Double pole circuit breakers for each circuit

[ayates]

The schematic excerpt is from a modern fire boat. Double pole circuit breakers for each of the DC circuits. Any idea of why this would have been done? I can't think of any reasonable fault mode where this would be advantageous.


Thanks,

Allan.

[Tomodore]

I am an electrician but not a marine electrician. On GFCI AC circuit breakers both the hot and neutral go to the breaker. For 12 volt DC the only advantage I could imagine is if the positive side of the breaker failed but not the negative side. Also if a positive wire touched the negative side of a circuit the 2pole side would trip. Both of these instances are far fetched in my non marine electrician mind.

[goboatingnow]

Originally Posted by ayates

The schematic excerpt is from a modern fire boat. Double pole circuit breakers for each of the DC circuits. Any idea of why this would have been done? I can't think of any reasonable fault mode where this would be advantageous.


Thanks,

Allan.

The idea is a trip in one isolates the other , rather overkill really

[noelex 77]

It is common with metal, particularly aluminium vessels.

Double pole circuit breakers offer some safety advantages, reducing the risk of fire, but their primary purpose is to reduce the chance of stray current corrosion.

They are (arguably) overkill for fibreglass boats, although double pole circuit breakers are sometimes suggested for the equipment that is most likely to induce stray current corrosion such as the autopilot and the anchor windlass.

There are certainly fault modes where they are advantageous.

[ayates]

FYI... It has been pointed out that this double pole circuit breakers are a common requirement for government boats, particularly with aluminum hulls.With ground fault detection, as seen in the top part of this panel, if a ground fault is detected, loads can be completely disconnected to isolate the fault


Thanks,

Allan.

[guyrj33]

When I look at the schematic, it looks like both poles of the breaker are switching the hot side of the circuit.
Am I reading the schematic wrong?

[smac999]

Originally Posted by guyrj33

When I look at the schematic, it looks like both poles of the breaker are switching the hot side of the circuit.
Am I reading the schematic wrong?

The wire is 2c (onductor). So the single drawn wire is 2.

The p1 p2 switch is Likly double pole pos and neg. Going to the double pole breakers at bottom.

A bit confusing when they split some into 2 wires and leave some together as one in drawing.

[guyrj33]

Originally Posted by smac999

The wire is 2c (onductor). So the single drawn wire is 2.

The p1 p2 switch is Likly double pole pos and neg. Going to the double pole breakers at bottom.

A bit confusing when they split some into 2 wires and leave some together as one in drawing.

Two wires drawn as one, confusing but if that is the case what about the connections labeled 1,2,3,4 all connected to P1. That sure makes it look like both poles of the breaker are connected to power.

[dick sargent]

This is an excellent method for isolating electronics from lightening damage through the ground system.

[noelex 77]

Originally Posted by smac999

The wire is 2c (onductor). So the single drawn wire is 2.

The p1 p2 switch is Likly double pole pos and neg. Going to the double pole breakers at bottom.

A bit confusing when they split some into 2 wires and leave some together as one in drawing.

The battery switch shown in the photo a Blue sea M series 4 position selector switch. This is a single pole switch.

A single pole battery switch on a vessel with a gound fault testing facility is unusual. Possibly this is not the main battery switch, or has been retrofitted, perhaps replacing an original double pole battery switch.