Dual Pole Breaker (or switch?) between PV array and Charge Controller?

[Dzl]

After all this time, I still can't wrap my head around when to use and why to use a dual pole (i.e. breaks both + and -) switch or breaker between the PV Array input and charge controller.

I see many people doing this, seemingly regardless of system specifics (grounded, ungrounded, etc). But I've seen guidance that I interpreted to mean a dual pole switch or breaker should be used for an ungrounded array (or system?), and a single pole switch or breaker with a grounded array (or system?). Its possible I was misunderstanding the guidance.

Below is an excerpt from the Victron Smartsolar manual:

• Provide a means to disconnect all current-carrying conductors of a photovoltaic power source from all other conductors in a building or other structure
• A switch, circuit breaker, or other device, either ac or dc, shall not be installed in a grounded conductor if operation of that switch, circuit breaker, or other device leaves the grounded conductor in an ungrounded state while the system remains energized.

Am I misinterpreting what this means?

When should a dual pole switch or breaker be used between PV array and SCC? Are there situations where it is not advised?


* note 1: grounded conductor =/= grounding conductor (green, green/yellow, bare copper wire)
** note 2: "current carrying conductor" = both positive and negative, hot and neutral.

 

[mopat]

Well I do not know if you are misinterpreting.
There are a lot of variables, with PV array configurations/size, your location in the world but (for USA)

Bullet 1--Provide a disconnect from the PV array to everything else. Makes sense, particularly for maintenance. Here the disconnect could be a breaker. Some now popular MPPT devices do not include a PV array disconnect within their unit and installation of a separate DC is breaker is handy. This breaker is installed as a disconnect and can be sized (amperage) as 1.56 times the Isc of the array. Overcurrent (not just disconnect) protection is required with more than 3 parallel strings in an array. Then both legs (+ & -) require this (overcurrent) protection--hence a double pole breaker.

Take bullet 2--a breaker shall not be installed on a grounded conductor. Each panel in a PV array (its frame) should be grounded to each other and to earth. You should not install a breaker, switch, or other device on this ground wire.

Are you asking about USA location, what size PV system & configuration?

Maybe you're looking for double pole breaker, consider Square D QO models.

 

[Dzl]

Thanks for the response/input!

Are you asking about USA location, what size PV system & configuration?

USA. Mostly I just want to understand conceptually, but I'm also curious about what is required by code, so thank you for explaining some of that below. Personally, I will be building a medium-small PV system <1.5 kW <150 Voc (probably about half that size), configuration as yet to be determined, vehicle based (so chassis-ground, not earth-ground).

Bullet 1--Provide a disconnect from the PV array to everything else. Makes sense, particularly for maintenance. Here the disconnect could be a breaker. Some now popular MPPT devices do not include a PV array disconnect within their unit and installation of a separate DC is breaker is handy. This breaker is installed as a disconnect and can be sized (amperage) as 1.56 times the Isc of the array. Overcurrent (not just disconnect) protection is required with more than 3 parallel strings in an array. Then both legs (+ & -) require this (overcurrent) protection--hence a double pole breaker.

For what reason do both legs need to be broken? Why would this be different from any other circuit?

My take on the two bullet points as best I can understand, is (1) all current carrying conductors (DC Positive, DC negative in this case) need a means of disconnection, but (2) DC negative should not be disconnected if it is grounded and disconnecting it would leave it ungrounded. But I very much do not trust my own ability to properly interpret this.

Take bullet 2--a breaker shall not be installed on a grounded conductor. Each panel in a PV array (its frame) should be grounded to each other and to earth. You should not install a breaker, switch, or other device on this ground wire.

I'm not sure this is the correct reading of that bullet point.
It is my understanding (and I might be misinterpreting something) that Ground/Earth/Green Wire = Grounding conductor, not Grounded conductor (which typically refers to neutral or dc negative, i.e. the thing being grounded by the grounding system).

Spoiler: For reference, here is an excerpt from a Magnum inverter manual defining these terms

(I've seen these terms defined similarly elsewhere, so I think these might be standard or semi-standard terms):

--

 

[Dzl]

I've seen many people here use or recommend using a dual pole breaker on this forum, can nobody explain why or when to do so?

 

[Dzl]

Bumping this up again, in hopes that one of the folks who reccomend, or chose, to use a dual pole breaker between PV and SCC can explain the logic behind the decision/reccomendation.

 

[John Frum]

After all this time, I still can't wrap my head around when to use and why to use a DPDT ('dual pole dual throw' i.e. breaks both + and -) breaker between the PV Array input and charge controller.

I think you mean DPST double pole single throw.
I think someone had a plausible explanation and that it involved grounding but I cannot recall who or why.

 

[Dzl]

I think you mean DPST double pole single throw.
I think someone had a plausible explanation and that it involved grounding but I cannot recall who or why.

oops, yes probably. edited DPDT to just 'dual pole'

 

[John Frum]

Actually I vaguely recollect its a switch not a breaker.

 

[Dzl]

Actually I vaguely recollect its a switch not a breaker.

I have seen both recommended. I think the primary purpose is a means of disconnection, so either could work if it were rated for the proper voltage.

Victron's partial guidance makes reference to both options.

 

[John Frum]

I have seen both recommended. I think the primary purpose is a means of disconnection, so either could work if it were rated for the proper voltage.

Victron's partial guidance makes reference to both options.

I think @JoeHam may have some input on this.

 

[tazmann]

Only thing I can think of, if there is a short in a panel or wires you could get power coming down the negative wire to the charge controller

 

[Semoreo]

I was thinking something similar. Since panels generate current if only one leg is broken maybe it could still push or pull electrons. If you break both then both would have to short to cause a problem.

 

[JoeHam]

Not sure I have much to add here except that if you use a 48v system most of the quality switches (blue seas, perko) cannot be used since they are only rated to 48v. Obviously a 48v system spends most of it’s time above that nominal voltage on either side of the battery. On the solar side I am routinely above 100v.

I have been using Schneider breakers like this:

Circuit Breaker 2P 250V 16A Low-voltage DC Miniature Circuit Breaker For Solar Panels Grid System Din Rail Mount - - Amazon.com

Circuit Breaker 2P 250V 16A Low-voltage DC Miniature Circuit Breaker For Solar Panels Grid System Din Rail Mount - - Amazon.com

www.amazon.com

Rated up to 250v and dirt cheap for a double pole so I use those. I can’t think of a significant downside to using double poles.

 

[Dzl]

Rated up to 250v and dirt cheap for a double pole so I use those. I can’t think of a significant downside to using double poles.

Can you think of a significant upside? (that would be more applicable to the PV <---> SCC circuit, than all the other circuits in a system that we seem to never even consider using double pole breakers on?

 

[JoeHam]

Can you think of a significant upside? (that would be more applicable to the PV <---> SCC circuit, than all the other circuits in a system that we seem to never even consider using double pole breakers on?

Nope.

The lack of a downside was enough for me.

 

[Dzl]

For anyone else researching this question now or in the future, here is the clearest answer I have found so far.

 

[Pappion]

Some controllers are negative ground, some are positive ground. That means they go strait thru that side and switch/regulate on the other side.
Positive ground will have battery voltage on solar +, Solar - could be -98v. Use a dual breaker.
Negative ground is safer and maybe it needs only 1 breaker on solar +. I bought a dual, looks nicer, not much more money.

 

[Pnw_steve]

Well I do not know if you are misinterpreting.
There are a lot of variables, with PV array configurations/size, your location in the world but (for USA)

Bullet 1--Provide a disconnect from the PV array to everything else. Makes sense, particularly for maintenance. Here the disconnect could be a breaker. Some now popular MPPT devices do not include a PV array disconnect within their unit and installation of a separate DC is breaker is handy. This breaker is installed as a disconnect and can be sized (amperage) as 1.56 times the Isc of the array. Overcurrent (not just disconnect) protection is required with more than 3 parallel strings in an array. Then both legs (+ & -) require this (overcurrent) protection--hence a double pole breaker.

Take bullet 2--a breaker shall not be installed on a grounded conductor. Each panel in a PV array (its frame) should be grounded to each other and to earth. You should not install a breaker, switch, or other device on this ground wire.

Are you asking about USA location, what size PV system & configuration?

Maybe you're looking for double pole breaker, consider Square D QO models.

In the NEC "grounding" conductors and "grounded" conductors are different animals. Keep that in mind when interpreting code.

 

[Dzl]

In the NEC "grounding" conductors and "grounded" conductors are different animals. Keep that in mind when interpreting code.

an important distinction

Funny enough, at this exact moment I am turned to the exact page in the NEC 2017 code, that defines these terms:

Grounded Conductor: A system or circuit conductor that is
intentionally grounded. (CMP-5)

Grounding Conductor, Equipment (EGC): The conductive
path(s) that provides a ground-fault current path and connects
normally non–current-carrying metal parts of equipment
together and to the system grounded conductor or to the
grounding electrode conductor, or both. (CMP-5)
Informational Note No. 1: It is recognized that the equipment
grounding conductor also performs bonding.
Informational Note No. 2: See 250.118 for a list of acceptable
equipment grounding conductors.

Grounding Electrode Conductor: A conductor used to connect
the system grounded conductor or the equipment to a ground‐
ing electrode or to a point on the grounding electrode system.
(CMP-5)

Grounding Electrode: A conducting object through which a
direct connection to earth is established. (CMP-5)

 

[Hedges]

From what I've read, initially opening the negative PV lead was forbidden because NEC knew you weren't supposed to do that.
Then they changed their mind and required it.

If a short between PV+ and ground could drive the negative wire to -480VDC, I want to disconnect it before touching wires or screws.
My older inverters with a "GFCI" fuse (one amp) connecting PV- to ground have a disconnect only switching PV+.
My newer transformerless have a 2-pole switch at the inverter, and fuses on both legs.
After shutting off any switches, I isolate both ends at MC connectors if working on that side of switch/touch-safe fuse holders.

I have been using Schneider breakers like this:

https://www.amazon.com/Circuit-Brea...s/dp/B086MYWFLX/ref=sxts_sxwds-bia-wc-p13n3_0

Rated up to 250v and dirt cheap for a double pole so I use those. I can’t think of a significant downside to using double poles.

I see "+" and "-"; they're polarized.
If oriented one particular way, they will break current from PV string if switched under load.
But if you use a bunch of these in a string combiner, and several strings backfeed into a shorted string, it'll open but fail to break the current.

Oh, "Schneider" breakers "like" this (provides link to "Yipiner"?)

Have a link to the ones you use? I find listings and some prices, but ain't cheap for the higher voltages:

https://download.schneider-electric.com/files?p_Doc_Ref=CA908061E&p_File_Ext=

https://www.grainger.com/category/electrical/fuses-circuit-breakers-safety-switches/circuit-breakers-panelboards-load-centers/circuit-breakers-accessories/din-rail-mount-miniature-circuit-breakers?brandName=SCHNEIDER+ELECTRIC&filters=brandName