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Old 30-01-2019, 14:24   #1
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Is it OK to use common earth and neutral for AC wiring routes?

I am thinking about adding a shorepower connection, a 240v to 12v battery charger, and a 1600W inverter to a boat that currently has only a 12v system. At the same time considering LiFePo battery. There is an obvious location for the shore power inlet in a cockpit locker. I realise that the battery charger and the inverter are best placed close to the batteries which are well forward near the mast. The 240v supply is mainly needed for galley equipment which is aft and close to the cockpit. So I was assuming that I would have one 240v cable running forwards from the shorepower inlet to the battery area then another running the opposite way back to the galley, following the same route as the first cable most of the way. The thing is that the likely route is through a tubular 'service duct' that at present carries four plastic water pipes but the space left in that duct is small, very tight and maybe even impossible to fit in two 240v cables side by side. I have read that I need something like H07 cable, for 16amp supply with 1.5mm2 per core thats about 10mm diameter, is that the right cable to use? Do I actually need two of these cables, with total of six cores? Obviously I need two live cores but can I have just one earth core and one neutral core in one four core cable? That would fit the limited space better and save a bit of weight - this is supposed to be a performance multihull so I am trying to watch the ounces. Maybe there is some very good reason this would not work or would be potentially lethal?
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Old 30-01-2019, 15:43   #2
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Re: Is it OK to use common earth and neutral for AC wiring routes?

Use a galvanic isolator between shore-power ground and boat ground !
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Steve .. It was the last one that did this !
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Old 30-01-2019, 17:11   #3
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Re: Is it OK to use common earth and neutral for AC wiring routes?

If you are going to do this yourself, please please go get some books on proper electrical installation, especially for marine applications and don't trust fools like me on the internet. I know there is some good stuff available specific to boat wiring. Better yet find an electrician buddy to help you.

You need 3 wires going to every ac appliance, hot neutral ground. Ground is there for safety. Hot and neutral are carrying current. If ground is omitted when there is a fault you can end up becoming the ground path and you can become dead.

For sizing the conductors they have to be sized to match the breaker, the breaker is sized based on the load. There are ABYC charts available if you dig around.

Not being mean, just trying to be helpful, people take electricity for granted because it surrounds us every day and seems benign. A miswired boat/house/rv can kill you. quickly.
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Old 30-01-2019, 18:39   #4
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Re: Is it OK to use common earth and neutral for AC wiring routes?

Quote:
Originally Posted by brownr377 View Post
A miswired boat/house/rv can kill you. quickly.
Not only can it kill you, but worse, it can kill someone else... even someone not on your boat.

If you are at all unsure of yourself, hire a competent professional. Talk to him (her), listen, watch, and learn. You will be better for it.

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Old 30-01-2019, 22:58   #5
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Re: Is it OK to use common earth and neutral for AC wiring routes?

you can't just run cables from the shore plug to multiple places. you run one cable from the shore plug to an AC panel with a main breaker and sub breakers. just like a house... from there you run your cables to the correct places.
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Old 30-01-2019, 23:51   #6
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Re: Is it OK to use common earth and neutral for AC wiring routes?

Putting the charger/inverter close to the batteries will minimize the length of the cable runs of the largest cables which are the DC cable runs between charger/inverter or separate charger and inverter. The AC cables are generally fairly small in comparison.
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Old 31-01-2019, 02:24   #7
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Re: Is it OK to use common earth and neutral for AC wiring routes?

i was an electrician on nuclear submarines for 3 years and have actually hooked up a nuclear.reactor. DON'T MESS around HIRE the right AND accountable electrician
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Old 31-01-2019, 02:33   #8
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Re: Is it OK to use common earth and neutral for AC wiring routes?

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Putting the charger/inverter close to the batteries will minimize the length of the cable runs of the largest cables which are the DC cable runs between charger/inverter or separate charger and inverter. The AC cables are generally fairly small in comparison.


Raymond,

The proper way is to run from the shore inlet to an ELCI breaker. From that breaker you connect two additional breakers each one feeding power to two different areas of the boat (galley & charger).

You may be thinking about how to run the inverter mains output back toward the galley. I think you need to consult with a qualified electrician. There are specific guidelines for safe installation of inverters. It may not be possible on your boat. But a marine electrician may be able to recommend a safe solution. Your situation does not seem well suited to internet guessing. As others have said there is a huge risk of injury with mis-wired mains installations.
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Old 31-01-2019, 09:13   #9
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Re: Is it OK to use common earth and neutral for AC wiring routes?

240 is usually made up of two 120 volt circuits. Unless you NEED 240 forward, you can run just one 120 volt leg forward for the battery charger, etc. If you don't have shore power now, then the assumption is you are adding the galley equipment as well. Why choose 240 volts? I could see an Air Conditioner being 240, but a small galley stove/refrigerator? What amp service are you planning to use? (30/50)


Wires are sized for the load, breaker is sized for the wire.
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Old 31-01-2019, 09:19   #10
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Re: Is it OK to use common earth and neutral for AC wiring routes?

And a GFCI circuit as well
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Old 31-01-2019, 09:23   #11
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Re: Is it OK to use common earth and neutral for AC wiring routes?

Suprised nobody else mentioned it but running mains cabling in duct shared by water pipes wold worry me a lot. When I say 'a lot' I mean I would not go on board even as crew. Combine this with cutting corners on earth lines and there is a definite possibility of all your water supply and fitting carrying live mains volts. Don't touch A/C unless you are sure you know what you are doing.
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Old 31-01-2019, 09:53   #12
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Re: Is it OK to use common earth and neutral for AC wiring routes?

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Originally Posted by OS2Dude View Post
240 is usually made up of two 120 volt circuits. Unless you NEED 240 forward, you can run just one 120 volt leg forward for the battery charger, etc. If you don't have shore power now, then the assumption is you are adding the galley equipment as well. Why choose 240 volts? I could see an Air Conditioner being 240, but a small galley stove/refrigerator? What amp service are you planning to use? (30/50)


Wires are sized for the load, breaker is sized for the wire.
The OP is in the UK, and they do things differently over there. 240 volts there is the standard, not 120. You've probably confused the hell out of him! :-)
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Old 31-01-2019, 10:39   #13
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Re: Is it OK to use common earth and neutral for AC wiring routes?

You want to do this in a 15 foot sailing dinghy??? What are your electric loads?
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Old 31-01-2019, 10:47   #14
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Re: Is it OK to use common earth and neutral for AC wiring routes?

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Originally Posted by OS2Dude View Post
240 is usually made up of two 120 volt circuits. Unless you NEED 240 forward, you can run just one 120 volt leg forward for the battery charger, etc. If you don't have shore power now, then the assumption is you are adding the galley equipment as well. Why choose 240 volts? I could see an Air Conditioner being 240, but a small galley stove/refrigerator? What amp service are you planning to use? (30/50)


Wires are sized for the load, breaker is sized for the wire.
This gentleman is in the UK. The mains power there is single phase, 220 volts, 50hz. As with US power, there is one hot and one neutral. The hot wire is at 220 all by itself. All of their appliances run on 220, not just high load ones.

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Old 31-01-2019, 10:55   #15
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Re: Is it OK to use common earth and neutral for AC wiring routes?

NO! Watch this for excellent hands on explanation with an ammeter:

https://youtu.be/lI59y1h3MxU
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