Lazy Daze Owners' Group

I dug out my 2004 MB circuit diagram which is slight different from the 2007 version. The diode isolator in 04MB was replaced by an ignition excited contact switch in 07MB. The large breaker on the left (100A in 04MB) protects dc wiring circuits to the diode isolator/contact switch and wiring to the gas generator. Any short occurred in that side of the wiring would trigger this breaker.

Andy, I do not claim to an electrical expert nor an electrician. I apologize for such a treatise but you asked “...what each of the two breakers under discussion here protects?”

There are two separate 12V systems in a Lazy Daze; the house and the chassis. They are only connected when the Isolator or Contactor is triggered by the ignition switch. This circuit is a direct connection between the house and chassis battery positive terminals. Its purpose is to allow the chassis alternator (which is also connected to the chassis battery positive terminal) to also charge the house battery bank, if needed. The breaker in that circuit protects from a potential fire along its entire path.

Let me summarize what Blue Sea Systems has to say about protecting DC circuits.

If more current flows in a wire than the wire is rated to handle, the wire can heat up, its protective insulation can melt, and the heated wire can start a fire. This overcurrent condition can occur, for example, when a short circuit occurs. Fuses and circuit breakers are used to limit the amount of current that flows through circuit wires. Except for those wires that are intended to carry starting currents, every positive wire in the DC main power distribution system must be protected. The goal of overcurrent protection is to provide protection at the source of power for each circuit. With DC circuits, the overcurrent protection is always placed in the positive side. Circuit protection should be connected as close as possible to the source of power.

Lazy Daze seems to loosely follow the American Boat & Yacht Council (ABYC) standards for boat building and repair.

The ABYC recommends that each ungrounded conductor connected to a battery, battery charger, alternator, or other charging source, shall be provided with overcurrent protection within a specified distance of the point of connection to the DC electrical system or to the battery.

I assume that is why Lazy Daze installed two breakers (and now three).

Charles

LD once belonged to RIVA and uses the Associations specifications. I don’t believe ABYC specs ever entered into the equation.
Steve isn’t a boat guy.

AFAIK, the generator start cable is not fused unless a fusible link has been installed somewhere inline. Fusable links are normally four wire gauge sizes smaller than the main wire.
Not fusing the starter's positive cable is commonly seen in vehicles, the starter’s amperage load is very high and a fuse woud need to be huge to hande the heat.

Larry