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Forum Index : Solar : Inline mc4 fuse
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renewableMark Guru  Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
Hey guys, just wondering if these are a good idea to fit at the panels for a little added safety. here My new setup will be 3 panels in series, then multiple strings going to the charge controler/s. So was thinking one fuse for each string up on the roof at the panel connection. Yes every connection has some losses so not great in that regard, but I really like fuses. Someone had a look at my 4wd dual battery set up once and he said, "jeezus you really like fuses don't you?" "I'll have some losses but never a fire" was my reply. Cheers Caveman Mark Off grid eastern Melb |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Only reason to fit a fuse to anything is to limit the maximum possible fault current. A fuse is basically there to protect wiring, and to prevent fires. Now a solar panel is a current source, and if the output is shorted, the panel itself limits the maximum current that can flow. In fact there will be on the rating plate, a short circuit figure for maximum current that should be well within the capability of the wiring. So really fitting a fuse to a solar panel is a complete waste of time. Circuit breakers are a good idea though, for isolation. But if your solar panel rated short circuit current is only nine amps, a ten amp circuit breaker can never trip. Cheers, Tony. |
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| Boppa Guru Joined: 08/11/2016 Location: AustraliaPosts: 814 |
I agree, a fuse is a waste of time on panels, but definitely need a breaker/switching mechanism of some kind. Even at 12v/40A I had issues if I had to disconnect for any reason during the day, a quite large arc could be drawn on the anderson plug while unplugging it, as for the higher voltage strings used on a house system, should you need to do any maintenance, you would definitely need to have some way of disconnecting it |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
Wouldn't a fuse pop if lightning hit? Cheers Caveman Mark Off grid eastern Melb |
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| greybeard Senior Member  Joined: 04/01/2010 Location: AustraliaPosts: 161 |
Only if the current path was through the fuse |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
If a lightning strike is sufficient to blow a fuse, it will very likely just arc straight across the fuse terminals. There is really no practical advantage in fusing a solar panel. A big fuse right at the battery, is a very worthwhile thing, and highly recommended. Also fuses can offer "some" protection for your inverter. But the solar panels are a unique situation. Cheers, Tony. |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
Thanks guys, I'm just trying to set it up as foolproof and safe as practical and not have to redo things down the track. Cheers Caveman Mark Off grid eastern Melb |
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Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
A fuse is absolutely no protection against lightning, if you had a 10A fuse and a 5,000V strike it could supply 50,000W of energy and not blow. DC Breakers are available on Aliexpress at a reasonable price, I have found Arlen & Alice to be quite good. DC Breakers should not be switched off under load, every time you do it it is damaging the contacts. Many charge controllers and GTI's can be switched off before turning off the breaker if you need to work on something. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| George65 Guru Joined: 18/09/2017 Location: AustraliaPosts: 308 |
I have put double pole AC breakers on both cables of the DC side so they switch together. Seems to work well and I never hear any arcing when I switch them under full load. Fusing panels is ultimately a waste of time because you can short the leads from an array and the current will plunge to a few amps which is insufficient to damage or over heat any wire of a suitable rating for the install anyway. |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
George you should look at this video. you are at serious risk of having a fire. AC breakers are designed for AC, not DC, that is why DC breakers exist and cost more. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
WTF is this guy on about? look at this here Cheers Caveman Mark Off grid eastern Melb |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
this is interesting. So if I were to use this the pos input is top left, pos output bottom left, neg input top right and neg output bottom right. Cheers Caveman Mark Off grid eastern Melb |
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| Pete Locke Senior Member Joined: 26/06/2013 Location: New ZealandPosts: 181 |
....When did bottom feeding a trip device become standard? Normal practice is to top feed a breaker, and the load is taken from the bottom. Well, that's AC anyway. Maybe DC is different? |
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| George65 Guru Joined: 18/09/2017 Location: AustraliaPosts: 308 |
Sorry, I disagree completely. If I can short the wires coming from the panels and they don't even heat up let alone burn, how am I going to have a fire? Fusing in that case is irrelevant. The gauge of wire I am using is about 3 times the current rating of the panels output. The voltage and amperage of the panels drops once it gets off it's curve or whatever you want to call it for a start further reducing the current. I can't speak for other peoples or commercial systems but I do know how I have done my own and I have tested this to know what I say. If you don't believe me and want to put a wager on it to make it worth my while, I'll do a fair and honest Video to show you and put it up for all to see. An 8Amp load is an 8A load be it put to work or be it a dead short. It's still 8A and if I am using wire rated at 27A.... It's not going to burn. The video you linked to is also completely irrelevant to what I said. Of course there is going to be severe arcing if you only switch one side. That was exactly NOT what I was talking about at all. I specifically said switch BOTH lines at the same time. Is there a video of that we can look at to see what happens in THAT setup? Maybe the breakers will only last 100 cycles instead of 10K like they would with AC but that's still OK to me and I doubt any system gets turned on and off under load that much in it's lifetime anyway. I know the result will be different if you switch both sides simultaneously because I switched one of my arrays with 2.8 Kw going through it at about 380V several times this afternoon when I was moving some panels around without problem and I have probably switched it under load 20 or 30 times at least in total. Again, I am using a breaker on both the pos and neg outputs from the panels, not just one side as one would do with AC. That makes a SIGNIFICANT difference in extinguishing the DC arc. If you can find a demonstration where the breakers arc at similar output and setup to what I am using, then I will revise my position. Until such time as then or I see a problem first hand, I'll go with the repeated and problem free experience I have. |
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Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
George, I'll put on my nit picking hat to tell you what you wrote above is not quite correct. Yes, you can short the leads but the current will *not* plunge "to a few amps". Instead, the short circuit current, which depends on the panel size and the amount of light falling on it, will flow. Now, for a single 24v panel with an open circuit voltage of 40 Volts or so its reasonably safe to do that, there will be a little arc if the short is not broken quickly and the panel is in full sun. But, for a string of panels (you mentioned "array"), not a good idea at all. High voltage DC creates frightening arcs if one were foolish enough to try that. Not much of a problem while shorted, only the max current of one panel in the string will try to heat the wire which should handle this easily. But, when opening the short the fireworks start! So, do the short circuit panel testing *only* with a single panel at a time. I tested all my second hand panels that way, luckily they were all very close to the SCC rated on the panel label. Klaus |
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| George65 Guru Joined: 18/09/2017 Location: AustraliaPosts: 308 |
I believe the setup he is referring to is the same as I was talking about. BOTH sides of the DC are switched together. He says he has seen fires with this setup and also says there has been water in the switch boxes which were a contributing factor. He also says that that method of isolation is still legal. If it were inherently wrong or dangerous,I'm more than confident they would have changed the regs given how pedantic and over the top all the rest of it is. I don't like to have any of my switches or inverters outside and they are all well under cover. I also have the AC side breakers as small as I can get them to carry the load the inverter will do. One inverter specifys a 25 A breaker when it is a 3.6 Kw unit. WTF would I fuse something at 20A when it will be flat out doing 15? In actual fact, the array I have it on has never gone over 10a so that's what I have the breaker at. Whats' the worst can happen?,the breaker trips? Went all summer without a problem so I'll stick with that policy of minimum breaker rating as well. As well as the inverters having their own minimal rated breakers, I have breakers on the mains for the shed itself at that end and at the other end in the fuse box. One thing I am going to change is to go to individual RCD switches. Mrs hosed the verandah the other evening and must have managed to get some water in the outdoor light fitting from hosing from below. RCD took out the whole house. I want to put the breaker RCD's on each circuit so the entire place don't shut down when just one circuit is tripped. pain in the arse having to reset every clock in the place when a light circuit tripped which is about the only circuit that doesn't have a clock of some sort on it. |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
Are you referring to this video? Looks like he set it up to fail and scare people into changing or "upgrading" their setups, notice how he gave his business a plug. Cheers Caveman Mark Off grid eastern Melb |
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| George65 Guru Joined: 18/09/2017 Location: AustraliaPosts: 308 |
I agree with what you said completely. My point was related to fusing and the lack thereof starting a fire if the load in th e wiring was too high. I certainly AM foolish enough to pull arcs with my arrays and have done it many times. I want to do a YT vid on it because people I have shown are amazed as I was at how low a voltage you can do it at. When you do it with an array of panels as I have which I tend to do in strings of 8 to give around 350-380V, it's Herman Munster and Hollywood effects type stuff in your own hands. I was wondering actually what I could use as electrodes to create an arc that would sustain it as long as possible? I was thinking maybe carbon rods or something of that nature. Thick nails don't last long that's for sure and I doubt metal of any common type would either. Pulling arcs with wires in my hands does not worry me in the least. Putting more panels on my 35o Pitched tin roof is something I'm very concerned about and won't be doing till I get some experienced and knowledgeable help and borrow a harness off a mate. |
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Revlac Guru Joined: 31/12/2016 Location: AustraliaPosts: 1024 |
Shouldn't we split this into 2 different sections 1 for the high voltage GTI strings and another for our low voltage High current (120VDC) SCC? As the setup could be rigged a little different. Cheers Aaron Off The Grid |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
Jeeeeeezusss F, wouldn't bloody catch me doing that. Cheers Caveman Mark Off grid eastern Melb |
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