Limit 400V three phase current - Page 1
Forum section: electronics / general

author: DefinitivVair0
author_rank: Contributor
timestamp: December 13, 2024, 12:55:13 pm
content: Hi there.Following situation:- generator has a 3phase 400V output fused to 16A- consumer (electric water heater) has 400V and is fused to 25A-> generator fuse blows the second that consumer is connected.So, my question is, is the current the problem?And if yes, how can I limit it to 16A?Thanks in advance

author: themadhippy
author_rank: Super Contributor
timestamp: December 13, 2024, 01:03:00 pm
content: Quotemight be, whats the water heater rating? could also be the initial inrush when the load gets connected.Less likely,but worth double checking is the 3 phases and neutral connections are correct and the incoming supply is definitely dead before the genny tries to connect.

author: DefinitivVair0
author_rank: Contributor
timestamp: December 13, 2024, 01:15:44 pm
content: Quote from: themadhippy on December 13, 2024, 01:03:00 pmThe connections are fine and since its almost never in use there is definetly no power on it when connecting. On line of the description on the heater says 8000W 400V. So I'm guessing its rated for 20A.

author: rogerggbr
author_rank: Contributor
timestamp: December 13, 2024, 01:27:49 pm
content: Quote from: DefinitivVair0 on December 13, 2024, 12:55:13 pmI doubt it can supply 16A for very long if that is the fuse rating. The fuse is usually there to protect the cables in the event of an overload. You need an electrician to look at this, and a bigger generator.If you had 2 x heaters you could hook them up in series to halve the load (assuming they are resisitive). This would then be called a bodge.

author: DefinitivVair0
author_rank: Contributor
timestamp: December 13, 2024, 01:48:51 pm
content: I doubt it can supply 16A for very long if that is the fuse rating. The fuse is usually there to protect the cables in the event of an overload. You need an electrician to look at this, and a bigger generator.If you had 2 x heaters you could hook them up in series to halve the load (assuming they are resisitive). This would then be called a bodge.So there is no way to just "limit" the consumption to 10 or 12A or whatever?

author: Siwastaja
author_rank: Super Contributor
timestamp: December 13, 2024, 01:56:27 pm
content: This doesn't add up. Heaters do not have inrush. 16A fuses can take 25A for minutes. The fuse should not blow in a second. What is the rated power (or current) of the heater? Maybe something else is blowing the generator fuse.Heater can be triac controlled, but probably finding a smaller heater is a better option. Also if the heater is connected in delta, it can be rewired in wye, but if it's already in wye then this option is out.

author: themadhippy
author_rank: Super Contributor
timestamp: December 13, 2024, 02:04:57 pm
content: Quotenope ,its 3 phase so its around 11.5 amps,on the genny fuse is there also a type letter or number?

author: Ice-Tea
author_rank: Super Contributor
timestamp: December 13, 2024, 02:07:54 pm
content: You haven't mentioned of the heater is 3 phase as well?

author: DefinitivVair0
author_rank: Contributor
timestamp: December 13, 2024, 02:18:31 pm
content: Hi there,first of, i messed something up in the description. The heater itself is NOT fused. It works fine when it is plugged into the normal power (32A) but blows the fuse of the generator. The heater itself also has not really a way to controll the incoming power but just a thermostat to regulate the temperature.I attatched the nameplate of the heater. I hope it helps (I can also look into the generators manual later)

author: Siwastaja
author_rank: Super Contributor
timestamp: December 13, 2024, 03:31:05 pm
content: At least I can't find any specs by Googling, but just sayin', could it be a 400V 1-phase heater? Those are pretty popular in some countries. Connected between two phases in a 400V/230V system, thus loading two phases out of three. Then this would be 8000W/400V = 20A. Still should not blow 16A fuses, though.

author: DefinitivVair0
author_rank: Contributor
timestamp: December 13, 2024, 03:33:43 pm
content: Quote from: Siwastaja on December 13, 2024, 03:31:05 pmI believe that it is 3-phase. I will open it up tomorrow and look, what we are working with.

author: DefinitivVair0
author_rank: Contributor
timestamp: December 14, 2024, 11:11:58 am
content: I checked and the heater defintetly seems to be 3-phase. (I attatched some photos so you can see for yourself)

author: Marco
author_rank: Super Contributor
timestamp: December 14, 2024, 02:32:35 pm
content: Put a clamp meter on the phases while it's running on mains to make sure it's running on three phases?

author: Siwastaja
author_rank: Super Contributor
timestamp: December 14, 2024, 03:00:44 pm
content: Well, if fuse blows quickly, it does not leave much other choice than a fault. Short circuit somewhere. That's what the fuses are for.

author: Gregg
author_rank: Super Contributor
timestamp: December 14, 2024, 10:08:26 pm
content: There may be a corroded spot on one or more of the heater elements that is causing current leakage to ground. If it were my heater I would megger the elements to ground.

author: Siwastaja
author_rank: Super Contributor
timestamp: December 15, 2024, 07:18:08 am
content: Heater elements are resistive wire within some sort of ceramic insulator material inside the metal tube. They wear from thermal cycling, the ceramic insulator gets damaged and the wire touches the metal tube (which must be protective earthed). And the fuse blows.One advantage of 3-phase wye wired heater is that you can run the three heaters separately, so if one is toast, you can disconnect it and keep operating.

author: DefinitivVair0
author_rank: Contributor
timestamp: December 15, 2024, 08:35:25 am
content: Quote from: Siwastaja on December 15, 2024, 07:18:08 amI dont believe that there is a short since it works fine on the 400V 32A normal power but blows the fuse on the 400V 16A generator. And since the heater seems to run on 20A that might be the problem in my opinion.

author: Siwastaja
author_rank: Super Contributor
timestamp: December 15, 2024, 09:37:24 am
content: It should not "run on 20A". 8000W/3/230V = 11.6A per phase.Some speculation:* Internal short which increases current beyond nominal* Heater is specified for wye but wired in delta, thus current is actually 400V/230V * 11.6 = 20A as you say, but this alone won't blow a 16A fuse in a second.* Generator outputs significantly more than 400/230 V, then current is also linearly more,Get a clamp-on meter and measure phase currents when running from mains - and again from generator.

author: DefinitivVair0
author_rank: Contributor
timestamp: December 15, 2024, 09:48:26 am
content: I will see what I can do. But I doubt that the wiring configuration is the problem since I did not change anything and I do not think that the manufacturer messed something up. Also, the heater only ran once or twice so there probably won't be any runtime related damage. I will try to check for obvious shorts and try to get my hands on a clamp-on meter.

author: rteodor
author_rank: Frequent Contributor
timestamp: December 15, 2024, 10:34:34 am
content: What is the generator power ? 16A fuse does not tell much about it (and it could be wrong). Type ? Specifications ? New ? Old ? Does it have voltage stabilization in it?

author: Roehrenonkel
author_rank: Frequent Contributor
timestamp: December 15, 2024, 10:49:50 am
content: Hi DefinitivVair0,Okay, we have all seen the heater, but what about a picture of the "generator"?What kind of generator? Water-/Solar-/Diesel-driven??Maybe you can connect the heater and then ramp up the generator slowlyso the inrush-current is dampend....Good luck

author: Siwastaja
author_rank: Super Contributor
timestamp: December 15, 2024, 11:06:28 am
content: Quote from: Roehrenonkel on December 15, 2024, 10:49:50 amResistive heaters do not have any significant inrush current. Furthermore, if generator slows down due to sudden load step, that would decrease its output voltage, and linear resistive loads wouldreducein current, not increase. Even if generator stalled, that would not blow the load fuses.Either fuses are faulty (probably not), or there actually is at least 25-30A or so, probably even more, current flowing (depending on the exact fuse type, and what "a second" exactly means). From Ohm's law, this can only result in from smaller than expected resistance (including extreme case of short circuit), or higher than expected output voltage of the generator. There are no other magical explanations.

author: Roehrenonkel
author_rank: Frequent Contributor
timestamp: December 15, 2024, 12:03:51 pm
content: Hi Siwastaja,well, guess you're right here. Probably i should have written "steep current-rise".Hence my question on the generator-type.What fuses are used? B16 Amps? Change them to "D"-type.Ciao4now

author: Siwastaja
author_rank: Super Contributor
timestamp: December 15, 2024, 12:08:33 pm
content: B type MCB is fine for heaters, even type A is. As said, heaters do not have inrush. Investigate why fuses blow. They have an important job, they prevent fire from faulty or miswired equipment. Instead of changing fuse type, you must investigate why the system is faulty and fix it.Fuses do not detect high current rise speed, they actually do the opposite, ignore fast changes, even the fastest types do that. Depending on fuse, it blows in a second somewhere between 1.5x - 3x its rated current. This means absolute value. "Quick rise" of current does not matter as long as it does not significantly exceed the fuse rating.C and D type MCBs are used with specific load types which have a lot of inrush current, e.g. large induction motors which take time to spin up to nominal speed and work with very poor efficiency (thus higher than rated current) during that spin-up. Or large power supplies with large capacitor banks.

author: DefinitivVair0
author_rank: Contributor
timestamp: December 15, 2024, 01:19:29 pm
content: Quote from: Roehrenonkel on December 15, 2024, 10:49:50 amThe generator is a HBM model 9063 7900W Diesel generator. I cant find the manual right now but the website says 400V 16A and 7900W wich is less than the heater "needs"...Btw, I can't really say anything about the fuses or the type. Its just 4 switches. 3 connected ones for 400V 3-phase and 1 single one for 130V. (And there is also a normal ceramic 10A fuse for 12V.)

author: themadhippy
author_rank: Super Contributor
timestamp: December 15, 2024, 01:39:19 pm
content: Quotelooks like your genny is 100w short of a full load

author: Siwastaja
author_rank: Super Contributor
timestamp: December 15, 2024, 01:47:28 pm
content: Oh, so information about "fuses blowing" was bogus; that changes everything. So it seems there is no fuse and probably not even an MCB, but some other kind of switch. It is well possible that this generator switch triggers at much less overcurrent than a fuse does.Water heater resistor kits are not expensive, instead of trying to limit the power of existing set it might be simpler to replace with a lower-wattage set, if you find one dimensionally suitable for the tank.

author: DefinitivVair0
author_rank: Contributor
timestamp: December 15, 2024, 01:52:06 pm
content: Quote from: Siwastaja on December 15, 2024, 01:47:28 pmOk. Thanks for the answer.But would there be a theoretically suitable way to limit the current flow to something under 16 or would that just not be possible? Just to finally put an end to this thread 😅

author: Siwastaja
author_rank: Super Contributor
timestamp: December 15, 2024, 02:29:31 pm
content: It depends what exactly is the problem - if it's "overload" of some sort, then how that overload switch works. For example, triac dimming could work, but no one can guarantee you that, maybe the switch would still trigger. You could also wire the resistors in series, but if you wire them in series then you are down to single-phase solution and lose probablytoo muchof the power.A beefy enough 3-phase triac dimmer is probably the simplest option you can try, but it is probably more expensive than a lower power resistor kit, and there is no guarantee of success.

author: langwadt
author_rank: Super Contributor
timestamp: December 15, 2024, 02:46:22 pm
content: Quote from: Siwastaja on December 15, 2024, 02:29:31 pmif the heaters are wired in delta it might be possible to wire them in wye instead

author: DefinitivVair0
author_rank: Contributor
timestamp: December 15, 2024, 02:48:09 pm
content: I attatched some images on an earlier reply. Maby you can tell what it is because I sure can't.

author: themadhippy
author_rank: Super Contributor
timestamp: December 15, 2024, 02:50:12 pm
content: Is this the badger?https://toolsidee.co.uk/product/hbm-7900-watt-standby-silent-diesel-power-generator-aggregate-P4461.htmlIf its is seems i was a bit out on being 100w short,from the specsQuoteso at least 1kva short,no wonder its getting upset.

author: DefinitivVair0
author_rank: Contributor
timestamp: December 15, 2024, 05:35:15 pm
content: Yea thats the one.

author: Gregg
author_rank: Super Contributor
timestamp: December 15, 2024, 06:37:10 pm
content: Your cheapest solution would be to buy another generator rated for at least 10% over the actual loadas measuredat the heater running on mains power.The rating of the generator you have are probably quite optimistic at best.

author: Siwastaja
author_rank: Super Contributor
timestamp: December 15, 2024, 07:39:30 pm
content: Quote from: Gregg on December 15, 2024, 06:37:10 pmLower power water heater is less than half of the price of the generator, even if you buy the whole thing new. Of course, question is how much heating power is truly needed. If it's totally tankless heater and OP wants to take hot showers with high flow rate, then they could be disappointed if they go much below 8kW.

author: DefinitivVair0
author_rank: Contributor
timestamp: December 15, 2024, 07:48:37 pm
content: The 8kW heater was picked because it was the rated power of the heat pump (idk if its the right word in english). But it is basically only used to prevent the underfloor heating from freezing in case of a power outage or heat pump failure. So less wattage would also work.So basically I will buy another heater or maby disconnect one of the three heating filaments. But thanks for the very helpful replies from everyone

author: Gregg
author_rank: Super Contributor
timestamp: December 15, 2024, 08:26:52 pm
content: Quote from: DefinitivVair0 on December 15, 2024, 07:48:37 pmDoes the same generator also run a circulation pump? If so what are its power requirements? The reason I ask is that it would be fairly simple to use the generator's 230V 3 phase settings for the heating elements for much reduced power requirements, but it may not work well with the pump.(edit:) Disconnecting one of the heating elements will lead to major phase imbalance in the generator.

author: DefinitivVair0
author_rank: Contributor
timestamp: December 15, 2024, 08:45:31 pm
content: The generator itself does not run a circulation pump. Also, I believe the 230V is single phase. But wouldn't it theoretically be possible to use a 3-phase transformer to step down the 400V to something like 200V but now with higher amperage? (Should result in about 31A)But on the other hand, a lower power heater is probably cheaper and easier to work with than a giant 3-phase transformer

author: themadhippy
author_rank: Super Contributor
timestamp: December 15, 2024, 09:09:23 pm
content: Quotewont do any good as youve still only got 7kva available from the generator ,

author: Gregg
author_rank: Super Contributor
timestamp: December 15, 2024, 09:14:17 pm
content: I just assumed from the limited specs of the link provided that the generator might be 400/230V 3ph switchable. It depends on how the thing is wound; you would know better than me as you can look at it.If the heating elements have separate connections, you could connect two of the elements in parallel and power them with the 230V single phase. A real nightmare to change over from mains 3ph when needed.Isn't the water you are heating treated and have anti-freeze for use in an area where freezing is expected?

author: DefinitivVair0
author_rank: Contributor
timestamp: December 15, 2024, 09:25:21 pm
content: The generator can be switched between 400V and 230V. I cant look at the manual right now but since there are three seperate "fuses" for 400V but only one for 230V, my guess is that 230V runs on a single phase. Also since its more or less for personal and not commercial use, most 230V devices that you plug in won't handle 3-phase. (For 230V its just a standart wall outlet socket)Also, to be totally honest here, I am not the one who built the whole heating construction. I am just the one writing the post. Weather its for the underfloor heating or for normal water supply or whatever. Its a heater for keepingsome kind ofwater from freezing. And this will be accomplished with a lower power heater.Btw., will a lower voltage like 230V even work or will the resistance of the heater filaments just be to high?

author: Siwastaja
author_rank: Super Contributor
timestamp: December 16, 2024, 07:54:25 am
content: Quote from: DefinitivVair0 on December 15, 2024, 09:25:21 pmWhen looking at the generator specs, I was already wondering what that even means. 3-phase it outputsisboth 400V and 230V at the same time. 400V between phases, 230V between phase and neutral. So maybe it's just marketing speak and there is no switching of anything?If there really is something to switch "between 400 and 230", it can only mean two things:Going from 400/230 to 690/400, or to 230/132V. Latter would be extremely useful for your need. But see the manual if it explains what this voltage switching means. But I would put my money on their "voltage switching" claims being bogus.One viable option, if you don't want to buy a new smaller heater, is to rewire two of the resistors in series and run it using a single phase:8000W / 3 / 230V = 11.59A230V/11.59A = 19.84 ohm (expected resistance of a single element, you can verify this with multimeter)Two in series, current = 230V / (2*19.84ohm) = 5.80A, power = 5.80A*230V = 1334WI'm quite sure keeping the circulation pump running and heating at 1300W is sufficient to prevent freezing. Unless you have some record-low -25degC sustained over a week or something.And then again, if you do this, a smaller single phase generator would be well sufficient. Something rated to 2000W continuous.

author: DefinitivVair0
author_rank: Contributor
timestamp: December 16, 2024, 08:07:05 am
content: Thanks for the answer,I will definetly take a look at the manual.Also, J have a feeling that my memory is wrong and it was in fact 230V 3-phase judging from the outlet. But I can't check on it until thursday so I'll keep this post updated once I checked it.

author: Siwastaja
author_rank: Super Contributor
timestamp: December 16, 2024, 08:29:05 am
content: Quote from: DefinitivVair0 on December 16, 2024, 08:07:05 amTerminology with 3-phase is confusing. 3-phase, with neutral available, always has two voltages 1.73x apart from each other. When someone says 400V 3-phase and someone else says 230V 3-phase, they probably mean the exact same thing!There are exceptions, e.g. IIRC in Norway neutral-less (3-wire, phases only) 3-phase 230V is available. So this is lower voltage, but absence of neutral prevents getting 132V out of it. Maybe the switching options refers to this kind of relatively rare "delta-only" system. If the generator can be switched to do that,andstill provide neutral, that would make it a special/rare 230V/132V system, which would be perfect for your needs.But Germany is 400V between phases and 230V between phase and neutral.

author: Wolfram
author_rank: Frequent Contributor
timestamp: December 18, 2024, 01:17:35 pm
content: If the generator is 400 V star with a neutral, and the heater is star-wired using 230 V elements, then you have another option as well. Just wiring up one of the elements between L and N will reduce the overall power to 1/3, but still draw the same current from the phase in use, potentially leading to problems. Disconnecting one of the phases between the generator and heater will reduce the power to 1/2, and draw current between two phases. Those two phases will then be loaded to sqrt(3)/2 times the current in the 3 phase case, which might be enough to save you here.