UF, NMB, or single strand in conduit?

[Bruce]

My friend who lives on the Chesapeake bay is running electrical wires to his dock for some new boat lift motors (two). Each motor draws about 12.3 amps under load and the run from the service panel is going to be about 150-175 feet. I know that because of the distance, voltage drop is a problem.

He does not want to install a sub-panel near the dock. Instead, he plans to run two 15 amp circuits, one for each motor. He plans to run the wiring in the grey, PVC-type conduit (schedule 40?) and bury it.

Questions (for those folks who are up on the NEC):

1) If he is using conduit, does he still have to use direct bury (UF) cable? Or can he use NMB in the conduit?

2) Does each cable have to be in its own conduit? (eg. Each length of UF or NMB in it's own conduit). Or can they share a conduit of sufficient diameter?

3) What diameter conduit? Given a run of 150'+, probably looking at 8 awg UF/NMB.

4) Since 8 awg is required, is single strand wire an option (better option)?

Thanks!

- Bruce

[zxcvbob]

I assume these are 120V circuits. I would run individual THWN (or equivalent) conductors in the conduit rather than multiwire cables, and connect the two circuits to opposite sides of a 2-pole breaker and let them share the neutral wire and ground wire. That will save you the cost of 2 wires, and if you ever run both motors at the same time they will work better. If these are 240V motors, they can only share a ground wire.

Are these going to be direct-wired, or connected with a cord and plug? If 120V and cord-and-plug I think you'll need GFCI's unless you use some kind of weird outlets, like twist-loks. Even with twist-lok outlets (so nothing can plug into the outlets except these motors) the GFCI might be a good idea. I don't have my code book handy to see what it says about docks and marinas.

I really don't think you'll need 8 awg wire for this, but I haven't calculated it.

Bob

[Mike Dobony]

I believe any outdoor or wet environment requires a GFCI. I would use GFI breakers.

[... ...]

NEC Article 555 Marinas and Boatyards

555.1 ........ Private , noncommercial docking facilities constructed or occupied for the use ofthe owner or residents of the associated single family dwelling are not covered b this article.

Now I would run #10 single strand wire on the pvc. type NMB and UF aren't supposed to be run in conduit . I would use GFI protection ,

Bill

[Greg O]

I am a little fuzzy on my NEC right at the moment, but I would think that 12 guage wire and a 15 amp breaker would be adaquate. 8 is way over kill, 10 guage would be a safe bet. Run two hots off a two pole breaker, one neutral and a ground wire, four wires total. 1/2" conduit would be fine. Greg

[MAG]

My suggestion is to check with the inspector who's going to have to sign off on it, and see what he/she feels is the right way to do it...

Marc

[John Hines]

A sub-panel would be the way to do it.

2 circuits, with EGC is 6 wires, 5 if you share EGC. You only need 4 wires for a sub-panel.

Not only that, but then the wiring to the device can be 12ga, and fit in the available connections.

Not to mention it saves 365 feet when (not if) the breaker trips, or there is an electrical problem.

No, you use THHN individual wires in a conduit, not a cable.

You can run more than one circuit in a conduit. Each circuit would be 3 wires, with EGC (black, white, green), you would have 6 wires for 2 circuits.

a SWAG says Inch and qtr.

Not unless you have an insane desire to make your job harder than it needs to be, in a word, no.

IMHO, run conduit, and qty 4 #8 (or #6) stranded THHN (black, red, white, and green) out to the dock, and install a 4 place 30amp subpanel. The ability to have an light or outlet for battery charger, or something in the future, not to mention saving an long conductor. Then there is also a single on/off.

[Jeff Cochran]

THHN/THWN. He *can't* use Romex or bundled cable.

No, six conductors in a conduit is fine.

I was thinking #10, but #8 would do. 1.5 inch conduit for that, assuming no or minimal bends.

Probably, though you may not find it locally.

Jeff

[Bruce]

Yes, 120V circuits.

Cord and plug, the motors come with a plug.

[Bruce]

Hi, what does "EGC" stand for?

[John Hines]

Equipment Grounding Conductor. It is the green wire in a cord, and the D shaped opening in a standard 15/20 amp outlet.

[volts500]

Don't use UF in conduit or NMB or at all. #8 wire isn't needed either. A

1/2" PVC with 4-#10 THHN/THWN conductors is sufficient. Two hots (black and a red or blue), one neutral (white), one equipment ground (green). The neutral can be shared, as can the equipment ground. The volt drop for a 12.3 amp load at 175' is 5.4 volts (4.5%) or 114.6 volts at the load. Since no feeder is involved, the total volt drop is still less than (NEC recommended) 5% total. At 150', volt drop is 4.5 volts (3.8%) with 115.4 volts at the load. 3/4" PVC isn't much more expensive and will make for a much easier pull. Be sure to use GFCI protected receptacles and weatherproof "in-use" covers for cord connected motors.

[John Hines]

Yeah, what he says. 3/4" and stranded wire for an EZ pull.

[HorneTD]

Not installing a sub panel may not be a choice he has. He would do well to check with his AHJ in advance. If the AHJ treats the dock as a structure; and if he would need a permit to build it they probably will; then it can only have one source of supply.

225.30 Number of Supplies. Where more than one building or other structure is on the same property and under single management, each additional building or other structure served that is on the load side of the service disconnecting means shall be supplied by one feeder or branch circuit unless permitted in 225.30(A) through (E). For the purpose of this section, a multiwire branch circuit shall be considered a single circuit. (A) Special Conditions. Additional feeders or branch circuits shall be permitted to supply the following: (1) Fire pumps (2) Emergency systems (3) Legally required standby systems (4) Optional standby systems (5) Parallel power production systems (B) Special Occupancies. By special permission, additional feeders or branch circuits shall be permitted for the following: (1) Multiple-occupancy buildings where there is no space available for supply equipment accessible to all occupants, or (2) A single building or other structure sufficiently large to make two or more supplies necessary. (C) Capacity Requirements. Additional feeders or branch circuits shall be permitted where the capacity requirements are in excess of 2000 amperes at a supply voltage of 600 volts or less. (D) Different Characteristics. Additional feeders or branch circuits shall be permitted for different voltages, frequencies, or phases or for different uses, such as control of outside lighting from multiple locations. (E) Documented Switching Procedures. Additional feeders or branch circuits shall be permitted to supply installations under single management where documented safe switching procedures are established and maintained for disconnection. (copyright 2002 the National Fire Protection Assocaition)

If there are no other loads on the dock then he can supply the two lifts from a single multiwire branch circuit. That is the type of circuit that [e-mail] was explaining to you were the neutral and the EGC of the circuit are shared between the loads. The much more likely state of affairs is that your friend will want a receptacle or lights or both on the dock. To serve those loads he will need to install a feeder supplied panel at or on the dock and supply the individual loads from that panel.

-- Tom Horne

[RB]

The first thing to do if he'll need an inspection is to speak with one of the inspectors to see what will float. I suspect he'll need a subpanel.

For my dock I elected to put a waterproof subpanel at the pier and then feed the dedicated outlets for my hoists and boat feeds from it.

A good guideline is to have no more than 3% voltage drop under load. For the situation that you put forth (assuming 120 volt devices) 3% in

3.6 volts. At 12.3 amps this is a maximum (two way) resistance of 0.2927 ohms. #8 copper has a resistance of 0.0008 ohms/ft. 175 feet (x2 conductors) is 0.28 ohms. You could run a #8 feed to the subpanel (I'd use #6 so I would have some head room for other loads.) Then from the subpanel I'd run 20 and circuits for the two lifts. With dedicated loads GFCIs aren't required and I wouldn't run them.

If you put in convenience outlets I'd use GFCIs though.

I haven't found GFCIs that hold up well in saltwater environments so I prefer to design around them.

RB

Bruce wrote: