November 28, 20241 yr Again I don't fully understand and need help please. My neighbour's installation has this marked DB. INVERTER ACDB. AC COMBINER DB. CAUTION ALTERNATIVE POWER SOURCE. Insde is a 63a dp isolator, two ac surge protectors, 40a sp inverter in breaker, eskom/ipnverter change over switch and a 40a sp inverter out breaker. My question is how do you isolate the inverter, as I see it if you switch the Isolator or the inverter in off its gonna act like loadshedding and the inverter is then running on batt power. I know if you switch the PV and batt also off then it should be fine. Not 100% sure? Thank you Edited November 28, 20241 yr by Herbie.
November 28, 20241 yr 1 hour ago, Herbie. said: My question is how do you isolate the inverter, To completely isolate the inverter you have to remove all 3 power sources, utility, pv and battery.
November 28, 20241 yr Author OK thanks. The DCDB has also got a 63A isolator, two DC surge protectors and a 20a sp breaker. I assume the black and red PV wires go through the isolator and the red then through the 20A breaker, nothing on the roof? Thanks
November 28, 20241 yr Author 1 hour ago, Virwat said: Nice pic or two can help? I tried but it's too large, don't know how to resize.
November 28, 20241 yr Lower the resolution of the camera then the photo become smaller or hold the camera closer to the object that must be photographed then the photo also becomes smaller.
November 28, 20241 yr 8 hours ago, Herbie. said: OK thanks. The DCDB has also got a 63A isolator, two DC surge protectors and a 20a sp breaker. I assume the black and red PV wires go through the isolator and the red then through the 20A breaker, nothing on the roof? Thanks Yes the logic of your explanation sounds about right but there is more to it on the dc pv side and that is of utmost importance that both the isolator and mcb are DC RATED it needs to state on the switchgear that much. Use the picture compressor suggested by @Virwat so we can scrutinize the dc side. For the battery you will find a battery disconnect fuse holder or dc breaker close to the battery and will not be located inside the dc db just for information purposes.
November 28, 20241 yr Author OK I took screenshot, the image resizing does not want to open. All I can see as DC are the search protectors.
November 28, 20241 yr The concern is the 1st creenshot dc pv db as the Hager MA120Z is a AC curve C 20A mcb and is not rated for DC curcuits. Compare the Hager isolator in the dc db against the isolator in the ac db they look the same and even the labeling is the same. I have not come across Hager DC mcb's as i only use Noark dc breakers for dc pv combiner boxes(db,s). I can not make out the part number on the Hager isolator but i suspect it is a ac isolator as well. This is potentially a disaster waiting to happen. Should the breaker or the isolator be opened under load it would arc across the contacts and be a potential fire hazard. There is 2 tell tales on DC mcb's to ensure that it is indeed DC rated, it should not have a frequency rating in Hz and for pv the connection terminals are normally marked + and - meaning it is a one direction mcb for use on solar charge controllers. The dc mcb's use for battery protection is multi-directional DC breakers for charge/discharge. Did the installer issue a COC for this installation? Below attached picture of Noark DC 20A single direction Mcb. Edited November 28, 20241 yr by TaliaB Spelling
November 28, 20241 yr Author Hi TaliaB, yes there is a COC but I don't want to get involved as it is my neighbour. The two main Isolaters have the same nrs SBN 263 63A. On the DCDB it says do not disconnect under load. In your picture of the DC breaker the + would be the panel side and the - the inverter side. On the black negative wire the same or is there no need tor a breaker. Thanks for the explanation of the frequency and arcing in the AC breaker. Is it the same for AC and DC fuses?
November 28, 20241 yr 5 minutes ago, Herbie. said: On the DCDB it says do not disconnect under load In case of emergency the label won't safeguard the component against an arc-flash it needs to be rated that even in the event it is opened under load it needs to do so safely.
November 28, 20241 yr Author Thanks, the DCDB label says do not disconnect under load. How are you going to disconnect or connect it when installing or doing maintenance, at night when there is no sun? Edited November 28, 20241 yr by Herbie.
November 28, 20241 yr 11 minutes ago, Herbie. said: Thanks, the DCDB label says do not disconnect under load. How are you going to disconnect or connect it when installing or doing maintenance, at night? AC circuit breakers are designed for alternating current, while DC circuit breakers are designed for direct current. They are not interchangeable. The speed at which the contacts pull apart is much faster in a DC breaker, the gap between contacts is larger, usually there is an ark shield and an air escape path to help extinguish the arc when disconnecting under load. People underestimate the dangers of DC current. The Arc that will be created when that AC breaker gets pulled under load will be significant. If anything has to happen and the insurance company picks this up, that become a very expensive exercises
November 29, 20241 yr Author Thank you all very much for this valuable info, I think many of us have learned a lot.
November 29, 20241 yr 11 hours ago, Herbie. said: How are you going to disconnect or connect it when installing or doing maintenance, at night when there is no sun? When starting up the inverter after connecting to the Mppt the load will gradually increace to full load if sun permits. Before you disconnect the solar array via fuses or mcb's you shut the inverter or Mppt off. You will then have dc voltage on the switchgear but no current flowing. Even with only voltage present there will still be an arc when disconnecting the fuses or mcb's but the magnitude of the arc will be much less. Even under no load condition ac switchgear might fail reasons explained by @I84RiS above. Edited November 29, 20241 yr by TaliaB Added text
November 29, 20241 yr Author I got this batt isolator with fuses and PV switch. No where on the fuses does it say DC. Any comments please.
November 29, 20241 yr 50 minutes ago, Herbie. said: No where on the fuses does it say DC Correct as it shows on the fuse that it is an AC fuse (~), it can work if there is no or low amp load when it breaks, but if under heavy amp load it could arc like crazy before breaking, best is to replace with a DC rated fuse in the same format. Edited November 29, 20241 yr by WannabeSolarSparky
November 29, 20241 yr 3 hours ago, Herbie. said: I got this batt isolator with fuses and PV switch. No where on the fuses does it say DC. Any comments please. Like @WannabeSolarSparkysaid safer to get them replaced with manufacturer rating for use on Ac or Dc. Below atrached.
November 30, 20241 yr Pictures, pictures and more pictures. You can never supply to many pics so that correct informative decisions can be made. (Too many a slip between the cup and the lip in wording) And even better if covers can be removed as well. I am a firm believer that the more pics a person can supply, the more help can be given by fellow forumites.
December 2, 20241 yr Author On 2024/11/29 at 1:28 PM, TaliaB said: Like @WannabeSolarSparkysaid safer to get them replaced with manufacturer rating for use on Ac or Dc. Below atrached. Hi TaliaB, this is the same spec as yours and 600v60v DC Edited December 2, 20241 yr by Herbie.
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