Grounding

KhellSk
KhellSk Registered Users Posts: 91 ✭✭
in General Solar Power Topics #1

Hello, this is going to be a Debutant question and im a bit ashamed to ask it

Do you, as you should for AC in a house, have to ground the circuit and the devices boxes ? I did ad a pigtail from the Return wires splice to the ground screw of my device box. I have a feeling this isnt right. Do you tie to a rod in the ground ?

Anyhow, Do you ground the circuits and how do you do it ( not talking about the panels frames here)


Thank you fellas

_____________________________________________
[3p3s 48w 15.9Vmp] [Flooded 2x 6v 150ah]
[Victron 50/100 700wMax MPPT]







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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    edited April 2019 #2

    I'm no code expert, but my understanding is small low voltage DC circuits (<48v, eg LED lights) often aren't grounded, but higher voltage ones (eg pv string voltage in combiner box) should/must be. Boxes generally have provision for grounding - eg Midnite mnpv combiners have a ground buss bar.

    I ran a ground wire from combiner to ground buss in an epanel, which is then grounded to main house ground.

    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #3

    Ground referencing a power system (tying the return--Negative Typically--To a common metal like cold water pipes, electrical boxes) is what allows us to use single pole breakers and fuses (overcurrent protective devices) only on the "hot leads". The ground bonded return leads never become "hot", so they do not need fuse/breaker.

    Now, that definition works in a home or vehicle (metal frame of vehicle).

    Floating supplies, while it is "safe" to short one wire to ground--But this now creates a "ground referenced" power system. And if the short to ground is not in the "fuse/breaker" protected line, it is very possible that a second short to ground will "go around" the OCP device and allow the wiring to catch fire.

    A ground rod, really does nothing for electrical safety--I.e., the ground bond to a ground rod does not carry enough current to even pop 15 amp 120 VAC breaker in a dead short.Tying all the ground bonded neutral, plumbing (cold water/hot water, natural gas pipes, etc. together with the "ground rod") ensures that a "short from hot to "any ground bonded stuff" wil pop a breaker.

    Specifically, what a ground rod does is provide static electricity grounding, and lightning strike grounding. Static grounding for things like a TV antenna on a roof (can get hundreds of volts of "charge" from natural electric field of the earth of ~100 volts per meter, and thousands of volts of charge if a thunder cell goes over your home). And to direct lightning energy outside of your home direct to earth ground rather than the lightning finding its own way through your house wiring and plumbing to earth).

    -Bill

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • KhellSk
    KhellSk Registered Users Posts: 91 ✭✭
    #4

    Well doest it garantee a path to somewhere else than my body if the return to battery was broken off ??fuse and breaker protects wire not ppl.

    So what happens if i ground the negative of the battery to the ground. Will it chose the ground instead of the battery ?

    _____________________________________________
    [3p3s 48w 15.9Vmp] [Flooded 2x 6v 150ah]
    [Victron 50/100 700wMax MPPT]







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  • Tecnodave
    Tecnodave Registered Users Posts: 437 ✭✭✭✭
    #5

    Bill,

    Well, I gotta differ from you on that statement. "the ground rod does nothing for electrical safety...I.e. the ground bond to the ground rod does not carry enough current to even pop a 15 amp breaker on a 120 VAC breaker in a dead short circuit"

    I personally have shorted out the main buss of a 200 amp service panel by accidentally shorting a grounded 14 ga bare wire to the breaker stabs.....The main 200 amp buss! The 200 amp main breaker banged off very fast! And the peice of 14 gauge circuit did not melt. It was about 10-12 inches of 14 gauge to the ground buss in this box which had a 6 ga. Copper wire running about 5 feet to a just driven 8 foot copper coated ground rod. I was in the process of upgrading the service in this house. The power was turned on before I was finished due to several newborns in the house. This was an emergency upgrade due to the renters situation. It was not a stress test! At the time I thought that the 14 gauge wire would melt.....vaporize.......it didn't! Giant crowbar! Got a new respect for the NEC that requires no larger than a 6 gauge wire for the ground rod up to 200 amps service. This was a brand new Schneider Square D division HomeLine 20/40 breaker panel. I had a small nick in the breaker stab, a nick in the wire and very frayed nerves after that.

    Seriously the ground rod system does work and does prevent accidental electrocution! If you don't have a secure ground the whole electrical system can float above ground and present a hazard. If in worst case the ground bond at the structure and the ground bond at the utility transformer were both broken then the electrical system could "float" hundreds or thousands of volts above or below ground. The primary winding of the utility transformer for a typical residential service is 5000 volts!

    I tinker with solar, my money is utility power. I change out 20-40 main panels a year and do 240 volt delta hi leg and 480 volt wye service for a living... I have done 100 h.p. 480 volt 3 phase live many times! Farmers cannot wait for PG&E to shut down power. They could lose >$100,000 a day without power. With homeowners its "how much to fix this"......farmers " can you get here now?" I'm more than $500 minimum to touch live 480.......often take home a thousand for the morning.

    david

    2 Classic 150, 2 Kid, 5 arrays 7.5 kw total  2ea.  2S6P Sharp NE-170/NE-165, 1ea. 12P Sanyo HIT 200,  2ea. 4/6P Sanyo HIT 200, MagnaSine MS4024AE, Exeltech XP-1100,  2 Banks L-16 battery, Rolls-Surette S-530 and Interstate Traction, Shunts with whizbangJr and Bogart Tri-Metric, iCharger i208B  dc-dc buck/boost converter with BMS for small form lithium 8S 16650 or LiFePO4,
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  • Tecnodave
    Tecnodave Registered Users Posts: 437 ✭✭✭✭
    #6

    Kshellsk,

    for safety do ground the DC ground at the main ground rod.....do not remove the AC ground.....get a ground rod clamp from home Cheepo and mount it next to the AC ground rod clamp. While you are there see if you can pull out the existing ground rod. When replacing panels I often find a 6 inch stub left of the original ground rod all corroded out from the current!

    david

    2 Classic 150, 2 Kid, 5 arrays 7.5 kw total  2ea.  2S6P Sharp NE-170/NE-165, 1ea. 12P Sanyo HIT 200,  2ea. 4/6P Sanyo HIT 200, MagnaSine MS4024AE, Exeltech XP-1100,  2 Banks L-16 battery, Rolls-Surette S-530 and Interstate Traction, Shunts with whizbangJr and Bogart Tri-Metric, iCharger i208B  dc-dc buck/boost converter with BMS for small form lithium 8S 16650 or LiFePO4,
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  • KhellSk
    KhellSk Registered Users Posts: 91 ✭✭
    #7

    @Tecnodave Heres my system, i dont have Ac

    /solarpanels/===line fuse===/charge controler/===lines fuse===/battery/===line fuse===/6inch pullbox with 12vcig plug & switched led strip/


    Thats litteraly it. No grounding frame or system. No inverter. No distributionPanel.


    Where would you add it ? Straight from the battery neg side to a rod ?

    _____________________________________________
    [3p3s 48w 15.9Vmp] [Flooded 2x 6v 150ah]
    [Victron 50/100 700wMax MPPT]







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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #8

    Don't even bother, by description it's extra low voltage Class 2, just use fuse or circuit less than 8 amps to be within the 100VA requirements of the classification. The voltage is not considered dangerous but a short circuit between + & - can melt unprotected conductors, the battery has enormous amounts of current, but if limited by the overcurrent protection device, the fuse in your case, it would be intrinsically safe.

    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #9

    The ground rod can have up to 25 ohms resistance to ground.

    120 vac / 25 ohms = 4.8 Amps

    A few people have found their electrician had tied L1 (120 vac to neutral) to their ground rod instead of the neutral from the pole transformer, and found the problem because the snow was melting around their ground rod.

    Bill

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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