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Old 11-02-2009, 22:30   #1
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Residual Current Device (RCD)

Does anyone know where I can get a Residual Current Device (RCD) as opposed to a Residual Current Circuit Breaker (RCBO)? I already have main breaker (30amp). I would want it to be 30ma. Is there any pluses or minuses not having the RCD combined with the breaker? Also wondering if they make them stand alone (with thier own housing)? I do see some BlueSea stuff, but all I see are RCBO's.

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Old 11-02-2009, 23:38   #2
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For those in the states, this is what we call a GFCI. 30ma is the difference in amps at which the switch opens, shutting down the circuit...theoretically protecting the user.

I wish I had an answer Extemp. Hopefully someone else will.
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Old 12-02-2009, 01:17   #3
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As David M said they are called GFCI in North America and can be had as stand alone duplex recepticles at any electrical outlet or a marinized version( higher price) at West marine. A recepticle appears to be what you want instead of a breaker. I have them in my boat in the engine room and lazarette.
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Old 12-02-2009, 04:48   #4
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I’m not aware of any readily available stand-alone 30Amp (overcurrent) 30milliAmp (RCD) device. If such is available, I would expect it to be cumbersone and more expensive than a Residual Current Circuit Breaker (RCBO).

I would recommend both 30mA whole boat (equipment) RCBO, and 5mA individual circuit (people) protection in the form of GFCI receptacle for each AC circuit.

Replace your existing 30A main breaker with a 30A RCBO, and install a GFCI receptacle as the first device in each 15A AC circuit.

North American electrical codes require GFCI devices intended to protect people to interrupt the circuit if the leakage current exceeds a range of 4-6 mA of current (the trip setting is typically 5 mA) within 25 milliseconds*.
* However, while they typically trip in 25 ms or so at fault currents exceeding 20 to 30mA, they are permitted by UL to take several seconds to trip at fault currents in the 5-6mA range.

GFCI devices which protect equipment (not people) are allowed to trip as high as 30 mA of current.

European RCDs have trip currents of between 10-300 mA, with “people protectors” being rated 6, 10, or 30 mA.
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Old 12-02-2009, 05:15   #5
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My understanding is that if you are doing this for a circuit of convenience outlets, if the FIRST one has a GFCI the others receive the ground fault protection if wired THROUGH the GFCI. I believe the Leviton allows this type of wiring.
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Old 12-02-2009, 05:36   #6
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My boat is wired the way defjef describes. I've popped the little breaker a few times, so they do work on the downstream recepticles.
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Old 12-02-2009, 07:08   #7
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Gord May,

Thanks for that input. I had read a piece by Nigel Calder in Professional Boatbuilder a while ago that also suggested the best solution would be both a RCBO at the shore power input and a GFCI on high risk circuits. Sort of the best of both worlds. Do I understand the following correctly:

The European shore power grounding standard is arguably more risky than the the US standard but they more than close the gap by mandating RCBO's (that have a 30ma trip level) at the shore power input.

The US GFCI with a 10ma trip does a much better job at protecting people but are too sensitive to be used for a whole boat. They trip too much. So US boats have no whole boat ground fault protection.

Even though you could be killed before a 30ma RCBO trips, in the real world it will usually trip before you are badly hurt. It seems unwise to have no ground fault protection on the argument that it sometimes doesn't trip soon enough. The old "perfect is the enemy of good" problem.

To Extemp's question. There are many online sellers of European parts(and even Ebay) in the UK who will gladly ship to places like the US. Blue Sea systems also has a unit that's quite expensive that fits their panels.

Gord May - Does a RCBO or RCD need to be specifcially rated for 110v? I found one line of RCD's that are labeled this way but do you know if a 230v one would work on 110v? Here's the link:

Electrical Wholesalers, Scolmore Lighting, Components, Spares - Online UK

Finally, does anyone understand what the difference is between a RCD and the new AFCI (arc fault circuit interupters) that are recently required by building code in US new house construction (not that there is much "new construction" right now)

Carl
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Old 12-02-2009, 07:42   #8
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The RCD and GFCI are close relatives designed to prevent electrocution. The AFCI is there to trip in the event that a potential fire or heat causing arc could occur.Mainly used to protect property rather than person.
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Old 12-02-2009, 08:42   #9
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Quote:
Originally Posted by defjef View Post
My understanding is that if you are doing this for a circuit of convenience outlets, if the FIRST one has a GFCI the others receive the ground fault protection if wired THROUGH the GFCI. I believe the Leviton allows this type of wiring.
No more calls, please! We have a winner! That's exactly how it goes with GFCI's.
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Old 12-02-2009, 09:00   #10
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Quote:
Originally Posted by GordMay
... Replace your existing 30A main breaker with a 30A RCBO, and install a GFCI receptacle as the first device in each 15A AC circuit...
Which is what I originally said.
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Old 12-02-2009, 16:13   #11
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In terms of receptacles, I did understand and did wire my house with one GFCI receptacles in front of a series of regular plugs to afford the same GFCI protection. I'll do the same on my boat. If I can't get a RCD then I will change my breaker and get a RCBO. Great stuff and thanks.
One more.
Does 50 vs 60Hz have any bearing in the discussion?

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Old 12-02-2009, 17:31   #12
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Not as far as I know. The question GFCI's answer is "is there stray current where it shouldn't be" - line frequency doesn't really figure into that.
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Old 13-02-2009, 03:33   #13
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UL Class “A” (4-6 mA) GFCI Receptacles are rated for operation at 50 - 60 Hz input.

A GFCI works by using a* summing toroid sensing coil (DCT - Differential Current Transformer). Both the "hot" line leaving the breaker and the “neutral” line returning to the breaker travel through the DCT/toroid. The DCT/toroid then sums the current in both of the wires and if more current leaves than returns the breaker will trip. At 60 Hz, the breaker will trip when approximately 5 mA of current does not return to the circuit breaker. Current not returning via the neutral represents the hazardous condition (including a ground fault) that a GFCI is designed to protect against, following an inverse time curve [ie: at 6mA; UL943 requires the GFCI to interrupt within 5594msec (5.6 seconds), at 25mA it must interrupt at 726msec (0.73 seconds) and etc.]

* May actually be 2 separate DCTs.
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Old 20-02-2009, 22:40   #14
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Not to muddy the waters but, the latest ABYC Standards includes a major rewrite to E-11 and it has this to say about RCBOs, RCDs, GFCIs, etc.:
11.11 GROUND FAULT PROTECTION – AC SYSTEMS
11.11.1 An Equipment Leakage Circuit Interrupter (ELCI) shall be installed with or in addition to the
main shore power disconnect circuit breaker(s) or at the additional overcurrent protection as required by E-
11.10.2.8.3 whichever is closer to the shore power connection.
11.11.1.1 This device shall meet the requirements of UL 1053 Standard for Safety for Ground-Fault
Sensing and Relaying Equipment and the requirements of UL 943 Ground Fault Circuit Interrupters with the
exception of trip level and trip time. Trip level shall be a maximum of 30mA. The trip time shall be a
maximum of 100ms.
NOTE: Trip levels of less than 30ma and times of less than 100ms may result in nuisance trips in
certain environments.
11.11.1.2 The ELCI shall be readily accessible.
11.11.2 If installed, a ground fault protector (GFP) shall only be used to protect equipment.
NOTE: A ground fault circuit interrupter (GFCI) may be used on single phase AC circuits to provide
additional protection for personnel and equipment.
11.11.3 GFCI breakers shall meet the requirements of Underwriters Laboratories standard UL 943,
Ground Fault Circuit Interrupters, and the requirements of UL 489, Molded Case Circuit Protectors for Circuit
Breaker Enclosures.
11.11.4 GFCI breakers may be installed as panelboard feeder breakers to protect all associated
circuits or in individual branch circuits.
11.11.5 Single-pole GFCI breakers shall only be used if:
11.11.5.1 the single phase 120 volt system has a polarity indicator, or
11.11.5.2 the system uses either a transformer, or
11.11.5.3 the system is 120/240 volts.
11.11.6 GFCI receptacle devices shall meet the requirements of Underwriters Laboratories' standard UL
943, Ground Fault Circuit Interrupters, and the requirements of UL 498, Electrical Attachment Plugs and
Receptacles.
11.11.7 GFCI receptacle devices may be installed as part of a convenience outlet installation either in
single outlet applications or in multiple feed through installations. (See E-11.13.3.5)

As has been mentioned, the EU has required whole vessel RCDs/RCBOs for several years. The US is simply catching up.
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Old 20-02-2009, 23:46   #15
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The good news is they haven't (yet) moved forward with AFCI over GFCI. The bad news is the "yet".
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