Learn from my mistake (load balancing)

[mikeywith]

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.  

[Steamtyme]

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

so that's more or less 9*S9s per phase or 28 S9s in total.
*snip*
" the burnt one" had already 10 gears on it , and I added 2 more S9E to it,

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?

[mikeywith]

Now I assume you thought you were adding to a line with 7 or less getting to a total of 9.

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.

Hopefully things remain stable for as long as your power deal stays in play.

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.

How long do you generally have to wait to get the repairs done on the panel?

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.

[taserz]

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.😁

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.

[Gabrics]

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...

[mikeywith]

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:

In = (Ir^2+Iy^2+IB^2-Ir*Iy-Iy*Ib-Ib*Ir)^0.5

Here In is neutral current, Ir is R phase line current, Iy is Y phase line current and Ib is B phase line current. Further ^2 stands for square and ^0.5 stands for square root. Neutral current is the vector sum of all three line currents.

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.

[danieleither]

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.

[mikeywith]

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.

[danieleither]

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.

[mikeywith]

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:

Clause 524.3 states that, for other multi-phase circuits, the neutral conductor may have a reduced crosssection if all the following conditions are met:
‹ the maximum expected current, including harmonics, if any, in the neutral conductor during normal service is not greater than the current carrying capacity of the reduced cross-sectional area of the neutral
‹ the neutral conductor is protected against overcurrent
‹ the size of the neutral is at least 16mm2 in copper or 25mm2 in aluminium.

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.

[NotFuzzyWarm]

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.

[arielbit]

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.

[thierry4wd]

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!

[mikeywith]

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 ...

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.

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!

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.

[thierry4wd]

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;)

[mikeywith]

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;)

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 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 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