DC MCBs for panels

SD_DRACULA

Wondering if it would help to add some of these DC MCBs in between the panels and inverter.

https://www.amazon.co.uk/gp/product/B09VYN1C93/ref%3Dewc_pr_img_1?smid=A3UCA042KBB2MP&psc=1

Currently panels go into projoy fireman switch and then into inverter. Doing some rewiring and was wondering whether to add these before the cables go into the inverter?

The panels are rated 10a but I think it might dip a little over that 11-12a, so would I need a 16a mcb or 10a is fine?

the_amazing_raisin

They certainly wouldn't hurt, I'd go with the 16A assuming the cables and connectors or rated for it

oaklands

https://www.boards.ie/discussion/2058358777/dc-mcbs-for-panels

I would verify from the data sheet exactly how long it takes to trip (If there is a DS available)….Thermal vs current based trip?.

graememk

Id argue that it could hurt.

It's another joint, another point of failure.

The panels are producing power, something fails in them, they stop producing, and still would never trip the MCB?

(Also it's a no name brand.. god knows what's actually inside it)

SD_DRACULA

So in the interest of full disclosure and the reason for this question, I ran new string cables and ended up about 1m short of the inverter. They were like 20m and four of them so the 100m roll is used up and they were a massive pain to run.

This is more of a fix than a necessity I agree.

Might just put one of these instead of the DC mcbs and then run the 1m cable to the inverter

https://midsummer.ie/buy/AC-and-DC-isolators/PEDSC100R-EL32R-4

But my thinking was that the DC mcb would add some sort of protection where the isolator does nothing for protection

graememk

https://www.boards.ie/discussion/comment/122354677#Comment_122354677

"Measure once, cut twice and it's Still too short 😂"

Having a DC isolator is nice to have beside the inverter, especially if you need to extend..

Just don't get them wet( it's been replaced, we think water was wicking down the conduit, measures have been taken to prevent it happening again... Also it stank!)

the_amazing_raisin

https://www.boards.ie/discussion/comment/122354635#Comment_122354635

I'd generally be of the view that every circuit should have some sort of over current protection. I know solar panels generally either work or do nothing but there's still scope for shorts outside of that

I do agree about avoiding the no name brand. I'll never forget Clive's notorious untrippable circuit breaker (complete with BS and EN compliant stamps)

https://youtu.be/2TJEzdqtXlQ?feature=shared

SD_DRACULA

https://www.boards.ie/discussion/comment/122354719#Comment_122354719

Actually I ran one cable end to end, measured it, and cut the rest the same size.

Then decided to change the path of the run ever so slightly and wondered why it wasn't good anymore 🤠

https://www.boards.ie/discussion/comment/122354769#Comment_122354769

Wouldn't the inverter have some sort of protection? I would guess yes but maybe not for the cable, where the mcbs come in.

I'll probably just use the dc isolator as my joining point.

the_amazing_raisin

https://www.boards.ie/discussion/comment/122354880#Comment_122354880

If you have to ask the question then it's probably better to put a circuit breaker on 😉

graememk

https://www.boards.ie/discussion/comment/122355705#Comment_122355705

Id take an isolator over a no- name MCB anyday, basically doing the same thing.

MCB/fuses protect cables and there is no scenario that the MCB would be in a position to trip.
Short out the panels, current will be well under the 16 amps, Looking at a random spec sheet of a 365w panel gives its short circuit current, and its only about 12 amps.

On batteries, Is a totally different story, the available current is only limited by the internal resistance of the battery.
[V=IR, internal resistance is >2.5mOhm, on a 3.2V cell, the available current is 1280A, Which would destroy the battery, but its there.]

allinthehead

https://www.boards.ie/discussion/comment/122355999#Comment_122355999

I'd agree with this, mcb would only act as an isolator in this case. A good quality dc isolator would be the way to go.

drury..

This is insane everyones an electrician now

Posters googling for advice on mcbs and isolators lol

allinthehead

https://www.boards.ie/discussion/comment/122356259#Comment_122356259

I am an Electrician 🤣

drury..

https://www.boards.ie/discussion/comment/122356369#Comment_122356369

Not you then the rest of its madness

I'm a spark but i wouldn't touch the stuff because I don't know and lads are firing batteries and sh1t into attics and posting about mcbs and isolators

allinthehead

https://www.boards.ie/discussion/comment/122356384#Comment_122356384

Strings of 2 or less in parallel don't require overcurrent protection. In fact it's pointless as a short can't draw enough current to blow the fuse or trip the mcb. Adding a dc isolator isn't a problem.

Buffman

https://www.boards.ie/discussion/comment/122354677#Comment_122354677

I'm assuming the inverter is visible and you don't want it looking too 'messy'? Otherwise some bespoke extension cables using MC4 connectors might the easiest way to get you to the inverter.

SD_DRACULA

https://www.boards.ie/discussion/comment/122368130#Comment_122368130

Can all be hidden in the trunking beside the inverter and yeah I could easily make some mc4 extensions myself.

Bought the projoy DC isolators in the end and using them as the hop between.