Comparative Safety: 12v v 24v v 48

[leftbrainstuff]

Originally Posted by ramblinrod

So in other words, you do not have a bachelors or masters degree in engineering, by any accredited university?

Isn't this required to refer to one's self, and provide service, as an "engineer"?

What kind of marine service did you say you provide?

In Australia the term Engineer is not protected so anyone can use it.

In Australia, and in the US, the term Professional Engineer has specific meaning.

[leftbrainstuff]

Originally Posted by Q Xopa

I dont know if you missed the previous links to the Automotive industry moving to 48, or maybe it was 42V (cant remember the exact specifics) in the next few years.

They must be throwing safety and switch reliability out the window?

What are they thinking? I guess profit margins rule?

Are you going to still be recommending 12V systems when newer alternators etc are higher voltages?

Just wondering.

The automotive industry isn't throwing safety out the door by moving to higher voltages.

During my automotive apprenticeship in the 1980s 42V and 1A was considered the 'lethal' threshold. Because one person died in the late 70s in Australia. This finding was based on a single coroners report, and in the absence of any other information, became an urban myth.

During my apprenticeship I worked with mechanics who could grab a distributor cap and ground over 70kV from competition multi spark discharge coils. For me a stray spark from a weak 12kV spark would render me wobbly for hours.

I've also seen experienced electricians use shielded side cutters to find live three phase wiring and then fear working on automotive DC systems.

Higher voltages tend to run along the skin. Anytime a person is subjected to a low voltage (< 100V) source with sufficient current to cross the heart will likely arrest. The exact V and A varies for each of us.

Weight is the big driver in the automotive industry moving to higher voltages. Also the increased duty cycle of starters, more electric systems, electric steering, electric transmission shifting all benefit from higher voltages and less heat in actuators and wiring. This improves durability. Heat is the key cause of reduced reliability in these systems.

[AKA-None]

Originally Posted by Dockhead

This is the one which is controversial.


But you are assuming that the resistance in the connector is the same in all cases. But in reality, the higher voltage system will have smaller connectors, won't it? Because it CAN?


I guess (assuming you are right about the basic principles, and other information posted on here is wrong) that higher system voltage will allow you to more easily oversize and overengineer the connectors, so that they are safer. But comparing standard systems with standard solutions, wouldn't there be less of an advantage than you are stating, for higher voltage systems?

You forgot to add all else being the same part. Your heart only requires a low current buy your dry skin resistance helps with low voltages. But get wet like in a salty environment then you have just changed things.
No math required

[Q Xopa]

Originally Posted by leftbrainstuff

The automotive industry isn't throwing safety out the door by moving to higher voltages.

During my automotive apprenticeship in the 1980s 42V and 1A was considered the 'lethal' threshold. Because one person died in the late 70s in Australia. This finding was based on a single coroners report, and in the absence of any other information, became an urban myth.

During my apprenticeship I worked with mechanics who could grab a distributor cap and ground over 70kV from competition multi spark discharge coils. For me a stray spark from a weak 12kV spark would render me wobbly for hours.

I've also seen experienced electricians use shielded side cutters to find live three phase wiring and then fear working on automotive DC systems.

Higher voltages tend to run along the skin. Anytime a person is subjected to a low voltage (< 100V) source with sufficient current to cross the heart will likely arrest. The exact V and A varies for each of us.

Weight is the big driver in the automotive industry moving to higher voltages. Also the increased duty cycle of starters, more electric systems, electric steering, electric transmission shifting all benefit from higher voltages and less heat in actuators and wiring. This improves durability. Heat is the key cause of reduced reliability in these systems.

I think you misunderstood the intent of my post. I fully agree with what you are saying. it was a tongue in cheek reply to illustrate the rediculious claims being repeated over and over on here.

[brownr377]

This mostly lurker here is gonna regret wading into this flogged horse of a thread. But holy moley what in the world? This ain't rocket science. There be volts and there be amps they both can be dangerous, that's why there are standards and well established practices to mitigate the risks from both of them. Batteries, yeah they're extremely dangerous, I hate working with batteries. They're heavy and they have death lurking inside but I do like electric gadgets so I deal with it. But the potential for shock hazard difference of 12V vs 24V is not even interesting. With all the upsides for higher supply voltages I'd switch tomorrow if it weren't major surgery to the boat.

If an end user can manage to shock themselves somehow on a 24 Volt circuit and that shock causes them to fling their appendage straight into a rotating machine, that was a terrible design to begin with and if I need to start ranking failure modes, the supply voltage would be somewhere down at the bottom of the list.

[CatNewBee]

12V on board of recreational vessels stems from old designs, where on board was only navigation lights and some basic electric wiring. It was easy to use and abuse a wet cell car battery, they were available and cheap.

Later as all the radar and electronics took more and more current, they switch to 6V golf cart batteries to avoid paralleling of 12V car batteries for obvious reason.

Later with power winches and windlasses, fridges and more stuff on board they startet to do paralle / serial configurations with all the drawbacks and pitfalls it brings.

Now lithium comes into play and makes both, one hand (loads) things easier and more reliable and stable and on the other (sources) more complex regarding cell monitoring, balancing and charging profiles.

Also the early entry level electronics become by the evolution more and more comparable to the professional level and get used in commercial vessels, so many can handle a wide range of 9...30V to operate in 12V and 24V installations, same for LED lights, tv sets and the like, only the electric drives and relays require a specific voltage, some devices can even be switched by a configuration or a jumper bridge between 12 and 24V.

Especially in the US market, where A/C on board is more important than a working engine, generators are very common, in contrast to european vessel, where A/C and generators are exotic, but there are many vessels with diesel heating installed. In the EU manufactured vessel's factory configurations you can chose none, heating (diesel air or water with heat exchanger), or A/C with generator, but not both A/C and diesel heater.

48V are a great thing in theory, but the electronics usually do not support it, so you need a separate 24V or 12V bus for them, not a big deal with a step- down converter, if anything else can run on 48V. Next challenge are the fridges and freezer, nothing available at 48V in the camping market, so the option is either to go residential at 110/240 on inverter or step-down again to 24/12V.

A good compromise could be to go all in on 24V, because most gear can use it directly or is available in a 24V flavor.

[Dockhead]

Originally Posted by AKA-None

You forgot to add all else being the same part. Your heart only requires a low current buy your dry skin resistance helps with low voltages. But get wet like in a salty environment then you have just changed things.
No math required

That's a non-sequitur. You didn't understand what we were talking about.



We were talking about possible safety advantages of higher voltage circuits because the connectors, which can handle less current for the same power, could be designed with greater design reserve. We were talking about the risk of fire, not the risk of shock.


Shock, of course, is a different hazard of electricity, and particular where salt water may be involved, and I think we all have a decent understanding of it. I think, however, that it is generally accepted that the risk of shock, even in wet salty environments, is not significant below 50v. So nothing to think about when considering 24v vs 12v, and only marginally so when thinking about 48v (48v nominal may be charged at something like 58v).



Here is an interesting discussion of risk of shock in 48v systems:


https://electronics.stackexchange.co...-48v-dc#267797


"48V is considered "safe", and that is for good reason.

First, the impedance of the human body at 50V is around 45kΩ (though measured on adults). While children are overall smaller and thus should have slightly lower impedance, it's the skin resistance which makes up 95% of that impedance (internal body fluids are pretty good conductors), so the size doesn't matter all that much.

"(Note how body impedance is a funny thing, it goes down rapidly as voltage goes up, at 240V it's 10-15 times lower!)

"Further, an electric current needs somewhere to go, obviously. No closed circuit, no current. That's why birds sitting on an overland line aren't fried.
These 48V are 48V against ground. In all likelihood, the next closest thing to "ground" that you have contact with is "parquet/laminate" or "floor tiles" or something similar, in other words, resistance around infinite, current zero.


"Even touching the hot wire on 240V has a good chance of "not much bad stuff happening", if you wear shoes and aren't precisely standing in a puddle of water (although for obvious reasons I wouldn't advise trying your luck!).

"Let's assume the absolutely worst case: a child puts one finger onto the ground pin on a wall plug, and sucks on the PoE cable (looks edible, doesn't it!). Against all odds, the PSE is broken or heftily non-compliant and instead of supplying 10.2V/4mA max as per default, it supplies full operational voltage, and unlimited current. Or, it takes some random pattern that the child accidentially made for a valid negotiation, whatever.
Also, for an unexplainable reason, the current doesn't short circuit over the data wires (the likely thing to happen would be exactly that, a little spark on the child's tongue, and the child dropping the cable in a fright).


"Let's just say there's actually 40V on the wire, and the current "decides" to go through the child's body, against all reason and against the laws of physics.

"Cable-in-mouth will eliminate one skin barrier and thus approximately halve the body impedance. That's 22.5kΩ remaining. Let's round down to 20kΩ to be sure. No, you know what, let's be outrageous, and say 10kΩ. 48V/10kΩ = 4.8mA.


"Which... is harmless even for alternating current. It takes about 8-10 times as much alternating current (of a frequency in the critical 50-60Hz range) to stop the heart.

"Now, on top of that, PoE doesn't have alternating current, it's DC. So the scary bit about cardiac arrest doesn't even apply.

"Of course, DC can in principle cause adverse effects other than stopping the heart (think of a surgical electro knife, or the "electric chair"), but given voltages in the two digit range and currents in the single-digit milliampere range, this simply isn't going to happen (but even if it was, it would primarily be local burns, not life threatening)."


Apparently a child can put a 40v conductor in his mouth and finger on the other conductor, and even with an unlimited current power supply, it's harmless.


If this is true, then shock risk is not even a factor in choosing system voltage in the range of 6v -- 40v, and probably higher. 48v nominal systems might see as much as 60v when charging, so probably there is some risk of a dangerous shock with a 48v system:





But I don't think it's essential to safety that the system voltage be set so low as to allow us to grab conductors with two wet hands and not feel it. That would be ridiculous overkill. We have 110v (or 230v) AC power on board, after all, which can definitely kill you by shocking you even through dry hands.


I think fire is the safety issue, where DC power on boats is concerned.

[Q Xopa]

Originally Posted by brownr377

This mostly lurker here is gonna regret wading into this flogged horse of a thread. But holy moley what in the world? This ain't rocket science. There be volts and there be amps they both can be dangerous, that's why there are standards and well established practices to mitigate the risks from both of them. Batteries, yeah they're extremely dangerous, I hate working with batteries. They're heavy and they have death lurking inside but I do like electric gadgets so I deal with it. But the potential for shock hazard difference of 12V vs 24V is not even interesting. With all the upsides for higher supply voltages I'd switch tomorrow if it weren't major surgery to the boat.

If an end user can manage to shock themselves somehow on a 24 Volt circuit and that shock causes them to fling their appendage straight into a rotating machine, that was a terrible design to begin with and if I need to start ranking failure modes, the supply voltage would be somewhere down at the bottom of the list.

Yes there is a lot of rediculous hysterics and scare mongering spewed out on this thread.

Rather entertaining if you dont take it seriously.

Akin to saying cars and aeroplanes are killers. Of course they are but we accept the risks and manage the dangers.

They also have a lot of uses and advantages that we mostly wouldnt do without. If the proper design and precautions are used then this stuff can serve us very well.

I dont think these posters are about to not use cars. Some people perhaps should consider some perspective.

Or perhaps consider a career in comedy.

[Jdege]

Perhaps the better question is what measures do you need to take to make 48v safe in a boat, and how did they differ from the measures you need to take to make 12v safe?

[Dockhead]

Originally Posted by Jdege

Perhaps the better question is what measures do you need to take to make 48v safe in a boat, and how did they differ from the measures you need to take to make 12v safe?

Indeed! That's actually a very clever question.





If danger went up "proportionately with voltage", as someone has insisted over and over again, then what about 110v AC? Or 230V AC? Death trap? Run away?



Shock risk is very serious from AC power systems, yet we have them. Because we know that we can make them very safe. And we choose to make them safe, rather than give up their advantages and do without them.


I think the evidence shows that there is some shock risk from nominal 48v (potentially up to 60v) DC systems. And that there is virtually no difference in shock risk between 6v, 12v, and 24v -- because the shock risk at those voltages is practically zero in any case. The evidence appears to show that some shock risk starts to appear in a 48v system, but if we merely treat 48v systems like we treat AC power, then that's gross overkill of safety, since 48v DC is vastly less dangerous than 110v or 230v AC. And we know how to do that; it's not rocket surgery. So shock risk does not seem to be a big deal and probably not a factor at all in choosing a system voltage.


And absolutely separate issue from shock risk is the risk of getting a wrench, watch, or ring across terminals with a lot of current potential. This can be really dangerous even at very low voltages, as one poster pointed out. So this safety issue has to be addressed with good design in any case, if we are handling large amounts of power, at whatever voltage.



Another different question is fire risk, and there's been some vigorous argument about whether that increases or decreases with DC voltage. I don't think there is a clear answer to that.



But as you correctly point out -- the main question is not actually whether there is more or less fire risk -- the real question is whether it can be made safe enough, at reasonable cost and trouble. There would not even be any problem with its being MORE dangerous, as long as it's not TOO dangerous.



In all design decisions, actually all of them, anywhere, we balance costs, risks and benefits. We can completely eliminate electrical fire and shock risks from our boats by simply eliminating electricity. But we accept some risks in order to have the advantages of having electricity on board, both AC and DC. So the question is whether the benefit of any given configuration, including system voltage, is worth the cost of making it safe.



I doubt that there would be any particular extra costs, to make 48v reasonably safe, and almost certainly not more than what is saved with lighter, more elegant cabling, switchgear, etc. And I have not heard anything in this thread, which persuades me that the risk of fire is even increased at all.

[ramblinrod]

Originally Posted by Dockhead

That's a non-sequitur. You didn't understand what we were talking about.



We were talking about possible safety advantages of higher voltage circuits because the connectors, which can handle less current for the same power, could be designed with greater design reserve. We were talking about the risk of fire, not the risk of shock.


Shock, of course, is a different hazard of electricity, and particular where salt water may be involved, and I think we all have a decent understanding of it. I think, however, that it is generally accepted that the risk of shock, even in wet salty environments, is not significant below 50v. So nothing to think about when considering 24v vs 12v, and only marginally so when thinking about 48v (48v nominal may be charged at something like 58v).



Here is an interesting discussion of risk of shock in 48v systems:


https://electronics.stackexchange.co...-48v-dc#267797


"48V is considered "safe", and that is for good reason.

First, the impedance of the human body at 50V is around 45kΩ (though measured on adults). While children are overall smaller and thus should have slightly lower impedance, it's the skin resistance which makes up 95% of that impedance (internal body fluids are pretty good conductors), so the size doesn't matter all that much.

"(Note how body impedance is a funny thing, it goes down rapidly as voltage goes up, at 240V it's 10-15 times lower!)

"Further, an electric current needs somewhere to go, obviously. No closed circuit, no current. That's why birds sitting on an overland line aren't fried.
These 48V are 48V against ground. In all likelihood, the next closest thing to "ground" that you have contact with is "parquet/laminate" or "floor tiles" or something similar, in other words, resistance around infinite, current zero.


"Even touching the hot wire on 240V has a good chance of "not much bad stuff happening", if you wear shoes and aren't precisely standing in a puddle of water (although for obvious reasons I wouldn't advise trying your luck!).

"Let's assume the absolutely worst case: a child puts one finger onto the ground pin on a wall plug, and sucks on the PoE cable (looks edible, doesn't it!). Against all odds, the PSE is broken or heftily non-compliant and instead of supplying 10.2V/4mA max as per default, it supplies full operational voltage, and unlimited current. Or, it takes some random pattern that the child accidentially made for a valid negotiation, whatever.
Also, for an unexplainable reason, the current doesn't short circuit over the data wires (the likely thing to happen would be exactly that, a little spark on the child's tongue, and the child dropping the cable in a fright).


"Let's just say there's actually 40V on the wire, and the current "decides" to go through the child's body, against all reason and against the laws of physics.

"Cable-in-mouth will eliminate one skin barrier and thus approximately halve the body impedance. That's 22.5kΩ remaining. Let's round down to 20kΩ to be sure. No, you know what, let's be outrageous, and say 10kΩ. 48V/10kΩ = 4.8mA.


"Which... is harmless even for alternating current. It takes about 8-10 times as much alternating current (of a frequency in the critical 50-60Hz range) to stop the heart.

"Now, on top of that, PoE doesn't have alternating current, it's DC. So the scary bit about cardiac arrest doesn't even apply.

"Of course, DC can in principle cause adverse effects other than stopping the heart (think of a surgical electro knife, or the "electric chair"), but given voltages in the two digit range and currents in the single-digit milliampere range, this simply isn't going to happen (but even if it was, it would primarily be local burns, not life threatening)."


Apparently a child can put a 40v conductor in his mouth and finger on the other conductor, and even with an unlimited current power supply, it's harmless.


If this is true, then shock risk is not even a factor in choosing system voltage in the range of 6v -- 40v, and probably higher. 48v nominal systems might see as much as 60v when charging, so probably there is some risk of a dangerous shock with a 48v system:


Attachment 186729


But I don't think it's essential to safety that the system voltage be set so low as to allow us to grab conductors with two wet hands and not feel it. That would be ridiculous overkill. We have 110v (or 230v) AC power on board, after all, which can definitely kill you by shocking you even through dry hands.


I think fire is the safety issue, where DC power on boats is concerned.

Yes, that thread is as bad or worse than this one for misinformation.

So lets look at the physical reality.

Human skin resistance averages around 5 kohms.

It can be much higher.

Between the fingertips of a dry person who works with their hands and has tough callouses, it may be 100Kohms.

On just about anyone who is sweaty the inside of the forearm may be only 2 kohms.

For someone who is sweaty and has cuts on their hands, it may only be 1000 ohms hand to hand (current path across the heart).

Now, if we search the internet, including all extremely questionable sources, we can find all kinds of different current thresholds capable of stopping the human heart. I have personally seen as low as 10 mA, to one case as high as 500 mA. I use the threshold taught to me in Grade 9 "Theory of Electricity" class, 80 mA. (Before anyone gets their nighty in a knot, it really doesn't matter what the actual value is for this discussion.)

So in that ridiculous thread on that other forum, there was one valid statement (IMHO).

"48V is reasonably safe for most people under normal conditions."

I absolutely agree with this statement.

My position has never been that 48 Vdc is extremely dangerous under all conditions.

It was simply, "The risk of danger increases with voltage". It does.

Earlier in this thread I gave a perfect example of how one who works with electrical wiring can easily have lower than normal skin resistance.

a) They are often working hard in hot, cramped quarters, with little ventilation, where they will become very sweaty, shirt and shorts soaked sweaty.

b) They are working with the ends of cut wire, twisting the ends between their fingers so they fit in the end of a crimp connector. If they forget or skip the gloves (because they keep catching the wire strands) it can cut their fingers.

c) They may be working in an area with a bilge, that may have accumulated bilge water, which is where anything dropped will try it's worst to fins it's way. Could be a crimp connector, nut off a battery terminal, tool, what have you, it WILL end up in the bilge.

OK, so now lets look at what happens with extremes of skin resistance, at various voltages, and assume a 100 mA threshold is capable of stopping the human heart.

1. 12 Vdc

a) 100 kohm skin resistance (about the most it can be without gloves).
I = E/R = 12 Vdc / 100,000 ohms = 0.12 mA. No electrocution.

b) 10 kohm skin resistance (actually pretty common across the hands).
I = E/R = 12 Vdc / 10,000 ohms = 1.2 mA. No electrocution.

c) 1 kohm skin resistance (not normal, certainly possible).
I = E/R = 12 Vdc / 1,000 ohms = 12 mA. Risk of electrocution, only if we take the lowest threshold purported.

2. 24 Vdc

a) 100 kohm skin resistance (about the most it can be without gloves).
I = E/R = 24 Vdc / 100,000 ohms = 0.24 mA. No electrocution.

b) 10 kohm skin resistance (actually pretty common across the hands).
I = E/R = 12 Vdc / 10,000 ohms = 2.4 mA. No electrocution.

c) 1 kohm skin resistance (not normal, certainly possible).
I = E/R = 12 Vdc / 1,000 ohms = 24 mA. Greater risk of electrocution, at the lowest threshold purported.

3. 48 Vdc

a) 100 kohm skin resistance (about the most it can be without gloves).
I = E/R = 48 Vdc / 100,000 ohms = 0.48 mA. No electrocution.

b) 10 kohm skin resistance (actually pretty common across the hands).
I = E/R = 12 Vdc / 10,000 ohms = 4.8 mA. No electrocution.

c) 1 kohm skin resistance (not normal, certainly possible).
I = E/R = 12 Vdc / 1,000 ohms = 48 mA. Greater risk of electrocution yet.

Clearly this shows, that under typical conditions, while one may not be electrocuted (and perhaps most likely won't) "The risk (or danger) of electrocution increases with voltage."

Now lets take a look at the lowest skin resistance I have seen, hand to hand, on my own body, after a hard day at work, with many cuts. 500 ohms.

At 48 Vdc, I = E/R = 48 Vdc / 500 ohms = 96 mA. This is damn close to that 100 mA, that I believe is capable of stopping a human heart.

Now lets look at the worst case scenario, one touches both battery terminals, at the same time, (on purpose (dumb), or accidentally (plausible), when the charger is on.

At 60 Vdc (charge voltage), I = E/R = 60 Vdc / 500 ohms = 120 mA. Pretty good chance of electrocution.

If we were talking a 12 Vdc system in this scenario...

At 15 Vdc, I = E/R = 15 Vdc / 500 ohms = 30 mA. Not much likelihood of electrocution.

Based on this, I conclude, that "Danger increases proportionally with voltage".

Even if we don't get to the actual threshold of electrocution under normal circumstances, we are working our way closer to it, and under worst conditions, we may already be there.

Now if we go way back in the thread, I proposed the phenomenon exists I referred to as "desensitization", or same may wish to consider it "complacency".

We hear these stories where residential electricians stick their finger in a socket to determine if it's live.

I have done that too.

When I was young and stupid and thought I was invincible.

Even with the experience of feeling this sensation many times, on one occasion of receiving an unexpected 120 Vac, I instinctively/involuntarily withdrew may so quickly and with such force, that shattered a window made of tempered, re-inforced safety glass, that was beside my work bench.

Now that I have tons and tons more experience, I am more careful, because I know what can happen when one becomes desensitized to or complacent with the danger of electrical current, even if it insufficient to even be felt, in the human body.

Because now I know, that I may contact 48 Vdc (or 60 Vdc charging) 1000 times and 900 times never even feel a tingle (and even this can cause some physiological damage), but it will only take that once, when conditions are working against me, that could be the last time.

Now, on the AC side, where the voltage is even higher yet, (and yes I do understand that we have a sinusoidal peak voltage that may more easily reach the skin resistance breakdown threshold), ABYC standards compliance requires that a GFCI receptacle be used, for any outlet where there is a good chance of moisture, such as a head, galley, weather deck, or anywhere water is likely to be in close proximity, (such as above a bilge, though not specifically stated).

The threshold for tripping to prevent electric shock is 5 mA.

As mentioned, there may be a difference between AC and DC voltage regarding the electrocution threshold, but since we are not sure what that is, or if it is even true, if look solely at the difference in voltage, the same level of protection for 12 Vdc would be calculated by direct assimilation...

GFI threshold 48 Vdc = 120 Vac / 48 Vdc * 5 mAdc = 12.5 mA

Even if we account for the difference between Peak AC voltage and constant DC voltage with respect to skin resistance breakdown potential (which we don't really know is a factor), then the difference would be 12.5 mA DC * 150% = 18.75 mA.

GFCI rely on hall effects sensor technology, that unfortunately will not work on DC.

So as it stands, we do not have an "always on" integral safety device to prevent people from being electrocuted by DC voltage.

If we did, then I would consider that a satisfactory "Mitigating Factor", to overcome the increased risk of electrocution by 48 Vdc than by 12 Vdc.

Now this is just the electrocution angle, then there is also the increased danger due to burns (one example illustrated by Growly Monster earlier in this thread) and yes of course, under less that ideal conditions one could be burned by 12 Vdc but because P (energy) = E (voltage ^ 2) / R, I know that mathematically (and barring any mitigating factors in practice) that the risk of a burn from 48 Vdc, is EXPONENTIALLY greater, than from 12 Vdc.

This same principle also applies to the risk of sufficient heat being produced due to a short circuit to start a fire.

So this is just a brief explanation of why I choose the lowest DC voltage possible that will satisfy loads, and believe it is the best policy to adopt for my business, to protect myself from possible liability claims, and my customers from possible danger.

But anyone who enjoys living on the edge and taking unnecessary risks can choose a higher electrical system voltage.

It is certainly possible.

But just because it is possible and may save some copper (usually minimal in the grand scheme), does not make this a wise choice, because, wait for it, here comes the generalization again, that so many love...

Danger increases proportionally with voltage (barring any mitigating factors).

The only reason I even care, is because desensitization to the risk, and a moment of complacency, could result in personal injury, death, or property destruction, that may negatively impact the individual making this decision, or their loved ones, or even total strangers (e.g. slip neighbours).

Of course anyone can knowingly or unwittingly disregard these risks, and go ahead and do it.

But, is it the right thing to do?

In my opinion, and perhaps solely in my opinion and nobody else's, I believe not.

I have not heard one argument nor seen one shred of evidence in this entire thread, that proves the facts, theories, and experiences that I have relied on to develop this position and policy over the last 40 years (actually 50 if we consider that I first learned of Ohms and Watts Law when conducting a research project in and advanced science class in Grade 6.)

I also learned in Grade 8, after conducting research into "The Candu Thermo-Nuclear Reactor", to never trust anyone who claims...

"Don't worry, I am more highly educated than you, and I declare it safe, therefore it is."

(Meanwhile, 50 years later, we are living near huge pools (25 years beyond life expectancy, and well beyond original design capacity) of untreated nuclear waste, just waiting for that one brief moment of complacency to unless its "gotcha".

Of course the consequence would likely be far greater, but the principle is the same as choosing a higher than necessary marine electrical system voltage.

Now some people have gone to all kinds of extremes to present "strawman arguments" (restating my position, or including mitigating factors, to intentionally change the meaning or veracity of my position), or challenge my education, experience, or very authority to even evaluate the risks.

But I know this fact won't change, when I evaluate and electrical system design, "I will choose (or recommend) the lowest possible system voltage to support the required loads, that is commonly in practice and for which parts are readily and economically available."

For a marine DC electrical system, to support loads up to about 6 kW for ~ 5 minutes, or ~ 3 kW for one hour, this is currently 12 Vdc.

For higher loads, I will choose 24 Vdc for loads up to about 12 kW (brief) and 6kW (extended).

For even higher loads, I will choose products that can be powered by the 120 or 240 Vac to be operated by that system that will already normally be present to handle higher loads than the lowest possible voltage DC systems.

(Note that by doing so, I have now introduced a mitigating factor (GFCI's and ELCI) to help negate the increased risks associated with higher voltage.)

If powering high load devices with the AC electrical system is not practical, I will chose (recommend) 48 Vdc for up to 24 kW or 12 kW respectively, and so on and so on and so on.

And this policy (rule of thumb if that makes some more happy) is because I know (absolutely) that barring the presence of any mitigating factor, danger increases proportionally with voltage EVERY SINGLE TIME. It has to, it's as simple as Ohm's and Watt's Laws that I learned 50 years ago, and have held true throughout my entire 40 year career, testing, troubleshooting, designing, prototyping, manufacturing, repairing, marketing, teaching, electronics and electrical products and systems.

One can try to justify going to a higher voltage than necessary any which way from Sunday, but it will be based on flawed arguments, willingness to accept higher risk than necessary, or to employ a higher degree of mitigating safety factors.

It's there choice.

My choice, and recommendation, is to not do so.

What's the problem people?!?!?!?!?

[transmitterdan]

The problem is that you continue to ignore the higher current danger which is very real. It is not just about saving on copper.

[ramblinrod]

Originally Posted by Jdege

Perhaps the better question is what measures do you need to take to make 48v safe in a boat, and how did they differ from the measures you need to take to make 12v safe?

Bingo!

What mitigating factors can we introduce, to reduce the increased danger associated with a higher voltage system?

There are many, (here are the first 10 that came to mind).

1. Installed electrically insulating barriers.

2. Electrical insulation less prone to chafing.

3. Bulkhead poke throughs less prone to chafing.

4. Working with rubber gloves and boots on.

5. Avoid becoming sweaty.

6. Use heavier contacts less prone to high impedance.

7. Use the heavier (more expensive) components readily available for 48Vdc.

8. Don't switch to a lower gauge cable (the very reason most switch to 48 Vdc).

9. Express to everyone that "Danger Increases Proportionally With Voltage" barring any mitigating factors.

10. Avoid using higher voltage than necessary.

[ramblinrod]

Originally Posted by transmitterdan

The problem is that you continue to ignore the higher current danger which is very real. It is not just about saving on copper.

Your error that you keep ignoring is that danger (the unintended release of energy in a potentially harmful way) does not increase based on current.

Your basic premise in this matter is flawed.

I've already responded to this many times.

You have yet to contradict my position with any evidence, theory, or assumption to support your position is correct and mine is not.

Instead you just keep repeating the same incorrect information.

[transmitterdan]

And as an electrical engineer I can tell you that energy can be stored in current. That’s how a lot of high power systems store energy.

The power delivered as a result of current is “current squared times resistance”. That is a fact that must be understood to have any meaningful dialogue on this subject. If you don’t believe that equation is right then there is no point in further discussion.