MCB panels

[Chae_73]

it looks like I will need to do [i.e. get someone suitably expert to do] fairly significant electric work on the boat this winter. Various things don't work, and the switch panel is ropey.

it seems logical to replace the original fused panel with an MCB panel - you wouldn't replace the consumer unit in your house with a fuse wire board. Having had a little look at the options I can find via google, it seems that MCB DC switch panels have circuit breakers rated at 15 amps - that seems like a very big load for most boat circuits, such as nav lights, cabin lights, instruments etc which i guess draw just a few amps.

Is this a problem / potential safety issue or not?

 

[jwfrary]

Your mcb protects the cable, so no not really unless your cable is to small.

A bit o variety on the boards would be nice though! You can change the breakers out for more appropriately rated ones, but the common practice is to fuse the spur independently to allow for this.

For example

From your instrument MCB rated at 15 amps you would have a 4cm wire connected to a fuse board of 4 ways with 3 amp fuses in for nmea2k, plotter, ais and gas alarm.

Those devices are then individually protected but the feed is also then protected.

Remember the mcb protects the conductor not the device.

 

[Stemar]

If breakers are tripping or fuses blowing, something's very wrong. Likewise if the fuses are giving trouble. I replaced those horrible ceramic fuses with blades on my last boat and am doing the same on my current one. In close to 20 years of boat ownership and many more years driving old bangers, the only issues I've had with fuses were due to ceramic fuses and their mountings corroding and my own occasional inability to turn things off before fiddling with them.

But then, I'm on a tight budget. If I were running a Halberg Rassey, with budget to match, I'd use MCBs

 

[Moodysailor]

If I were replacing a fuse panel and had the space, I'd go with MCB nowadays. There is also a lot of kit that will fit on a DIN rail (relays, timers, etc), so it's neat mounting solution.

Edit: You can get DC MCB down to 6A, so you can size for the consumer, not just the cable if needed. As with all these things, it pays to go simple though... some thought should allow you to use one rating for a majority of kit.

 

[prv]

If breakers are tripping or fuses blowing, something's very wrong. Likewise if the fuses are giving trouble. I replaced those horrible ceramic fuses with blades on my last boat and am doing the same on my current one. In close to 20 years of boat ownership and many more years driving old bangers, the only issues I've had with fuses were due to ceramic fuses and their mountings corroding and my own occasional inability to turn things off before fiddling with them.

Agree. I fitted a fusebox that uses automotive blade fuses and am very happy with it. In ten years I’ve had to replace precisely one, when I forgot to turn off the power to the instrument circuit before fiddling around with the Seatalk wiring and shorted the positive and negative together.

Pete

 

[Moodysailor]

I think the two comments are both valid. If replacing a panel, going with an MCB setup is definitely a valid option, IMO.

And with whatever circuit protection exists, if there are issues with breakers or fuses tripping then this needs rectifying.

 

[Buck Turgidson]

When I did my re-wire I initially though about MCBs as cost was secondary but almost all of my equipment specified much lower rated protection so I went with spade fuses in a block from Blue sea systems in the end.

 

[BabaYaga]

For example

From your instrument MCB rated at 15 amps you would have a 4cm wire connected to a fuse board of 4 ways with 3 amp fuses in for nmea2k, plotter, ais and gas alarm.

Those devices are then individually protected but the feed is also then protected.

Remember the mcb protects the conductor not the device.

Perhaps I'm missing something, but in your example I can only see that the MCB is protecting the 4 cm wire going to the fuse board (and the internal wiring in the fuse board upstream of the fuses). If the wiring leading to the devices are to be fused anyway, is that MCB really worthwhile?
Also, for those using MCB based switch panels, how are the wiring feeding into the MCBs generally protected?

 

[migs]

Send your main battery feed (suitably fuse protected) to:

1. A fuse distribution board (can be hidden) for things that you don’t normally switch on and off e.g. battery monitor, electric wc, main cabin lights feed etc.

2. An mcb distribution board for things that you regularly switch on and off e.g. fridge, fresh water pump, instruments, nav lights etc.

Best of both worlds…

 

[PaulRainbow]

it looks like I will need to do [i.e. get someone suitably expert to do] fairly significant electric work on the boat this winter. Various things don't work, and the switch panel is ropey.

it seems logical to replace the original fused panel with an MCB panel - you wouldn't replace the consumer unit in your house with a fuse wire board. Having had a little look at the options I can find via google, it seems that MCB DC switch panels have circuit breakers rated at 15 amps - that seems like a very big load for most boat circuits, such as nav lights, cabin lights, instruments etc which i guess draw just a few amps.

Is this a problem / potential safety issue or not?

Not an issue if the wiring is rated in excess of 15a. So, if everything was wired using a minimum of 1.5mm cable, it'll be fine.

Be careful with off the shelf switch panels, they don't always come with decent quality components.

 

[Moodysailor]

Not an issue if the wiring is rated in excess of 15a. So, if everything was wired using a minimum of 1.5mm cable, it'll be fine.

Be careful with off the shelf switch panels, they don't always come with decent quality components.

I was waiting for the expert to arrive. The rest of us were padding... ?

 

[PaulRainbow]

Perhaps I'm missing something, but in your example I can only see that the MCB is protecting the 4 cm wire going to the fuse board (and the internal wiring in the fuse board upstream of the fuses). If the wiring leading to the devices are to be fused anyway, is that MCB really worthwhile?

Depends on the routing/distance of the 4cm wire, but chances are, for the typical yacht, it will not be serving any useful purpose in terms of circuit protection, for the reasons you give. But, if the whole panel is otherwise using MCBs it keeps everything looking neat, tidy and uniform.

Also, for those using MCB based switch panels, how are the wiring feeding into the MCBs generally protected?

The same was as any other panel is protected.

 

[PaulRainbow]

Lots and lots of ways to construct switch panels, all of which can be correct. You can use switches and fuses, switches and thermal breakers, or combined switch/breakers. The important thing is to use good quality components. If you build something from crap components, all you get is a big pile of crap. Look for names such as ETA or Carling.

Do not get hung up on fuse/breaker ratings. In the majority of cases the fuse is there to protect the circuit (as already mentioned). So when you look through all of your equipment manuals and jot down a list of fuses, you'll have almost as many different ratings as you have items of equipment, which means a big box full of spare fuses.

Consider cable sizes. Again, you could calculate the currents and voltage drop for each device and use whatever cable that calculation comes up with, but why bother ? If something is rated at 3a, with no voltage drop allowance that's 0.3mm cable, that'll last about 5 minutes on a yacht. Current regs state a minimum of 1.0mm cable, i prefer to use 1.5mm as a minimum (with exception for stuff like networking). So, taking voltage drop into account, anything that's rated less then 21a would be OK with 1.5mm cable. But, it's not often that we can ignore voltage drop, so a decent rule of thumb would be anything less 10a and below can be wired with 1.5mm cable and a 10a fuse/breaker. Then we go up to 2.5mm cable, rated at 30a. The 1.5mm cable will have done most circuits, so we'd typically be left with things like water pumps, bilge pumps etc, these would usually be fused at 15a/20a/30a, as appropriate. So far, we need a maximum of 4 spare fuse sizes. If we were using breakers, that's a max of four different breakers.

Anything that needs thicker cable than 2.5mm cable will be one off circuits, such as fridge, maybe radar, heating etc. Typically, the cable would be rated higher for voltage drop reasons, rather than constant current, so we'd still not be using anything over the 30a fuse/breaker.

There is also the valid "satellite" panel that Jon mentioned in post#2. If you have a few devices in a location away from the main panel, you can run a thicker cable to a secondary panel. For instance, i recently wired a 50ft yacht with a central galley, for accommodation, aft accommodation and a wheelhouse. The main electrical "nerve centre" was just aft of midships, where the batteries, chargers and main switch panel etc were installed in a cabinet. Rather than run 6 pairs of cables to the galley we ran a pair of 10mm cable (from a midi fuse, no switch) to a secondary panel in the galley. The panel was then fuses accordingly for the individual devices in the galley. The same was done for secondary panels in the forward and aft accommodation. etc, etc

 

[Moodysailor]

Lots and lots of ways to construct switch panels, all of which can be correct. You can use switches and fuses, switches and thermal breakers, or combined switch/breakers. The important thing is to use good quality components. If you build something from crap components, all you get is a big pile of crap. Look for names such as ETA or Carling.

Do not get hung up on fuse/breaker ratings. In the majority of cases the fuse is there to protect the circuit (as already mentioned). So when you look through all of your equipment manuals and jot down a list of fuses, you'll have almost as many different ratings as you have items of equipment, which means a big box full of spare fuses.

Consider cable sizes. Again, you could calculate the currents and voltage drop for each device and use whatever cable that calculation comes up with, but why bother ? Is something is rated at 3a, with no voltage drop allowance that's 0.3mm cable, that'll last about 5 minutes on a yacht. Current regs state a minimum of 1.0mm cable, i prefer to use 1.5mm as a minimum (with exception for stuff like networking). So, taking voltage drop into account, anything that's rated less then 21a would be OK with 1.5mm cable. But, it's not often that we can ignore voltage drop, so a decent rule of thumb would be anything less 10a and below can be wired with 1.5mm cable and a 10a fuse/breaker. Then we go up to 2.5mm cable, rated at 30a. The 1.5mm cable will have done most circuits, so we'd typically be left with things like water pumps, bilge pumps etc, these would usually be fused at 15a/20a/30a, as appropriate. So far, we need a maximum of 4 spare fuse sizes. If we were using breakers, that's a max of four different breakers.

Anything that needs thicker cable than 2.5mm cable will be one off circuits, such as fridge, maybe radar, heating etc. Typically, the cable would be rated higher for voltage drop reasons, rather than constant current, so we'd still not be using anything over the 30a fuse/breaker.

There is also the valid "satellite" panel that Jon mentioned in post#2. If you have a few devices in a location away from the main panel, you can run a thicker cable to a secondary panel. For instance, i recently wired a 50ft yacht with a central galley, for accommodation, aft accommodation and a wheelhouse. The main electrical "nerve centre" was just aft of midships, where the batteries, chargers and main switch panel etc were installed in a cabinet. Rather than run 6 pairs of cables to the galley we ran a pair of 10mm cable (from a midi fuse, no switch) to a secondary panel in the galley. The panel was then fuses accordingly for the individual devices in the galley. The same was done for secondary panels in the forward and aft accommodation. etc, etc

What @PaulRainbow has written above is exactly the way I would do it too. Electrical installations are one area where KISS is compatible with modern kit.

If looking at a partial rewire, it may be easier to start again (or start modifying with a different mindset) - running loads of 1.5/2.5mm wires through a boat is tiresome, expensive and inefficient, so running larger diameter cables and having smaller local 'hubs' is a much smarter way to do it, IMO.

 

[jwfrary]

Perhaps I'm missing something, but in your example I can only see that the MCB is protecting the 4 cm wire going to the fuse board (and the internal wiring in the fuse board upstream of the fuses). If the wiring leading to the devices are to be fused anyway, is that MCB really worthwhile?
Also, for those using MCB based switch panels, how are the wiring feeding into the MCBs generally protected?

Wire to the distribution could be any length, a no compromise installation is likely both expansive and expensive!

 

[Chae_73]

Many thanks for all the replies - most helpful.

I don't have any reason the believe that here is an active fault with the current panel, perhaps my description of "ropey" was not 100% accurate. However it is 33 years old and the switches feel like they could fail. I need to find out why the masthead light doesn't work but suspect more likely to be to do with the deck fitting than the panel.

Rationale for changing it is that I need electrical work done and it would seem to make sense to start with a new panel. I had in mind one of the Blue Sea Systems ones, perhaps like this:

https://www.bluesea.com/products/1464/12_Position_Switch_CLB_+_Meter_Square

I don't know anything about this brand, the price suggests it should be decent quality but welcome views of anyone who has used their products.

 

[Tranona]

Also worth looking here axoncontrol.co.uk/panels not quite as swish as the Blue Sea, but the cheaper range still has good quality components.

 

[Chae_73]

Also worth looking here axoncontrol.co.uk/panels not quite as swish as the Blue Sea, but the cheaper range still has good quality components.

Thanks - less than half the price of BSS and look pretty good. Seems ideal.

 

[PaulRainbow]

Many thanks for all the replies - most helpful.

I don't have any reason the believe that here is an active fault with the current panel, perhaps my description of "ropey" was not 100% accurate. However it is 33 years old and the switches feel like they could fail. I need to find out why the masthead light doesn't work but suspect more likely to be to do with the deck fitting than the panel.

Rationale for changing it is that I need electrical work done and it would seem to make sense to start with a new panel. I had in mind one of the Blue Sea Systems ones, perhaps like this:

https://www.bluesea.com/products/1464/12_Position_Switch_CLB_+_Meter_Square

I don't know anything about this brand, the price suggests it should be decent quality but welcome views of anyone who has used their products.

Most (possibly all) Blue Sea panels use ETA switches/breakers, which are very good quality, although the panels are very expensive.

Tranonas suggestion of an Axon panel is sound, most of their panels use Carling switches/breakers, although the cheapest ones don't, so make sure it states in the description "Carling". Not as fancy looking as the Blue Sea panels, but component wise, every bit as good quality.