DC Breaker Wiring

fatheadl · January 2009

Hi all,

I would like to know the right way to wire "line" and "load" terminals in the following situations:
1)Between PV and charge controller
2)Between charge controller and battery
3)Between battery and inverter.

Thanks in advance
fatheadl

crewzer · January 2009

Re: DC Breaker Wiring

fatheadl,

Here's a link to "Example Systems" by John Wiles: http://www.nmsu.edu/~tdi/pdf-resources/pdf%20version%20divided%20PV:NEC/APPENDIX%20E.pdf

HTH,
Jim / crewzer

fatheadl · January 2009

Re: DC Breaker Wiring

Hi Jim,
The link does not answer my question. I interpret the "line" side of a DC breaker to be connected to the source of the power and the "load" side to be connected to the load that is using the power. I saw an installation instruction of a battery charger that says the battery should be connected to the "line" side and the charger connected to the "load" side which is opposite to what i think.

Thanks
fatheadl

BB. · January 2009

Re: DC Breaker Wiring

If these are standard breakers, line/load should not matter--especially since in DC systems (and solar RE), sources and sinks of current are not always consistent... For example, a battery is a load during charging and a "line" during discharging. A GT Hybrid Inverter is a load during charging/low sun, and a "Line" when the sun is up and it is feeding energy back to the home/utility grid.

My two cents would be to connect the Line Side to the battery (common rail/bus) and the "load" sides to the individual branch circuits.

For a solar panel array to controller/inverter combiner--the "loads" should be the individual branch circuits, and the Line side is the combined bus for connection to the charge controller/inverter.

-Bill

fatheadl · January 2009

Re: DC Breaker Wiring

Thanks for the responses

crewzer · January 2009

Re: DC Breaker Wiring

The link does not answer my question. I interpret the "line" side of a DC breaker to be connected to the source of the power and the "load" side to be connected to the load that is using the power. I saw an installation instruction of a battery charger that says the battery should be connected to the "line" side and the charger connected to the "load" side which is opposite to what i think.

fatheadl,

Got it. I think Bill and I are in agreement on this one.

Yeah, many DC breakers are now polarized, which I believe is part of thelr arc management strategy. I think that such breakers should be installed based on likely worst case scenarios.

For example, the breakers between the batteries and the controller and inverter should have the (+) terminal (line?) connected to the battery. The battery can source a lot more current than the controller or inverter's DC terminala.

The breaker(s) between the PV array and the controller are not quite so straight forward. One fault condition might be all other array strings ground faulting through a single string. I suppose it's also possible that the battery bank could discharge through the PV array during a catastrophic controller failure. These scenarios would suggest connecting the breaker's (+) / line terminal to the controller input and not to the PV module (+).

HTH,
Jim / crewzer

icarus · January 2009

Re: DC Breaker Wiring

In any event, it is always a good idea to add a fuse in the battery leads. I use one cable from the battery to the controller fused to the minimum wire size on the PV side. I use another cable to the loads, fused to the wire size of that wire before the DC breaker box that fees the inverter and the 12vdc loads. I also fuse the battery charge lead, sized to the maximum amps from the battery charger, (but smaller than the wire size fuse requirement).

These are fuses mounted on terminal blocks. This way there is no piece of wire connected to a energy source that is not fused.

I have asked the question here before as to whether or not you need a fuse at the panels to protect the wire to the controller and the consensus was that it wasn't needed.

Good luck,

Tony

BB. · January 2009

Re: DC Breaker Wiring

You may need a series fuse to protect the panels though...

Check your panels, there should be an Isc rating (short circuit current).

And there may be a Series Fuse rating too.

Typically, the series fuse rating is a little over 2x the Isc rating of the panel.

So, if you have two or less strings in parallel, then you don't need the series fuse (one per string).

If you have three or more strings in parallel, then you will need a series protection fuse in each string (or circuit breaker). This protects a panel with an internal short being feed too much current from the rest of the parallel connected panels.

If you have a large number of panels in parallel--the series fuse can also protect the branch wiring to each string from over current at the common connection point just before the controller home run.

-Bill

icarus · January 2009

Re: DC Breaker Wiring

Good point Bill,

I have two strings in parallel.

T.

Ecnerwal · January 2009

Re: DC Breaker Wiring

icarus wrote: »

In any event, it is always a good idea to add a fuse in the battery leads. I use one cable from the battery to the controller fused to the minimum wire size on the PV side. I use another cable to the loads, fused to the wire size of that wire before the DC breaker box that fees the inverter and the 12vdc loads.

IMHO, in the fairly common case of having a parallel string battery, each string of the battery should be fused. ie, 16 6 volt batteries wired for 48V should have two fuses, wired for 24V, 4 fuses.

crewzer · January 2009

Re: DC Breaker Wiring

Here's a link to Wiles' article on parallel PV strings and OCPD's: http://www.nmsu.edu/~tdi/pdf-resources/CC125.pdf

HTH,
Jim / crewzer

eltonsh1 · February 2017

simple question please, i got a solar panel and a 16 a dc breaker. Please how to connect my panel and inverter to this breaker? do i just connect the panel wires to the below point and the inverter to the above points?

Estragon · February 2017

If the breaker is polarized it should be marked with "+" or "line" on one end. That end connects to the wire from PV panels.

mike95490 · February 2017

fatheadl said:

.......... I saw an installation instruction of a battery charger that says the battery should be connected to the "line" side and the charger connected to the "load" side which is opposite to what i think. Thanks fatheadl

Unless a power line falls on the PV array and wires itself up to the array wires, properly sized wire (say 60A) from the controller to battery is safe, the array can't burn that wire under any condition. But at night, if a gecko was to get into the controller and short it out, the battery would try to dump 100's of amps into the shorted controller. And a breaker wired thusly, protects things,

Johann · February 2017

This may explain some.

https://www.youtube.com/watch?v=Mtq3cs9Gucc

Also see this pdf.
http://greenforcesolar.com.au/wordpress/wp-content/uploads/2011/11/Discussion-Paper-Correct-Wiring-of-Double-Pole-DC-Breakers-LVL2-131210-v2.pdf

DC Breaker Wiring

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