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Old 05-05-2018, 12:53   #1
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RCDs and switches for generator and inverter

One of the survey recommendations on our new boat was to fit a ground fault detector to the output of the generator. Is there any reason not to fit an RCBO here instead of just an RCD?

The current wiring also has the inverter permanently on. The outputs then go through a relay and then to two power outlets. I haven't followed all the cables yet but I am guessing that the purpose of the relay is to only pass the output from the inverter to the outlets when there is no shorepower.

The inverter is only 500W so will be upgrading it to ~2000W. I can't get my head round how this should be protected though. Should there also be a RCD or RCBO on the inverter output? And should there be a circuit breaker on the inverter input? Is it usual for the inverter input to be direct from batteries and not through panel?
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Old 06-05-2018, 08:29   #2
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Re: RCDs and switches for generator and inverter

Quote:
One of the survey recommendations on our new boat was to fit a ground fault detector to the output of the generator. Is there any reason not to fit an RCBO here instead of just an RCD?
Since you are more or less in Europe :-), here is the applicable standard: ISO 13297-2012
8.2 The craft shall be provided with earth-leakage protection in all a.c. sources by one or more double-pole RCDs having a maximum nominal trip sensitivity of 30 mA and 100 ms maximum trip time.

Since an RCBO provides all of the functional protection of the RCD, fitting an RCBO makes perfect logic.

Quote:
Should there also be a RCD or RCBO on the inverter output?
Another AC source, another RCD/RCBO to stay in compliance with the ISO standard.

Quote:
And should there be a circuit breaker on the inverter input?
Yes. The installation manual will require it as well as ISO 13297-2012:
Quote:
7.2.1 Double-pole circuit breakers shall be installed in conductors to all supply circuits.
Quote:
Is it usual for the inverter input to be direct from batteries and not through panel?
Absolutely! A 2kW inverter/charger or straight inverter will require 2/0 to 4/0 cable (67mm^2 or 107mm^2) and, typically, a Class T fuse within a prescribed distance from the connection to the battery or battery B+ buss. I recommend installing a simple on/off switch in the B+ supply to the inverter.

Hope this helps.
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Old 06-05-2018, 15:09   #3
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Re: RCDs and switches for generator and inverter

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Originally Posted by CharlieJ View Post
Since you are more or less in Europe :-),
Yes, at least for time time being!

Thanks for your comments, that really helps.

The existing 500W inverter is by the nav station. I suspect the wiring won't be enough for a 2000W inverter so plan to move it nearer to the batteries.

Is the existing relay (fm2ac/230) setup the right way to go? I intend to run the output to another outlet but otherwise keep the same functionality so only a couple of (marked) outlets will run off the inverter.
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Old 06-05-2018, 17:47   #4
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Re: RCDs and switches for generator and inverter

the bigger inverters will likly have a built in pass through. and do it automaticly themsevles.

you'll have the 2000w inverter within 5' of the batteries. you'll be redoing the DC and AC wiring.
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Old 07-05-2018, 07:14   #5
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Re: RCDs and switches for generator and inverter

As smac99 said, all modern marine inverter/chargers have a pass through capability with an internal transfer relay so the legacy relay will not be needed with your new installation. RecommendVictron, Magnum or Mastervolt equipment.
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Old 17-05-2018, 01:05   #6
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Re: RCDs and switches for generator and inverter

We have shorepower and generator outputs wired to a transfer switch by the nav station, and the current inverter is just below that. If we're replacing the inverter with a larger passthrough one nearer the battery bank then presumably the AC in to the inverter should come directly from the shorepower/generator transfer switch? The AC output from the panel could then either go directly to the main panel, or to specific outlets? We would probably do the latter to avoid accidental high loads / powering the charger.

Our generator is a Dynamica Mini 40 which is advertised as 3.5kW. The manual lists the rating at 3600 rpm as 4.77kW so presumably this should be used for overcurrent protection sizing? That gives a theoretical max of 20.7 amps so do we size down slightly to 20A for the RCBO, or up to 25A?
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Old 17-05-2018, 03:43   #7
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Re: RCDs and switches for generator and inverter

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The AC output from the panel could then either go directly to the main panel
That should have read "The AC output from the inverter could then either go directly to the main panel"
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