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er9 · 09-11-2020, 16:48

I just realized i dont actually know how to choose the proper Amperage busbar for my DC positive and negative loads.

i want to feed all my charge sources to a single positive busbar and have one, possibly two negative busbars to consolidate my grounds.

do we size it according to max amperage of all the charge sources feeding it or max draw amperage for all the devices that would draw from it? neither?

**tkeithlu** · 09-11-2020, 17:09

Draw from it. Add up the uses. How are you going to isolate the sources? 1-2-all switch?

The posible amps from the sources doesn't matter, assuming there is a fuse or circuit breaker in there in case of a short, because current that is not being used at the other end doesn't go through the busbar.

er9 · 09-11-2020, 17:16

Quote:

Originally Posted by tkeithlu

Draw from it. Add up the uses. How are you going to isolate the sources? 1-2-all switch?

The posible amps from the sources doesn't matter, assuming there is a fuse or circuit breaker in there in case of a short, because current that is not being used at the other end doesn't go through the busbar.

Correct. Definately everything will be properly fused between sources and the bus bar.

I dont have a complete list of gadgets that will draw from it (positive busbar/house bank) but it (my house bank) will also do starting duty as well as supply all DC loads at the distribution panel.

Bycrick · 09-11-2020, 17:41

Check all the ratings of the busbar. Not all amp ratings are for the same heat rise. Also, some are rated for Max current end-to-end while others are center-to-end.

**tkeithlu** · 10-11-2020, 04:05

And then leave a generous margin. Electronics draws tend to proliferate.

er9 · 10-11-2020, 07:41

Quote:

Originally Posted by Bycrick

Check all the ratings of the busbar. Not all amp ratings are for the same heat rise. Also, some are rated for Max current end-to-end while others are center-to-end.

Noted, ty.

er9 · 10-11-2020, 07:43

Quote:

Originally Posted by tkeithlu

And then leave a generous margin. Electronics draws tend to proliferate.

any harm in grossly over-sizing a busbar since its essentially just a pass-through? i can see how under-sizing might be an issue but over-sizing?

rslifkin · 10-11-2020, 07:57

Quote:

Originally Posted by er9

any harm in grossly over-sizing a busbar since its essentially just a pass-through? i can see how under-sizing might be an issue but over-sizing?

No harm. Only penalty from over-sizing is that you end up with a heavier, bigger, more expensive bus bar. But functionally, it'll be as good or better.

chowdan · 10-11-2020, 08:19

I chose to just over size my bus bars. All my switched and unswitched bars are 600amp powebars from blue seas. Even everything running I should at very most be around 280-290, and that's if my short power and alternator is pumping max into the system.

Shrew · 10-11-2020, 08:21

Quote:

Originally Posted by chowdan

I chose to just over size my bus bars. All my switched and unswitched bars are 600amp powebars from blue seas. Even everything running I should at very most be around 280-290, and that's if my short power and alternator is pumping max into the system.

280-290amps......DC?? DC bus bars for Shore power? Are you possibly mixing AC and DC concepts here? I've never seen DC Shorepower.

er9 · 10-11-2020, 08:24

Quote:

Originally Posted by rslifkin

No harm. Only penalty from over-sizing is that you end up with a heavier, bigger, more expensive bus bar. But functionally, it'll be as good or better.

wow yeah they do get expensive quick. if i can get away with it though, i think its worth it. i much prefer to overbuild systems when i can.

er9 · 10-11-2020, 08:27

Quote:

Originally Posted by Shrew

280-290amps......DC?? DC bus bars for Shore power? Are you possibly mixing AC and DC concepts here? I've never seen DC Shorepower.

maybe he means AC shore power through charger outputting 60 (or whatever charger outputs) AMPs DC to charge bus? with engine running alt could be pumping another 60+ easily it seems if you run everything to a single charge bus.

er9 · 10-11-2020, 08:31

Quote:

Originally Posted by chowdan

I chose to just over size my bus bars. All my switched and unswitched bars are 600amp powebars from blue seas. Even everything running I should at very most be around 280-290, and that's if my short power and alternator is pumping max into the system.

interesting, thanks. i was looking at those. Mainesail has a couple left on his website (650 AMP) version. my credit card is going to melt but at least my wires wont.

**s/v Jedi** · 10-11-2020, 08:45

You only need to look at the connected battery banks. If you have one bank then the busbar must be at least rated for the value of it’s fuse. If you have multiple banks, sum their fuses.

You basically choose between 250A and 500+A. That’s where most busbars go from one size to the next. A 300/400A battery fuse puts you into the expensive category.

BTW, buy a bigger busbar rather than two. Each stud can have up to 4 terminals but see my recent thread about that as stud height limits that number when they are all bug sizes. I would limit it to 2 per stud for the big ones (3/0 and 4/0) then add at most one 2/0 or 1/0 plus a small one. This allows washer and nut to fit on there comfortably.