Switched and fused at the ground connection!!

[JB]

I've been wiring up boat stuff for over 50 years but I ran into something new to me today.<br /><br />I bought a SeaChoice 6 gang switch and fuse panel for rewiring my boat. Danged expensive at over $60, even from iboats.<br /><br />Pulled it out of the package and found it is set up to fuse and switch the ground side of each circuit, not the "hot" side.<br /><br />Strikes me as really DUMB.<br /><br />Anyone ever seen this sort of lashup before?<br /><br />No. Of course I wont wire it that way. I will put 12V to what they set up to be a ground bus and install a seperate ground bus for the return circuit.<br /><br />Yes, it would protect the circuit, but only if the device in the circuit shorted to the ground lead. Any other short, like a short of the hot lead to ground, and I would probably have a fire on my hands.<br /><br />I can't believe they would get away with that.

 

[Silvertip]

Re: Switched and fused at the ground connection!!

Big discussion about switching and fusing ground. It is not recommended. Is it done? Yes --but not for boat circuits. Just make sure what you understand what you are looking at before doing the wiring.

 

[crab bait]

Re: Switched and fused at the ground connection!!

yeah that's odd..<br /><br />but many trucking firms are wiring there trucks that way ,,i hear.. an don't really know why. except they say it causes no oxidation ..

 

[Paul Moir]

Re: Switched and fused at the ground connection!!

There's a specific rule against it in our code, so I'm sure there's one for yours. It goes <br />

<br />8.9.1.2 <br />Every ungrounded, current carrying conductor shall be protected by a manually reset, trip-free circuit breaker or fuse that shall be: ....<br />

Since return conductors are all grounded by the engine in small boats, they don't need to be fused. But that's it. <br />Why, who knows? Perhaps because they could. I suppose if you had an engine with a positive frame, you would actually be required to fuse your accessories that way.

 

[tommays]

Re: Switched and fused at the ground connection!!

Dont a lot of big rigs use a positive ground ?<br /><br /><br />tommays

 

[bsh21wash]

Re: Switched and fused at the ground connection!!

Since you guys are on the topic I have some questions. I went to do my wiring on my boat today, well kinda mapping it out if you will. A lot of mumble jumble, anyways what I found was there is a + wire coming from the battery (no fuses anywhere)going to the bow, all thats hooked up to it is the bow light and the horn. Do any of the instruments need a power wire? All thats there is a gas gauge, horn switch and light switch. Also the gas tank has two wires coming of it that go to the back of the fuel gauge, but there is no + wire going to it? Is that right?

 

[Silvertip]

Re: Switched and fused at the ground connection!!

Older Mac trucks used a positive ground as did Chrysler cars of years gone by. Switch ground on your electronics (stereo for example) and you will find out in a hurry that station memory selections are not retained and the clock will never be right. Motor vehicles have traditionally used negative ground and there is no need for a ground buss as the entire vehicle is ground (although with more plastics being used, many of the circuits have dedicated grounds in them.

 

[Silvertip]

Re: Switched and fused at the ground connection!!

Older Mac trucks used a positive ground as did Chrysler cars of years gone by. Switch ground on your electronics (stereo for example) and you will find out in a hurry that station memory selections are not retained and the clock will never be right. Motor vehicles have traditionally used negative ground and there is no need for a ground buss as the entire vehicle is ground (although with more plastics being used, many of the circuits have dedicated grounds in them. With more sensitive electronics being added with every new model (boats, cars, trucks, etc) ground loops can be a problem so single ground points are becoming more important.

 

[Paul Moir]

Re: Switched and fused at the ground connection!!

bsh21wash, those are normally run from the engine's wiring harness which provides power taken from the starter cables. There's usually a fuse on the engine itself or something for them.<br />All lines except the starter cables ought to be fused within a few inches (7) of the battery. You might be into some upgrading.

 

[KaGee]

Re: Switched and fused at the ground connection!!

JB,<br /><br />Technically, current does flow negative to positive. But I'm surprised at that set up.

 

[DangerDan]

Re: Switched and fused at the ground connection!!

I recently saw a post discussing a "Star Ground" could this Star ground be as effective say at the motor block versus the battery terminal via a buss bar. The reason I ask is that the engine is grounded at the battery. Shouldn't the other ground circuits be grounded in the same place?

 

[Silvertip]

Re: Switched and fused at the ground connection!!

A single ground point is the desireable configuration. This is especially important if a boat has a bunch of really sophisticated electronics since scattered grounds can create ground loops that drives electronics nuts. However, most recreational boats don't have much in the way of sophistication so this isn't "currently" a problem. That said, with the new engines using elaborate ECU's, fly-by-wire- control systems, and fancy instrumentation, grounding may indeed get to be an issue down the road.

 

[--GQ--]

Re: Switched and fused at the ground connection!!

Hmmmm that is weird. the liability issue is plain and clear. If a fire should happen on a boat after such a device is installed, you can bet your retirement check the company will be sued. The Head Line would read something like this.... Boat Caught on Fire. Faulty Wiring to Blame.

 

[swist]

Re: Switched and fused at the ground connection!!

I am missing something here. I do low voltage DC wiring in my job and as long as you are wiring inside something non-conducting (like a wood and fiberglass boat), and there is no external ground reference (like the earth), it doesn't matter whether you fuse feeds or returns, nor does it matter which is positive and which is negative UNLESS you have devices that are polarity sensitive (motors, solid-state stuff: yes; relays, light bulbs, no).

 

[byacey]

Re: Switched and fused at the ground connection!!

It doesn't matter if it's a positive ground system or negative ground system. The whole point of fusing is to: 1)protect against wiring harnesses burning up (or the whole boat). 2)ensure the other circuits continue to operate should some devices start drawing excessive current. 3) Protect the defective load from further damage by opening the circuit in an over-current situation. <br /><br />If the ground returns were fused - and a short develops and partially melts the supply line insulation before the fuse blows (and it may never blow because the current has found a more convenient path to ground), or if the insulation wears through from vibration, or getting physically pinched, you will still have an active short should that supply line wire touch the metal hull of the boat; even if the fuse is blown. Things will get hot and you will have at the very least smoke and burning wiring.<br /><br />As mentioned above, fuses should be installed as close to the power source as possible - in this case the battery, and connected to the live side of the supply, not the ground. Obviously some things are not fused in the traditional way, like the heavy cable going to the starter. In some cases fusible links are installed within the cable that will burn up safely an open the circuit should a short develop. Other times this wire has no protection, and is carefully routed to avoid potential insulation breakdown. In the case of wooden or fibreglass hull boats, this isn't as great danger, but the potential still exists for short circuits.

 

[Paul Moir]

Re: Switched and fused at the ground connection!!

The regulation doesn't say it has to be positive common or not. Can be either way as far as it's concerned. What it does say that grounded power lines don't need protection devices. And in small boats the negative common is grounded due to the engine.<br />The corresponding ABYC rule is E-8.11.6.

 

[--GQ--]

Re: Switched and fused at the ground connection!!

What the heck is "positive ground". I don't think the word positive should be used to describe a ground when dealing with electricity. <br /><br />Bill, I can give you so many scenarios why you should never switch on the ground side. I hink you trying to pull a fast one...lol. Explain youself.....

 

[--GQ--]

Re: Switched and fused at the ground connection!!

You have to remember right after the dinosaurs got "poofed" off the face of the earth (maybe the mods had something to do with it) and caveman stop pulling their women by the hair, electricity was discovered supposedly by this dude flying a kite with a key attached to the end of the string in the middle of a thunder storm, on top of the highest hill, during a 40 mph wind, all by himself the world never lookd back. In those days, things were done out of convenient. No safety issues. No liability issues. No lawyers to sue anyone.<br /><br />Funny thing about electricity is that you can hook it up wrong and it will work. But when an unfavorable condition should occur, it can be very dangerous. Folks read my lips, NO SWITCH/FUSE ON GROUND WIRES.

 

[Dunaruna]

Re: Switched and fused at the ground connection!!

Originally posted by --GQ--:<br /> What the heck is "positive ground".

Three words - 'Prince Of Darkness'!

 

[byacey]

Re: Switched and fused at the ground connection!!

double post