Bus Bar

czyhorse
czyhorse Solar Expert Posts: 42 ✭✭
in PV Installers Forum - NEC, Wiring, Installation #1
I have decided that I need to incorporate a positive and negative bus bar due to numerous connections in my Midnite Solar e-panel.

Since I am grounding the negative end of my system, does my negative bus bar need to be insulated, or could I just use a run of the mill bus bar and attach it directly to the chassis of the e-panel?

Any thoughts?
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #2
    Re: Bus Bar
    czyhorse wrote: »
    I have decided that I need to incorporate a positive and negative bus bar due to numerous connections in my Midnite Solar e-panel.

    Since I am grounding the negative end of my system, does my negative bus bar need to be insulated, or could I just use a run of the mill bus bar and attach it directly to the chassis of the e-panel?

    Any thoughts?
    I'm pretty sure that that would defeat the ground fault protection. It would bypass the low current breaker that trips the main.
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  • czyhorse
    czyhorse Solar Expert Posts: 42 ✭✭
    #3
    Re: Bus Bar

    I don't have ground fault protection on my system. I know it's called for in the NEC, but I know of others that question its safety and usefulness.

    Aside from bypassing GFI (if I had one), would there be any other reason to insulate the bus bar?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: Bus Bar

    GFCI is an 'AC thing'.

    We're talking about the DC charging source here. I think you'll find that negative is chassis grounded anyway in the charge controller.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,637 admin
    #5
    Re: Bus Bar

    There should be only one place in your system where DC return (- lead) and safety/earth ground should be bonded together.

    If your uninsulated bus bar is that single point--then you should be OK.

    If there is another point in your system where DC and safety ground are bonded--then no--You do not what that because your DC return current will be sharing the two paths (safety and return paths) which can cause problems (many times, the DC return current is larger than the safety ground can handle... And the safety ground could over heat--as one example).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #6
    Re: Bus Bar
    Cariboocoot wrote: »
    GFCI is an 'AC thing'.

    We're talking about the DC charging source here. I think you'll find that negative is chassis grounded anyway in the charge controller.
    ???

    From the NEC2008, Article 690.5: "Grounded dc photovoltaic arrays shall be provided with dc ground-fault protection meeting the requirements of 690.5 (A) through (C) to reduce fire hazards."

    It works; on one system we had a damaged module where its negative connection became shorted to the frame, which tripped the ground fault protection and disconnected the array.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,637 admin
    #7
    Re: Bus Bar

    AC Ground Fault for a home is a transformer coupled circuit that measures unbalanced current in the 0.005-0.015 amp range and trips open if the current is exceeded. This one is to limit current through the human body--and prevent heart failure in wet condition electrocution (sinks, pools, outdoor tool use, etc.).

    DC Ground faults are (typically) a DC fuse or circuit breaker between the solar panel ground (or battery/solar panel for off-grid systems), that, if tripped (more than 1 amp of current flow) will disable the Grid Tied Inverter or trip a companion breaker from the solar array (think dual pole 240 VAC breaker with one 1 amp breaker, tied between DC ground and Safety Ground, tied with a 60+ amp breaker in the positive lead). If either breaker exceeds rated current flow, both breakers open/trip. This type is intended to prevent some ground shorts and reduce possibility of fire.

    I have serious reservations about DC Ground Fault systems--But that is what US code requires. Note that this puts a fuse/circuit breaker in the safety ground connection and causes it to open in the event of a failure--Absolutely the opposite of the requirements for a safety ground circuit in any other code installation.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #8
    Re: Bus Bar

    Bill;

    Thank you for clearing that up for me; I was beginning to think I'd had another 'incident'. :blush:
    I don't believe we have that reg in Canada, even though our code almost always mirrors the US. As you say, it seems contra-indicated or at least counter-intuitive. Still, they must have had a reason (although sometimes it seems the reason is some bureaucrat had nothing to do one day so he added something to the code).
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  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    #9
    Re: Bus Bar

    Am not a real Code expert, but thought that the 2008 NEC required GFCI on the PV input ONLY for Solar Panels mounted on roofs of dewllings. Do not have my code book here, but that was my recollection.

    More to the topic, OB and Midnite make busbars with 4/3 colors in medium, and Short lengths, respectively, ie OB makes medium length BBs in BK, RD, WH & BLu, Mn in BK, RD, & WH as shortys -- at least that is what is listed on the great host of this site's store.

    Good Luck, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 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.
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