How interchangeable are AC and DC circuit breakers?

A friend recently asked my engineering opinion on the matter of using DC (Direct Current) circuit breakers in the place of AC (Alternating Current) circuit breakers in a circuit. Now I’d be there first person to tell you that my engineering skills are a bit rusty, but I guess like learning to ride a bicycle it never quite goes away. Forward, onto the breach!


I’m not an expert even though I sometimes pretend to be one online. This advice is for information only and it is up to YOU to ensure that your electrical installation meets local laws and guidelines.

AC in the place of DC

Now this seems to be the most common situation. People want to use the more commonly available AC MCB (Miniature circuit breaker) for their DC based system. This is a bad idea. For exhibit one I call the following video:

This video shows the fundamental difference between AC and DC currents. AC current has a handy zero crossing every half cycle that makes it easy to extinguish an arc. DC on the other hand is full on, all the time. It takes a lot more effort to extinguish the arc in a DC circuit. DC circuit breakers are specially designed to extinguish DC arcs and have special magnets to pull the arc away to get it extinguished.  Thus, don’t use AC MCB’s for DC circuits. For a more in depth explanation have a look at the links below.


For further reading have a look at

DC in the place of AC

This arrangement is a bit more tricky. From the outset it looks like this arrangement should be fine as long as the breaker meets the required voltage isolation levels. However therein lies the rub, if the device does not meet the required isolation levels or have the right approvals, it does not meet legal requirements. There are certain MCB’s that can be used for both AC and DC circuits but these would be clearly marked. Information on this arrangement was a bit harder to find. Have a look a the thread below.


For further reading have a look at

Other considerations

This diagram from an ABB MCB datasheet shows how the trip curves differ for AC and DC. So in other words the performance varies depending on the current type. This is another reason not to use these breakers interchangeably without proper design consideration.

Screen Shot 2016-05-09 at 8.44.31 pmThis is for a circuit breaker that is designed for both AC and DC. You can find the datasheet here.

For a much more detailed discussion on the intricacies of DC circuits and safety I can heartily recommend the ABB circuit-breakers for direct current applications technical application papers.


My recommendation would be to use DC MCB’s for DC and AC MCB’s for AC. There are special design considerations that go into the design of these devices and as an ex-colleague told me when I asked him to check this article: “I got burnt with 110V DC in a panel so don’t play with that thing. Make sure its the right breaker that trips fast.
Can’t argue with real world experience.


What stops people from becoming themselves?

What stops people from becoming themselves? This is a strange question since you can argue that we are already ourselves. It is a valid point, but if you consider a plant growing in an ideal environment, with all the nutrients and support it needs it would grow differently than one germinating under a bridge in the city.

I think the biggest factor that affects us is our environment. We are social creatures and peer pressure, culture and habit play a much larger role than we would like to admit. To this end I believe that the biggest factor that prevents us from in not becoming ourselves is the mould we are forced to grow into by our parent’s and greater society’s beliefs. All the beliefs we would never choose for ourselves but internalise anyway. Take for example political affiliation. If you had absolutely no political affiliation up until the age you were able to vote would you still choose the same party you associate with now, or along similar lines for religion? If you had no exposure to religion and had the opportunity at the age of 18 to pick one would you still end up choosing the same beliefs?

Much of who we are is shaped by who we think we are. If we just took the time every once in a while to look at our beliefs in an objective light, view them as an ignorant outsider, we might get a glimpse of how to better become ourselves.

[Inspired by this passage from HPMOR]

She let him go on like that until she’d finished pouring herself a glass of grapefruit juice, and then she said, “I’ve got a question for you, Mr. Potter. How do you think people fail to become themselves?”

What??” said Harry.

She looked at him. “Pretend there isn’t all this stuff going on,” she said, “and just say whatever you’d have said yesterday.”

“Um…” Harry said, looking very confused and worried. “I think we already are ourselves… it’s not like I’m an imperfect copy of someone else. But I guess if I try to run with the sense of the question, then I’d say that people don’t become themselves because we absorb all this crazy stuff from the environment and then regurgitate it. I mean, how many people playing Quidditch would be playing a game like that if they’d invented the game themselves? Or back in Muggle Britain, how many people who think of themselves as Labour or Conservative or Liberal Democrat would invent that exact bundle of political beliefs if they had to come up with everything themselves?”

Regarding the 2011 suicides at the iPhone manufacturing plant

To be soaked in materialism, to directly and indirectly champion it, has also brought guilt. I don’t know if I have a right to the vast quantities of materials and energy I consume in my daily life. Even if I thought I did, I know the planet cannot bear my lifestyle multiplied by 7 billion individuals. I believe this understanding is shared, if only subconsciously, by almost everyone in the Western world.

Every last trifle we touch and consume, right down to the paper on which this magazine is printed or the screen on which it’s displayed, is not only ephemeral but in a real sense irreplaceable. Every consumer good has a cost not borne out by its price but instead falsely bolstered by a vanishing resource economy. We squander millions of years’ worth of stored energy, stored life, from our planet to make not only things that are critical to our survival and comfort but also things that simply satisfy our innate primate desire to possess. It’s this guilt that we attempt to assuage with the hope that our consumerist culture is making life better—for ourselves, of course, but also in some lesser way for those who cannot afford to buy everything we purchase, consume, or own.

When that small appeasement is challenged even slightly, when that thin, taut cord that connects our consumption to the nameless millions who make our lifestyle possible snaps even for a moment, the gulf we find ourselves peering into—a yawning, endless future of emptiness on a squandered planet—becomes too much to bear.

When 17 people take their lives, I ask myself, did I in my desire hurt them? Even just a little?

And of course the answer, inevitable and immeasurable as the fluttering silence of our sun, is yes.

Just a little.

Joel Johnson

Can we change?

“I know what you are saying. I try not to think about it. But it’s not that unusual. Over the course of history, billions of people have lived this way. Think back to when you were living in suburbia. Your parents had a 3,000 square foot house and the pool at the turn of the century. You were living it up. Unfortunately, at that moment in history, there were billions of people around the world living in poverty — they were living off a dollar or two per day. Meanwhile, your family had 300 dollars a day. Did you do anything about it? Billions and Billions of people living in third-world countries, squatting together in the dirt, crapping in ditches. They would walk down by the river just like we are doing right now and say to each other, ‘There must be a way out.’ They could see that they were lost — totally wasted human potential trapped in a terrible situation. Their kids and their kids’ kids forever would live like this because there was absolutely no way out. Did anyone stop to help them? Did you stop to help them? No. You were too busy splashing in the pool. Those billions of people lived and died in incredible poverty and no one cared.”

From Manna


I met a traveller from an antique land
Who said: Two vast and trunkless legs of stone
Stand in the desert. Near them, on the sand,
Half sunk, a shattered visage lies, whose frown,
And wrinkled lip, and sneer of cold command,
Tell that its sculptor well those passions read
Which yet survive, stamped on these lifeless things,
The hand that mocked them and the heart that fed:
And on the pedestal these words appear:
“My name is Ozymandias, king of kings:
Look on my works, ye Mighty, and despair!”
Nothing beside remains. Round the decay
Of that colossal wreck, boundless and bare
The lone and level sands stretch far away.

I think I finally get it.

Intrinsic and Extrinsic Value

What is the difference between intrinsic and extrinsic value with relation to currency? Lets have a look at a 2009 South Africa 5c coin. The face value of the coin states that the bearer is entitled to trade the coin for R0.05 worth of goods. This extrinsic value however is only based on the faith of the currency and the country backing it. The face value refers to the extrinsic or external value. The internal value needs to be calculated.

A standard 5c piece has the following dimensions:

Diameter: 21mm

Thickness: 1.94mm

Weight: 4.4g

The weight of the coin with the current copper price gives us an estimated intrinsic value of R0.2196 or about 22c! If this was the case it would have been more profitable to melt the coin down for its copper than to use it for monetary exchange.

Have a look at the picture. The section of the coin shows that the copper is only a superficial layer. The majority of the coin is made of steel. Lets assume that the coin is made of 100% iron for comparison. Based on the current iron price the intrinsic value is about R0.000924 or 0.092c. Lets double this amount to account for other metals in the steel and the copper plating. Now the intrinsic value of the coin is approximately 0.2c (a fifth of a cent). This makes more sense since it is now more profitable to use the coin as currency rather than to melt it down.

This disconnect between the intrinsic and extrinsic value of our currency is one of the causes of inflation. It also places the management of the stability of our currency in the hands of our governments and central bankers. Since there is no barrier to creating money backed by real value governments can, and do, print money backed by no value.  This is what happened to the Weimar Republic and more recently to Zimbabwe.

There is an old bit of wisdom that states “He with the gold rules,” I believe that in our current financial paradigm it is more accurate to say that he who prints the money rules.

Precious Metal Buying in South Africa

I believe that the best type of investment is in tangibles. Things like gold, silver and property can’t be electronically disappeared or inflated away. I would like to share a few of the things I have learned through my research.

Forms of precious metals:

There are 3 main forms of owning precious metals. These are:

  • Bullion – amounts of precious metal where the weight is the only determining factor on the value.
  • Jewelry – I have no information on the use of jewelry as a form of investment.
  • Collectors Coins – mostly coins, where the weight as well as the face of the coin determines its value. Like a cross between bullion and a collectors item.

To summarise: I you melt down bullion into a blob no value would be lost, but if you melt down a collectors coin you would lose a great deal of value.


The international standard of measurement for precious metals is the Troy ounce. One Troy ounce is equal to 31.1034768g. Collectors coins are usually sold in ounces or fractions of ounces. ½ and ¼ ounce sizes are common. With collectors coins the face value has no effect on the value of the coin. Bullion can be sold in ounces or in grams or in any other weight measurement.

Prices and Value:

The price of various precious metals vary greatly. The value of bullion can be easily determined by multiplying its weight by its spot (current price). Collectors’ coins value is determined on a willing buyer, willing seller principle. This aspect of perceived value is a negative aspect of collectors coins in my opinion. You will pay a certain percentage above spot price to buy bullion and you will mostly sell it for a percentage below spot price. These two links will be very useful to South Africans who want to get a price in Rand per gram: [Gold] & [Silver].


I don’t see precious metals as form of investment but rather as a store of value. There is a well worn quote that sums this principle up quite well:

Under the Roman Empire, an ounce of gold purchased a Roman citizen his toga, a leather belt, and a pair of sandals. Today, one ounce of gold will still buy a man a suit, a leather belt, and a pair of shoes.

I feel that this is honest and fair and does not unrealistically create (or extract) value from some obfuscated source.


See for yourself:

Where to buy:

The best place I have found to buy bullion is MetCon. I haven’t bought from them yet and they seem to be very expensive especially for silver. They do have online ordering and they are situated in the Cape. Other suppliers that I know of are the SA Mint and the SCoin shop (the retail arm of the Gold Coin Exchange). The easiest way for South Africans to buy gold bullion is to purchase Kruger Rands. Just be careful since there are bullion and collectors coins types of Kruger rands.


I hope this gave you a better idea of the precious metal picture. I am still trying to find somewhere to buy silver at a few percent over spot price. Silver is know as the poor man’s gold. Just make sure that you don’t pay too much over spot price for bullion since you will have to sell at a few percent below spot price in the future.