Too many large wires in circuit panel, is it ok to step-down large wires to 10ga for panel interior?

[Revolutionary]

I have a Blue Sea Systems panel with 30+ circuit breakers (it is a live-aboard sailboat, lots of pumps and electronics). I have 2/0 gauge cables running from the battery banks to the panel, and a mix of 2ga 4ga, 6ga, and 10ga wires connecting pumps, electronics, etc. to the individual circuit breakers. It is a mess of large wires in there, making it difficult to work behind the panel, and the large gauge wires are stiff enough to put pressure on the circuit breaker terminals (one circuit breaker already broke because of this).

The question is: can I use step-down connectors on the large gauge wires before the wires enter the circuit breaker panel so that all the wires entering the circuit breaker panel are 10ga?

For example, a 2ga wire is used for the macerating toilet. Can I use a step-down connector to change the toilet wire from 2ga to 10ga right before it enters the panel? That would make the toilet wire around 21 feet of 2ga wire with the final 2 feet of it being 10ga wire before it enters the panel.

Can this be done, and could it cause any problems? Or is this what people have been doing all along?

Thank you.

 

[rgranger]

There are several issues to consider. The current carried by the wire should be what determines the gauge. If you try to push too much current through an undersized wire you will get heating in the wire and you will also create a larger voltage drop. Think of voltage like the pressure in a pipe and the gauge of your wires like the diameter of a pipe. If your appliance needs a certain volume of water per second and you put a restrictor (small pipe) in line, then the appliance cannot get enough water. Your smaller gauge wire into the box would be analogous to the restrictor pipe with the added risk of fire.

It is possible that the PO used oversized wires and you may want to research the amp draw of each device.

 

[Don S/V ILLusion]

I wouldn’t…

The unbroken large gauge wire is used for a reason.


Putting aside the current rating of smaller gauge wire, the numerous added connections required become problematic both in terms of integrity and increased resistance if/when a connection is no longer secure and un- corroded. You also introduce an additional periodic inspection and maintenance chore to ensure everything is as it should be which can require taking apart every connection to clean and reattach. And all of it behind a hidden panel where “stuff happens”.

Having said all that, very short runs of smaller gauge wire aren‘t inherently unsafe as voltage drop diminishes with smaller length.

 

[leo310]

You have to remember that the breaker panel is to protect the wire to the device and if required a fuse at the device to protect the device. I have rewired using only 10 gauge to all devices but the ones that I knew that had higher loads then it was 6 or 4 depending on the length of run to reduce line lost. The big thing is label the wires for what they are for.

 

[Revolutionary]

There are several issues to consider. The current carried by the wire should be what determines the gauge. If you try to push too much current through an undersized wire you will get heating in the wire and you will also create a larger voltage drop. Think of voltage like the pressure in a pipe and the gauge of your wires like the diameter of a pipe. If your appliance needs a certain volume of water per second and you put a restrictor (small pipe) in line, then the appliance cannot get enough water. Your smaller gauge wire into the box would be analogous to the restrictor pipe with the added risk of fire.

It is possible that the PO used oversized wires and you may want to research the amp draw of each device.

Thank you for the reply, I appreciate it. I converted the boat from a day sailer to a live-aboard and did all the wiring. I used oversized wires because of inexperience combined with paranoia about the risk of fire. Now I'm just regretting it because I have ended up with a real mess of oversized wires running through the boat and to the circuit breaker panel.

 

[Revolutionary]

I wouldn’t…

The unbroken large gauge wire is used for a reason.


Putting aside the current rating of smaller gauge wire, the numerous added connections required become problematic both in terms of integrity and increased resistance if/when a connection is no longer secure and un- corroded. You also introduce an additional periodic inspection and maintenance chore to ensure everything is as it should be which can require taking apart every connection to clean and reattach. And all of it behind a hidden panel where “stuff happens”.

Having said all that, very short runs of smaller gauge wire aren‘t inherently unsafe as voltage drop diminishes with smaller length.

Thank you for the reply, I appreciate it.

But in most cases, a smaller wire (often 10ga) terminates at the pump/electronic device and this wire is permanently connected to the device during manufacturing . This wire is what the larger gauge wire I used is step-down connected to right before the device. So what's the difference between the wire ending in 10ga right before the device, and now installing a wire starting at 10ga coming out of the circuit breaker panel with 2ga wire connecting the two 10ga wires at the ends of the wire run?

 

[Revolutionary]

You have to remember that the breaker panel is to protect the wire to the device and if required a fuse at the device to protect the device. I have rewired using only 10 gauge to all devices but the ones that I knew that had higher loads then it was 6 or 4 depending on the length of run to reduce line lost. The big thing is label the wires for what they are for.

Thank you for the reply, I appreciate it.

Yes, I definitely need labels!

 

[dlochner]

It all depends. There are many ways to skin a cat.

First check to see that the existing wires are appropriately sized for the device and not excessively oversized. Using 8ga and 10ga wires in the panel should not be a problem, at least they are not on my panel.

I checked a randomly selected electric head to see the amperage/wire size recommendations. The 4ga you have is probably too large, a 2ga would do. (Check your manuals). https://www.defender.com/pdf/AtlantesFreedom_OwnersManual.pdf

Move large current draws, like electric winches, windlasses, etc out of the panel and their own separate breaker. Depending on the device there will be different options. The Blue Seas website has several different kinds. Beside to match the type of breaker/fuse to the application.

When you use a step down wire it changes the current capacity of the entire circuit to that of the smallest wire, no matter how short it is. Thus if you stepped down from 2 ga to 10ga the maximum safe current would be that of a 10ga wire. This is separate from the voltage drop issue. In very short sections a wire one size smaller will have little effect on voltage loss, but a big affect on safe current carrying ability.

 

[dlochner]

Thank you for the reply, I appreciate it.

But in most cases, a smaller wire (often 10ga) terminates at the pump/electronic device and this wire is permanently connected to the device during manufacturing . This wire is what the larger gauge wire I used is step-down connected to right before the device. So what's the difference between the wire ending in 10ga right before the device, and now installing a wire starting at 10ga coming out of the circuit breaker panel with 2ga wire connecting the two 10ga wires at the ends of the wire run?

How many pumps on the circuit? The loads on a circuit are additive, 3 10amp devices draw the same current as 1 30 amp device.

 

[Revolutionary]

It all depends. There are many ways to skin a cat.

First check to see that the existing wires are appropriately sized for the device and not excessively oversized. Using 8ga and 10ga wires in the panel should not be a problem, at least they are not on my panel.

I checked a randomly selected electric head to see the amperage/wire size recommendations. The 4ga you have is probably too large, a 2ga would do. (Check your manuals). https://www.defender.com/pdf/AtlantesFreedom_OwnersManual.pdf

Move large current draws, like electric winches, windlasses, etc out of the panel and their own separate breaker. Depending on the device there will be different options. The Blue Seas website has several different kinds. Beside to match the type of breaker/fuse to the application.

When you use a step down wire it changes the current capacity of the entire circuit to that of the smallest wire, no matter how short it is. Thus if you stepped down from 2 ga to 10ga the maximum safe current would be that of a 10ga wire. This is separate from the voltage drop issue. In very short sections a wire one size smaller will have little effect on voltage loss, but a big affect on safe current carrying ability.

Thank you for the reply, I appreciate it.

I assume you meant that the 2ga wire is probably too large and a 4ga wire would do? I believe the manual did call for a 4ga, but I went a size larger on everything because I have long wire runs and prioritized safety.

Good point on the current capacity. I don't believe I have any devices that came with anything larger than 10ga wire coming out of them, so that shouldn't be an issue (I'll double check though). I was more concerned with voltage drop in this case.

 

[Revolutionary]

How many pumps on the circuit? The loads on a circuit are additive, 3 10amp devices draw the same current as 1 30 amp device.

Every pump has its own positive and negative to the circuit breaker so I can turn on/off the watermaker, freezer, water pressure, and toilet pumps individually.

 

[Scott T-Bird]

I checked a randomly selected electric head to see the amperage/wire size recommendations. The 4ga you have is probably too large, a 2ga would do. (Check your manuals). https://www.defender.com/pdf/AtlantesFreedom_OwnersManual.pdf

This doesn't even make sense ... 4 awg is smaller than 2 awg. Using the notation ga (shorthand for awg?) is not appropriate in this situation when discussing a topic that requires clarity. The manual you cited references 10 awg for most typical runs. It only references 2 awg for a 50-foot run on a Seawater model at 12 vdc. I doubt this is the application ... the correct application is all important, though.

@Revolutionary , I think you should have done a little more reading before re-wiring. I think you created a nightmare that you will need to correct.

First of all, congratulations for installing the Blue Sea Panel. 30 circuit breakers? What amperage are the circuit breakers? Are they all 15 amp or do you have a mixture including some that are higher rated? Your wire sizes should be correctly sized to match the specific load and so should the breakers be sized to protect the wires and cables. Most of your electrics should have relatively low amperage and can adequately be served by 16 or 14 awg wires on a 15 amp circuit breaker (even ganged on one circuit in some circumstances). I don't really know why you would have such a tangle of 2, 4, 6, 8 awg wires and cables. What are the loads on those runs? We can't help you if you aren't specific.

Your macerator pump probably requires only 8 awg or 10 awg (mine does). I can't imagine using 2 awg for this unless there is some very unusual circumstance. It does not help you to oversize the wires and cables if it creates havoc behind your panel. It doesn't sound like you have logically thought out your proposed step-downs. If you are stepping down in size to get to the load, then why in the world would you have a larger wire or cable in the panel? Where step-downs are applicable (I have a fuse panel that takes a 1/0 feed and steps down to smaller cables (3) but only fused appropriately at the step-down). But this does not go through the house panel. I consider the house panel loads to be typically the smaller loads, served by 15 amp breakers, and smaller wires. My feed to the house panel is significantly stepped down just after the selector switch on a fused step-down. I think I have nothing bigger in size than a 6 awg feed to the panel and maybe an 8 or 10 awg load wire at most. I don't have any high loads coming out from the house panel. The macerator pump is probably the largest load.

You really do need a diagram for anybody to help.

 

[twalker H260]

For large current items - if they can’t be relocated closer to the power source and use smaller wires (pumps should be able to be placed just about anywhere and have plumbing run the long distances), I would look at putting in buss bars with appropriate fuses to run the power and use a relay on a switch(breaker) to control the device on/off.

If the larger wires were really to prevent voltage drop over Long runs then there likely isn’t a reason you couldn’t step down to match the wire size at the end of the run (using appropriate terminal blocks) for a short distance to the panel. This does however introduce at least 2 more connections for potential failure/corrosion. -this also requires you fuse for the smallest wire in the circuit. (Which should be the case anyway.)
As mentioned by others - more detailed information is required for proper responses.

 

[Revolutionary]

This doesn't even make sense ... 4 awg is smaller than 2 awg. Using the notation ga (shorthand for awg?) is not appropriate in this situation when discussing a topic that requires clarity. The manual you cited references 10 awg for most typical runs. It only references 2 awg for a 50-foot run on a Seawater model at 12 vdc. I doubt this is the application ... the correct application is all important, though.

@Revolutionary , I think you should have done a little more reading before re-wiring. I think you created a nightmare that you will need to correct.

First of all, congratulations for installing the Blue Sea Panel. 30 circuit breakers? What amperage are the circuit breakers? Are they all 15 amp or do you have a mixture including some that are higher rated? Your wire sizes should be correctly sized to match the specific load and so should the breakers be sized to protect the wires and cables. Most of your electrics should have relatively low amperage and can adequately be served by 16 or 14 awg wires on a 15 amp circuit breaker (even ganged on one circuit in some circumstances). I don't really know why you would have such a tangle of 2, 4, 6, 8 awg wires and cables. What are the loads on those runs? We can't help you if you aren't specific.

Your macerator pump probably requires only 8 awg or 10 awg (mine does). I can't imagine using 2 awg for this unless there is some very unusual circumstance. It does not help you to oversize the wires and cables if it creates havoc behind your panel. It doesn't sound like you have logically thought out your proposed step-downs. If you are stepping down in size to get to the load, then why in the world would you have a larger wire or cable in the panel? Where step-downs are applicable (I have a fuse panel that takes a 1/0 feed and steps down to smaller cables (3) but only fused appropriately at the step-down). But this does not go through the house panel. I consider the house panel loads to be typically the smaller loads, served by 15 amp breakers, and smaller wires. My feed to the house panel is significantly stepped down just after the selector switch on a fused step-down. I think I have nothing bigger in size than a 6 awg feed to the panel and maybe an 8 or 10 awg load wire at most. I don't have any high loads coming out from the house panel. The macerator pump is probably the largest load.

You really do need a diagram for anybody to help.

Thank you for the reply, I appreciate it.

The circuit breakers are of various amperages depending on the device connected. They are all corrected sized.

The toilet is a SeaEra QC seawater model. The wire run (roundtrip) is approximately 40 feet from circuit breaker to the SeaEra QC.

I did attempt to calculate the correct wire gauge before installation, but probably went too cautious in often sizing up when it was a close call between two wire gauges.

I have unusually long wire runs because my pumps are mounted under one of the cabin seats, which then require 25 to 40 feet roundtrip wire runs depending on the pump.

 

[Revolutionary]

For large current items - if they can’t be relocated closer to the power source and use smaller wires (pumps should be able to be placed just about anywhere and have plumbing run the long distances), I would look at putting in buss bars with appropriate fuses to run the power and use a relay on a switch(breaker) to control the device on/off.

If the larger wires were really to prevent voltage drop over Long runs then there likely isn’t a reason you couldn’t step down to match the wire size at the end of the run (using appropriate terminal blocks) for a short distance to the panel. This does however introduce at least 2 more connections for potential failure/corrosion. -this also requires you fuse for the smallest wire in the circuit. (Which should be the case anyway.)
As mentioned by others - more detailed information is required for proper responses.

Thank you for the reply, I appreciate it.

The relay on a breaker to turn the device on/off might be a good solution for me. I don't have room to relocate the pumps, and having them under the seat muffles pump noise quite well.

 

[dlochner]

This doesn't even make sense ... 4 awg is smaller than 2 awg. Using the notation ga (shorthand for awg?) is not appropriate in this situation when discussing a topic that requires clarity. The manual you cited references 10 awg for most typical runs. It only references 2 awg for a 50-foot run on a Seawater model at 12 vdc. I doubt this is the application ... the correct application is all important, though.

Good catch, I committed the noob error. The OP used 2awg cable when 4awg would have been sufficient. He did mention that the run was 21 feet, which doubled is 42 feet, so 4awg would be appropriate.

 

[twalker H260]

If going the relay route you could also do a single larger guage wire, appropriately fused to supply a buss bar under the settee which would then feed power to all pumps. What is the aggregated amperage of all the pumps there? Your 2awg wire should be good for 50amps at 3% drop and 40 foot return distance. You could also put a small switch panel at or in the settee to turn pumps on and off if using the single larger power feed instead of using relays.

 

[Ward H]

It would help to know the year and model of your C30. On my 93 MkII the DC panel is over the nav station on the starboard side. Most of my heavy amp draw loads going to the DC panel are located on the port side. Most of my cable runs cross the boat port to starboard just forward of the engine. The longest wire run would be the Sea Era QC head. I measured the run to be between 30' to 40'. The manual calls for 6AWG for 40' so that is the wire size I used. Other than the head, my cables going to the DC panel are mostly 12awg or smaller. Might have a 10awg.
MkI models may have the DC panel located in other locations or require a different path to run the cables.

You probably want to drop down to a smaller wire size just before the panel to save yourself the work and expense of rewiring those circuits that have larger than necessary wire sizes.

I would connect all the incoming wires to terminal strips mounted on a back plate behind the DC panel. Then run the appropriate sized wire to the breakers on the panel. That way you could drop down to the appropriate size wire easily. Plus you take the weight of the incoming wires off of the DC panel breakers.

Make a list of the amp draw of your various pumps and other devices. Then use a wire size calculator to determine the correct wire size for the device amp draw and wire length. I like this calculator at Genuine Dealz. Then use that size wire between the terminal strip and breakers.

A couple of other options to make it less crowded behind the panel.
1. I moved the battery switch to below the DC panel. Takes the weight of those large cables off the panel.
2. I took the panel door frame off, outlined it with 3/4" square teak on both sides and across the bottom, then reinstalled the frame. This gave me an additional 3/4' of space behind the panel. It did create an angled space across the top which I haven't filled in. I will someday.

You can see the gap in the first photo. The second photo shows how I used the terminal strips to take the load off the DC panel. It also shows that I installed a new back plate to mount terminal strips and other things on.

 

[Scott T-Bird]

Ward's installation is an exceptionally neat, organized and logical example. Take note!

 

[Richard19068]

A couple of other options to make it less crowded behind the panel.
1. I moved the battery switch to below the DC panel. Takes the weight of those large cables off the panel.
2. I took the panel door frame off, outlined it with 3/4" square teak on both sides and across the bottom, then reinstalled the frame. This gave me an additional 3/4' of space behind the panel. It did create an angled space across the top which I haven't filled in. I will someday.

You can see the gap in the first photo. The second photo shows how I used the terminal strips to take the load off the DC panel. It also shows that I installed a new back plate to mount terminal strips and other things on.

View attachment 202420 View attachment 202421

Beautiful work!

I often think about the things i would do if I had to lay up my boat for the winter. That might be one of them.