Wiring question-need a pro

Still working with my friend on his system. He wants to install a square d qo load center/main breaker in his utility room(rated to 48V DC). This would require two positive wires from the battery buss and one ground from the battery buss. I need to know how to calculate the proper size ground wire. Thanks for the help and if more info is needed, please ask. 

Comments

  • WaterWheelWaterWheel Registered Users Posts: 326 ✭✭✭
    Is that SquareD load center designed for DC?        If not it won't do well with the large arc DC can produce.

    Conext XW6848 with PDP, SCP, 80/600 controller, 60/150 controller and Conext battery monitor

    21 SW280 panels on Schletter ground mount

    48v Rolls 6CS 27P

  • westbranchwestbranch Solar Expert Posts: 5,142 ✭✭✭✭
    edited January 2016 #3
    they  are certified for MAX 48 Volts DC...as are the "QO" CBs
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • VicVic Solar Expert Posts: 2,970 ✭✭✭✭
    foolami said:
    Is that SquareD load center designed for DC?        If not it won't do well with the large arc DC can produce.


    YES,   BUT,  ONLY for breakers with Handle Ratings between 15A and 70 A,  inclusive,  And  only for QO,  QOU,  and QOB breakers.

    Do NOT use the Tandem breakers  --  the QOTs  --  as,  they have no DC rating at all.

    Expect that these QO breakers would not quite be acceptable with a 48 volt nominal battery voltage (IMO).

    AS I read the SQ D specs,   Vic

    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • VicVic Solar Expert Posts: 2,970 ✭✭✭✭
    King-01 said:
    Still working with my friend on his system. He wants to install a square d qo load center/main breaker in his utility room(rated to 48V DC). This would require two positive wires from the battery buss and one ground from the battery buss. I need to know how to calculate the proper size ground wire. Thanks for the help and if more info is needed, please ask. 


    By the "ground"  believe that you are referring to the battery negative ?   The battery DC Negative cable and the DC Positive cable should be sized such that the circuit breaker adequately protect these two cables from damage,  during a Fault.

    There are Ampacity Tables that will give you a good idea about correct conductor sizing.

    Is this a DC-only system?  That is,  NO inverter of AC power distribution?

    If so,  seems to me,  that you could run a maximum of a 70 A breaker as the Main.   And,  if the plan is to feed DC to each side of the QO load center,  that you would need two battery negative cables that land on the Neutral Buss.

    I am not a Code exoert,  so there are probably other things to watch out for.

    One other thing,  is that there are not really any standard DC outlets,  and perhaps few DC rated light switches.

    Perhaps I have assumed way too much.   Thanks for any clarification,   Vic

    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • King-01King-01 Registered Users Posts: 28

    Vic,

    I am referring to "ground" as the negative leg. Pos and Neg battery cables are protected by Mersen class T fuses. The Square D load center/main breaker is located in the house, separate from the other protective systems/battery room. This is a 13.8V system DC only system.

    I assume that it is "code" that would necessitate having two "ground" legs instead of only one.  

    Using UL listed RV light switches. Haven't gotten to the outlet part yet, suggestions are appreciated.

  • XizangXizang Registered Users Posts: 50 ✭✭
    edited January 2016 #7
    I'm watching with interest regarding 12 VDC outlets and light sockets.   Not keen to seeing cigarette-lighter sockets everywhere, there must be an acceptable 12 VDC electrical outlet that can't be confused with 120 VAC.  Likewise lighting sockets and LED/flourescent lamps.

    This is the best I've found, to be used in nice cabins, yachts, and quality homes...

    https://www.bluesea.com/products/1478/360_Panel_-_12V_DC_Socket_and_Dual_USB_Charger


    .
  • King-01King-01 Registered Users Posts: 28
    Xizang said:
    I'm watching with interest regarding 12 VDC outlets and light sockets.   Not keen to seeing cigarette-lighter sockets everywhere, there must be an acceptable 12 VDC electrical outlet that can't be confused with 120 VAC.  Likewise lighting sockets and LED/flourescent lamps.

    I'm running Sylvania LED 12V MR16 GU5.3 bulbs in both recessed lighting cans and light bars. These put out sufficient light and can handle the voltage generated during battery equalization (15V) but normally run at 13.8V. The Tech at Sylvania confirmed an even higher operating voltage since they are chip regulated.
  • XizangXizang Registered Users Posts: 50 ✭✭
    King-01 said:
    Xizang said:
    I'm watching with interest regarding 12 VDC outlets and light sockets.   Not keen to seeing cigarette-lighter sockets everywhere, there must be an acceptable 12 VDC electrical outlet that can't be confused with 120 VAC.  Likewise lighting sockets and LED/flourescent lamps.

    I'm running Sylvania LED 12V MR16 GU5.3 bulbs in both recessed lighting cans and light bars. These put out sufficient light and can handle the voltage generated during battery equalization (15V) but normally run at 13.8V. The Tech at Sylvania confirmed an even higher operating voltage since they are chip regulated.
    WHERE can they be purchased?
  • King-01King-01 Registered Users Posts: 28
    I buy them at my local Lowe's store and an electrical supplier that I have an account with.
  • VicVic Solar Expert Posts: 2,970 ✭✭✭✭
    King-01 said:

    Vic,

    I am referring to "ground" as the negative leg. Pos and Neg battery cables are protected by Mersen class T fuses. The Square D load center/main breaker is located in the house, separate from the other protective systems/battery room. This is a 13.8V system DC only system.

    I assume that it is "code" that would necessitate having two "ground" legs instead of only one.  

    Using UL listed RV light switches. Haven't gotten to the outlet part yet, suggestions are appreciated.


    OK on the Class T fuses.    As long as those are sized to protect the cable that they feed,  this should be fine.

    Regarding the QO Load Center;  Then,  that Main breaker should not be larger than 70 Amps to meet the specs for DC ratings.   That 70 A breaker can be a QO double pole breaker.

    And,  OK on the DC switches that you are using.

    If you are using a two pole main in the load center,  then you should run a pair of battery Negative cables to the load center Neutral buss,   IMO.

    Most smallish DC systems do not need inspection,  and the code provisions that apply to safety are good guidelines to try to reduce the likelihood of   fires   and so on.

    It does look like you are off to a good start on the system.   Good Luc,   Vic

    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • BB.BB. Super Moderators, Administrators Posts: 29,489 admin
    Anderson connectors are very common. The small ones (Power Pole models) are good to 15 amps.

    http://www.solar-electric.com/installation-parts-and-equipment/wiring-cables-and-connectors/anhicupoco.html

    And if you want, HAM Radio guys have lots of "interesting" solutions:

    http://www.westmountainradio.com/kb_view_topic.php?id=ST166
    http://www.aesham.com/ham-radio-accessories-powerpoles/

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Ethan BrushEthan Brush Solar Expert Posts: 231 ✭✭
    I question whether it is worth going with 12V distribution, even for a small system.  Have you checked out the morningstar 300W suresine inverter?  I can understand having a 12V panel for a few select loads such as a laptop if you use it a lot, cell phone charger, fridge.  But you really cant go wrong running general stuff off that great little inverter. 
  • BB.BB. Super Moderators, Administrators Posts: 29,489 admin
    I too really like the MorningStar 300 Watt TSW inverter... It is much easier to wire up for even smaller loads. Here is the inverter Ethan talked about:

    http://www.solar-electric.com/inverters-controllers-accessories/inverters/moin/mosu300wasiw.html

    -Bill


    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • westbranchwestbranch Solar Expert Posts: 5,142 ✭✭✭✭
    WIKI only has 2 plug in types listed, but a lot of connectors (already mentioned)...https://en.wikipedia.org/wiki/DC_connector

     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • King-01King-01 Registered Users Posts: 28
    I question whether it is worth going with 12V distribution, even for a small system.  Have you checked out the morningstar 300W suresine inverter?  I can understand having a 12V panel for a few select loads such as a laptop if you use it a lot, cell phone charger, fridge.  But you really cant go wrong running general stuff off that great little inverter. 

    He is working on his off grid cabin with minimal power requirements
  • BB.BB. Super Moderators, Administrators Posts: 29,489 admin
    edited January 2016 #17
    Roughly, you are only talking about adding ~15% to your panel/battery capacity to make up for the inverter losses.... If it makes wiring/sending power farther distances easier, it is not a big penalty.

    Today, many of the AC appliances are very energy efficient (sometimes even more energy efficient than the 12 VDC versions). Not like 20+ years ago where AC Appliances wasted a ton of power (I have an old stereo that takes 20 Watts turned off just to run the clock/memory).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Ethan BrushEthan Brush Solar Expert Posts: 231 ✭✭
    IMO, going 12V to everything isnt worth it.  Everything is more of a pain, funky parts, expensive/limited bulbs and fixtures..  You may find yourself deciding to plug in a lamp somewhere and not have a 12V bulb, not having the right cord end.......Or what about when your friend comes there and wants to charge his cell phone or other electronic widget.....Maybe that electric shaver......Just stuff to think about. 
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