Topic: Learn from my mistake (load balancing) (Read 2197 times)

In my aforementioned course I learned that it's very common for wires to be mixed up, even by professionals, usually because they run out of one color so use another. They do this between phase and neutral, because in most cases it doesn't matter, but when it matters, accidents happen.

Very true

It is wrong to use a different colour code which is not the standard for wiring installation which was the first mistake made.
The load was not balanced on all the phases as one phase was overloaded because of this mistake made.
Sorry about your loss man.. I believe you would have learnt from your mistake and be cautious next time.

You were lucky this breaker didn't cause a fire !

I also learned something about these bizarre cables, and I'm French. Next time I see an uncle of mine who has a company making large machines using big electric motors I will ask him about it. I know that when one motor is running, the wifi goes down !

Also I had heard about balancing the loads on "triphasé" but I hadn't realized the implications, very interesting. At work I get a 1-day course on electric dangers every two years, I mostly take of out it : don't touch that shit !

Yup, I have smaller amp rated MCBs which should trip before the cable gets too warm since that main breaker is larger than what the cable can handle.


I do have one, actually, if you clamp the N wire alone you get a clear idea of how balanced/unbalanced the load is, a perfectly balanced setup will result in 0 amps reading on the neutral wire, the higher the current the more unbalanced your phases are, and just for fun below is the formula for "Neutral Curren In Unbalanced Load":

N current = (Phase1 ^ 2 + Phase2 + Phase3 ^2 - Phase1* Phase2 - phase 2* phase 3 - phase1* phase 3 ) ^ 0.5

Assuming phase 1 = 10amps, phase 2 = 20amps and phase 3 = 30 amps we get:

N = (10^2+20^2+30^2-10*20-20*30-10*30)^0.5  = 17.3A

I understand better now actually, you should invest in a circuit breaker suitable for your output cables, because in this configuration you only have to protect absolute short circuits: s which is not really good for safety. Or add a DIN type circuit breaker, much less expensive and just as efficient, preferably of curve C;)

I usually touch cables from time to time to watch that it does not heat up precisely ... you should also invest (if it is not already the case) in a current clamp, it is not worth much thing, and you can very easily check your load balance, check cable by cable, and normally, if you take the 3 phases with the clamp, it will only indicate the unbalance value, ideally if good balance, close to ZERO;)

I believe the standards we have here are french, so that makes sense, but if you are not using a neutral how are you getting 220v? suing 3P will give you 380V which isn't suitable for mining operations.


The root cause was that load imbalance, the breaker is larger than what the cables can handle ( a terrible set-up) so the only safety measurement I have is by perfectly balancing the load on each phase so that all 3 phases stay within their limits and the N phase stays as close to 0 amps as possible (impossible to get it down to 0 unless 100% of the load comes from 3P (380v) machines.

Anyway, the problem was solved, and I hope to never face it again.

Hi, I confirm, in France, we also have this kind of cable, because in industrial installations, 99% of the equipment is simply 3p + T, so have never used the neutral, except for some application like computer and lights, for example, on my site we use about 250KW per hour, but only 20kw max in 220v ...

Regarding the circuit breaker which burned, I wouldn't say a load imbalance, (although it could be present), but I would rather say a badly tightened terminal block! normally, this kind of circuit breaker is equipped with 3 independent thermal, therefore, say a 3p 20A for example, if only one phase exceeds 20A then it falls ... the quality of the contacts is essential!

You accidentaly added 2x s9e and it burned the breaker ?

That breaker is already hot/warm from your load. And it finally get cooked after little push.

80amp breaker at 60amp load is warm some breaker are already warm at 40-50amp loads.

A bigger amp rating of 100amp can solve that problem, but the danger is overloading the wires since you get confused by your endpoints/outlets. I used this as a solution so i can max out my mining, here is the catch, the way i setup my outlets is that they rather burn at the endpoints when overloaded than burning the mains and taking everything down, will only affect around 2 rigs.

Got yer PM as I was signing in to add my input on that...
1st a question: I take it that metal foil shield I see in the pic is the ground? If it is that ties in with what you posted about US NEC & IEC neutral size as well. For both ground and neutral it *is* permitted to use a smaller wire size as long as:

a) it can safely carry enough fault current to rapidly trip a breaker or open fuses feeding the equipment
  and
b) You are sure the neutral will not be overloaded from unbalanced or high-harmonic content loads.

That said, I too have never seen that style cable and I've been designing/building high power industrial electronics of 1 sort or another for global usage since the mid 1970's. I've only applied the smaller (ground) wire setup to wiring ran in conduit or wiring trays where ya pick and choose what each wire is based on its purpose. I would NEVER skimp on the neutral size... For power cordage/cabling I've only seen and used all the same size.

edit: Just looked at the link on that cable and it is for buried underground power distribution usage. What I took for 'foil' is a lead sheath with steel armor layer as well to resist penetration. That is an entirely different beast vs normal power cable... Nice paper on it from the same company you linked to (Nexans)

As a general rule, in the US a 5-wire system (3 lines, 1 neutral, 1 ground) is only ran when equipment is going to use the neutral as a lower voltage source for auxiliary equipment like contactors, panel lights, fans, etc. and even then is only really common on equipment that runs off of 440-480VAC. My preference is to not use a neutral but rather have a controls transformer fed from across 2 phases to step-down to desired aux voltages (normally 220V and 110V)

In the US 208-240V 3-phase equipment or 3-phase runs from transformer to a 208-240V (no 110V) distribution panel normally gets 4-wire cords or wiring - 3 lines and a ground because pretty much all aux equipment is readily sourced to directly run on it so no need for a neutral.

The product above is sold in France so my guess is that the French use it, I know Italy make such cables too (Not sure if they do use it), anyway reading further about this matter in this topic, and if I understood it correctly it does say that NEC code (used in the U.S) allow for smaller N conductuer in certain cases, also in this article which uses the IEC code (Used in Europe) states the following:


These standards aren't so easy to understand, but my take on it is that in some SPECIAL cases (when you are 100% the load across all 3 phases will always be equal or pretty close to equal), using a smaller neutral conductor is fine, perhabs that's why these companies make these "3.5 cores" or else - nobody would use them, but having said that, it's always better SAFE than sorry, so just go for 4 cores of the same size that can handle 125% of the load.

NotFuzzyWarm understands these stuff much better than most people here, so perhabs he could chime in with some information.

Fascinating - I've never seen that cable before! I've just checked on my regular cable supplier sites in UK and can't find anything like that. I guess it must be a standards thing and not used here in UK or perhaps Europe.

It isn't really "labelled and sold" as such 4X16mm², but rather 3x16mm² + 1*8mm², maybe I haven't made that clear enough, here is an example:



So these cables could be "3x95 + 1x50" or 3x120 + 1x70, not sure about the U.K but i am sure this is international, if i am not mistaken, some people refer to it as 3.5 core cable instead of 4 cores, I mean who wouldn't want to save a ton of money when buying cables of extended length? espcially if it goes to a warehouse / garage that mostly uses 3-phase machines where current in N is always near 0?

With that being said, since you can't guarantee this in a standrad single phase operaiton like mining, it would be pretty risky to do so, it's safe to have N size just the same as the phase wire size.

What country are you in? Here in the UK, if you buy a 4x16mm² cable, it will have 4 x 16mm² cores - no question about it 100%.

It seems bizarre that any cable anywhere would be labelled or sold as having 16mm² cores but in reality they are 12mm and 8mm respectively.

Yes 3 phases and one neutral, most 4 wire cables (1 large cable with 4 wires inside) has a neutral wire with just about half the cross section of the other wires used for L, simply put, in a perfectly balanced load system the current in N will be 0 amps, I suppose the techincal term is (3 phase star connection), you could use this equation to find out the N current:


source: https://www.quora.com/How-do-I-calculate-the-neutral-current-of-a-three-phase-transformer-under-unbalanced-load-conditions-and-under-balanced-load-conditions

So as long as you got all 3 phases drawing the same amp the current in N will be 0, and here is an example of all R,Y,B drawing 10 amps each

(10^2+10^2+10^2-10*10-10*10-10*10)^0.5 = 0 amps in N

Now let's assume R = 20a, Y = 40a and B = 60.

(20^2+40^2+60^2-20*40-40*60-60*20)^0.5 = 34.6A

Now assuming your total load is 120A so 40A on each phase, you go ahead and do your cable size and say you get 16mm2 can handle 64 amps, so you buy 16mm2*4 cable where in reality that cable will have 3*12mm2 + 1*8mm2 for N.

8mm2 is only good for half those 64 amps so that's 32 amps, despite the fact that on all phases you stay below 64 amps, just by having such an unbalanced load, the N will have to pass 34.6A where it could only handle 32A, and this causes the  netural to be set on fire and if by any chance it touches one of the phases, fireworks will start.

A safe approch we use here would be not buying those cables with 4 wires, but instead buy 4 seperate wires of the same size, and they assume that in the worst case your numbers will be:

(0^2+0^2+60^2-0*0-0*60-60*0)^0.5 (0 Amps on 2 phases and max amps on a single phase) will result in 60 amps on the N wire, so even the worst unbalance will survive, but such wiring cost alot more than going with the regular 1*4 cables, and since people "suppose" they have contorl over the load, it makes sense to go with the cheaper option and balance the load across all phases so that my N wire has close to 0 amps run through it.

What the size of the neutral? As you are pulling 220V from three phases to one neutral I would worry about the size of that cable...

I like to thank some of the hidden goodies and quirks you find in NYC buildings to the fast New York built up sooo fast.

This is exactly what happened, the mistake was made due to wrong internal wiring colors, I hope this point is clear, if not I can explain more, probably with pictures.


So far so good, I checked the wires, they are not hot, just a bit warm, but normal , amperage is almost the same on all 3 different phases, voltage is regulated by the voltage regulators, everything seems to be working perfectly so far.



It depends on your attitude and relationship with the guys in charge, if you are an asshole, they might keep you waiting for days, maybe even weeks, they can simply say " We sent your information to the technician, he will contact you soon" and  "soon" might be weeks, in my case , if it's day time , especially in the morning, they will come in 30 mins or so if they are not doing something else very important, I treat them very nicely ( I am a nice person anyway   ) but really I try to keep these guys happy, I get them food, cold drinks and make sure they leave the place with a big a smile on their face so that next time I call , they will come to solve my issue right away.

After this problem happened, I realized how important relationship with these guys is, I now have the guy personal phone number, he said I could call him directly if the company took more than an hour or two to send him or someone else , so long story short, be nice to those guys if you want VIP service.

Just came across this. Man glad that's the worst thing that came of this. I know it shouldn't happen again but might want to start thinking of playing with a wider safety margin, especially after I read these 2 statements lol
Now I assume you thought you were adding to a line with 7 or less getting to a total of 9. Hopefully things remain stable for as long as your power deal stays in play. How long do you generally have to wait to get the repairs done on the panel?

A couple of S9s would have fit on that 10 guage cable, with free power you could have roied the mining gears as well as pay rent or some of it, unfortunately it is unlikely that you are ever going to have such a free power source anymore.

Myself on the other hand still have access to good amount of free power, i make sure I fully utilize it before a new government comes in and decide to charge a lot for power, i don't see that happening anytime soon but I am always prepared for such a thing to happen , and that is one of the reasons why I always buy gears that have a maximum of 6 months Roi in the worst case, tho the average is 3-5 months and thankfully I have already roied more than 80% of all gears I ever bought, except for some unfortunate D3 that I had to throw away at about 70% roi.  

Well that was the mystery since it did not attach to any meter in the apartment building.

And it did not attach to the main transformer on the street.

NYC is pretty old not crazy old links Europe cities or some Chinese cities.

So it does have some hidden spots. We were a mile from a large con-Ed power plant maybe the wire tapped into an underground cable. I  will never know but I do wonder about it every once in a while since it was a pretty cool mystery and in my favor.😁

Did you manage to know where the hell did that 10gauge wire come from?? that is a bit strange, it goes to show how fucked up the set-up is , but that was almost 30 ago, I am sure things are not as bad today , are they?

I can tell you strange stories about my country too, sadly nobody would believe it , I see it with my own eyes and I can hardly believe it.

Not too long ago, maybe around 2000-2002 we went to spend the summer in my hometown, there was an issue with the power meter , it was not reading , so dad calls in and they sent someone to fix it, after he was done, the meter was spinning backwards, the number of kwh was decreasing and not increasing, my dad only noticed that a while later, he called again and said there is still an issue but he didn't tell them what happened exactly, he was afraid that technician would be fired or something, so they sent the same guy again, and he was like , oh i must have missed up the wiring, and he came without any tools, he told my dad , listen just leave it be I will come tomorrow to fix it , he came 2 weeks later , not only we enjoyed free power for 2 weeks, we got to unload a good chunk of the bill   , despite power being too cheap to the extent that people don't bother about turning off their ACs before going out, it was really funny to watch the meter go the opposite direction for 2 weeks.

I could tell you stories  about NYC  apartment living  when I was first married  but I will tell just two.

I was in Astoria, Queens  Just across the river from the UN building.  This leads to having a lot of diversity it is the most diverse zip code in the USA.

It was 1987  or 1988 long before BTC  personal pc's were still rare.  It was a hot night in August  and boom a blackout.  All of Queens Bronx and ½ of Manhatten shut down.  So  my wife and I said we just filled the refrigerator we will lose all our food. Since our stove was gas feed and worked I told my wife we can cook all the food. I open the refrigerator and it had power!!!   I said WTF  looked out my window and no light for miles.
 I went out side not a single light of any kind.  So I told my wife I have no idea what they did but we are good. I check it out when power came up.  I turned off all breakers in my small sub-panel and refrigerator worked! My meter for the bill read zero.
  So I knew I had a line that tapped into some source of power.  I opened the small receptacle and it was  10gauge not 12 or 14.  So I know I could pull more juice then the fridge.  I ran 1 air conditioner for free  from 1987/1988 to 1992 along with the fridge.  Good thing there was not any mining  it would have been tempting to max that line out.

Second story my friend did New York state taxes for the New York state government  he went on an audit of a fairly famous metal work artist.  Was looking at the  workshop and saw a door  asked the guy where does it go?  guy opens the door  walks in a 50 foot long tunnel  and goes into a 3000 square foot store room with 12 foot ceilings.   The metal work guy had access to an old hidden store room used to hid booze during the 1925-1936 prohibition of booze in the USA.

the room was not even in his building it was across the street!  lots of lights and power etc.  certainly not up to code.

Not sure I quite understand the question, but here is the set up , I have 4 wires coming in , 1N and 3L , when you measure the voltage between two phases you get 380v, between any phase and neutral you get 220v, so I pull 220v from phase to neutral,i hope this answers your question !!



Thanks , I will ask them to do it, I am afraid to do it myself and then later on if any problem appears, they will blame me for putting the rubber grommets  


This makes perfect sense, I think this is exactly what happened.



lol , no that is not exposed copper, those guys don't do these things in  perfect manners, but not to that extent   , the copper-like color that appears in the image is like sponge pieces stuck on them,not sure how they got there.


I understand, and I can relate, my dad saw this shit and he said he wouldn't put a 5$ machine behind this set-up , but I really have no other option, and since I don't pay for power, I don't expect them to provide me top notch setup, as long as it works and it's not too bad, I am satisfied,

Oh, you mentioned neutral currents from an unbalanced load and taking another look at the 1st pic I see that only 1 wire is burnt telling me you are not pulling power from across the phases (2 wires would be burnt)  but instead pull from phase to neutral right? The pic also clearly shows that the breaker burnt from bottom-up meaning the burning wire under it was cause.

Do keep in mind that when the electric company said the wiring was only good for 60-65A they meant it. With any wiring when pulling max current continuously the wire WILL become rather warm. In fact alarmingly so to the touch. If the insulation is not rated for high temperatures to allow for that then danger is brewing. Since the breaker is 80A it is more than happy to provide it (and more) through that one pole as the wire cooks...

Now about the 2nd pic after repairs....
PLEASE PLEASE PLEASE AT LEAST put rubber grommets around the bare metal holes in the electrical box!!! You are just asking for more trouble there! Did the wire burn just from the box to breaker? If so it is because the insulation softened and sitting against a bare metal edge it then flowed out of the way... And please tell me that I do not see exposed copper on one of the heavy gauge lines on the far right feeding the box..

Sorry, having designed/built/repaired all manner of power systems and power electronics  from milli-watt to megawatt since the mid 1970's things like that make me cringe.

Holy crap.

That could have ended very bad indeed.

Ok, to clear the issue: Most circuit breakers found in older homes and businesses are mainly thermally operated devices that rely on heating of a bimetallic thermal link to trip the breaker, the magnetic component of them is reserved for tripping under direct short circuits. Depending on their class they can pass varying percentages of over current - total and per-pole - for different amounts of time before tripping. A wire getting getting hot/burning due to wrong size WILL NOT trip the breaker as long as the current remains below the breakers trip point. Again, that is the whole point of codes requiring that ampacity of the wiring be matched to breaker size so even under worst-case conditions the breaker will trip before the wiring fails.

Typical class-C or class-D breakers will hold 100% load indefinitely, 125-150% load for several minutes and >200% load for several seconds to 10's of seconds but those ratings assume even loading across all poles. Unbalance the loads and the trip points get a bit higher with the pole running higher load being able to pass higher current w/o causing a trip because the lighter loaded poles are not helping to force a trip. Yes eventually an overloaded phase will force a trip, just at a higher than expected value. In any case that undersized wire will have ample time to cook before the breaker trips.

That said, these days in the US, Canada and many other countries most codes will require using AFCI breakers in at least some locations of a home. Reason is the previously mentioned issue of connections loosening. An AFCI not only looks for over current but also contains electronics that look for low-level, high-frequency signatures that any sort of arc produces. If a connection gets loose and there is even the tiniest bit of sparking, the AFCI trips, if a wire burns and starts to short out, AFCI trips before a standard breaker will trip.  ref https://en.wikipedia.org/wiki/Arc-fault_circuit_interrupter Wikipedia also has a nice graphic showing trip time vs current vs class https://en.m.wikipedia.org/wiki/File:Standard_Trip_Characteristic_of_a_Thermomagnetic_Circuit_Breaker.svg

Can't disagree, however these kind of discussions are supposedly good for everyone, it's a good way to learn , but first you must admit that you don't know everything and there is always something to learn from everyone, that is why I without a shame admitted that I am not any where near expert in the electric field, in fact not even close to average  


I didn't think that was possible in a state like New York , but now that you mentioned it,and since I do trust you I am feeling kind of relieved that these things happen else where and not only in the shit-hole I live in  

@ mikeywith and jbillk you are both right. leave it at that.

The english language  plus internet can lead to this apparently contradictory statement I just made..

I see and read both points  and both are correct.

As for 50 amp or 80 amp breaker vs correct wires.

code = 50 amp

but it is China

I grew up in New York City and in a lot of places or sections of NYC  work is done against code.

This is so wrong, unbalanced load leads to the same result, you can read about the distavtanges of having an unbalanced  3 phase system, one of those is the increase of the returned current on the neutral wire, which can eventually lead to a lot of troubles, you are stating the obvious , in fact the breaker should have tripped even if the wire size wasn't able to handle that much current flow.

This of course does not mean you are wrong by saying  "The cables have to be rated for the installed breaker." , but in a case like mine where i can't change the wire size neither the breaker, load balancing is the only thing I can do to fully utilize the power I have.

This has nothing to do with load balancing. The issue was improper sized cables. The cables have to be rated for the installed breaker.

Doesn't matter if it was not balanced or not.  If it was too un-balanced, the breaker would have safely tripped, and no damage. You can safely run unbalanced loads as long as done to code and properly engineered.

yeah they can loosen up. Also a bit of grease helps the contact not oxidize. We just did some maintenance on a 250kwatt inverter we greased it tightened it. Went to roof worked on panels two hours later tightened the contacts.

Honestly I always touch all the wires to check if they get hot or not, and usually they are just a bit warm during noon time, there are many factors that could cause these wires to heat and melt, the technician who came to change the breaker suspects that the wire was a bit loose , he said these wires need to be tightened every now and then because they get loose over time , not sure how accurate this piece of information is, but I took it into consideration and i will add that task to my to-do-list whenever I go there to dust off the gears.

Yeah, but over time the overloaded wire can degrade and fail slowly, so the resistance at a failure point can keep increasing. With the same current draw and increasing resistance, the wire gets hotter and hotter. Eventually it can essentially turn into a heating element, and that could have cooked your breaker.

@wndsnb

Yup, wire size must be larger than what the breaker can handle, but honestly I think the breaker was bad, i don't understand how these breaker function, but common sense states that if the wire got way to hot to the extent that it melted, the breaker should have sensed that and did the exact thing it was made for "kill the power" but the response took way too long till the breaker went on fire.

I think the lesson to be learned here is just make sure the correct size breaker is installed. The same meltdown could have occurred if a power supply failed in the right way. The cost of a 50A breaker isn't much compared to the damage that could have occurred.

I don't live in the U.S , life here is a lot  less complicated  

The electric company will follow the rules and codes all the way to the 11kv level, they don't play around with those, but once the wiring gets to 380v they usually work with what they have, so instead of installing a 50amp breaker they went ahead and used whatever was available which is the 80amp ( i paid for it by the way)

Phil , yes I do have voltage regulators at this location, so balancing the load was pretty accurately done.

I will mention I was up in Clifton today.

We have three phase and we are having a low voltage issue.

I know you mention you have some low voltage protection gear in some of your installs.
I am not sure if this install is using any low voltage protection.
But if you balanced wrong and volts drop to say 190 or 185 many psu’s will attempt to continue to run.

So try and check if that spot has good voltage levels.

A 210 volt setup will do 12600 watts and take 60 amps

A 200 volt setup will do 12600 watts and take 63 amps

A 190 volt setup will do 12600 watts and take 66.3 amps

I am glad it was just a melted breaker.

.... Given that you said WHY on earth would they even do the install??? NEC and no doubt local electric codes specifically forbids it for this very reason...

This is important for those who  have 3 phase wiring, but it's also important for "internal" load balancing to those who have a single phase set-up.

So yesterday I added 2 S9E (will make a review on those tomorrow there it is )to this small mining farm , went home and everything was working just fine , woke up and found "low-hashrate" notification from the pool, checked the gears and they were all offline.

I went there early in the morning and found this  



so how did this happen? where did I go wrong??

So the electric company installed this 80amp breaker and said the wire size will only handle 60-65amp on each phase, so that's more or less 9*S9s per phase or 28 S9s in total.

My mistake was that I "by mistake" missed up with the wiring colors because I ran out of wires when I was installing this location, I ended up plugging more miners on one of the phases  ," the burnt one" had already 10 gears on it , and I added 2 more S9E to it, and boom!! burned the shit of that Schneider breaker (the wire did handle that for couple hours , gotta give it that) and technically it should have tripped, but that shit didn't happen.

Anyhow, I called the electric company, and had them change it,  i could have done it myself but I don't have access to the main breaker so it would have been super risky to do so.



And I of course learned from my mistake, spent the whole day balancing those phases and so far everything seems to work just fine.

Now by all means, you should always hire an expert to do these kind of stuff, but there are cases where you have to do the wiring yourself, hope this bit of information will be of any use.