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So if my neutral-earth bonding happens on the service panel (house side of c/o switch), where do I need to install an RCD/GFCI?
Discuss Generator feed to 2L+1N system in the UK Electrical Forum area at ElectriciansForums.net
Yes, without a changeover switch, this is how it is setup. The N and G are tied in the main panel of both buildings.OK, from your description, I think this is what you have before adding any changeover switch etc :
View attachment 63362
For the most part, I understand but I thought that (at least for the US and the Philippines) the standard is to bond N-E at the main panel alone? The main panel (distribution board as you call it) is AFTER the changeover switch. You also mentioned earlier to bond both B1 and B2 earth rods through the main panel ground bus bars. How does the grounding/earthing be reliant on the switch if N-E are bonded on the main panel?And after a bit of thought, this is what I think you need :
View attachment 63363
For your changeover switch, note that the N-E bonding is done BEFORE the switch - that avoids having a switch in your earth connection which (apart from some very specific situations) is expressly prohibited in our UK regs. Just to be clear, your earthing must not be reliant on any switch working properly.
Understood and I think this is what's happening to my installation now because the generator does not have a neutral. So when the B1 main panel is switched over to gen power, the B1 socket connections are:And while you correctly point out that your two boards have their earth terminals connected together via the neutrals, I would explicitly bond them with an earth wire. Actually, I'd consider splitting the earth off the neutral at your meter (so L1, N, L2, and E from meter to each board) and avoid having the shared PEN (protective earth and neutral) internally - again it's something that's expressly prohibited in our regs. The issue is what if someone comes along and starts working on the system, on the assumption that (having pulled the supplier fuses) it's OK to disconnect the neutral. You now have an installation where part of it is supplied by a generator, and the earthing is split across two separate earth electrodes. Under fault conditions, that disconnected neutral could now carry a hazardous voltage relative to other neutral/earth conductors/terminals.
This is either-or - you don't need to run a separate earth wire from the meter location to each board AND also run a dedicated bonding wire between them. Either way, you'd have a solid single earth reference for the whole installation regardless of what's being done to the wiring. Also, this can be done just with conections to the earth bars in each board - you don't need to dig anything out to access the earth electrodes.
What kind of RCD should I be looking at and should it have a larger trip current than the changeover switch breakers? I thought RCD's should be very fast acting? With a time-delayed RCD, are those just used to protect equipments? If we're talking about RCD's in subpanels, these should be very fast in case a person touches a live wire, isn't it?Now the fault protection.
As you can see, the neutral from the auto-transformer is connected to the earth bar. This means that (within the ability of the genny and transformer), an L1-E or L2-E fault within the installation will trip it's respective breaker. But the genny and/or transformer may not have the "oomph" to trip anything more than a smaller breaker so you could overload one or the other for an extended time. An RCD (GFI) would trip on the imbalance and disconnect the whole board.
With the assumption that the installation is otherwise adequately protected, this RCD is only to protect the equipment - so it can be of a larger trip current and time delayed (time delayed being the most important part) to give you some discrimination between that and what you have in the distribution board. E.g., if you already have an RCD/GFI on a circuit with a fault, then the one in the board would trip and disconnect the fault, while the time delay on the supply from the transformer will mean that it won't trip as well. But if you have a fault on a non-RCD/GFI protected circuit, then the RCD/GFI in your transformer supply will disconnect the whole system - inconvenient, but better than burning out your equipment.
So is it going to be like this?You may have noticed an additional breaker on the output of the genny. This needs to be a true 2-pole (i.e. senses in both poles) breaker to protect the genny.
The genny only has a single pole breaker in one line, if there is an internal fault to earth, then a large current could flow with nothing to trip - and again there's a risk of burning out the genny or transformer. Consider fault between the genny winding on the side with the internal breaker and earth - then draw the path the fault current would take and you'll see what I mean.
Selecting this breaker could be tricky. Too low a tripping current and you'll get nuisance tripes, too high and the genny won't be able to drive enough current through it to trip. Another RCD/GFI might be more appropriate.
It seems this thread has run and run!@pc1966 do you have any comments on this BEFORE or AFTER changeover switch N-E
I apologize if the thread has run longer as it should.It seems this thread has run and run!
The critical point is you should NEVER be without a ground connection no matter what the switch is doing (even if stuck half-way).
Typically here we separate N & E from the incoming supply before you do anything, so in that sense the bond is before a changeover switch, but then we don't haver the link in the DB panel as you do which would normally be after a change-over switch.
I see what you're saying. Now circling back to what you mentioned in the beginning of this thread, I thought that we should NEVER let the neutral of the generator touch the supply neutral? If N-E are linked before the panel, then both neutrals are linked through the ground connection. Wouldn't that have the same undesirable effect?To some extent if you are linking N-E before the panel you might as well have only L1 & L2 switched as N & E are always common, and that would also be the auto-transformer centre tap (after any protection).
I see a 3-pole MCB appears above, it could be for the 100% load with the transformer rated at 50% as then the tap is good to that current anyway. So a 5kVA transformer on a 10kVA generator and a 40A or 45A 3-pole MCB is a sane choice, etc.
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