If you have a shorepower installation (Question 4)

[Moe]

This is a poll about shorepower installations.

[mike]

Funny that you brought this up... I've been meaning to ask a question about this. My boat's shorepower installation (which I believe was done by the dealer) was a bit strange. It has a Blue Seas panel with 1 double main breaker and 6 single breakers for circuits, but the main breaker wasn't used.

In other words, the neutral and ground from the inlet are connected directly to their respective bars, with only the hot going through of the single breakers, which functioned as a main switch. A couple of the other single breakers were used for circuits (outlets, battery charger).

A few weeks ago, when running a circuit for the Engel refrigerator I finally got around to reworking this panel and the main double breaker is now in service.

But I'm left wondering... why would they have done it that way? Is there some benefit to having the neutral directly connected to the bar? Made me nervous, so I'm glad it's correct now.

--Mike

[Dimitri-2000X-Tampa]

Mine was likely done by the original dealer and there is no breaker. I suppose I should put one in some day. There is a GFCI though. Is there a requirement for a two pole breaker?

[Moe]

ABYC requires that 120/240 VAC single-phase (50A 4 wire service) only have ganged breakers on the two ungrounded hot leads. The center tap neutral, which is grounded at the main panel on shore, is directly attached to the bus. Perhaps the dealer did Mike's setup this way out of habit.

ABYC requires that both the ungrounded (hot) and grounded (neutral) of 120VAC single-phase (including 30A 3 wire service) be run through ganged breakers. I guess they do this so there would be overcurrent protection even if the hot and neutral were swapped (reverse polarity) at the dock outlet. You might not notice that without an indicator (which is also required on all shorepower installations). If a hot and neutral are reversed on a 50A outlet, one of the legs has 240VAC on a 120VAC circuit and will hopefully trip a breaker before damage occurs (but don't count on it). It WILL be noticed!

--
Moe

[Dimitri-2000X-Tampa]

Moe, how do you get 240V on a single phase circuit (I thought you needed 2 phases)? Also, why is reverse polarity a problem for an AC circuit?

[Moe]

Moe, how do you get 240V on a single phase circuit (I thought you needed 2 phases)? Also, why is reverse polarity a problem for an AC circuit?

120/240 VAC power, like you have in your house, is 240VAC single-phase, divided by a neutral line. There is 240 VAC between leg 1 and leg 2 and 120VAC between either leg and neutral. The legs are 180 out of phase with each other, with respect to neutral, but in the overall scheme of things, they are in phase, as two flashlight batteries stacked on top of each other in the same direction would be. Imagine putting a leg at each end of the stack and a neutral between the batteries. [on edit] Something else to keep in mind is that if there are equal 120V loads on each leg, there is no current on the neutral line. It only carries the difference current, and the most it carries is the maximum current of one leg.

Neutral is grounded, and SHOULD BE 0 volts, while hot is expected to be dangerous. That's why residential lamps have polarized plugs now, so that you won't get shocked by touching the bulb base sides. In practice, there is often some small voltage above ground potential on a neutral line, created by the voltage drop of current from other appliances on the circuit running back to the panel.

--
Moe