Is there some property of AC that makes grounding more necessary or more effective? Or is it simply that AC is more of a danger as it tends to be higher voltage and/or more adept at screwing with the heart?
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Why do DC systems not make use of grounding to the same extent as with AC
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Bob B
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DC is generally lower voltage .... and therefore not as dangerous. If you get into higher voltage DC, however, it is more dangerous than the same AC voltage.
If you grab high voltage AC with your hand it will throw you off .... If you grab DC, it will cause your muscle to clench and you may not be able to let go. I don't know what the grounding rules are for higher voltage DC.
If you grab high voltage AC with your hand it will throw you off .... If you grab DC, it will cause your muscle to clench and you may not be able to let go. I don't know what the grounding rules are for higher voltage DC.
Interesting, I didn't know that about the different physiological reaction.
The problem is first terminology: in AC systems 'ground' is meant to be earth, with neutral the return path (I'm European, keep your split phase nonsense) 
. In DC systems, 'ground' is meant to be the 0V reference potential, for example the chassis of a car is 'ground' there. That's why we tend to speak about 'earthing' when we talk about the wiring that usually does not carry any current in normal operation and is there for safety.
If you run higher voltage DC systems you absolutely have a 'ground' (earth) in the AC sense of the meaning. It's just that DC is considered (according to European norms) safe until 150V, but most DC systems are well below that. There is a reason solar panels for example should be grounded (earthed) since you tend to have higher DC voltages there than on your battery side. Ground (earth) for e.g. 48V isn't really needed for safety.
We can actually now go further and if you check the rules, you'll see that in mixed systems that are grid tied you will have separate earth connections for DC and AC, whereby the correct way to implement this (look up functional earth as well, as some devices need this besides for safety) depends on the type of earth system in your place, e.g. TT, TN, etc.
. In DC systems, 'ground' is meant to be the 0V reference potential, for example the chassis of a car is 'ground' there. That's why we tend to speak about 'earthing' when we talk about the wiring that usually does not carry any current in normal operation and is there for safety.If you run higher voltage DC systems you absolutely have a 'ground' (earth) in the AC sense of the meaning. It's just that DC is considered (according to European norms) safe until 150V, but most DC systems are well below that. There is a reason solar panels for example should be grounded (earthed) since you tend to have higher DC voltages there than on your battery side. Ground (earth) for e.g. 48V isn't really needed for safety.
We can actually now go further and if you check the rules, you'll see that in mixed systems that are grid tied you will have separate earth connections for DC and AC, whereby the correct way to implement this (look up functional earth as well, as some devices need this besides for safety) depends on the type of earth system in your place, e.g. TT, TN, etc.
Yes, fully agreed with that. It's just proper design.
JeepHammer
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Two entirely different types of electricity that have very little in common other than moving electrons.
This is an argument every single time when AC & DC guys meet on forums...
Virtually noting in common between AC & DC other than electrons and materials that will conduct/transmit electrons.
AC has a FREQUENCY (Like radio signals) and is 'Transmitted'.
Now, you can't explain this to the AC guys, but there is a reason AC wires are called 'Transmission Lines', the guys that did have it figured out named it correctly, and they haven't got around to screwing with it... Yet...
AC IS ACTIVELY SEEKING A 'GROUND', like a radio signal is seeking something to act upon, like an antenna, or the food in a microwave.
AC will 'Leak' (path of least resistance) to moist air, it casts ions out looking for ANYWHERE with lower electrical potential to 'Ground'.
It does NOT seek a direct path back to 'Source', it 'Seeks' ANY lower potential conductor, and 'Ground' is handy way to dispose of escaped current safely, so it's widely used to dispatch the electrical potential power rather than knocking the snot out of YOU...
You being conductive and lower electrical potential, you don't have to be 'Grounded' to get the snot knocked loose.
DC 'Seeks' to complete the circuit back to 'Source', and DC is CONDUCTED (not 'Transmitted').
Since DC seeks it's polar opposite, 'Earth Ground' is virtually useless as a 'Safety'.
Unless you are the circuit completion, as in have one hand on the negative and the other on positive, you DON'T get the snot knocked out of you, DC isn't 'Seeking' earth ground or lower potential, just it's polar opposite.
(Every 'Electrical Engineer Type just hit the ceiling, head exploding...
Since the core differences aren't taught in 'Engineering School' this always drives the EE types up the wall since they have never heard it before)
Not exactly the question you asked, but maybe should have asked?...
DC is directly the electro-magnetic link, a force of nature, or a force of the universe, like gravity,
OR,
It's a chemical reaction (Batteries), and again, a force of nature or a force of the universe.
DC happens all the time, everywhere, like in every nerve impulse in your body or the constant positive/negative charges in the atmosphere.
Always one polar opposite seeking connection back to 'Source', a DC Circuit being completed.
From a nerve impulse you never think about but happens a billion times a second in your body, to lightening strikes, it's all a force of nature and polar opposites seeking to complete the circuit.
Nature doesn't produce 'AC',
AC is entirely man made and it's unstable, seeking ANY conductor with lower potential.
You can't store AC power, it's generated and used immediately or lost.
There is no such thing as a chemical AC reaction, so no such thing as an AC battery.
Maybe I hammer on the electro-magnetic link too much, but without an understanding of the core, you can't really understand the rest...
But then again, I have no issues what so ever building generators (100% electro-magnetic link) or with AC/DC wiring,
I understand the differences and the rules for each...
'Knowing How' something works, and actually building it to do a specific job are two entirely different things,
Like a 'Line Man' can do connections, but can't build a generator with specific output, or a radio guy can't do an AC line man's job...
And keep in mind I'm no 'Genius', I simply have a curiosity born of need, while the circuit designer can work with every type of small electrical component, because that's their field of study...
My field of study is keeping my eyebrows on my face while I'm building a specific circuit and wiring things to run...
Don't ask me about specific transistors, ICs, ect., but if you want an ignition system that will ignite exotic fuel, or you want a generator that will produce in a specific amp/volt range, and has bearings that will be long lived, I do know about that...
Call it 'Electro-Mechanical', making machines that do a specific job efficiently, and without a rock solid background in the electro-magnetic link you can't do that efficiently.
See the threads (several) on 'Solenoids' (Actually electrical relays) and you will see a crap ton of confusion...
Every bit of the confusion is not understanding the electro-magnetic link,
Not only what happens when the relay is activated, but what happens when that big electro-magnetic field collapses around the magnetic ferrite core THROUGH a bunch of wire windings when the circuit opens and creates reverse polarity discharge into the DC electrical circuit, it's a 'Transformer' when the circuit collapses, and without understanding the electro-magnetic link, they don't connect the dots...
I guess exploding heads once in a while isn't a bad thing, but I do hope they do a little research before posting a rant because they never 'Studied' that before...
The problem is first terminology: in AC systems 'ground' is meant to be earth, with neutral the return path (I'm European, keep your split phase nonsense)
Thank you for the insightful answer.
The mixed terminology perturbs me, as it muddies the waters, and makes an already confusing topic somewhat more confusing. I'm not informed enough to know if there is a reason the terminology is thus, but it seems less than ideal. I try to avoid the term ground when talking about the DC negative wire (maybe this is misguided).
I may be misunderstanding something, but it seems like the DC 'ground'/negative/black wire is conceptually similar to the AC neutral/white wire, is it not? And that ground or earth is a safety feature that provides an alternate route back to the source (earth or ground in most but not all cases). Maybe its an oversimplification but in a sense ground is just a backup neutral is it not?
Can you elaborate on what this means, how its determined?
One more unrelated/semi-related question. Would it be correct to say that grounding/earthing in the AC sense of the term (unlike fusing) is a safety feature intended to protect living things, not to protect the system itself or prevent fire or damage?
It's basically whatever you consider to be the reference point. Usually 0V (think car chassis, connected to the negative of the battery), but you could easily design a system where 12V can be your reference. You choose it when designing the system, but you have to make sure you're compatible with other systems you connect to.
If I were to attempt to distill this down to one simple distinction that I can wrap my head around, would it be correct to say that DC wants to return to its source, AC wants to go anywhere with lower electrical potential (i.e. lower voltage), and both will preference the path of least resistance?
If its not too broad a question, what are the practical implications of this distinction?
@JeepHammer Some examples of the complexities and requirements when we talk about DC earthing and why this needs to be taken into account:
https://www.cisco.com/en/US/product...stallation_guide_chapter09186a0080104666.html
https://ieeexplore.ieee.org/abstract/document/8726920
Selecting circuit breakers for DC systems according to earthing system:
https://download.schneider-electric.com/files?p_Doc_Ref=CA908061E&p_File_Ext=
From the 2019 draft standard of battery installations in Australia (section 5.3.1.7):
https://www.smartenergy.org.au/site...bsite-content/dr2_as_nzs_5139_2019_pc.pdf.pdf
https://www.cisco.com/en/US/product...stallation_guide_chapter09186a0080104666.html
https://ieeexplore.ieee.org/abstract/document/8726920
Selecting circuit breakers for DC systems according to earthing system:
https://download.schneider-electric.com/files?p_Doc_Ref=CA908061E&p_File_Ext=
From the 2019 draft standard of battery installations in Australia (section 5.3.1.7):
https://www.smartenergy.org.au/site...bsite-content/dr2_as_nzs_5139_2019_pc.pdf.pdf
JeepHammer
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Two different sciences, two different disciplines in application, two different educations, two different vocabularies...
The guy that mixes terminology is usually a beginner, so you steer him towards corrections.
DC never has had, and never will have a 'Ground' or 'Earth Ground'.
AC electrical engineers hung 'Chassis Ground' on vehicles a long time ago, which got shortened to 'Ground'.
Vehicles are still DC, there is no 'Earth Ground', and there *Should* be a clean negative path back to the battery for every positive wire that goes to lights & accessories, but it's 'Cheaper' to attempt to use the body/frame and call it a 'Chassis Ground'...
There is a reason 'No Fail' vehicles like combat military vehicles specify a negative wire back to 'Source' instead of 'Chassis Ground' that rusts, corrodes and fails regularly...
Keep in mind, when YOUR negative path fails at the 'Chassis Ground', it's money in the bank for the dealership shop!
They are more than happy to fix your rusted wire/bolt issue for $75 or $100 an hour shop time!
A dedicated negative path wire would have stopped 100% of those issues, but the shop wouldn't make $75 or $100 an hour for something easily 'Fixed' (that WILL corrode/fail again, and you get to pay them even MORE to get it 'Fixed' again and again)...
There is a reason your CONSUMER vehicle doesn't get $3 worth of negative path wire from the factory, and if you don't believe that, you are the perfect 'Consumer'...
When you get tired of the fails, you 'Consume' another vehicle! They get you coming and going... There is a reason it's called a 'Consumer Economy'...
The absolutely correct term is Negative Circuit Path in DC wiring.
All DC wiring has just two 'Paths', the 'Positive' conductor, or the 'Negative' conductor.
(DC is 'Conducted', not 'Transmitted' like AC is)
The 'Chassis Ground' was the metal body or frame, steel is a HORRIBLE conductor of electricity (compared to silver, copper, brass, bronze, gold, ect.).
Steel is actually an electrical 'Resistor' if you want to get down to conductivity scale references...
Nope.
AC is transmitted, and it's seeking ANY lower potential conductor, 'Earth Ground' is that lower potential (zero volts) conductor that is the path of least resistance, so it's used primarily as a 'Safety' to shunt AC safely away.
DC is Conducted, and seeks ONLY the polar opposite.
You have to be touching BOTH the 'Positive' pole, and the 'Negative' pole to get shocked.
If it's a completed circuit, it's safe for you to touch since the path of least resistance is the closed circuit and NOT you.
Touching low powered DC circuit anywhere is only ONE connection point, you are not connected to the polar opposite, so you don't get zapped...
Think of it this way,
Hundreds of AMPS in a car battery, Thousands of times what it takes to stop your heart.
All that connected directly to every metal part of the vehicle... Yet the vehicle is dead safe to touch anywhere without getting zapped or killed, and since it's on rubber tires, exactly Zero parts of that vehicle are 'Grounded' in any way.
You can have a million volt AC line drop on the car, and as long as you don't step out and make the earth ground connection, you won't get cooked...
FUNDAMENTAL DIFFERENCE in the way AC works compared to DC, touch ANY AC line with 1,000 amps and you get cooked like a hotdog.
Any crossing of technical terms between AC & DC are laymen produced, or AC guys that don't understand DC.
[/quote]One more unrelated/semi-related question. Would it be correct to say that grounding/earthing in the AC sense of the term (unlike fusing) is a safety feature intended to protect living things, not to protect the system itself or prevent fire or damage?
[/QUOTE]
AC 'Grounding' is necessary first for life & limb, then to protect the equipment and circuit.
With DC, unless YOU complete the circuit between 'Positive' and 'Negative', you really can't get cooked.
If you do complete that circuit, DC CAN take a real bite out of you, more than twice the energy in DC circuits over AC circuits.
DC Seeks ONLY it's polar opposite, not any available conductor, YOU must complete the circuit, where AC will nail you simply because you conduct electricity and you are lower potential than the 'Hot' line you come into contact with, and that is a HUGE safety issue when working with AC,
The 'Earth Ground' is there to be the path of least resistance when something goes wrong since AC is actively seeking ANY conductor with less potential.
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Please check IEC 60364-1
Summary article: https://electrical-engineering-portal.com/direct-current-distribution-systems
Summary article: https://electrical-engineering-portal.com/direct-current-distribution-systems
Solarfun4jim
Solar seduced :-)
One more unrelated/semi-related question. Would it be correct to say that grounding/earthing in the AC sense of the term (unlike fusing) is a safety feature intended to protect living things, not to protect the system itself or prevent fire or damage?
[/QUOTE]
AC 'Grounding' is necessary first for life & limb, then to protect the equipment and circuit.
With DC, unless YOU complete the circuit between 'Positive' and 'Negative', you really can't get cooked.
If you do complete that circuit, DC CAN take a real bite out of you, more than twice the energy in DC circuits over AC circuits.
DC Seeks ONLY it's polar opposite, not any available conductor, YOU must complete the circuit, where AC will nail you simply because you conduct electricity and you are lower potential than the 'Hot' line you come into contact with, and that is a HUGE safety issue when working with AC,
The 'Earth Ground' is there to be the path of least resistance when something goes wrong since AC is actively seeking ANY conductor with less potential.
[/QUOTE]
Brilliant.....this drives home the understanding of the negative return path rather than the chassis return path.....been trying to get to this a while. Thanks for this.
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I can have a 5V AC source capable of delivering hundreds of AMPS as well and touch that without issue, even holding both wires. You need a combination of both volts and the capability to deliver the amps to cause harm.
One of the reasons you care about earthing DC is that you can prevent accidents: if the negative of a DC source accidentally gets grounded (to earth) by e.g. water, nothing seems to happen - but now when you are standing on the ground (earth) you can get shocked and have current flow through your body because the path is completed and there is nothing to stop this. Same when the positive accidentally gets earthed, you can get shocked by touching the negative. Which is why you need a ground fault protection here as well as you need it in AC.
JeepHammer
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Yes, I'd say so...
Others want to quote 'Code' instead of see the practical application. Their choice and they are welcome to what they want to believe...
It's usually the same guys that drag 'Skin Effect' and 'Ground Loop' into NON-AC and NON-High Frequency discussions... Just something they stumbled onto or saw on boobtube and like to quote.
We are talking basics here, not some 'Code' written about a specific application that created a problem when 'X', 'Y', and 'Z' all went wrong at the same time.
So for simplicity sake, and for education purposes, lets say you have it down pretty well...
DC is ONLY attraced to it's polar oppsite, the path back to it's source...
AC will ACTIVELY SEEK ANY CONDUCTOR OF LESSER POTENTIAL, that includes your fingers, heart, liver, ect.
Keep in mind that 'Earth Grounds' are WAY over sized for a reason, it's *SUPPOSED* to handle 100% of the current so all you get is a mild shock, if anything, since AC doesn't care if YOU are 'Grounded' or not... AC is still going to try and knock the snot out of you if it can...
That's the reason for all the 'Grounding Codes' in AC wiring first off,
And secondly is to keep that AC from seeking lesser potential on something that will catch fire,
THIRD is saving any of the equipment from damage...
Life & Limb, Fire Potential, Equipment & wiring... In that order.
Keep in mind in the early days of AC, a LOT of people died, were maimed/disfigured, handicapped, ect.
Every code has a reason, but its mainly about keeping people alive and keeping the place from burning down.
I'm sure others will argue, but with low voltage DC most of the 'Safeties' are built into the circuit itself simply because DC seeks ONLY it's polar opposite, and path of least resistance.
Generally, you won't be either what completes the circuit, as in contact with BOTH poles, and/or you won't be the path of least resistance.
DC car batteries produce way more, several thousand times more than it takes to kill a human, and yet about every DIY guy has messed with car batteries without harm or death.
You can't say that about guys running ladders into AC lines at only 230-240 Volts and only 50-60Hz...
They get smoked REGULARLY.
Every shade tree mechanic that ever got a spark off a car battery with a wrench handle would be dead if it weren't the case...
The WRENCH is contacting both poles, and the WRENCH is the path of least resistance, the shaved monkey on the wrench doesn't feel a thing, just gets surprised by the sparks...
But given a 1,000 Amp AC circuit in the same situation, that same shaved monkey would be seriously shocked or cooked.
It's two entirely different animals,
Think lap dog and 600 pound tiger, both *Can* bite you, but which one is more likely to kill you outright on the first encounter?
Both are animals, AC & DC are both moving electrons in wires, but which one kills people regularly?
---------------------------------------------------
Look at it another way,
DC, the force of nature electrical current, is used for virtually everything.
The first thing many appliances do is convert the AC into usable DC using a transformer & rectifier.
AC has one good quality, it Transmits through conductors really well, which is why the millions of miles of power grid lines are AC.
DC does more work, does things AC simply can't, so AC gets converted to DC when it gets to the appliance/Application and does the work.
Pretty much all raw AC can do is make a magnetic field, so it's good for motors, and it makes heat when it's 'Shorted' through a resistor, like an electric heater.
You can't put AC down for what it does do, humans NEED motors for production, and they NEED heat to survive in most of the world, it transmits through conductors quite efficiently compared to DC, so it can be moved hundreds of miles fairly easily.
DC does everything else.
No TV, No radio, little communications past Morse Code, no electrical storage, no display electronics, no digital/binary data storage without DC, and that's just a few things you can't do without DC, the list goes on for way longer than I can type...
Everything comes with a 'Wall Wort' transformer for DC, or the transformer from AC to DC is built in, otherwise it wouldn't exist.
jasonhc73
Cat herder, and dog toy tosser.
The most basic fundamental of an electric circuit.
JeepHammer
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No offense intended,
Name a SINGLE COMMON 5 Volt source with 1,000 Amps a SOLAR USER is likely to come into contact with...
On the other hand, 12 Volt, 1,000 Amp car batteries ARE COMMON, AND ARE USED BY SOLAR USERS.
There *HAVE* been cases of car batteries killing people, roasting fingers off, ect, but for the BILLIONS of car batteries, these events are quite uncommon, and frankly, you have to be the most unlucky, or special kind of stupid... to kill yourself off a car battery...
BASIC EDUCATION here, not the reasons for 'Codes'...
That comes with ADVANCED EDUCATION.
At no point in the conversation did anyone ask about the 'CODE' for downed solar panel lines, with insulation stripped, still connected, in a water puddle... I can't even believe that made it into the conversation about the basics between AC & DC when the user doesn't have the two differentiated yet...
I didn't drag a guy with a pacemaker into any electrical conversation for several reasons, but there are 'Code' requirements based on people with heart pacemakers...
Once the user has figured out the difference, and settled on a SPECIFIC APPLICATION, then, and ONLY THEN, does the 'Codes', and specific safeties come into the education process.
Learn to craw before you try and set a land speed record for fastest human alive...
