoor lighting. An inverter if it has a transformer inside gives you isolated power on both legs as long as neither has been bonded to ground. This output will not give you a shock unless you bridge both wires. An RCD is designed to measure the difference in current flowing on the live and the current flowing on the neutral, obviously it should be the same, or +/- 30ma. Is the output of the inverter neutral bonded to ground or is it floating??
Logged

marcus
Sr. Member
****
Offline Offline

Posts: 372


« Reply #7 on: May 20, 2019, 09:30:23 PM »

It's curious that you get a different result from using the rotary isolator vs the main switch/breaker at the CU as they both should be double pole. The only thing I can think of off-hand is that the EPS RCD socket incorporates an RCD with 'functional earth' - in regular RCD/RCBO's this is a small white wire connected to the earth bar of the consumer unit - I'm not sure if it would be apparent on an RCD socket.

The point is that an RCD with functional earth will trip if the voltage between Neutral and Earth rises above 50v(IIRC) to protect against 'loss of neutral' faults. If your EPS output is 'floating', i.e. not N-E bonded (almost certainly is floating) then when the isolator is opened the RCD will trip. The fact that it doesn't trip when the C.U. isolator is used might suggest that there's enough N-E leakage in the rest of the house (possibly via surge suppression devices in electronic psu's and the like) to hold the floating EPS neutral below the RCD trip threshold.

That's my best guess
Logged
book_woorm
Full Member
***
Offline Offline

Posts: 114


« Reply #8 on: May 25, 2019, 04:02:25 PM »

I think that Marcus has hit the spot on this problem. I've now has the opportunity to open everything up and can report the following:-

  Sofar unit is earthed to the CU by the earth wire in the T&E supply cable.(Not the MET as I was told by the installer).
  The MCB for the Sofar does not have a RCD it comes straight after the main breaker.

  As installed the rotary isolator brakes the neutral and line as it should.
  If I loop the neutral through the isolator so it is not broken when the isolator is turned off the problem does not happen!!

  The EPS is connected to the socket with T&E.
  The EPS output Earth is bridged to the Sofar units earth connection to the consumer unit. So neither have an independent earth connection to the MET

  The neutral to earth voltage on any 13 amp socket in the property is 280mV (the rings have their own MCB's and are on a 63Amp RCD in the CU)
  The neutral to earth voltage on the EPS RCD socket is 2.4V in any mode other than EPS.
  The neutral to earth voltage on the EPS output in EPS mode is 16.5V. So surges on switching could easily exceed the 50V limit if the Socket RCD is the 'functional earth' type. I will need to contact the manufacturer as the only information given with the unit is that its double pole and 'Conforms to BS7288:1990 and BS1363.

I don't like either the 2.4V or the 16.5V . It means that the EPS Output is neither truly bonded or floating. It must be a function of the way the internals are designed. My ultimate aim is to use the EPS with an auto change over switch to keep some hard wired pumps supplied if the grid goes down. Given that the wiring for them is buried in walls under plaster board etc then the 18th edition means that those circuits will need an RCD in their supply.

Meanwhile I'm going to rummage in my 'come in useful box' to see what other types stand alone of RCD's I've got. I might also try some surge suppresors but I've never had much joy with them in 60 years of working with wiggly amps.
Logged

2.4 Kw Kyocera Panels (west facing) Feronius inverter; Sonenkraft Solar Thermal with Twin 180Lt & 280 Lt Thermal Stores; SAP 'A' rated property with UFH & wood burner. Full weather compensation on the UFH buffer temperature & differential controller decides where the heat from the wood burner goes.
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.20 | SMF © 2013, Simple Machines
SMFAds for Free Forums
Simple Audio Video Embedder
Valid XHTML 1.0! Valid CSS!