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Old 05-05-2016, 09:30 AM   #21
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Originally Posted by O C Diver View Post
While I only glanced over the table, I didn't see the compensation for length of the cable. Normally 120 vac wiring charts specify a wire size or amperage limit based on the length of the cable. As an example: you can use 10 gauge wire for 30 amps, but not if the length is over 30' (depending on the wire size table).

Ted
I'm not saying you're wrong, but I don't believe you are right. In residential wiring, the length of a run is generally based only on the current, not the length. All the conductors feeding receptacles will be #12 regardless of the length. We're not talking about docks or outbuildings, but a house, for example. The run to an outlet on the far side of a house from the panel could easily exceed 100'. The concern for voltage drop is much less at 120 volts than at 12 volts.

That said, like so often happens, much more is being made of this project than needs to be made. #14 for 15 amp, #12 for 20 amp. 20 amp is better. That's all he needs to know.
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Old 05-05-2016, 09:34 AM   #22
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Originally Posted by djmarchand View Post
Irrespective of what the ampacity calculators or charts say, NEC specifies a minimum of 14 gauge wire for a 15 amp breaker and 12 gauge wire for a 20 amp breaker.


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Old 05-05-2016, 10:29 AM   #23
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Use 12/3 throughout for 20amp or 15amp loads. It's just not that difficult. So, same awful labor; some extra cost.

Get a load of the receptacles on Revel. No doubt original 1984 install. Wire is stranded. Part of me wants to keep 'em for the conversation value; I've never even heard of such devices!
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Old 05-05-2016, 11:32 AM   #24
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Quote:
Originally Posted by WesK View Post
I'm not saying you're wrong, but I don't believe you are right. In residential wiring, the length of a run is generally based only on the current, not the length. All the conductors feeding receptacles will be #12 regardless of the length. We're not talking about docks or outbuildings, but a house, for example. The run to an outlet on the far side of a house from the panel could easily exceed 100'. The concern for voltage drop is much less at 120 volts than at 12 volts.

That said, like so often happens, much more is being made of this project than needs to be made. #14 for 15 amp, #12 for 20 amp. 20 amp is better. That's all he needs to know.
Wire Loss Table

The above table is for:
120 volts
5% voltage drop
75 degrees C temperature

Clearly there is a length limit without significant voltage drop.

According to the table, #14 should be fine.....as long as you're ok with up to a 5% voltage drop.

Not on my boat.

Ted
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Old 05-05-2016, 12:20 PM   #25
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AC wiring on boats is very similar to house wiring. The NEC covers house wiring and should also apply to the AC system on boats. ABYC goes beyond NEC for marine issues, like tinned wire for corrosion protection.

The NEC doesn't even consider voltage drop for branch circuits like 15 or 20 amp home outlets. 14 gauge only hits a 5% voltage drop (which isn't going to hurt anything, but is a good limit) until the one way run length gets beyond 75'. That may happen in houses but it ain't going to happen in 99.9% of the boats that TF members own.

So just remember the NEC rule: 15 amp breaker = 14 gauge and 20 amp breaker = 12 gauge and quit worrying about ampacity and voltage drop calculators. Those are fine for 12 V where a 1 volt drop matters, but 1 volt is peanuts for 120 V.

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Old 05-05-2016, 12:35 PM   #26
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Originally Posted by djmarchand View Post
The NEC doesn't even consider voltage drop for branch circuits like 15 or 20 amp home outlets. 14 gauge only hits a 5% voltage drop (which isn't going to hurt anything, but is a good limit) until the one way run length gets beyond 75'. That may happen in houses but it ain't going to happen in 99.9% of the boats that TF members own.
David
In theory yes; in reality no.

You're assuming 120 volts at the pedestal. Reality is that often during peak season, at the end of the dock, voltage is already down significantly. On a hot summer day, you might be surprised at how much of a voltage drop there is with all the boat AC units running.

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Old 05-05-2016, 06:44 PM   #27
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Thank you for the link, this is consistent with the ABYC standards book I'm reviewing. Based on the above link, why is 14/3 AWG not large enough to feed a duplex outlet? Breakdown as follows.

•*My shorepower service is 120v 30A one leg. Generator is 3600w single phase, but only one leg is feeding selector switch on panel. However, ignore the generator for now.

• Outlet circuit breaker is either 15A or 20A, TBD, but lets assume 20A.

• Page 41, Table 5A "Allowable Amperage of Conductors of 50 Volts or
More When No More Than 2 Conductors are Bundled"

2 conductors table selected based on this statement, page 50, #4 "If the electrical system is 50 volts or more, determine the number of current carrying conductors
(grounding conductors are not normally current carrying) that will be bundled together. "

Table 5A
14 AWG 105 temp rated = 29.8amp for inside engine space

Unless I'm missing a variable here, 14AWG is 1/3rd more capacity than I need for a 20A max load on the outlets. Yes?

EDIT - less than 1V volt loss from pedestal to end of longest run, outlet at transom. I will meter again tomorrow, but it was so small, that I don't consider increasing cable gauge to compensate for voltage drop as an issue.

I'm not against 12/3 vs 14/3. However, based on all the documentation it doesn't appear necessary.
The appropriate table for 12/3 -- 14/3 is 5B on pg. 41,
3 wires bundled (3 in a flat sheath qualify for that)
14g. max current for 105 degree wire: 24.5 OE, and 20.8 IE
12g. max current for 105 degree wire: 31.5 OE, and 26.8 IE

As you can see the allowable current for the x/3 flat cable is a lot lower than single wire ratings. It is really really rare to have a wire bundle of just 1 - 14/3 flat cable in it coming from the distribution panel. A lot of wires (single and cables) running along with each other is considered bundled for worst case temperature rise consideration. That is the typical situation near the panel.

While it's probably safe to assume no builder designs for the conditions O C Diver described in the preceding post (unfortunately), that is a very realistic condition that can occur. Throw in terminal corrosion of 10 year old pedastals and you can dip below 90 VAC easily.
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Old 05-05-2016, 07:52 PM   #28
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Sounds like they guy just wants affirmation. He's already made up his mind. So,,, yeah, it'll work just fine.
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Old 05-06-2016, 07:12 AM   #29
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In dirt houses the power company broadcasts when a brownout will happen.

At most marinas mid summer and mid winter are almost always low voltage times.

An electric toaster wire heater mid winter will simply put out less heat , no big loss.

Most large motors today do not have brushes so the power consumption is measured in watts.

a 10A motor on a 120V source is 1200W

That same 1200w motor on 100V is going to use 12Amps running.

With a low dock voltage providing that extra 20% may tax the boats breakers and wiring.

Size does matter .
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Old 05-06-2016, 08:54 AM   #30
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AC wiring on boats is very similar to house wiring. The NEC covers house wiring and should also apply to the AC system on boats. ABYC goes beyond NEC for marine issues, like tinned wire for corrosion protection.

The NEC doesn't even consider voltage drop for branch circuits like 15 or 20 amp home outlets. 14 gauge only hits a 5% voltage drop (which isn't going to hurt anything, but is a good limit) until the one way run length gets beyond 75'. That may happen in houses but it ain't going to happen in 99.9% of the boats that TF members own.

So just remember the NEC rule: 15 amp breaker = 14 gauge and 20 amp breaker = 12 gauge and quit worrying about ampacity and voltage drop calculators. Those are fine for 12 V where a 1 volt drop matters, but 1 volt is peanuts for 120 V.

David


Yes, you may have lower voltage at the last slip in a marina but you can't raise it up by using larger wire in your boat.
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Old 05-06-2016, 10:57 AM   #31
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When our marina installed new docks a couple of years ago, they did it up right with modern 30 / 50 amp weather protected pedestals and separate water supply for each slip. With power distribution handled from sub stations out on the docks, voltage runs at a solid 120v year round.

The old docks varied anywhere from 105V to 115V mainly in the winter and when it rained, it wasn't uncommon to see steam rolling off a hot unprotected box. You could expect to go through a power cord dock end plug and socket every year.

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Old 05-06-2016, 05:13 PM   #32
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Yes, you may have lower voltage at the last slip in a marina but you can't raise it up by using larger wire in your boat.
The reason for using larger wire with lower voltages is for compressors. They pull more current at lower voltages. Thus larger wires gets lower voltage drops lower current rise and lower wire temp.
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Old 05-06-2016, 05:35 PM   #33
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Originally Posted by WesK View Post
I'm not saying you're wrong, but I don't believe you are right. In residential wiring, the length of a run is generally based only on the current, not the length. All the conductors feeding receptacles will be #12 regardless of the length. We're not talking about docks or outbuildings, but a house, for example. The run to an outlet on the far side of a house from the panel could easily exceed 100'. The concern for voltage drop is much less at 120 volts than at 12 volts.

That said, like so often happens, much more is being made of this project than needs to be made. #14 for 15 amp, #12 for 20 amp. 20 amp is better. That's all he needs to know.


And I would really run the larger cable, you will not regret it.
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Old 05-07-2016, 07:01 AM   #34
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you can't raise it up by using larger wire in your boat.

TRUE!

However the less voltage drop , from the dock or inside in your boat the better.

Remember a motor starting (LRC) amperage can be 300% of the run amps , so the rotten voltage is magnified by 3 times.

Makes one want to discard the thermostat and run the air cond 100% of the time !

A good V meter like a Fluke will record the lowest voltage (or highest) and can make interesting viewing.
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Old 05-21-2016, 11:55 PM   #35
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Update. Solid core wire runs removed and replaced. Everyone's advice followed, 12/3. The outlet breaker is 15 amp.

I thought the new wire runs would be a nightmare and swapping duplex outlets to GFCI outlets easy. The process was the opposite. The factory wooden duplex boxes had to be chiseled larger, which took hours. One box split but was salvaged with epoxy.

I will post some pictures tomorrow once the sun is up.

Thank you all.
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Old 05-22-2016, 07:59 AM   #36
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Originally Posted by winty View Post
Update. Solid core wire runs removed and replaced. Everyone's advice followed, 12/3. The outlet breaker is 15 amp.

I thought the new wire runs would be a nightmare and swapping duplex outlets to GFCI outlets easy. The process was the opposite. The factory wooden duplex boxes had to be chiseled larger, which took hours. One box split but was salvaged with epoxy.

I will post some pictures tomorrow once the sun is up.

Thank you all.
And that is exactly why I ran 14/3 to some of those idiotic teak outlet boxes...no room inside and the 12/3 is difficult to jam in there.

Appliances and certain outlets all get their own oversized circuit and breaker anyway...so voltage drop to important components isn't an issue. Manufacturer wiring in older trawlers can be insane. My entire boat collection of outlets was on ONE 20 amp breaker. Now I have seven circuits, six 15 amp, one 20 amp. Plus the separate circuits for appliances that draw near 15 all the time or have buried outlets. Even some of the 15 amp circuits have 12/2 to the first outlet in that circuit.

For the circuits most likely to see 15 or more amps continuously, I went with the larger dual outlet boxes and painted them white to match the walls. Made the wire runs easier in some cases as I just used conduit instead of the totally insane tiny routed channel behind the teak vener.
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