Wiring in 2000w inverter

Well the topic is open again.

No apparent conclusions about the "conflicting technical safety issues" I thought the powers at Moderation HQ might have obtained an some authoritative guidance from a top marine electrical engineer , but no!

Having looked at Matthew's videos again what I still dont understand is why the RCD did not trip with a full 30mA "fault" applied between live and earth ( 1st video at around 7 minutes) Why did it not create the necessary imbalance to trip it ? ( A later fault applied between outgoing live and incoming neutral, around 9 minutes, tripped it Ok )
 
matthewriches said:
Wasn't a case of working out how it worked, it was an investigation into an unknown inverter and a question as to whether it was centre tapped or not.

That type of inverter that the OP has would be potentially lethal if used in such a way as you mention.
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Still waiting for your explanation of how i'm going to get electrocuted.

Still waiting to hear how it should be wired.

Do you actually have any answers ?
 
VicS said:
Having looked at Matthew's videos again what I still dont understand is why the RCD did not trip with a full 30mA "fault" applied between live and earth ( 1st video at around 7 minutes)
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"I expect the RCD to trip" .......... "erm, er, it didn't trip"

Why did it not create the necessary imbalance to trip it ? ( A later fault applied between outgoing live and incoming neutral, around 9 minutes, tripped it Ok )
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How, in the real World, would you get a fault between the outgoing live and the incoming neutral ? Bit of an odd test ?
 
PaulRainbow said:
"I expect the RCD to trip" .......... "erm, er, it didn't trip"
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My point.... why did it not trip ?

How, in the real World, would you get a fault between the outgoing live and the incoming neutral ? Bit of an odd test ?
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Maybe but it served the purpose of demonstrating how an RCD trips when there is an imbalance between the live and the neutral . It also proved that the RCD was functioning correctly .

The important thing to expain is why the RCD did not trip with a live to earth fault. I suspect because of the centre tapped earth , which IIRC Durite told you was "tied", not being a genuine centre tap.
 
Graham376 said:
Whether it's used stand alone or wired into the boat's circuit, it needs an RCD. If used stand alone, then use one of these - https://www.screwfix.com/p/masterplug-rcd-adaptor/63731
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The RCD normally needs the supply to have an earthed neutral. This is probably not going to have that and the experiments Mathew carried out failed to show it would work with the inverter's centre tap earth any way

Graham376 said:
Most rcds I've fitted IIRC are rated at 40ma trip.
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I think you may have remembered incorrectly
 
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VicS said:
My point.... why did it not trip ?



Maybe but it served the purpose of demonstrating how an RCD trips when there is an imbalance between the live and the neutral . It also proved that the RCD was functioning correctly .

The important thing to expain is why the RCD did not trip with a live to earth fault. I suspect because of the centre tapped earth , which IIRC Durite told you was "tied", not being a genuine centre tap.
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It was Mathews test, and he was expecting it to trip, so i'll let him explain why it didn't trip.
 
VicS said:
What did you do about the earthing in the end?
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With any luck he ignored all of the incorrect advice to try and Earth it. That way his installation is an isolated one. His inverter is fully isolated and it does not need an Earth connection. Adding one increases the risk of shock. Without one, he'd need two simultaneous faults to get a shock in an isolated installation. There would also need to be some issues with the safety protocols within the inverter.

Remember, this is a portable setup, it is not an installation. An installed inverter is a different animal and has to be connected in the same way as any other AC power source (shore power or genset).
 
VicS said:
If you know why it did not trip please will you explain why it did'nt
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As i said earlier, it's Mathews test, so it's really up to him to explain why the RCD disn't trip.

If he's unable to do so, i'll offer my thoughts as to why. Perhaps whilst he's explaining why his tests didn't work as expected he'll cover what he describes as "weird behaviour" with the PE link. He might also explain, especially for the benefit of the OP, how his installation puts him at risk of electrocution and how it should be wired.

I wait with baited breath. (Though not holding it) :)
 
PaulRainbow said:
As i said earlier, it's Mathews test, so it's really up to him to explain why the RCD disn't trip. ...)
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Normal reason for a Residual Current Device not tripping is 'no residual current'.

An RCD is a device for protecting circuits where there's a path for residual currents because N has a path to GND/Earth/Chassis somewhere upstream, i.e. it's not floating or isolated.
Other schemes are available to protect floating or isolated systems.

As has been hinted at, it takes two 'faults' for a floating system to be properly dangerous. The name of the game is either to avoid faults, or detect the first fault, so it can be fixed before a second fault occurs.
 
lw395 said:
Normal reason for a Residual Current Device not tripping is 'no residual current'.

An RCD is a device for protecting circuits where there's a path for residual currents because N has a path to GND/Earth/Chassis somewhere upstream, i.e. it's not floating or isolated.
Other schemes are available to protect floating or isolated systems.

As has been hinted at, it takes two 'faults' for a floating system to be properly dangerous. The name of the game is either to avoid faults, or detect the first fault, so it can be fixed before a second fault occurs.
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The point is that Matthew was using a Megger MFT, a pretty standard piece of kit which can be used for testing RCDs, for his demonstration. The RCD failed to trip when subjected to the basic test at 30mA
The question remains, why did it fail to trip?
Matthew was clearly puzzled. I dont know why it didn't.. Rainbow obviously doesn't either.
 
VicS said:
The point is that Matthew was using a Megger MFT, a pretty standard piece of kit which can be used for testing RCDs, for his demonstration. The RCD failed to trip when subjected to the basic test at 30mA
The question remains, why did it fail to trip?
Matthew was clearly puzzled. I dont know why it didn't.. Rainbow obviously doesn't either.
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Either the tester is broken, the RCD is broken, or the tester is being used wrongly.

The test device either did or did not subject the RCD to a sufficiently large residual current which should have tripped it.
 
OK, I'm bored, I gave in and watched the video....
matthewriches said:
The video I made regarding the use of an RCD with a centre tapped inverter. For the purposes of this thread http://www.ybw.com/forums/showthread.php?500331-quot-Occasional-quot-240v

Part 1...

Part 2...

Part 3...
https://www.youtube.com/watch?v=WLrMMO6d6eU

These were "open eyed" videos made on peoples suggestions of how to get the RCD to trip and whether it was or not actually centre tapped :disgust: It wasn't an instructional video or a how to.....
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The key to understanding this is in the first video.
We'll use the 3 pin plug conventions for the wire names.
Live to Neutral out of the inverter = 230V
Live to Earth 110V
Earth to Neutral 96V
(as I recall the voltages, I can't be arsed to rewind and find the exact numbers)
Since these voltages are measured with a high impedance Fluke Yellometer, they are telling us that what we absolutely do not have here is a simple centre tapped inverter.
If the 'E' terminal looked anything like a centre tap, then if you measure the voltage E to L and E to N, there is no way the voltage from N to L can be more than the sum of those.
Whatever the phases of E-L and E-N.
That's making a few simplifying assumptions about how a Fluke measures an RMS voltage if it's not a sinewave of reasonable frequency perhaps.

Once you get rid of your preconceptions of what the 'Earth' socket is actually like, everything else is completely explicable.
 
VicS said:
The point is that Matthew was using a Megger MFT, a pretty standard piece of kit which can be used for testing RCDs, for his demonstration. The RCD failed to trip when subjected to the basic test at 30mA
The question remains, why did it fail to trip?
Matthew was clearly puzzled. I dont know why it didn't.. Rainbow obviously doesn't either.
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The impression I got when I watched the first video is that the mega was initially connected between the line and neutral on the supply side of the RCD. This will NOT cause the RCD to trip as there is no residual current flowing through the RCD. The same when the line/neutral was shorted to the "earth" (centre) tap.

It was only later in the video that the output of the RCD/MCB was shorted to earth (centre tap) or line/neutral.

If I am wrong please tell me.
 
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