Article 555 of the 2014 Edition of the NEC provides the electrical installation requirements for various types of marine installations (see SIDEBAR 1: Where Do These Rules Apply?).
Unless the installation is a small dock for a private residence, it’s probably covered by the requirements set forth in this Article (Photo 1).
Datum plane
Article 555 provides a detailed definition of the “electrical datum plane” (EDP) [555.2], but uses this concept only in four sections. It requires the following to be above the EDP:
• The bottoms of transformers [555.5].
• Conductor splices (unless they are in approved junction boxes and use sealed connector systems listed and identified for submersion) [555.9].
• Receptacles (when on a fixed pier) [555.19].
• Motors and controls for marine hoists, cranes, railways, and monorails [555.23].
So what is the datum plane about? Don’t let the word “datum” confuse you. In this usage, it has nothing to do with data — it just means a line of reference.
In drafting, a “plane drawing” is one that shows the building or object such that you can see its vertical dimensions. If you made a plane drawing of a boat dock, the person viewing the drawing would be able to tell the dock is some distance above the water. If you add scale and dimensions, he’d be able to tell what that distance is.
The electrical datum plane is a reference line on that type of drawing. It’s the distance above the highest expected water level. The exact distance depends upon the application (see SIDEBAR 2: Electrical Datum Plane Minimums).
Service and distribution
You must know how a floating dock or marina is constructed before installing the service equipment. You have to install that equipment adjacent to, but not on (or in), the floating structure [555.7]. It can be confusing visually to use the walkway from a fixed structure to a floating structure as your means of locating a suitable service location. Look under the structure to see if it’s on fixed footings or not. Once you’ve decided on the service location, you must consider some other factors before finalizing the design:
• Yard and pier distribution systems can’t exceed 1,000V phase to phase [555.4]. This has implications for voltage drop, transformer size, and possibly load equipment selection.
• Transformers and enclosures must be specifically approved for the location [555.5]. This means the exact size or rating needed might not be available, which can create space and mounting issues.
• The main overcurrent protective device (OCPD) must have ground fault protection no greater than 100mA [555.3]. Alternatively, you can install GFCIs on each branch or feeder circuit. Though not expressly stated in Art. 555, one implication of this GFCI requirement is you’re not going to have UPS-protected loads in this area; that would defeat the purpose of the GFCI protection.
Enclosures
Install your electrical boxes before running conduit to them. There are two good reasons for doing this. You can ensure the boxes:
1) Won’t interfere with mooring lines [555.10(B)]. You select the exact location, rather than letting the conduit dictate that.
2) Are substantially supported by structural members rather than by the conduit [555.10(A)]. The enclosures should help support the conduit, not the other way around.
If you use mounting screws that penetrate the enclosure, seal the holes so water doesn’t come in. If a gasket kit doesn’t come with the mounting hardware, what can you do? A multipurpose marine sealant is appropriate for this job, as it’s designed to withstand the environment. But don’t just glop it on over the screw heads. With the mounting screws in the mounting holes, run a bead under each screw head before tightening down. Then neatly run a bead around the penetration point from the inside and another bead around the perimeter of the screw from the outside. This method may seem excessive, but it will keep the water out.
Tighten the mounting hardware to the correct torque specifications. Doing this will help prevent those mounting bolts from working loose and leaking despite your best sealing efforts.
If your gasketed enclosures are going to contain any switches or circuit breakers, they must be of the type that permits operation of the switch or breaker without exposing the interior of the enclosure [555.11]. Each such enclosure must also have a weep hole to let condensation out. This might seem to defeat the purpose of a gasketed enclosure, because it could also let moisture in. However, the enclosure isn’t being submerged. It’s just exposed to a damp environment. You want to minimize the entry of moisture (thus the gasket) while allowing condensation to drain (hence the weep hole).
Load calculations
Calculate loads the normal way (per Art. 220). But for each service and/or feeder supplying receptacles that provide shore power for boats, also apply the demand factors of Table 555.12 instead of the demand factors of 220.16(B).
Wiring methods
You must use wiring methods identified for use in wet locations [555.13(A)(1)]. You can’t use EMT; you must use RMC, RTRC, or PVC suitable for the location [555.13(B)(5)]. Fittings must be listed for use in damp or wet locations, as applicable.
You can’t use temporary wiring to supply power to boats (except as permitted by Art. 590) [555.13(A)(3)].
Portable power cables must be rated for extra-hard usage [555.13(A)(2)]. They must be properly supported and protected from damage [555.13(A)(4)].
Install overhead wiring in a way that minimizes interference with masts or other parts of boats [555.13(B)(1)]. Keep conductors at least 20 ft from any portion of the boat yard that can be used for moving vessels or stepping/unstepping masts.
Conductors of outside branch circuits and feeders must be at least 18 ft above grade [555.13(B)(2)], except those described by [555.13(B)(1)].
Grounding
The grounding requirements of Art. 555 are fairly standard, but observe the following:
• The meaning of “Equipment to Be Grounded” [555.15(A)] is “equipment to be bonded” [Art. 100]. Don’t use the water as a bonding jumper; that sets up an electrocution hazard.
• The equipment “grounding” (bonding) conductor (EGC) must be insulated and either green or green with yellow stripe(s), but the EGC of Type MI cable can be identified at terminations.
• The EGC must be at least 12 AWG.
Shore power receptacles
You need a disconnect to isolate each boat from its power connection(s) [555.17]. Make sure:
1) It’s identified as to which receptacle it controls and is less than 30 in. from that receptacle.
2) It’s readily accessible.
Receptacles must be at least 30A [555.19(A)(4)] and housed/installed in one of the following [555.19(A)(1)]:
• Listed marina power outlets.
• Listed enclosures protected from the weather.
• Listed weatherproof enclosures.
Other than shore power receptacles
Receptacles not used to power boats (Photo 2) must be marked to clearly indicate they aren’t used for boat power [555.19(B)(2)]. They must also be protected per 210.8(B), unless they are 15A or 20A receptacles installed in:
• Structures used for storage, maintenance, or repair.
• Outdoors.
• In boathouses.
These receptacles must be provided with GFCI protection [555.19(B)(1)].
Classified locations
Repair facilities containing flammable gases or liquids must also comply with Art. 511. Think of how broad that requirement is. Examples of such items include:
• Common solvents.
• Acetylene torches and gas welding rigs.
• Many types of paints, varnishes, and other coatings.
• Fuel.
Planning is key
Some years ago, a walk through a popular pier near Melbourne, Fla., revealed many Code violations. Instead of conduit, the raceway was an elastopolymer tubing. The boxes were at random heights and distances. The raceway wasn’t supported, and in many places it wasn’t even connected (you could see the conductors). It looked terrible and was unsafe.
To ensure you have a safe, eye-pleasing installation, decide on the locations of boxes first. Base the locations on good aesthetics, user friendliness, and adequate distance from the water.
Lamendola is an electrical consultant located in Merriam, Kan. He can be reached at [email protected].
SIDEBAR 1: Electrical Datum Plane Minimums
The electrical datum plane is the horizontal reference line you draw above one of three other horizontal planes, depending upon the application:
1) Land areas subject to tidal fluctuation (2 ft above the highest normal tide).
2) Land areas not subject to tidal fluctuation (2 ft above the highest normal water level).
3) Floating piers and landing stages. If they rise and fall with the water level and can rise to the EDP of 1 or 2 above, then the EDP is 30 in. above the water level and 12 in. above the deck.
SIDEBAR 2: Where Do These Rules Apply?
Article 555 pertains to fixed or floating docks, piers, or wharves and in other areas such as:
• Boat basins
• Boat condominiums
• Boathouses
• Boatyards
• Docking facilities associated with residential condominiums
• Marinas
• Multiple docking facilities
• Yacht clubs
• Similar areas
It also applies to facilities used (or intended for use) for small craft berthing, fueling, launching, repair and storage, as well as moorage of floating buildings.
It doesn’t cover private, noncommercial docking facilities that are for the use of the residents or owner of the associated single-family dwelling.
