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Old 15-06-2021, 09:46   #1
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Turning off a sub panel.

I want to install a DC sub panel in the cockpit next to the helm that would contain all my switching for electronics nav lights, auto pilot etc...I want to be able to cut power to the panel from inside the boat at the main distribution panel.

Would it be good enough to just wire the sub panel to a single pole breaker/switch on the main DC distribution panel or should the sub panel be on its own double pole breaker thats seperate from the main DC panel?
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Old 15-06-2021, 09:47   #2
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Re: Turning off a sub panel.

Feeding the sub panel from a breaker in the main panel should be sufficient. The 2 fuse blocks under my helm for electronics are powered that way and have been for many years with no issue.
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Old 15-06-2021, 09:50   #3
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Re: Turning off a sub panel.

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Originally Posted by rslifkin View Post
Feeding the sub panel from a breaker in the main panel should be sufficient. The 2 fuse blocks under my helm for electronics are powered that way and have been for many years with no issue.
Ok good to know. It would certainly save me a little space not having to install the separate two pole switch if i dont have to.
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Old 15-06-2021, 20:11   #4
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Re: Turning off a sub panel.

depends how many amps you need at the panel. the biggest normal panel breaker is 50a. if that is enough you can feed it from the main panel. asuming the feed from battery switch to main panel can handle the load of both panels.

if you need more then that, then feed the sub panel directly from the battery switch with a fuse or surface mount breaker
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Old 15-06-2021, 20:58   #5
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Re: Turning off a sub panel.

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Originally Posted by smac999 View Post
depends how many amps you need at the panel. the biggest normal panel breaker is 50a. if that is enough you can feed it from the main panel. asuming the feed from battery switch to main panel can handle the load of both panels.

if you need more then that, then feed the sub panel directly from the battery switch with a fuse or surface mount breaker
Oh yeah the feed from the battery switch could easily handle it. I dont have all the devices yet that will go on the sub panel but i cant imagine its going to be more than 10 amps or so.

Basically, i want to take these devices off the main DC panel that im replacing and relocate them from inside the boat to the helm where it makes more sense to have them. it will also allow me to downsize my distribution panel i want to re-locate to the nav desk, which has limited space.
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Old 15-06-2021, 21:33   #6
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Re: Turning off a sub panel.

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Originally Posted by BAD ORCA View Post
or should the sub panel be on its own double pole breaker thats seperate from the main DC panel?
A double pole on a DC system means you would cut the DC negative when you throw that breaker. This is illegal in Canada and contrary to ABYC Standards.
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Old 15-06-2021, 21:50   #7
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Re: Turning off a sub panel.

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A double pole on a DC system means you would cut the DC negative when you throw that breaker. This is illegal in Canada and contrary to ABYC Standards.
OK, I never knew that! What is the reasoning behind this rule?
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Old 15-06-2021, 22:13   #8
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Re: Turning off a sub panel.

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OK, I never knew that! What is the reasoning behind this rule?
I was just going to ask the same question.

The more i think about it the less it makes sense to use a double pole breaker ayways, but i'd be curious to know the reasoning myself. The only thing i can think of would be in the extremely unlikely event that one of the two wires came into contact and shorted against another hot wire at some point after the breaker. Im guessing this could energize the circuit with no path to ground?

My plan as of right now would be to run a DC ground from my main DC Neg bus (which is closer) to the sub panel and then run the DC pos from the sub panel back to a breaker on the Main DC distribution panel inside the boat at the nav desk.
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Old 17-06-2021, 18:08   #9
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Re: Turning off a sub panel.

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Originally Posted by Wotname View Post
OK, I never knew that! What is the reasoning behind this rule?
Quote:
Originally Posted by BAD ORCA View Post
I was just going to ask the same question.

The more i think about it the less it makes sense to use a double pole breaker ayways, but i'd be curious to know the reasoning myself. The only thing i can think of would be in the extremely unlikely event that one of the two wires came into contact and shorted against another hot wire at some point after the breaker. Im guessing this could energize the circuit with no path to ground?

My plan as of right now would be to run a DC ground from my main DC Neg bus (which is closer) to the sub panel and then run the DC pos from the sub panel back to a breaker on the Main DC distribution panel inside the boat at the nav desk.
As BP is staying quiet on this question perhaps someone else might venture an opinion on the illegality of cutting the negative by using a double pole breaker on a DC system and the rationale behind banning such practice.

Note - I can't see any reason for doing so except maybe on an aluminium hull.
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