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Old 31-05-2009, 17:19   #31
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I don't know what inverter you have but RCD's do not necessarily work reliably on the output of an inverter due to harmonics. Many inverter manufacturers provide lists of RCD's they have tested on their inverters.

Quasi sinusoidal inverters are obviously the more problematical but I would not blindly rely on a sine wave one either as I have known harmonic sensitive equipment to fail on them too.

We elected to not have one on the output of our own inverter (quasi-sinusoidal) as the risk inside our boat is extremely low (the engine and all internal metal fittings apart from the propellor shaft are isolated from AC earth). But as we have a metal boat I am careful on the rare occasion that I use power tools powered from it on deck as I have found portable RCD's also to be either obviously unreliable or not trustworthy.

I haven't checked but I think in recent times ABYC, if one intends following it, requires an RCD on inverters - Gord or someone could probably clarify that if it has not already been so in this thread. ISO requires a 30mA RCD on the "main power supply" which one assumes to mean on each power supply and so on an inverter, but gives the alternative option of using 10mA RCD's on all receptacles in the galley, bathroom, machinery space and weather deck instead (for those spaces we only have receptacles in the galley). As always the standard should be itself checked in order to be sure if intending to rely on this advice.
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Old 02-06-2009, 16:45   #32
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Thinking about it more as to the placement of these, I'm wondering if I need 3 of them??
  1. Where my shore power comes in, before my Isolation Transformer.
  2. After my Isolation Transformer (for loads not going through the Inverter).
  3. And one after my Inverter (For the 120 Volt that the Inverter is producing from the Batteries).
Is this getting silly or do I indeed need 3 of them?
Perhaps I can get away with 2 (I sure hope) if I take everything through the inverter. Don't know if this will cause undue wear on my system as I really don't need and didn't want all my 120 V with that UPS type supply.

If I want proper whole boat protection (GFI) are there any other options and/or do any of you have any comments or suggestions?

Please let me know.
Thanks,
Extemp.
Giving this more thought, I questioning what value/safety having an RCDB before my Isolation Transformer provides?
  1. If it trips, I still have a ground fault out on the deck of my boat because the shore power breaker would not trip.
  2. I still have everything grounded after my Isolation transformer.
Some would say that if it tripped, it would at least provide indication there is a problem and I guess I'd have to agree. Having said that, is there a simpler/cheaper device that could tell me if there is reverse polarity and a faulty ground? Would such a device not provide almost as much protection?

This is from my Isolation Transformer manual:
"Figure 5: Output neutral grounding
A Residual Current Device (RCD) or Ground Fault Circuit Interrupter (GFCI) must be installed in the output cable of the isolation transformer. For this RCD to operate correctly, the output neutral must be connected to ground (= all the metal parts in the boat). This is achieved by placing a jumper on male pushon connectors J21, J33 (see fig 5), and by grounding the enclosure of the isolation transformer."

I do realize that this may just speak to the Transformer part of things.

Am I correct or am I missing something?
How do others see it?

What do you think?
Extemp.
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Old 02-06-2009, 17:27   #33
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You should not install a GFCI between shore and transformer. The ground wire from shore is only connected to a shield around the primary winding inside the transformer. The hot and neutral are only connected to the primary winding. The ground from shore provides all the protection you need inside the transformer.

I think that this is the reason the manual doesn't state you need an GFCI before the transformer's input ;-) I do think that ABYC wants you to install a regular breaker instead, protecting the wiring between shore power inlet and transformer but I am not sure of that... better check it.

cheers,
Nick.
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Old 02-06-2009, 20:30   #34
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You should not install a GFCI between shore and transformer. The ground wire from shore is only connected to a shield around the primary winding inside the transformer. The hot and neutral are only connected to the primary winding. The ground from shore provides all the protection you need inside the transformer.

I think that this is the reason the manual doesn't state you need an GFCI before the transformer's input ;-) I do think that ABYC wants you to install a regular breaker instead, protecting the wiring between shore power inlet and transformer but I am not sure of that... better check it.

cheers,
Nick.
Thanks Nick.
I think I'll install a breaker regardless of its requirement (good to have a disconnect there). If I can get one that indicates reverse polarity and/or faulty ground (if this is possible), all the better.

Regards,
Extemp.
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Old 03-06-2009, 05:53   #35
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... Having said that, is there a simpler/cheaper device that could tell me if there is reverse polarity and a faulty ground?...
Essentially, a Reverse Polarity Indicator (RPI) is just a 120V light (LED or Neon) and a 25,000 Ω (min.) Resistor, wired in series between the AC Neutral (White) and AC Ground (Green).
A Normally Open “Push to Test” button may also be wired in series, in which case the RPI is not automatic .
A “Correct Polarity” indicator cct. would be wired between Hot (Black) and Neutral (White).

The Ideal 61-051 Receptacle Tester (pictured below left) tests for seven conditions including: ground fault interruption, open ground, open neutral, open hot, hot/ground reverse, hot/neutral reverse, and correct wiring.

See also, Marinco's GalvanAlert™ Shore Power Corrosion Detector with Reverse Polarity Indicator (below, right)

Blue Sea Systems Explains AC Reverse Polarity (when the neutral and hot are reversed):
Reverse Polarity Indicators - Resources - Blue Sea Systems
AC Reverse Polarity - Resources - Blue Sea Systems

Or see page 149 in Charlie Wing’s excellent book, “Boatowner's Illustrated Electrical Handbook”
Boatowner's Illustrated Electrical ... - Google Book Search

or
Page 144 in Don Casey’s “Sailboat Electrical Systems”
Sailboat Electrical Systems ... - Google Book Search
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Old 03-06-2009, 13:01   #36
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Ha Ha Ha, finally I see Gord taking a wrong turn ;-) All the info about the reverse polarity posted is correct of course but the nice thing is that you don't need it, you don't even care about it!!! That's one of the nice things with an isolation transformer: polarity doesn't matter!

ciao!
Nick.
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Old 03-06-2009, 13:03   #37
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Ha Ha Ha, finally I see Gord taking a wrong turn ... but the nice thing is that you don't need it, you don't even care about it!!! That's one of the nice things with an isolation transformer: polarity doesn't matter!
True; but I was merely responding to his querry, not judging it's applicability, in context of all his previous posts.
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