1Pawn
Standard Member
When you disconnect it from the grid, the house is just a parallel of some loads
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Gadget Geek
Prominent Member
Sounds like an entry for the Darwin Awards to me. 
1Pawn
Standard Member
It's fine, it's all happening in my house, not yours. You are safe and sound. Sleep wellSounds like an entry for the Darwin Awards to me.
Coulomb
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I didn't realise this; thanks. So the car's internal RCD is effective: it detects a leakage from live or neutral to its sensor wire (called protective earth). In order to get shocked, a human touching live has to have another path to neutral, which will usually be via metal on the appliance and leakage to live and/or neutral (leakage to either will do, as the load itself will provide the path to the other).
I assume that a 5kΩ resistor from neutral to "earth" will also trip the car's RCD? It would be interesting to know how they do this.
As for how to protect the house, that's an interesting question. If a generator is expected to provide the neutral-earth bond, it seems to me that you'd have to ignore the car's "earth", and connect neutral to earth at the "generator" input, since the changeover switch presumably disconnects the house's normal neutral to earth bond. The house would then be protected by its own RCD(s), not the car's.
Nicko
Established Member
Neutral and earth connected at the generator and a separate earth rod for the generator?
Tim Green
Established Member
Coulomb: when I use my generator ( as yet only in test mode), I use a special spur wired into the consumer unit that goes to the shed housing the generator. This spur has an old fashioned trip switch in the consumer unit, rather than an RCD. I plug the generator output (which itself has some sort of trip on it) directly into that spur, and of course turn off the main isolator for the consumer unit. Thus the generator is feeding directly onto the bus-bars that power all the RCD's in the house. Although it works fine on test, I have not yet tried a fault situation on any of the house circuits.
Staffex
Established Member
I've just taken a measurement to determine the trip current of the car's 'RCD'. I measured 84.1V across the N & E terminals of the 13A plug on my inspection lamp. Then I bridged N & E with successively lower value resistors until the discharge was halted on reaching 51kohms. It was repeatedly happy with 56k, across which was 63.6V appeared. So the trip current flowing in the 'PE' terminal is just over 1mA; compare that to a domestic RCD's 30mA! Incidentally, I counted about 9 seconds between pressing 'start discharge' and power being delivered from the V2L, accompanied by various bonks and clonks from beneath the bonnet.
I think PE (protective earth) in this context is misleading. The pin should really be called Residual Current Detector as it's not hard-bonded to the car's chassis or its V2L 'N' output. The car itself is a floating source. If I were to connect 'L' on the V2L socket directly to an earth stake absolutely nothing would happen, my lamp would continue to shine. However, if I connected a kettle with a leaky element or a damaged flex/extension lead, the small current flowing in the PE wire would immediately halt the discharge. If it's of any help the IET On-Site Guide has plenty of information concerning earth bonding, protective conductors, earthing of portable generators etc. John Ward has made some excellent YouTube videos on the subject.
1Pawn
Standard Member
Can you please try to do the following: ignore the PE from the car, wire the line and neutral to an External RCD, and connect the ground wire going to the load together with the neutral (before the RCD).
Then check if the external RCD is correctly tripping, while the one from the car doesn't.
Then connect the ground to the load with the ground in the house (earth stake).
I guess this would be the only way to safely use the MG as V2H without the intervention of the internal RCD.
Tim Green
Established Member
Interesting Staffex. If you read my post 86, connecting the car as with my generator, I think it would work. This is because, as the house incoming mains switch is off, there would be no ground to Neutral link. But the house ground would be connected to the car PE. As long as there were no leaks to ground of 1mA, it should work and I think the house would be protected by the car’s
RCD.
Incidentally, if I remember right,medical RCD’ are 5 or 1mA, depending on required level.
RCD.
Incidentally, if I remember right,medical RCD’ are 5 or 1mA, depending on required level.
Staffex
Established Member
Why do you wish to introduce another RCD into the feed between the car and your house? Post #73 describes how to supply the consumer unit from a car instead of a substation. I suggest you retain the connection to PE at the car end (only) because that would stop the discharge if the cable connecting it to your house was damaged. If L & N are connected to the CU as in post #73 all the existing RCD and MCB protection will be retained, along with all the N-E bonding, regardless of whether your mains supply is TN-S or TN-C-S (see https://electrical.theiet.org/media/1549/earthing.pdf).
Hmmm. It would be preferable to use a changeover switch to swap the incoming Live supply with the one from your generator so that all your domestic circuits would keep their protection. And it would save you from having to replace the fuse in your switched fused spur if you were to operate your switches in the wrong sequence!
It's reassuring to learn that medical RCDs have a high sensitivity - I wouldn't fancy having 30mA flowing around my brain if something went wrong during electrocauterisation surgery
Tim Green
Established Member
I don't see how a changeover switch helps actually. It would have to be break-before-make so there is always a loss of supply, as you state. (staffex).
Your back- feed through the ring main is very similar to mine, except that you will be back-feeding an RCD which worries me. Some circuit analysis would be required, which I have not done.
Your back- feed through the ring main is very similar to mine, except that you will be back-feeding an RCD which worries me. Some circuit analysis would be required, which I have not done.
Staffex
Established Member
My CU is populated with RCBOs only, no MCBs or RCDs but I'm sure your back-feed arrangement will work as well as my quick and dirty Death Lead does. I hastily devised the the Death Lead when I was plunged into an unannounced power cut. I was annoyed that it didn't work at first because of the unusual method of protection adopted by MG and that led me to discover that PE sits 83V above N. For that reason PE cannot be allowed to connect to the domestic earth (which is bonded to neutral).
I assumed that I could use my Death Lead to power all the other circuits in my house by switching off the CU's 2-pole 100A main switch. However, on reflection I've realised that the N-E earth bonding takes place on the supply side, before the main switch (which isolates both L & N). So, if the main switch was open the N-E bonding would be lost and all the RCBO (or RCD) protection on the circuits I was powering would fail to work. And for that reason I suggested it would be preferable to use a c/o switch on the L side only.
I only intend to use my Death Lead in emergencies and I would certainly take special precautions if my grandchildren were visiting. I thought your generator situation was more permanent, hence my c/o suggestion. No harm will be caused by back feeding an RCBO or RCD. John Ward has done an interesting breakdown of an RCBO here:
And finally, post #79 criticises my Death Lead. Yes, it's potentially dangerous - hence the name and the copious warnings I've given. I trust that members of this forum will have the common sense not to start the car's discharge until the 13A plug has been inserted into the appropriate socket! I like MG's warning on p147: "...please pay particular attention in protecting the discharge gun from water, rain or snow...in cases of peculiar smells, smoke emission or overheating the electrical circuit must be disconnected immediately and the discharge operation stopped".
1Pawn
Standard Member
Staffex, you are suggesting to connect the neutral of the car with the neutral of the grid, only because you want the bond between neutral and ground.
I would disconnect the grid completely with a transfer switch, and connect the ground of the house to the neutral of the car, solving your bonding issue
I would disconnect the grid completely with a transfer switch, and connect the ground of the house to the neutral of the car, solving your bonding issue
blippy
Established Member
There are very specific arrangements for island mode (powering a house in a power cut) - both L and N conductors must be isolated from the supplier, the supplier earth cannot be relied upon (local earth rod required) and a N-E bond is required at the inverter.
Also not all RCBOs are bidirectional. Hager for example have specific models that would be compatible. And they need to be type A in any case.
Also not all RCBOs are bidirectional. Hager for example have specific models that would be compatible. And they need to be type A in any case.
Staffex
Established Member
I am on a TN-S supply and don't have an earth stake as my earth derives from the substation. I've just been reading about 'island mode' which seems to apply to DC-derived storage or solar PV sources that normally operate in parallel with the grid in 'connected mode'. Presumably the DC-AC inverter syncs in phase and amplitude with the incoming supply to allow this to happen. Obviously there's no way to sync the car's invertor.
This guidance document
Island mode earthing arrangements: New Guidance in the Second Edition of the IET Code of Practice on Electrical Energy Storage Systems
Introducing the concept of prosumer’s electrical installations (PEIs), and operating modes for a electrical energy storage systems (EESS) and examining the earthing arrangements for island mode operation for PEIs with EESS.
electrical.theiet.org
Forum members must decide for themselves whether to adhere to this stringent guidance. For myself, I'm content to keep my death lead safely locked away until it's needed.
I was puzzled by your statement 'not all RCBOs are bi-directional', which made no sense until I read: "Circuit-breakers e.g. an MCB marked “in” and “out” or “line” and “load” or with arrows indicating the direction of power flow can have their arc extinguishing / short-circuit characteristics impaired if they are incorrectly connected". https://www.beama.org.uk/static/c39...onal-and-Bidirectional-Protective-Devices.pdf
Good idea! In the rare event of a power cut I could open the 100A main switch in the consumer unit to completely isolate L & N from the grid. Then I'd plug the Death Lead plug with linked N & E terminals into a 13A outlet in the garage. And after switching off the RCBOs in the consumer unit associated with circuits that I don't want to remain powered I 'd start the V2L discharge.
I'd have to carefully label the 13A plug with shorted N & E of course, because if I were to plug that into the V2L trailing socket by mistake the discharge would refuse to start. I'd also have to confirm the integrity of the garage wiring beforehand because the correct operation of the RCBOs relies on a good N-E bond. There is some concern about feeding a unidirectional RCBO in reverse (see post #96) but I'll take that risk.
Thanks for your suggestion - I'm annoyed that I didn't think of it myself!
blippy
Established Member
Honestly, if you want island mode operation, just get a solar PV system that supports it (eg Solis) and stop messing around with half arsed manual bodges - unless you are particularly keen to have a knock on the door one day from the boys in blue wanting your help with their enquiries into the death of a worker resolving a power cut.
1Pawn
Standard Member
He just needs a cheap generator transfer switch (30 pounds), not an expensive hybrid solar inverter (1000 pounds)
Tim Green
Established Member
I bought my generator about 3 years ago and, apart from testing the system works as an emergency supply in case of blackouts, I have not used it. Long may that last!
Nowadays I spend my time trying to cram as many loads as possible into the 00.30 to 4.30 time slot. At least that pays for itself.
Nowadays I spend my time trying to cram as many loads as possible into the 00.30 to 4.30 time slot. At least that pays for itself.
Staffex
Established Member
Thank you for your well considered comment that contributes so much to the discussion on this thread. But before I invest £7000 (according to the Energy Saving Trust) on a solar PV system - and that doesn't include battery storage - please would you answer a couple of questions:
1) In the event of a power cut by what magical process could the 218V generated by my V2L bridge an open RCBO, RCD, MCB or main breaker?
2) Assuming the fairies were playing tricks, how many millivolts could my V2L deliver (before tripping) to the load presented by 25+ properties sharing the same phase between here and the nearest substation?
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