Looking for a higher voltage bus bar

blakeloverain
blakeloverain Registered Users Posts: 1
in PV Installers Forum - NEC, Wiring, Installation #1
Hi,

I'm (DIY) installing some Sharp 250W panels to my MPPT charge controller and was looking for a bus bar (such as below) that would allow me to put several panels together to the same charge controller:

http://www.amazon.com/gp/product/B000K2MABA/ref=oh_details_o02_s00_i00?ie=UTF8&psc=1

Unfortunately this bus bar is rated at 48VDC only and I plan on taking the 34V panels in series of 2 (68V) and then put those sets in parallel. I'm doing so simply because I wanted to save on the MC4 wiring which is really expensive. I would just cut them in half, connect two wires of a panel set together, and then connect the two cut wires to the bus bar.

Does anyone recommend a simple general use bus bar (it doesn't need to be a dual bus bar like these) that would work for 68VDC?

Or might the one I show above work? What might happen to the bus bar with an extra 20V? Would the metal get hot and/or possibly melt? It is a pretty large and heavy duty unit. I'm curious how the AC rating can be quite high (300VAC) and the DC rating be so low. Everything by this manufacturer seems to be rated at 48VDC.

I'd like to keep my costs low and hopefully something similar in concept to what I've been looking for so far. I don't want to get more wires or change any configuration.

Thanks!
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Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Looking for a higher voltage bus bar

    Welcome to the forum.

    I have to advise against cutting the MC4 connectors from your panels: it is considered a "modification" and can void the warranty.

    As a rule a bus bar (nor any conductor) will not care how much Voltage is put through it. Current is the thing that will melt conductors. Voltage becomes important with insulation/arc over issues. There is no reason why a conductor would handle AC Voltage differently than DC Voltage (except for "skin effect" and frequency considerations). I do not know why they give such a disparity in rating for the unit you linked to.

    How many strings of panels are you looking at? If it is only two then you can use MC4 'Y' connectors. If it is more than two then every string should have a fuse/breaker on it to protect in the event of a shorted panel/string.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #3
    Re: Looking for a higher voltage bus bar
    blakeloverain wrote: »
    Or might the one I show above work? What might happen to the bus bar with an extra 20V? Would the metal get hot and/or possibly melt? It is a pretty large and heavy duty unit. I'm curious how the AC rating can be quite high (300VAC) and the DC rating be so low. Everything by this manufacturer seems to be rated at 48VDC.

    1. Bus bars combined with fuse holders may have DC voltage limitations based on the arc potential at the fuse holders, and this may just have been carried through inadvertently to the rating of the bus bar only devices.
    2. The testing requirement for high DC voltages are different from the requirements for the same AC voltages and they may just not want to invest in high voltage DC test equipment.
    3. The stress on insulation long term, as well as the possibility of corrosion and the development of a conductive surface deposit are all greater for DC than for AC for a given voltage.
    4. The result from a loose connection or anything else that starts arcing will be worse for DC than for AC since the arc will be harder to stop once it starts when DC is present. An AC arc sees the current go through zero 120 times per second. This makes it a lot easier to stop an AC arc if one gets started.
    SMA SB 3000, old BP panels.
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