Paging ARW - generators bla bla

bonding,

tapped

Aye, in theory it is trivial to make the connections and be fine under no fault conditions. It's handling the many "what if" fault conditions and still meeting the regulations for supply and installation when on grid power and when on generator power.

Which is why I use extension cables to the appliances I wish to power from the generator during power cuts. But having more than one appliance connected to a "live" and "neutral" floating generator isn't strictly legal either.

I have thought about replacing the isolator switch on the genset with a 16 A DP RCBO but if both "live" or "neutral" are floating there is no fault circuit via "earth" to unbalance the the "live" and "neutral" currents and trigger a trip.

One possibilty is to connect the earth pin of the genset output socket to the "neutral" pre the RCD. But that doesn't produce a trip if the still floating "neutral" has an earth fault condition, only if the "live" does, I think!...

I don't think there is 1/2" of regs just for generator/grid power installations/switching.

Reply to
Dave Liquorice
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It gets trickier when one of the appliances is a boiler that has an implicit reference to earth too.

I suppose on one hand, even if the supplier earth failed as part of the outage, the inside of the house would be an equipotential zone, no matter what.

The problems get more interesting when you have extraneous conductive parts like an outside water tap or gas feed pipe that are now doing random stuff with respect to the actual ground nearby, especially in the rain.

I have it on reasonable authority from someone who specialises in generators that the correct thing to do is to add sufficient local grounding to the MET - and further reading suggests this is the only practical way to be bomb proof - but there remains a danger that under certain local area faults you could be providing a path to earth for your neighbours so it needs doing properly.

I do not have chapter and verse on what "properly" entails - but it is something I've been considering in case I wanted to have an independent radial circuit supplied from a generator with sockets in key locations (fridge, internet stuff, boiler).

Because I have bonded copper pipes running in touchable positions outside of my house, I'd personally be inclined to take (insured, indemnified, written) engineers advice before doing anything permanent.

But the real sticking point is the boiler. If it were just a few internal appliances, then it's probably all fine on an extension lead.

True - I was making a general conclusion that nothing is actually as simple as they might appear.

Reply to
Tim Watts

Ah, the damned worms got in the way. I didn't mean "plug each end" rather hard wired at the dizzy board but plugging it into the genny.

Reply to
Paul

That is probably the best reply to this thread.

Now after reading the rest of the posts we can conclude that the OP has a TT supply (or a Spanish equivalent) and that the house CU will have RCD protection (a quick Google search suggests that Spanish electrical installations require DP switched RCDs/RCBOs on all circuits).

So the OP now needs to suck it and see. Your point about the genny being a

110-0-110 V centre tapped earth supply does not preclude it from operating most of the house electrical supply.

It will not matter if the genny is supplying 110-0-110V or 220V to most equipment - the waveform of the gennys output is more relevant and might cause some items not to work.

Reply to
ARW

As others have said it is possible to tie one end of the winding to earth.

One thing you should watch out for is that the output of your generator is unlikely to be sinusoidal, and whilst it's fine for powering tools and the like, some electroinc equipment (computers, etc) might be very unhappy about it. Best to use a sine wave generator for electronic gadgets.

Generator v pure sine wave inverter:

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Reply to
John

Heh. When the old-time sparky came around to look at my swimming pool pump, he saw my Avo-meter on the shelf. He said "next time you need a new pump, we'll do a deal for that meter" - pumps cost about 200 euros.

Actually he didn't say that, he said "la próxima vez que necesites una bomba..." - oh never mind.

But I do also have one of those 3 quid plastic things for when accuracy isn't an issue ;-)

Reply to
Paul

If it stops raining for a minute[1], I'll nip out into the garage and prod things with a meter. Just for a laugh. I'm tempted to carry on with the plan, but I'm now a bit scared I'm going to kill my UPSs.

Praps I should buy one of those inverter jobbies. Or make one. Can't be difficult - I have a few soldering irons.

Reply to
Paul

Bugger. Forgot the footnote.

[1] The rain in Spain normally falls mostly in the mountains, but this week it's mostly falling on the plain, which is where I am.
Reply to
Paul

ok that tells us something useful - that you have a similar live and neutral setup to the UK rather than a split phase system like some of the US. So as long at the generator does not have the earth terminal connected centre tapped to the winding (unlikely) then you should be able to connect it up in a sensible fashion.

Reply to
John Rumm

Done that. Earth connector short circuit with chassis and with earth terminals in sockets.

Res between earth and red - inf. Res between earth and blue - inf. Res between red and blue - 5 ohms. Not many windings there then.

Reply to
Paul

Even that has problems since it means when on normal mains power, that plug is now live. The "correct" way is using a "break before make" transfer switch. This ensures that only one feed can be connected to the house electrics at any one time, and that one feed cannot back feed the other.

Reply to
John Rumm

This will apply with any TN style supply. However in the OPs case it does sound like he is TT which makes things much easier since he is not sharing earthing with anyone else (assuming that his earth electrodes are far enough away from the neighbours')

Yup a boiler will typically need a proper earth reference to do flame sensing.

Reply to
John Rumm

This much is true.

However your conclusion that the observed behaviour of a neon screwdriver lighting on both sides of the winding indicates its centre tapped is doubtful.

Take the other more likely possibility that the winding on the genny is not centre tapped, and both sides are floating WRT earth. Both sides will likely still appear "live" to a neon screwdriver since the current flow to light it is so small.

Reply to
John Rumm

Well, probably a fair few, but heavy gauge wire.

Reply to
Tim Watts

Which is why I fitted this:

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Before anything else. Mainly so as not to kill the bloke mending the fallen cables etc.

Reply to
Paul

Heh. What is this "flame" of which you speak? I threw away our butane water heater a couple of years ago as I was fed up with going out onto the patio nekkid and soapy to change a gas bottle. All electric now.

Reply to
Paul

It will also depend a bit on the technology used in the UPS.

If the genny has a 12V DC output, then the type used for running mains appliances from a battery may work.

Reply to
John Rumm

Yup, that's pretty much as expected.

Good. That confirms the output is floating and not centre tapped.

5 ohms is a fair length of copper wire!

So based on that you should be able to safely connect the genny to earth (and the house earthing system), and then also connect[1] one side of its output to earth to get you a neutral and a live.

[1] Using a transfer switch
Reply to
John Rumm

Funnily enough, I had a UPS battery die on me t'other day so I have a UPS without battery. Could just connect that up I spose. I don't know what the power throughput would be like though. Worth a try with not much to loose.

Reply to
Paul

This begins to sound doable apart from the risk to my office kit.

Reply to
Paul

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