Marine Grade Wire

What is Marine Grade Wire?

 So we get to tackle the subject of what exactly is a marine grade wire and you're going to learn more about what constitutes a marine grade wire than you ever imagined.

We will be dealing with boats as covered and defined in USCG CFR Title 33 Covering Navigation and Navigable Waters and gasoline engine boats (not outboards) and we are NOT dealing with Shipping Vessels as listed in CFR Title 46 which have their own separate rules for wiring. 

     To start with, let's define what marine grade wire means. Marine grade is not a specification or an exact measure of a certain wire type but is really
just a generalized description referring to electrical wire that would be suitable to use in wiring a boat.

     Let's begin with the law of the land, the Federal Law as defined in Title 33, CFR 183 Subpart I which covers compliance for boat manufacturers and as the USCG puts it:

While we encourage recreational boat owners to use the information for their benefit, compliance with the regulations is the responsibility of the boat manufacturers.

     This is an excerpt from the USCG's Boating Safety Division's  Boatbuilder's Handbook and we will highlight the important concepts and discuss below after the code:

Electrical Systems - Manufacturer Requirements

183.430 - Conductors in Circuits of Less Than 50 Volts

(a) Each conductor in a circuit that has a nominal voltage of less than 50 volts must:
(1) Meet the requirements of 183.435 (which are the cables in red below); or
(2) Meet:
(i) The insulating material temperature rating requirements of SAE Standard J378; and
(ii) SAE Standard J1127 or SAE Standard 1128.
(b) This section does not apply to communication systems; electronic navigation equipment, resistance conductors that control circuit amperage; and pigtails of less than seven inches of exposed length.

This section allows alternate choices of conductor requirements for circuits less than 50 volts. Conductors less than 50 volts may be used if they:
(a) meet the requirements of SAE J1127 "Battery Cable" or SAE J1128 "Low Tension Primary Cable" and the insulating material temperature rating requirements of SAE J378 "Marine Engine Wiring" such as those designated:
GPT, HDT, SGT, STS, HTS, and SXL, or
          (the following are from 183.435 over 50V which are allowed for the under 50V applications)
(b) are classified as moisture resistant and flame retardant in Article 310 of the National Electrical Code, such as those designated:
(c) are flexible cords type SO, STO ST, SJO, SJT, SJTO, SE, SEO, SJ, SJEO, SJTOO, or STOO listed in Article 400 of the National Electrical Code (see Table 6), or
(d) are conductors that meet the IEEE Standard 45, such as those designated:
R, B, T, V, AV, TA, M, S, or
(e) are conductors that meet the requirements of UL Standard 1426.
Conductors for circuits of 50 volts or more must comply with 183.435
Conductors, as purchased, often do not indicate whether or not they conform with the above requirements and standards. If the conductors or their packaging are not so marked, then an alternate means of assurance of compliance should be obtained. Certification of compliance by the wire vendor is one acceptable means.

  • All conductors for use in circuits of less than 50 volts meet 183.435, or,
  • Meet the requirements of SAE J1127 or SAE J1128 and the insulating material temperature requirements of SAE Standard J378.

     So, as you see above, there are many allowable wire styles suitable for use in wiring boats. Such is true in any industry that there is always a minimum allowable standard for a specified product and then there are choices that have more advantageous features and will perform better and for longer time periods than just the bare minimum.
     Aside from the specific wire choices above there are some general rules regarding electrical conductors on boats so let's take a look at those:

§183.425 Conductors: General.
(a) Each conductor must be insulated, stranded copper.
(b) Except for intermittent surges each conductor must not carry a current greater than that specified in
Table 5 for the conductor’s gauge and temperature rating.
(c) For conductors in engine spaces, amperages must be corrected by the appropriate correction factor in note 1
of Table 5.
(d) Each conductor in a multiconductor sheath must be at least a No. 18 AWG conductor.
(e) Each conductor installed separately must be at least a No. 16 AWG conductor.
(f) Each No. 18 AWG conductor in a multiconductor sheath may not extend out of the sheath more than 30 inches.
(g) This section does not apply to communications systems; electronic navigation equipment; electronic circuits having a current flow of less than one ampere; conductors which are totally inside an equipment housing; resistance conductors that control circuit amperage; high voltage secondary conductors and terminations that are
in ignition systems; pigtails of less than seven inches of exposed length and cranking motor conductors

     In summation, the basic requirements are pretty lax with regard to what is considered wire that is suitable to use in a boat. To further the vast array of choices, these rules are set for manufacturers and don't cover what you do with your boat. I'd like to side with logic and common sense and say that these are minimum guidelines for what you should be installing on your boat.
     A great reason to keep work up to standards is that a marine / boat surveyor will be looking at your boat to make sure it meets manufacturer specifications and safety standards. If wiring has been done improperly and not up to the manufacturer standards then you'll fail the inspection.
     When it comes to marine grade wire you have many options but the simple and easy way to know you are using the correct wire is to use UL listed UL 1426 Boat Cable as it meets the specifications for over 50V and by default meets the requirements of under 50V, it will have flexible stranded copper conductors and will have a 105 degree Celsius insulation rating dry and 75 degree wet (know as BC5-W2). In addition to the basic construction of a UL1426 Boat Cable most reputable manufactures will feature the fully tinned copper conductors and the stranding will be Class K (Type 3) 30 AWG copper strands which are very flexible.