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Marina eWof requirements


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It seems that you are someone who knows a fair bit about electricity, but not as much about NZ electrical regs. To be fair, I haven't read the boat regs, but after talking to the inspector, seeing what is at the marina, and reading what has already been posted here I think I know what they are asking for. The big assumption that I am making here is that boats are required to have a MEN distribution board. IT could confirm/deny this as I am not going to buy a copy just for the sake of this thread.

 

Hi Bazza. NZCE Electrical engineering, but no registration. I have copies of the standards and regs. Really enjoying the feedback on this, as it illustrates the wide variety of "requirements" that are acceptable. Most do not meet the standard. The standard is quite clear. All metal parts must be earthed and the boat must have a conductor to seawater for Earth, off the top of my head, it has to be better than 1 Ohm.. Can't remember if it has to be MEN. Don't think so. I think you can run an isolating transformer.

 

1. Not sure how your fault loop impedance theory works. It would be so little difference that it would make no odds, and has nothing to do with having a sea bonding plate! The earth lead bonded to your boat exposed metal is enough. 

 

You can only install an independent earth (eg sea bonding plate) when it is put in as part of a MEN distribution board as per nz regs. Putting an MEN point in drops the impedance of the fault loop as it now has 2 conductors to go back through, as well as bringing the surrounding "ground" to neutral potential.

Yes, but just having the separate earth does that. The only advantage I can see in the sea plate is that if you get a phase fault to the sea water it may trip the breaker. RCDs are more effective! Current in, current out. Easy! Which NZ regs? :-). I am referring to NZS3004.2. It seems the inspectors pick and choose what they want. No common requirement.

 

2. Your exposed metal explanation makes no sense. If your exposed metal is at Phase potential with regard to earth and you grab it, you get a shock as the current path is looking to go to Earth due to our MEN system. If the exposed metal is at neutral potential, you will only get a shock if you are holding a phase wire. If the metal is bonded it is at neutral potential anyway.

 

Think about the insulating properties of our most common boatbuilding material and read my post again. Gotcha. Extremely unlikely as that means 2 seperate faults in two seperate areas with diferent conductors! Again, protrected by RCD.

 

2. If you are only running a dehumidifier and a battery charger via an extension lead, your chances of having a phase or neutral conductor earth on a metal item on the boat are slim. The highest risk would probably be through the lead which is inspected anyway.

 

I completely agree

 

3. Short circuits are covered by the Breakers on the marina side and on the boat box.

 

Yes, but it takes surprisingly little to lift the impedance high enough to start a fire instead of tripping the breaker. A 16A circuit requires a fault loop impedance of less than 1.9 ohms to safely trip the breaker. To start a fire, surely you need a dead short? Again, RCD will help.

 

4. Any earth leakage over 30mA will trip the RCD. It is not just a circuit breaker, it measures current in and current out. If the difference is more than 30mA (Or whatever the rating) it trips. There are two of these. One in your boat (In the box that your lead is connected to) and one on the marina dock.

 

I assume you wrote the first half of that for the sake of anyone following this. At tauranga bridge marina there is no rcd on the dock. I can see where they used to be, but they have been removed. If boats are required to have a MEN distribution board inside of them, then you couldn't have an RCD on the dock without it tripping all the time anyway. This is why I have assumed that the boat regs ask for a MEN distribution board. Sorry, referring to Westhaven and Bayswater. I would have thought that they were manditory under the marina wiring standards which I think is a subset of NZS3004.

 

5. This system is not universal. On the ship I work on, we do not run neutral to Earth. Earth is insulated. Any single phase circuit requires breakers/and/or RCDs in both lines as both lines have potential with regard to earth. One of the reasons this is run is that it is SAFER than an MEN system, as you need two faults to get a shock or short circuit..

 

I am with you on this. I've never been a fan of the MEN system. I won't forget the time I had to convince another electrician that the neutral is an active conductor and needs to be treated as such. Unfortunately it is universal in NZ. Always good when they swap them over in a circuit and have no neutral link. Come across this in a few factories in Auckland. Isolated the circuit at the board and got a huge belt. Phase and Neutral swapped, and Earth link removed, probably because the breaker kept tripping! LOL.

 

The more you learn, the more you question!! I guess having worked with a lot of electricians who blindly work without any understanding, I always question why, and sometimes they really have to think and research before they answer. I'm not saying I know that much, but I like to ask questions!

 

Good on ya. I find that many sparkies think they know what the regs say and how things work, but very few really do. I won't believe what any sparky says that's different to what I already know unless they can point it out to me in the regs.

 

Thanks for the detailed replies. They all make a lot of sense!! Smithy.

 

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Hi Dtwo. So no ground to Seawater then, just a ground wire to the marina?

No, no seawater ground.  I only have 12V throughout the boat, and the negative is the battery bank rather than the engine as I understand some boats have.  Keeping the electrics in it's own contained system seems to make sense to my simple mind.  The only metal parts I have in the water are prop shaft and prop (stainless steel), rudder shaft (stainless), rudder shoe (bronze) and SSB ground plates (sintered bronze).  The engine is not connected mechanically to the prop shaft or electrically connected to the boats systems.

 

Time will tell if it is an approach that works!

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Belt?

 

But it's still mechanical (I was being a bit tongue in cheek, there...)

Belt and braces.  My bad, not connected electrically - isolated via flexible mount.  Tough school.

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The engine is not connected mechanically to the prop shaft or electrically connected to the boats systems.

 

IT beat me too it. The motor certainly will be connected to Neg. All senders like Water temp, Oil pressure etc.and most importantly, the starter motor will be earthed. If you did not have a good size battery cable connecting the Neg of the Starter, then you would fry every low current cable to the engine connected to the senders, Hence then why the main Neg feed goes from Battery to Starter Motor Engine Bolt and from there, a decent size Neg feed up to the Switch board.

If you have a shaft that is isolated from the engine via a rubber coupler, then you need one of two things. Either a wire across the two halves of the coupling, or best practice is a shaft brush that runs against the shaft and connects back to the block. The reason why this is best practice is that then no possible stray current can run back through the gearbox bearings to the engine.

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Yeah MB, but without the ewof the marinas won't let you connect.

Part of this stupid rules effects, is that we won't let a foreign cruising boat connect without a Nz ewof. No other country I've been to by boat does this... :-(

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Most battery charges these days bond the AC Neutral and DC Neutral together which creates a lot of  the potential problems* (*Note coffee not had so may be wrong)

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O.M.G. Thank goodness I got my EWOF today. Fault Loop Impedance - WTF? FFS KISS. And yes, I've got NFI.

 

You guys rock.

Excellent! I will try the same path!

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Becarra, ABYC E11 states same as AS 3004.2, the AC earth/ground (not neutral) and the vessel's grounding system (which will be connected to the DC negative) shall be connected.

The MEN system in NZ sees the AC Neutral and earth connected at the point of "generation". If there is an onboard generator or inverter, these are required to make this connection when in use.

 

DTwo, pleased you had a good outcome with Enertec

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but I cannot accept that an extension lead with two trip switches on either end that powers a dehumidfier or battery charger requires the same level of certification.

MB, it's not a law, it is a thing Marinas are wanting. I am not right up to play anymore, but it used to be that it was OK for an extension lead to be used if you were present, but not if you were not at the boat. So in other words, a Battery charger or dehumidifier could not be left running while nobody was on board.

 

Bang on Beccara. That's why I use an el cheapo charger with a transformer inside of it instead of a fancy 20 million stage battery regenerator charger that has a switch mode power supply.

 

Not all SMP type chargers have earthed outputs.

So if you have a cheapy charger, what do you do about regulation? Or do you just connect for short periods of time?

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I know that u know your stuff wheels, so can u explain to me how a switch mode power supply can isolate its output from earth?

 

As for charger regulation, my house battery bank is 2x 6v 220 ah. I have a 2 amp charger that turns off when it senses enough voltage, but even if it didn't I'm pretty sure I could run it all day every day and my batteries would scarcely be effected. A bit like trying to sink a frigate with a garden hose...

 

If we got too much drama about the ewof I would have just gone solar for battery charging... Dehumidification isn't worth hole(s) through the hull and lots of $$ and time in bullshit additions.

 

Thankfully the inspector is reasonable and I think that the eWOF is a good thing provided the inspectors keep turning a blind eye to the crazy standards that make little sense.

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