Fuse question

[John Langford]

My 1999 Mk II does not have a fuse in the 9 inch 10 gauge line between the common terminal of the battery switch and the many circuit breakers on the electrical panel. I have noticed that this is a common feature on more contemporary boats. Any views on whether this would be a necessary or prudent addition?

[mainesail]

Unless that wire is in some for of protective conduit between the "C" post and panel it requires a fuse to meet the safety standards. That is unless the entire system is wired with 10GA and there is a fuse at the battery.

Any time you step down in wire size the larger wire size you stepped down from is essentially your "source". The fuse goes at the step down point to protect the smaller wire. If the fuse supplying the large feeder wire is small enough, to adequately protect 10GA wire, then no additional fuse would be required.

This is one of the most widely violated over-current protection violations in regards to ABYC standards. If your battery bank has a 250A to 300A fuse, and it should, then you can't protect 10GA with those fuses.

[KWKloeber]

My 1999 Mk II does not have a fuse in the 9 inch 10 gauge line between the common terminal of the battery switch and the many circuit breakers on the electrical panel. I have noticed that this is a common feature on more contemporary boats. Any views on whether this would be a necessary or prudent addition?

John.

I am going to disagree with RC on this one.  Based on both ABYC but especially my "common sense code."

The "encased in a sheath ... or conduit exception" pertains to the LOCATION of the fuse -- NOT whether or not you NEED a fuse.

In this example, if the wire is protected, the fuse needs to be "as close as practical" but not more than 40-inches from the power source (C post of the switch.)

Being a wire supplying power to a panelboard, there must (no exception) be a fuse @ no more than 100% of the wire capacity AT THE SOURCE of the power to the panel (ie, the C post).  No exceptions to that (e.g., not for the wire being encased/protected, or being less than 7" long, or being sized 10 times larger than the needed capacity, etc.) 

That also passes my "common sense rule"  -- Why? 
Because it's feeding a panel, there's a possible scenario where the entire panel circuits could draw more than the safe capacity of the 10 awg power feed wire.  Whether or not the feed wire is protected in a conduit (protecting it from harm) is irrelevant -- the concern is not damage to a wire behind a panel, it's over current and exceeding it's capacity.  You wouldn't want it over current, and melting the insulation, even if it's in a sheath.  Plus, being in a sheath the situation is worse (no air circulation, temperature rise) in melting the insulation.

That's my story and I've got a sticking Toit.  ;-)

A fuse wouldn't be needed there if the feed wire was the same gauge as your battery cable AND all panel jumpers were the same (if fuses/breakers are not on a buss) AND your battery was fused (within 7-inches.)


An aside - One thing I did was feed my (way old style) panel w/ 2 banks of switches/fuses from both ends to reduce V loss.  There was inherent v loss with every jumper wire and terminal as power hopped from switch to switch.


ken

[mainesail]

Ken,

Your points are good but I suspect you missed a point in regards to how Catalina looks at this.. It is a 9" long wire because the battery switch is physically mounted in the DC panel board.. Catalina is likely trying to skate around the ABYC standard by considering this a "pigtail of less than 7"". IMHO this is an incorrect interpretation/application, but the standards need a lot of tightening up of wording.

There are three general options:

1 - In general (not applicable to far too many Catalina's), if it is a "7 inch or less pigtail" or short jumper you could put it it in a protective sheath or conduit so long as the main DC panel breaker (most Catalina's don't have a panel mounted DC Main Breaker) is not going to allow you to overdraw the wires max ampacity of 60A. The 10GA is likely suitably sized to meet the 3% max voltage drop requirement, but not appropriate per the standards, for more than 60A, regardless of length.

In this situation, due to the very short length, it is unlikely that 3% VD would be the issue, but pushing the wire beyond it's max ampacity of 60A in free air could be. The DC panel on our 36 footer is fed by 1GA wire and fuse at the "source" and the panel has a DC Main Breaker of 100A... This option only works it you have a DC main breaker at the panel and most Catalina's do not. Later Catalina's used 6GA & occasionally 4GA pigtails between the "C" post and breaker busbars but still no breaker and non-complaint OCP..

2- Add a fuse at the "C" post or a DC main breaker within 7" of the "C" post. This is really the only option when Catalina does not offer a DC Main breaker.

3- Best - Install larger wire and a fuse at the "C" post or add a DC main breaker.



Like many other builders Catalina cuts a lot of corners with electrical systems. They place battery switches in AC / DC panels, perhaps to avoid having the added expense of a "DC Main Breaker", yet they then violate the part of the standard that requires battery switches to be as close as practicable to the batteries. What they save in main breaker expenses they more than eat up in wire costs. The wiring on our 2005 C-310 was atrocious and our late 80's C-36 about 40X worse than the C-310..... D'oh...

In a good DC panel design there is always a DC Main breaker. Some builders put this breaker right at the battery switch, to follow the standard, and keep the battery switch as close to the batteries as possible.

Here is but one example. The batteries are less than 30" away from the battery switch, & fused, and the DC Main breaker is also right at the battery switch to power the DC panel.



When considering feed wire to a DC panel always consider the maximum voltage drop.... I have measured far too many boats exceeding 6% or more voltage drop between battery voltage and navigation lights. 

11.14.1.2.6 Voltage Drop - Conductors used for panelboard or switchboard main feeders, bilge blowers, electronic equipment, navigation lights, and other circuits where voltage drop must be kept to a minimum, shall be sized for a voltage drop not to exceed three percent. Conductors used for lighting, other than navigation lights, and other circuits where voltage drop is not critical, shall be sized for a voltage drop not to exceed 10 percent.

[KWKloeber]

It is a 9" long wire because the battery switch is physically mounted in the DC panel board..

Rod,

Yep I knew that, but just so I don't mis-interpret, I'm not sure the reason why you are calling that out. 
Can you clarify?

My point was merely that a sheath/conduit can't substitute for a fuse (in this particular situation.)

As far as having a main breaker, Ha Ha.     Good Memorial Day humor!!



Cheers,
Ken

We're lucky the old Seaward panels had a main AC breaker!
"sister" panel:

[J_Sail]

In a good DC panel design there is always a DC Main breaker. Some builders put this breaker right at the battery switch, to follow the standard, and keep the battery switch as close to the batteries as possible.

I'm curious, in the case where the battery switch is at the battery box and there is a suitable fuse near the battery switch protecting the wire to the Main DC panel, do you consider it poor practice to not have a readily accessible Main DC breaker somewhere (breaker rather than fuse)? I realize it's nice to be able to use a breaker to turn off the Main DC Panel, and one could argue that there is a safety benefit to being able to quickly restore power to the Main DC Panel after an overload, but are either of those sufficient to warrant a breaker over a fuse in order to be considered "good design"? I know it's a judgment call, but I would value your professional insight.

[KWKloeber]

In a good DC panel design there is always a DC Main breaker. Some builders put this breaker right at the battery switch, to follow the standard, and keep the battery switch as close to the batteries as possible.

I'm curious, in the case where the battery switch is at the battery box and there is a suitable fuse near the battery switch protecting the wire to the Main DC panel, do you consider it poor practice to not have a readily accessible Main DC breaker somewhere (breaker rather than fuse)? I realize it's nice to be able to use a breaker to turn off the Main DC Panel, and one could argue that there is a safety benefit to being able to quickly restore power to the Main DC Panel after an overload, but are either of those sufficient to warrant a breaker over a fuse in order to be considered "good design"? I know it's a judgment call, but I would value your professional insight.

J


Why not replace the fuse w/ a surface breaker, or thru-mount breaker next to the switch?  (seems best of both world's option)
Or leave the fuse, and put a switch only at the panel to disconnect the feed?


ken

[mainesail]

I call that out because Catalina likely interprets those 9" wires as "pigtails" which does not technically eliminate the need for a fuse or DC main breaker. If there was a DC panel main breaker, as many boats have, then one could use conduit or sheathing to "protect" the wire from a short (up to 40") but the breaker still needs to be there to prevent pulling more ampacity than the cable can pass.

[J_Sail]

In a good DC panel design there is always a DC Main breaker. Some builders put this breaker right at the battery switch, to follow the standard, and keep the battery switch as close to the batteries as possible.

I'm curious, in the case where the battery switch is at the battery box and there is a suitable fuse near the battery switch protecting the wire to the Main DC panel, do you consider it poor practice to not have a readily accessible Main DC breaker somewhere (breaker rather than fuse)? I realize it's nice to be able to use a breaker to turn off the Main DC Panel, and one could argue that there is a safety benefit to being able to quickly restore power to the Main DC Panel after an overload, but are either of those sufficient to warrant a breaker over a fuse in order to be considered "good design"? I know it's a judgment call, but I would value your professional insight.

J

Why not replace the fuse w/ a surface breaker, or thru-mount breaker next to the switch?  (seems best of both world's option)
Or leave the fuse, and put a switch only at the panel to disconnect the feed?
ken

Ken,
All of those are options, each with their own pros and cons. For example, the placement of a toggle circuit breaker in or at the battery box (which you present as best of both worlds) also opens the possibility of something inadvertently turning of the Main Panel, a risk not present with a fuse. These tradeoffs can be debated endlessly.

My posting, though, was specifically to solicit MaineSail's opinion as a leading professional in the field for his view of acceptable best practice.

[KWKloeber]

I call that out because Catalina likely interprets those 9" wires as "pigtails" which does not technically eliminate the need for a fuse or DC main breaker. If there was a DC panel main breaker, as many boats have, then one could use conduit or sheathing to "protect" the wire from a short (up to 40") but the breaker still needs to be there to prevent pulling more ampacity than the cable can pass.

Thanks RC.  I understand.  I knew that the 9" (7") didn't app'y here. Great points about the V loss -- that's essentially what I did by doubling up on the feed wire to the switches ahead of the fuses. 


As far as your point on Catalina, who ever knows what CTY/Seaward/Bristol/Universal thought about when building in the wiring deficiencies.  The panel may be the least of them.  My personal pet peeve is the dangerous engine harness, but sometimes it's like talking to a wall.


Cheers
Ken

[John Langford]

Great debate but it does leave the unwashed with some puzzles to work through.

First, a correction and a bit more information. Since so much attention is being focused on the pigtail connecting the common terminal to the boat's DC  circuits, I remeasured and it is less than 7" long. Not only is there no fuse there, but there is no master fuse between the the batteries under the starboard bunk and the battery switch several feet away above the nav table on the port side.

So what to do? I can easily put a 40-60amp inline fuse in the 10 gauge pigtail line. But is it worth the extra trouble and expense of putting in a main breaker between the batteries and the battery switch? I assume this would have to be breaker rather than an inline fuse. In fact I wasn't aware that you could get an inline fuse much over 60 amps. More important, wouldn't I have to install two master breakers to cover the house and start batteries since I would want to position a main breaker close to batteries that are far away from the battery switch? So, what to do?

[J_Sail]

All of those fuses should be there, but in my book the more important of the two is to have a fuse at the battery. Fortunately, if you have a little bit of headroom, BlueSea makes a Marine Rated battery Fuse and holder that mount directly onto the battery post.  Take a look at:
https://www.bluesea.com/products/5191/MRBF_Terminal_Fuse_Block_-_30_to_300A

Mainesail has discussed them on his site and on various forums.
http://www.pbase.com/mainecruising/battery_fusing

[KWKloeber]

john, 

If you look thru the 101 electrical topics there's probably a discussion of fusing (I'm sure Stu will point to it!!)

But, understand that the length of that "jumper" (not pigtail) wire has no bearing on this particular situation. 

1) There is no "exception" to having the feed to the 12v breakers or fuses (whichever you have) "fused."   Up until the 10 awg wire leaves the C post, the switch is part of the starting circuit (exempt from fusing requirement -- but not a good idea.)

2) The 7" length pertains to a different situation (most commonly at the connection to a battery post.) 

3) Also, that wire isn't a "pigtail" anyway.  A pigtail has two common meanings:

      a.) If you crimp, say, 4 wires together, and one of them is a jumper (typically of the same gauge, e.g., to a switch, or a power source, etc..) that wire is a "pigtail."  So a pigtail is a single wire "joined to" multiple wires.

light 1 --------\
light 2 ---------|------------- power source
light 3 --------/    ("pigtail")

      b.) In ABYC it is also the short (<7"), light-gauge wires on, for instance, a bilge pump (to which you connect your heavy the power and neutral wires to the pump.) 
______
| Bilge  | ---------------||====== heavy-gauge feed from panel
| Pump | ---------------||====== heavy-gauge neutral
| ____  | (<7" pigtails)

In other locations if you drop down to a lighter gauge there must generally be overcurrent protection for the lighter wire.  Not so on that type "pigtail."  The exception is there so dirtbag manufacturers can continue to supply light gauge wiring on the marine equipment they sell to us.  (yeh, why wouldn't we want to butt crimp, say a 12 gauge or 10 gauge power feed to a 16 gauge pump wire???)  They get away w/ it because the pigtails can handle the current, so cost prevails over common sense and avoiding voltage loss, not to mention that you need a special butt crimp to drop from 10 or 12 gauge to 16 gauge.)

Due to the potential for very high current, you want a marine-rated fuse (instead of a breaker) [size=78%]on the main feed to the selector switch[/size].

ken

First, a correction and a bit more information. Since so much attention is being focused on the pigtail connecting the common terminal to the boat's DC  circuits, I remeasured and it is less than 7" long. Not only is there no fuse there, but there is no master fuse between the the batteries under the starboard bunk and the battery switch several feet away above the nav table on the port side.

So what to do? I can easily put a 40-60amp inline fuse in the 10 gauge pigtail line. But is it worth the extra trouble and expense of putting in a main breaker between the batteries and the battery switch? I assume this would have to be breaker rather than an inline fuse. In fact I wasn't aware that you could get an inline fuse much over 60 amps. More important, wouldn't I have to install two master breakers to cover the house and start batteries since I would want to position a main breaker close to batteries that are far away from the battery switch? So, what to do?

[Roc]

John
Your hull number is not that far from mine. Near the floor under the nav table I have a push/pull breaker between the battery and battery 1-2-all switch. Pull that switch out and power to panel is off. I would think yours is wired that way too.

[John Langford]

Nope. The push/pull switch under my nav table controls the power to the windlass. It is rated at 135 amps. When it is on, a red light on the electrical panel comes on. There is no draw unless you engage the windlass with the foot switch in the anchor locker.