What wire size please

[John Timmins]

I need to run wire from the panel in the garage to my boat lift motors. The wires will be underground in conduit for about 125 feet from the breaker to the motor operating switches.

There are two 120 volt motors. They are single phase and both are 3/4 H.P. motors.

I can't tell you the amperage they draw, but my Alumacraft aluminum boat only weighs about 220 pounds. This lift might be used for a much heavier boat one day, and the lift is rated for 6000 pounds.

I would like to get ample sized wires for any future heavy boat. I plan on pulling stranded wire so it will be easier. I don't know if it makes a difference stranded or solid wire....

Please suggest what size wire I'll need for my project. Thanks in advance ! John

 

[wyliesdiesels]

Ok do these motors have a single motor starter?

Where are these motors located? In a boat shed?

If theyre located in a building, is there existing electrical in said building?

 

[John Timmins]

the motors are mounted on pilings outdoors in a dock. The house is new. I tore the old house down and am having a new one built. After I get a CO on the house I will rent a ditch witch trencher thing and run PVC conduit from the panel to the motors

The peckerhead of the motors is small. I don't think there is a starting capacitor in there.

Both motors plug into a double GFCI outlet. Between the GFCI outlet and the motors are two on-off switches. You operate both motors at once. Each does one side of the lift cradle

 

[mike93lx]

Will the building have other electrical? Do you need outlets for other items?

Imo, i'd run a larger feeder and put in a small 6 space panel. That will allow for lights, audio, a fridge, etc.

Mobile Home Feeder is about the cheapest option and is direct burial. 2-2-2-4 is good for up to 90a, but you can always use it for less

 

[alfredeneuman]

The OP said that the run will be in conduit.
#10 Cu with a #10 Cu ground will be good for 1 motor, with a voltage drop <3%.
If you run a multiwire circuit, it will only take 2 hots, 1 neutral, & 1 ground.

Any receptacles on the dock will require GFI protection.

 

[alfredeneuman]

Imo, i'd run a larger feeder and put in a small 6 space panel. That will allow for lights, audio, a fridge, etc.

Saltwater laden air really does a number on panels.

 

[Stuart in MN]

Will the building have other electrical? Do you need outlets for other items?

Imo, i'd run a larger feeder and put in a small 6 space panel. That will allow for lights, audio, a fridge, etc.

There is no building, it's just a lift at a dock.

 

[matt_i]

3/4 hp * 750 W/hp / 240vac = around 2.5A FLA.

I would make it 5A per motor due to inrush even though a 1.25 multiplier will work.

Now you have to size for voltage drop which is lookup from a table for the amperage and distance.

Without looking it up I'd guess that #12awg is going to work well, to be clear, 1 homerun per motor.

 

[sberry]

They are 120v. If they are cord and plug they need gfci. This is the ideal place for 20A multi wire. Could do it with 12.

 

[75gmck25]

If 20 amps is enough, I'd probably use wet rated 10/3 in conduit to reduce the line loss, and then set it up as an MWBC with a 20 amp dual breaker and a GFCI for each circuit. This would give you two 20 amp circuits at the lift. 12/3 may also be fine for 125 feet, but you would have to calculate the line loss to be sure.

Bruce

 

[John Timmins]

The original wiring to the boat lift came from a panel box in a workshop that has been torn down. I hired an electrician and he pulled the permit. the building inspector had already been around to approve the location and construction of an 8x10 dock and pilings parallel to the seawall that would support the lift.
There is a motor to control each side of the boat that have wires to a cradle under the boat.
Each motor has a motor operating switch in series with the electric outlet and motor.
the electrician ran 2 20amp wires to the boat lift piling that has an watertight electric box conduit goes to an outlet box that has a GFCI outlet. Both motors plug into that outlet like plugging in a toaster of something.
the other wire run from the other 20A circuit breaker to the watertight electric box is for 120 volt service - an electric outlet or a light that I've never installed. It is also a GFCI outlet.
the length from the circuit breakers to the lift motor outlet was maybe 35 feet. The power coming from my garage to the outlet at the lift is going to be maybe 120-125 feet.

The old wiring was #12. I wonder if I should get #10 ?

Another question....the electrician said the GFCI was a different kind than the kind in the house indoors. I don't know what that means. Are there different kinds ?

 

[John Timmins]

here is the lift when it was new about 8 years ago

To lower the boat I lift off a piece of the dock. My 1978 Mercury 9.8 HP and Alumacraft T14V

What does FLA mean under VOLT ?

 

[CNGsaves]

FLA is Fully Loaded Amps (respective for either 120v or 240v).

 

[alfredeneuman]

3/4 hp * 750 W/hp / 240vac = around 2.5A FLA.

Regardless of the actual load, the motors have be wired according to NEC Table 430.248, which lists a 3/4hp motor at 115V @ 13.8 Amps.

Edit:The actual figure to compute hp is 745.7 W/hp. That doesn't take into account any losses due to motor efficiency (No motor is 100% efficient) or power factor.

 

[rlitman]

...Another question....the electrician said the GFCI was a different kind than the kind in the house indoors. I don't know what that means. Are there different kinds ?

Yeah. It's a new thing, but there are GFI's nowadays that are meant for wet locations. They have plating on the terminals and innards that protects them from corrosion. It's a little more expensive, but is a good idea. You'll still need an "in-use" cover for the plugs.

 

[John Timmins]

the Outlet box has a cover that goes over the plugs. I think it's a real hokey set-up myself. I was an engineer on ships for 30 years in the merchant marine. I wouldn't might some braided armored hard wire in metal watertight boxes with stuffing tubes but then again I'm not in the North Sea in the winter anymore !

I understand power factor One ship I was on had a power factor meter on the switchboard. I paralleled generators all the time. One ship had a power factor meter so I could adjust for minimum "wattless energy"

I will probably run 10 guage. I measured today and it is closer to 135 feet. I'll talk to an electrician and get him to pull the permit. I'll rent the ditch witch and gather all the pvc pipe and fittings and do the bull work

 

[wyliesdiesels]

Regardless of the actual load, the motors have be wired according to NEC Table 430.248, which lists a 3/4hp motor at 115V @ 13.8 Amps.

Edit:The actual figure to compute hp is 745.7 W/hp. That doesn't take into account any losses due to motor efficiency (No motor is 100% efficient) or power factor.

To add to this, you would then take the 13.8a from the Table 430.248 and multiply by 1.25= 17.25a. This is the minimum ampacity the wire needs to be rated for and would mean #12 THWN. However, theres more...

You also have 2 motors, which is another calculation that i forget @ the moment and will look up later.

And Keep in mind this doesnt factor in length of wire and possible voltage drop.

I would use #10 THWN at a minimum...

Breaker can be up to 250% of Nec Table FLC. In your case this is 13.8a x 2.5 = 35a. This is only for one motor....

Heres some food for thought for you.

According to the motor nameplate, it can run on 240v.

Have you considered running these on 240v instead of 120v?

It would help with wire size AND voltage drop....

 

[John Timmins]

I never thought about running 240 ! there is room in the new service box in the garage for the breaker. I'll talk to the electrician about this. I would still want 120V out there for a lamp and electric plug

I will also need 240 in the garage for my air compressor but it is seldom used....just like the boat lift. It raises the boat up and down quickly.

Like I said above the boat only weighs 400 # with the motor and gas can, but I need to be thinking about a heavier boat one day

 

[wyliesdiesels]

If you also want 120v outlet, then this is a prime case for a feeder and small subpanel.

I would just run #6 THWN and #10 green THWN for ground and use 60a breaker. You will need 2 ground rods and an isolatedneutral bar as well as a ground bar.

 

[rlitman]

...Have you considered running these on 240v instead of 120v?

It would help with wire size AND voltage drop....

I saw that, and considered suggesting this. But it makes the plug situation more difficult. And then it would need a GFI breaker (though this is a good idea near water anyway).

 

[sberry]

I would run a multi wire 20 to common gfci. This is effectively running 240v.

 

[sberry]

While the wire needs to be calculated the actual won't be that, under run V drop is only fla, not much more than half the capacity of the 12 if cable and less for calculation of single conductors. Most all this was calculated when nominal v is way less than it is.
It can be upsized but the owner, the motor will never know the difference, so effeciency gains, even if it was used 24 times a day wouldn't save a quarter in a year.

 

[alfredeneuman]

The actual what?

While the wire needs to be calculated the actual won't be that, under run V drop is only fla,

 

[sberry]

Actual current. Watching tv as i do that.

 

[alfredeneuman]

The OP doesn't know the actual current.
I based my reply in post 5 on the the values given in the Code (13.8A)

(I'm watching a TV show on the Wildlife of Costa Rica as I type this)

 

[sberry]

The picture of the label was 11 or so. While it needs to be wired for the code the actual v drop isn't going to be that, isnt going to be 17A draw.

 

[alfredeneuman]

Aah, I didn't see that... Thanks

So at 11Amps if wired separately, the voltage drop would 2.29% with #10s, and 3.64 with #12s

 

[John Timmins]

I mentioned above that I'm having a new house built. This morning the electricians came to finish putting up lamps etc. The owner of the company came by.

I told him I might want him to wire my boat dock and he said the best thing to do was run a new sub panel 240 Volt ON the dock and then have a breaker for 120v for a lamp or something out there. He said the motors could be rewired at the terminals for 240, then less wires to run out there and more options for a sprinkler pump circuit or other ideas.

There are two spare breaker places in the panel in the garage.

Now I have to figure how to wire the air compressor for 240 outlet....

 

[mike93lx]

I mentioned above that I'm having a new house built. This morning the electricians came to finish putting up lamps etc. The owner of the company came by.

I told him I might want him to wire my boat dock and he said the best thing to do was run a new sub panel 240 Volt ON the dock and then have a breaker for 120v for a lamp or something out there. He said the motors could be rewired at the terminals for 240, then less wires to run out there and more options for a sprinkler pump circuit or other ideas.

There are two spare breaker places in the panel in the garage.

Now I have to figure how to wire the air compressor for 240 outlet....

Awesome idea! Wish i would have thought of that

 

[wyliesdiesels]

I mentioned above that I'm having a new house built. This morning the electricians came to finish putting up lamps etc. The owner of the company came by.

I told him I might want him to wire my boat dock and he said the best thing to do was run a new sub panel 240 Volt ON the dock and then have a breaker for 120v for a lamp or something out there. He said the motors could be rewired at the terminals for 240, then less wires to run out there and more options for a sprinkler pump circuit or other ideas.

There are two spare breaker places in the panel in the garage.

Now I have to figure how to wire the air compressor for 240 outlet....

Is the compressor 240v and what is the HP rating on the motor?

 

[alfredeneuman]

You also have 2 motors, which is another calculation that i forget @ the moment and will look up later.
.

The actual nameplate loads are used for voltage drop calcs. (11A in this case)

The formula for feeders for multiple motors is 125% of the largest motor, and others at 100%.

 

[John Timmins]

the compressor motor is 240 V 3 HP. I'm thinking about how many spare places are in my panel

 

[sberry]

The actual nameplate loads are used for voltage drop calcs. (11A in this case)

The formula for feeders for multiple motors is 125% of the largest motor, and others at 100%.

Yes, that is kind of what i was getting at with the calc. To reduce equipment a multiwire with gfci recept on each post. Could plug other stuff in, doesn't mean you got to run lift at same time as a sprink pump etc. All standard easy light wire. Over current at house, 20a circuit.

 

[alfredeneuman]

I told him I might want him to wire my boat dock and he said the best thing to do was run a new sub panel 240 Volt ON the dock...

I had the not so pleasant experience of opening up a flush mounted panel in Oceanside CA about a half mile from the Pacific. The entire bottom was rusted out. I can only imagine if it had been on a dock.

A Ruby's Diner at the end of the Seal Beach Pier burnt down because of corrosion in the breaker panel (as later confirmed by a team of forensic arson investigators). It burnt the entire end of the pier.
You might want to think twice about the decision.

 

[rlitman]

I had the not so pleasant experience of opening up a flush mounted panel in Oceanside CA about a half mile from the Pacific. The entire bottom was rusted out. I can only imagine if it had been on a dock...

Sounds like the difference between a NEMA 4 enclosure (which is fine for the outside of your house), and a 4X, which is what you need on a dock.

 

[alfredeneuman]

It was a NEMA 1 panel in an apartment building on the interior side of an outside wall.

NEMA 4X enclosures are mega$$ and in short order would drive the price up exponentially.
When I've ordered them (directly from Hoffman), there was a few weeks long lead time as well.

(Edit)
If you want to get the "Full Monty" get one of these (they are even more $$ than 4X, but designed specifically for docks)

http://www.eaton.com/Eaton/Products...inaPowerandLightingSolutions/Marina/index.htm

.... or you could just stick to the original plan for a couple of receptacles for your winches.