ground for AC

[Colin A]

Originally Posted by sailabroad

In the article's example, "Live Case" the RCD's will trip when the human earths the case even without the AC to DC grounding connection, or even if the marina's shore side ground is poorly maintained.

Putting a screw through the power cable and not shorting against Neutral while energizing the metal?! not plastic case - one in a million chance Darwin award.

Not quite 1 in a million but possible. When I used to PDI new boats for delivery I found screws in wiring harnesses a number of times. Luckily they were all DC.

I think the AC grounding to DC ground bond is one of those argue forever things like which anchor is best threads. I see the reason why for both ways. That said with a RCD or similar device and a a good path to ground thru shorepower, several things would have to go really wrong for the onboard safety ground to be needed.

[sailabroad]

"Over current devices" are very poor at saving lives..hence the development of RCD's.

To get electrocuted we need all of the following,

(1) Careless guy/girl screws through power cable
AND (2) doesn't somehow short to neutral (over current protection triggers)
AND (3) somehow energizes the case (now most are plastic?)
AND (4) marina has poorly maintained earth (actually would need to be disconnected)
AND (5) somehow the RCD doesn't trip.

The AC - DC grounding only prevents (4) and definitely causes a lot of really shitty corrosion problems, if there's an AC fault you also run some risk of frying all your 12 volt stuff.

[BlackHeron]

Originally Posted by sailabroad

"Over current devices" are very poor at saving lives..hence the development of RCD's.

To get electrocuted we need all of the following,

(1) Careless guy/girl screws through power cable
AND (2) doesn't somehow short to neutral (over current protection triggers)
AND (3) somehow energizes the case
AND (4) marina has poorly maintained earth (actually would need to be disconnected)
AND (5) somehow the RCD doesn't trip.

The AC - DC grounding only prevents (4)

The overcurrent device is good at eliminating the source, and opening the circuit in the event of short cicuit or overcurrent conditions, but is only ONE part of the overall electrical system safety protocol. They may not do it fast enough for optimal life safety, but do a great job of protecting equipment from damage, and obviating the risk of fire to the maximum extent.

RCD is yet another layer of electrical safety but DOES NOT replace proper grounding practices.

I am also a big proponent of using an ELCI main breaker in marine AC panels as well as GFCI on branch circuits with receptacles where portable appliances of any unknown type could possibly be used. If someone has a corded electrical device and it is possible that it fits into the receptacle outlet you can damn well assume that eventually it will find its way into being plugged in at some point. You have no control over this regardless of how well you vet guests and their inspect their gear whenever they board your boat.

My own boat uses a Blue Sea Systems 30A ELCI main breaker panel, plus the GP receptacle circuit is protected by a GFCI outlet which is first in line and mounted right below the panel at the Nav station. I only have 2 AC circuits on the whole boat: GP receptacles and battery charger. The battery charger is not on a GFCI outlet but is protected still by the ELCI. the only receptacle for it is a single dedicated box inside the battery compartment for the charger to plug into.

[sailabroad]

Hmm, Actually

(4) would have to be 'Marina has poorly maintained earth',

AND

(5) EVERY OTHER boat in the marina with a shore power connection has NO AC - DC ground connection - Currently not very likely

SO if you disconnect your AC - DC ground aboard, and you have an AC fault your neighboring boat might also ground your AC fault, triggering Over-Current-Protection &/OR your RDC

[smac999]

Originally Posted by sailabroad

Hmm, Actually

(4) would have to be 'Marina has poorly maintained earth',

AND

(5) EVERY OTHER boat in the marina with a shore power connection has NO AC - DC ground connection - Currently not very likely

SO if you disconnect your AC - DC ground aboard, and you have an AC fault your neighboring boat might also ground your AC fault, triggering Over-Current-Protection &/OR your RDC

you're not going to get 15a flowing through the water, enough to trip the breaker.
that is why they made the ELCI. so only 30ma has to flow into the water.

[Zil]

Thinking of all the electric related deaths in fresh water marinas being in the news, should we trust any marina's ground path?

[sailabroad]

smac999

"&/OR your RDC"

RCD = ELCI

[BlackHeron]

Originally Posted by sailabroad

smac999

"&/OR your RDC"

RCD = ELCI

ELCI is a type of RCD. They are not equivalent and shouln't be used interchagibly.

You can't say RCD =ELCI any more than you can say RCD = GFCI -or GFCI= ELCI for that matter.

A lemon is a kind of citrus fruit, and so is a grapefruit. But you can't say that citrus = lemon.