Marine alternator..spark protected.
Originally Posted by donald branscom
Automotive alternator...not spark protected.
Gasoline vapor + Oxygen + spark = Boom!
Your choice. Generally, one tries to avoid das Boom!Effekt onboard one's boat.
Here's a digest of the law, courtesy of http://www.daviscoltd.com/public/eng...nts/ignpro.htm --
33CFR AND NFPA REQUIREMENTS:
Under 33 CFR183.410 Ignition Protection is defined as follows:
(a) Each electrical component must not ignite a propane gas and air mixture that is 4.25 to 5.25 percent propane gas by volume surrounding the electrical component when it is operated at each manufactures rated voltages and current loadings, unless it is isolated from gasoline fuel sources, such as engines, and valves, connections, or other fittings in vent lines, fill lines, distribution lines or on fuel tanks in accordance with paragraph (b) of this section.
(b) An electrical component is isolated from a gasoline fuel source if:
(1) a bulkhead that meets the requirements of paragraph (c) of this section is between the electrical component and the gasoline fuel source;
(2) The electrical component is:
(i) Lower than the gasoline fuel source and a means is provided to prevent fuel vapors that may leak from the gasoline fuel source from becoming exposed to the electrical component; or
(ii) Higher than the gasoline fuel source and a deck or other enclosure is between it and the gasoline fuel source; or
(3) The space between the electrical component and the gasoline fuel source is at least two feet and the space is open to the atmosphere.
(c) Each bulkhead required by paragraph (b)(1) of this section must:
(1) Separate the electrical component from the gasoline fuel source and extend both vertically and horizontally the distance of the open space between the fuel source and the ignition source;
(2) Resist a water level that is 12 inches high or one third of the maximum height of the bulkhead, which ever is less, without seepage of more than one quarter fluid once of fresh water per hour; and
(3) Have no opening located higher than 12 inches or one third the maximum height of the bulkhead, whichever is less, unless the opening is used for the passage of conductors, piping, ventilation ducts, mechanical equipment, and similar items, or doors, hatches, and access panels, and the maximum annular space around each item or door, hatch or accessory panel must not be more than one quarter inch.
NFPA 302 Pleasure and Commercial Motor Craft states the same regulations under section 7-9, with the exception of section 7-9.2 which deals with LPG or CNG devices which cycle automatically. As this article is not covering all concerns of LPG or CNG we will not examine it.
Electrical components are tested in a propane gas and air mixture because of its ability to defuse and fill any space in a short time. This means that when a test tank is filled with the propane air mixture to the 4.25 to 5.25 percent propane gas by volume level the mixture will easily enter the electrical component inside of the tank. When the component, such as a starter, is then operated the electrical arcing between the brushes and armature inside the starter will ignite the mixture that has entered the starter. If the ignited mixture inside the component is then able to ignite the mixture in the tank it is not considered ignition protected. The component is considered ignition protected if it does not ignite the mixture in the tank, thus containing the explosion inside of the component.
Speaking with UL Laboratories, Marine Products Division, we found that in order for an electrical component to be considered UL Marine Ignition Protected the component must pass the above test with a few alterations. The same test is run but the mixture is also induced directly into the component, thus insuring that the propane air mixture is present. If operation of the component will not ignite the mixture then a spark ignition source is then added to the component. The results are required to be the same for consideration, with the exception that the same component must pass the same test between 150 and 200 times without igniting the propane air mixture once. So as you can see if a product is rated UL Marine Ignition Protected it has been thoroughly tested.
The placement and design of the bulkhead, or bulkheads if the fuel/ engine compartment is midships, described is necessary to consider when determining what parts are necessary to be ignition protected as the engine compartment usually houses bilge pumps, solenoid switches, trim tab pumps, fresh water pumps, possibly air conditioning pumps or compressors and a possible array of equipment to long to list. As all of these items are electric components, they are required to meet the above regulations. The amount of equipment needed to be checked for ignition protection will vary greatly depending on the hull layout and bulkhead placement (Figures 1-6).