How to Specify & Install a DC Isolator 👉kzfaq.info/get/bejne/h5l5abV9lda0o6M.html

I was expecting to see arc suppression blades inside the DC switch. Seems that printing a lower rating on the outside is actually the cheaper option. 😀

I served as a junior electrican for one trip when I was an engineer in the merchant navy. We used DC back then (45 years ago) for motor control, it was very good for it, pumps could be easily controlled for pressure and flow just by altering resistances. But the worst burn I ever saw while I was away was when (another junior electrician) told the senior electrician that he had isolated the main engine cooling pump. He had actually isolated the main engine oil pump. Due to the construction and access to the knife isolators, when he pulled the knife isolator it arced across and basically evaporated the skin off the back of his hand, 250 amps at 220 volts is really not good for you. Due to the pump stopping, the engine lost cooling water pressure and also stopped, so the engine room was full of people to assist in less than a minute.

Worked on a 1940’s cargo ship that had massive DC contactors. They made and broke the connection via a sacrificial carbon brush before the main contacts opened or Closed. There were arc diverters and suppressors. It was pretty epic testing those circuits and pushing in contactors with broom sticks when needed...

Another critically important factor is the actuator (knob on the front panel) of the switch. Most dc ones I see have an impulse mechanism (like engine magnetos) to rapidly snap the contacts apart to their maximum distance. Do not mix and match switch components.

Fast DC breakers used in trains and trams running off DC overhead wires are enormous. Some are even preloaded with compressed air and have arc quenching chambers. With modern approach and in HVDC you typically have thyristor based breaker (to bring down the current) and physical disconnect in series

Back in the 90s In South africa, the DC switches and breakers, weren't always available. We used to take a 3phase contactors, and wire the contacts in series(to increase the switch gap), and de-rate the current rating for DC. We sometimes used 3pole switches wired in series aswell. I remember experimenting with small permanent magnets to blow out the arc. I tried fitting magnets to 2pole circuit breakers, to 'blow' the arc into the arc splitter/shoot. DC deserves a lot of respect, but it's not as dangerous as people make it out to be.

Excellent demonstration. There was quite a difficulty in obtaining DC switchgear (isolators and contactors) in the 1980s. Power stations use a lot of DC supplies, 240V and 110V for HV switchgear operating solenoids (hence highly inductive) and also emergency lighting and power supplies, but with the original suppliers defunct, obtaining equipment for a new workshop test facility was problematic. One of my colleagues eventually sourced some contactors after speaking with the manufacturers and they were wired as per your isolator with multiple contacts in series.

i once ran a hot air gun directly of 230v dc from solar panels. Worked just fine, worked so good it even worked when I tried to turn it off :P

Also you will find a lot of DC isolators are very much directional, in that you must mount them so current flow is according to the direction of flow marked on the switch, so for things like a battery disconnector you need to have 2 poles doing the switching action, as current can flow into and out of a battery. However for things like a solar panel or inverter they will havv a defined direction of current flow, and if the inverter has a battery charger there will be a separate isolator for the battery charger output. This because they use a magnet to direct the arc into an arc breaker, so that the arc itself can be cooled down to the point the ionised air no longer conducts. Thus another difference between SELV and PELV DC and higher voltage, in that SELV and PELV DC circuits are so much less likely to have the energy to draw an arc, and the separation to disconnect can be less rigorous. Incidentally that breaker shown is no longer recommended for new installations in certain countries, like Australia, as they have had a good number of them that have failed in use, and there have been recalls to install upgraded isolators with higher specification, and larger separation, plus also having magnetic arc diverters to more effectively break the circuit when operated under load.

It's refreshing to see a company's channel that that actually educates with their products as examples instead of just faffing about how great their products are. This is better than any advertisement, really.

DC arcs can be beautiful to watch.

Brilliant demonstration, two bits of food for thought, 1 as the two switches are identical could th AC switch have the two link wires installed there by making it a DC switch? And take them out of the DC switch there by making that into an AC switch , after all some room stats can be modified to work with different boiler systems by adding or removing a link wire. Point 2 could you not use that wood switch to try and prove once and for all AFDDs work or not? As you know there is a long running debate weather theses things work at in a domestic installation. Brilliant video as always Joe 👍👍👍 Come on Joe

Having been brought up on diet of DC mains supplies I was very aware of the difference berween switching DC as opposed to AC. Even in domestic installations 'quick make and break' switches were generally employed to overcome the problem until AC became more generally used, I think GEC brought in the 'Mutac' switch early on to avoid the massive 'clunk of the QMAB switch when DC had long gone. Magnetic blowing is often used today even on AC circuits.

Very well explained Joe. An AC current is much easier to interrupt than a DC one because the current flow is zero every half cycle or 100 times every second.

another great question answered. great video

That first demonstration of the arc was really graphic showing the difference between ac and dc. Colleges should do that demo. Though perhaps with a slightly less ‘Heath Robinson’ apparatus 😮

This was also a legitimate question/concern 150 years ago in the 1870s when household electricity was being introduced in the electrical format war between Thomas Edison's DC system and Nikola Tesla's AC system.

Great explainer. Some of the nastiest isolator burnouts I’ve dealt with have been 4 pole AC with links made from 4mm DC solar cable.

With out the sufficient amount of knowledge about DC switching, lives could be lost. A friend of mine had such a problem with the PV breaker. The electric arc set fire to the PV BREAKER. luckily no one was hurt.

I placed an AC isolator in my PV DC circuit, purely because of cost. It was a factor 5 cheaper. (10 years ago). Six months later we smelled something burning, and it turned out to be the AC isolator, completely burned inside. We were lucky to find out in time, while being home. Don't ever go cheap on isolators!

As always Joe, very well explained 👊😎👍💙

Excellent demonstration!

Made teaching media for lectures very well.

Excellent demo ... I never knew DC could generate such a 2 inch plasma arc, incredible!

Excellent video Jo. I have learn’t something very important there… not to cut corners with DC and just use an AC isolator instead as i may happen to have one in the van. 👍

Very good information Robinson.,

Expertly explained, as always, eFIXX. Great demo!

Excellent explanation ! 👍

I worked for over 30 years on the power systems of the London Underground. We had equipment from the 1930s as well as modern when i started. The sound of a DC CB coming out at 8000A wakes you up. Old CBs had magnetic suppression of arc. Later, smaller form factors combined magnetic and air puffers which stretched the plasma and thus reduced the arc. Typically the contacts needed occasional light redressing depending on the section of track they served. Your demonstration rig was not greatly dissimilar to the 22kV isolators on the old equipment. Opened with a pole and a hook, but of course not under load. The first couple of times of doing it was a buzz in more than one sense.

Just in case it's not obvious, that arc is 'plasma', which is a fourth type of material after solid, liquid, gas, and importantly, while it's doing its thing (so 'hot' that the electrons and the nucleus of the atoms separate), it is a very good conductor, which has a great similarity (for those who like their physics) with the 'conduction band' in metals where all the electrons can go for a wander rather than staying with their nucleus as happens in non conducting insulators. Lovely visual effect. There is plenty more interesting arcs and sparks stuff. Just beware those arc flashes!

Good stuff Joe.

An excellent demo and simple explanation of the basics. One vital factor you did not mention is that with dc switching you have to ensure (I.e. check, do not guess) that the time constant (L/R ratio usually expressed in milliseconds) of the load is also less than that for which the switching device is rated for. Also watch the number of switching cycles that the dc power device is rated for when breaking current (the on load rating). The dc number is significantly (multiples) less than that for ac where a device has a dual rating and a lower voltage rating will often be applied too. Whoa betide you if you exceed the number of cycles; it’s crucial that maintenance and replacement are carried out accordingly. On dedicated dc circuit breakers you can get blow out coils, arc splitters and runners within an arc chute. Orientation of the device can be critical in some cases, as is the clearances on the exit side of the arc chute. This so the arc is, stretched, cooled and quenched as the device designer intended (same for dc contactors too) My guidance is do not play with dc power unless you thoroughly know what you are doing and qualified/ supervised accordingly. As your demo if you contact dc your muscles will go into spasm and it’s difficult to let go as no current zeros, I have never got caught on that one, this after a long career in dc and ac drives, be extra careful! Hope helps Stephen

Pretty sure the sparks that did my PV back in 2013 just stuck an AC isolator in as I suspect they knew no better - fortunately it’s on SolarEdge optimisers so the likelihood of the isolator ever having full whack going through it if it needed isolation is highly unlikely - I did make the installer return to add a separate RCD rather than leaving it piggy backed onto the existing one which feeds the rings 🤦‍♂️🙄

Ah yes. The forbidden arc welder.

I've just got a course on this, really neat, My DC weder is also making big arcs at 30 Ish volts 😊

It is not just switches (which means relays and breakers as well of course), but you can get the same issue with fuses. Now I don't suppose the everyday sparky is going to be designing circuits at this level, but it's interesting to not that some fuses have different voltage ratings for AC than for DC (the current ratings are the same). The reason for this is that, when a fuse blows, there will briefly be an arc set up which is caused by ionised air providing a low-resistance path for current to flow. That ionised low resistance route will last as long as a lot of current flows as it self-generates. With AC, the current drops to zero twice every cycle, and that will normally be enough to kill the arc. With DC, it's different as the current will continue to flow through the ionised gas, and that very current will sustain the ionised gas (called a plasma). If the gap is fairly small, and the voltage is high enough, that process can be entirely self-sustaining, which is highly dangerous, especially in a fuse, which is there purely to break the circuit in the case of a gross overload. So, whatever anybody might say, many fuses do have different voltage ratings for AC and DC. There is another issue with breaking DC into inductive loads. There can be a vicious reverse voltage spike when cutting off the current, and that can cause very large sparks or even weld contacts together. Often flyback diodes are installed to conduct those reverse voltage spikes which could otherwise cause a low of contact damage. This can happen in very low voltage circuits as what matters is the energy stored in the inductive component's magnetic field, not whatever voltage it is working at.

Clearly this is something I will try at home while showering.

Great demonstration video... but @ 2:29 there is a lovely hum during the DC break-arc and its DC? since when does DC Hum?

Looks like a clever way for manufacturers to re purpose some double pole AC switchgear into single pole DC switcher by just putting terminals in series to increase the air gap! 🔥

Besides the ultimate gap length, the other features affecting arc quenching (at same voltage and current) are at least a speed of the contact opening and added quenching means (cooling and magnetic blow). The opening speed is inadvertently affected by applying a freewheeling diode across the coil of the device! That relates to DC operated coils, of course. But it can be clearly seen on ordinary 24 V DC coil relays...

Have to say whilst this was an interesting video I am worried you could have inadvertently done more harm than good. Looking at the comments a lot of people will be under the impression that all you have to do to convert a AC switch to DC is series the contacts and derate the current and voltage. I am not at all impressed with the build up of the dc isolator you have shown, would be interesting to see how it performs under its rated loads.

2:57 - I assume that DC arc is supplied from a transformer and hence the 50hz hum in the background. Last time I saw a DC arc, it hissed and was almost silent.

What happened to the old fashioned arc shields that used to be fitted to DC switches.

I've used high voltage DC relays in the past that had a strong permanent magnet adjacent to the contacts to blow out the arc. I'm surprised the SCARME DC isolator doesn't include this, as it works so well.

Boats make extensive use of DC circuits, 12V or 24V for house loads, depending. Electric propulsion is becoming more popular, which is often 48V DC.

My rule of thumb is to half the current and then only use an average of 60% of that, and to keep the voltage well below 75% of the rated voltage when using DC on an AC switch (many will even have their DC equivalent ratings o the switches to give guidance for dual-use). The other differences usually include a little bit of silvered coating on the contacts. So far, so good. Also, I expect the lifespan of a DC switch to be shorter than the AC equivalent. of course, there's more to it than I mention, but the ball-park works, just make sure to not use AC isolators as a main DC-bus switch as technically it's a safety device, not just an isolator.

That's some Ark, even Noah would have been proud of that one. Thanks for sharing Joe.

As a railway enthusiast who lives in an area where DC conductor rail (750v= ca. 50KA) is in use, I am trying to think just how *beefy* DC traction supply isolation gear must look like. Perhaps arching is the _real_ reason why DCCR electrification enforces a painfully slow speed limit of just 100mph? 🚄💨⚡😉

You should make video about C loads and the gear required to switch that.

Do car relays work for 30amp DC for safe rapid switching?

DC is not to be laughed at. When adding two 12V Car batteries to make a 24V system, and then accidentally shorting the opposite poles, it melted an inch of length off of a 1/4 inch threaded steel rod in seconds. I sat on top of that with just a padded seat between, and that was the most brown alert moment in my life still almost 30 years later. Solar roofs when connected the wrong way can be 1500V and capable of delivering about the same current as a car starter battery...there is a reason there are so many electrical house-fires after cheapest contractor with east-state labor have been on site assembling.

So pretty much exactly the same switch just rated differently... And given that at CEF a 20A 3P AC is £30.79 and the DC Variant is £81.10, SCAM is the right name for this company, yes, I know I dropped the E off the end 😇

Would a circuit breaker technically work as a DC isolation supply, just asking as it has the grill that can dissipate arcs in it, or would the arc be too strong for it then?

“Don’t try this at home”. Hold my beer 🙄

The noise of a DC arch reminds me of photonicinduction.. 😔

I'm courious about the shape of the arc. Seemed to be wider at the top, was that from direction of gravity or direction of current.

Before anybody thinks of doing this (despite the warning not to!) that D.C. arc is hotter than the surface of the sun.

I always see that happening here in the USA, people use AC disconnects for DC and will burn out quite quickly. Never use AC disconnects for DC loads! 😁👍

I undetstand switch designed for AC can be problem with DC, but is there similar/other issue using a switch designed for DC with AC?

That's a thicc arc alright😍

You didn't actually explain how the DC isolator prevents or suppresses the arc.

The question ultimately is, who is isolating a DC supply when its under load? That's where the problem occurs. Little bit misleading in that if you did a comparison with the heater off load, that arc wouldn't pose a risk because it wouldn't be there. Also, you wouldn't use an resistive load on such a high DC voltage, which was intended for use in AC supply only, because once the power is applied you're in a no return situation. It would have been a laugh to see the thermostat kick out when up to temperature and see the amazing arc within the casing of that heater.

Why is the D.C. arc at 2:33 making the classic 50-60hrz sound of A.C.? D.C. arc's don't sound like that. How many volts. How many amps. I feel like there is something amiss here.

Why seperate DC isolators are still needed, modern string inverters do have those Dc isolator inside those ???

Then Can a DC one be used for AC isolation given we are under the spec for amperage and peak voltage?

Why does the DC arc have a 50hz ish buzz to it? Just a consequence of rectifying AC to DC?

Great video Jo, Could you just remove the links from the DC switch to have it act the same as a AC switch

😊imo for dc or scame the only ones i use in solar 😮

The best way to explain this is just a good old welder. Because that is the effect trying to be avoided.

Breaking a DC load is Big Boy's stuff versus an AC load

If I need a DC circuit breaker of 20 Amps, but I only have AC circuit breakers, what formula must I use to know what amperage AC circuit breaker to use

The logic behind using two switch contacts in series for DC switching is that one set of contacts will randomly open slightly before the other and be subject to the arc's thermal and electromagnetic effects so that (in theory anyway) the switch will have a greater operational life with the two (rather than just the one) set of contacts.

What is safer DC or AC?

Does pulsed DC behave differently?

Some rotary DC isolation switches have opposed terminals... eg: T1 is top left but switches T2 bottom RIGHT (not bottom left as people wrongly assume) This can result result in a major DC short across say two strings in an incorrectly wired 4 pole DC switch isolating 2 PV strings, kinda surprised this wasn't mentioned that certain DC isolator switch terminals can have the contacts arranged DIAGONALLY than regular vertical arrangement. Of course, it goes without saying RTFM & also wise to double/triple check the arrangement is correct/continuity across the poles to avoid risk of high voltage shorts or even reversing the polarity at the inverter etc... But it has been known for people to wrongly assume the pinout is obviously the same standard, only to find out on some DC isolation switches they are crossed over & rotary terminals are stepped/layered/stacked Some may already know this about DC switches, but others may not & there has been some costly lessons learnt when using different/unfamiliar DC isolation switches, not RTFM & assumption being the mother of all... Double check all your wiring, but maybe closely triple check your DC wiring to avoid a DC short or reversing the polarity of MC4 connectors as they connect to the inverter

"The Jaw-Dropping Difference Between AC & DC Isolators" -> Proceeds to show no difference between them...

You know ya'll zap alike!

You have a welder in DC

*_Very informative... Great Video.. Learned New Information..._* I have a question... Is 200 volts DC actually used in Residential Houses? I live in the States. We have 120 and 240 VAC. We use 480 VAC in Commercial Buildings. Solar is being installed everywhere now in different configurations; 12, 24, 48 VDC to Batteries then Inverter. It is converted to 120 or 240 VAC there and then into Household wiring. I have a 16 KW Propane Fueled Generac Emergency Generator. There is an auto transfer switch preventing my lethal AC voltages from leaking back on Public Power Lines. Switch over is less than a few seconds. UPS's on critical computers, servers, and communications don't need to be very large. At most they run 5 seconds before generator is at full power. I bought my UPS's before getting generator. They were sized to run critical equipment for 1 hour. Outages rarely exceed 15 - 30 minutes. *_Saw an article recently about newer Solar Panels that have their own builtin Inverters._*

Well that's quite an unfortunate brand name right there

I would assume that the DC switches, for the *same current load,* would have wider gaps between switch points. The switches shown in the vid are _identical,_ as shown by Joe, so they frigged the switch by dropping the current load for the DC version and using two switches in series. Personally I would rather have a DC switch with one switch with a larger gap between the points. Something tells me the 1st switching points in the two series switches may wear out quite quick.

So exactly the same hardware just wired up differently and derated.

I'm at that great point where I know enough to be dangerous, so thanks for this. I plan on putting some solar on my garage next year.

I will have have expected a better isolation in the DC switch, with a physical disconnect, like something that break the ark for sure

4:25 - no magnets in the DC breaker? Can you please poke around with a steel screwdriver or similar, to discern if there are hidden magnets near the electrodes in the DC-breaker?

From my college electrical but mainly electronic training and working with dc circuits and batteries of over 30 years It’s all about RMS ac = dc but dc does not fluctuate like ac 50 full 360 degree cycles a second. What multi meters read when you measure ac is the RMS value of the peak not peak - peak. High power DC circuits are getting more common with solar battery banks so things can be gone in a flash lol 😂 just wait and see with the DIY market growing…

Hm seems as they just use a jumper to connect two contacts in series and call it a day. Changed the markings on the AC one, seems like it anyways.

Seems like the exact same product with the same specs that are obviously different for AC and DC voltage

wait hold on why would a company put scam in their name? all they did is add an e at the end.

I am disappointed that the series connection of the DC contacts are joined by what looks to be field removable jumpers. It is just a matter of time before the jumper wires are removed, allowing the switch to be used as individual contacts (up to 4PST) with a much inferior performance.

why dont we just make all switched dc ???

So in reality we could use an ac isolator if we use double the contacts and half the current? Also I'd ad that I think that the reason the arc if so much bigger on the dc is because the ac value is only at its peak for that short interval, the rest of the time its decresing or increasing, or at zero! Good video 👍

I wonder if a large capacitor in paralell with the isolator would do the trick? Once the isolator is made open circuit, the capacitor charges, effectively meaning that the breaker disconnects at 0v. After a second or two, another isolator in series with the capacitor could be opened to completely seperate the circuit.

4:23 idk why they didn't just print AC and DC data on same device and sold it as one unit.... less packaging, less hassle in warehouse switches are marked this way....example 12V DC 20A / 24V DC 16A / 125V AC 20A / 250V AC 16A

You didn't explain the physics. You only talked about rating, and the fact AC and DC are very different, but you did not say why.! On AC, when the contacts start to break, the small spark occurs because the AC sinewave drops briefly to ZERO stopping the spark from arcing. On DC the voltage never goes to zero, it always stays the same, so the spark never gets broken, the ionisation continues freely, till the gap is big enough. I used a 10amp double pole relay in a 10amp DC power supply, by utilising both poles in parallel, the spark is halved, and the rating is also halved by using both poles to switch. Electricians need to study the background physics behind DC switching, now that we have an ever growing amount of equipment running on DC. Solid State switching might be a good way around this arcing problem. THOUGHTS.?? David G1ZQC.

Off topic , but it should be mentioned that the convector heater you use , having almost no moving parts will last for DECADES ! .. ( unlike fan assisted heaters that get " fluff " in the bearings ... and .... the AWFUL cheap ( modern ) radiant heaters that burn FAR TOO HOT and burn out in a few months use ) ... the old ( 1960's ) style radiant heaters are no longer sold ( ? ) but last many years ......... DAVE™ ...............

omfGAWD 👽 💥

The DC uded on the wooden switch still makes a 50Hz sound, so it's not even clean battery DC, which would be much worse.

The very MIA JW showed similar thing few years ago, DC on AC switches a no no... BTW ... A U D I O..... you're about 20db down.... very quiet