Grounding the negative terminal..... should I?

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Shadow_Storm56
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Grounding the negative terminal..... should I?

Post by Shadow_Storm56 »

One thing I never did since the early days of working with solar and wind on my farm is running a ground line directly to the negative post on the battery terminal of my battery bank. I ground everything else as you are supposed to but never did that as it caused terrible things in my first system so I didn't see the benifit.

My first ever system was in a greenhouse and I ran a wire from the battery negative out to a seperate ground rod like recommended. It turned the entire greenhouse into a reference to the negative terminal on the battery and weird stuff happend..... charge controllers would still operate without a negative connection.... as would inverters or anything in a metal box.

I just never liked having everything metal being 1 wire away from having the full short circuit force of the battery flow to it even if they did have fuses to protect them.

So my question is what's the benifit? Everything in the system is grounded as per usual so why do I want to make everything.... even the outside case of the main inverter reference to terminal negative? Please explain...

I have had zero issues with having the negative terminal not connected directly to ground but I always like to learn new information so I thought I'd ask
raysun
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Re: Grounding the negative terminal..... should I?

Post by raysun »

Not knowing anything about the prior system, it would be difficult to comment on the "weirdness". However, back in the day, my Austin Healey and much solar gear had positive ground. Connecting the most power-laden negative potential to positive ground equipment would cause some interesting effects.

Many systems can work quite successfully with a "floating" ground. That is, until something comes along to upset the apple cart, and set it on fire.

The two main reasons to establish a good and consistent ground are:

• To keep exposed metal objects from becoming an accidental conductor in the case of a short circuit in the equipment. Grounding the case to the lowest potential available (earth) is a mechanical, or equipment ground, and is meant to provide a path for errant electrons, other than the hapless victim who might touch an energized metal case.

• To provide a safe exit path for surges and transients. This is an electrical ground. Many pieces of electrical equipment have transient protection circuitry. If they absorb a voltage spike, and have no path to ground, the circuit becomes all stressed up with no place to go. It will end up venting its pent up potential into other circuits, or someone's circulatory system. Both are bad, best to channel that stuff to ground.

Ground means the lowest potential. It doesn't necessarily mean the core of the Earth. If a spike, short, or other errant electron gang doesn't get a dirt nap, however, its likely to congregate on some unwanted circuit corner. Which one is easiest? You guessed it, Battery Negative. Apply a jolt of White Heat to a Pillar of Lead, and what do you get? Molten Slag. That might be a name you'd find in red lights on a Soho Walk-up, but isn't a good look for a battery. Best provide a path to ground.
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Re: Grounding the negative terminal..... should I?

Post by fcwlp »

raysun wrote: Tue Oct 05, 2021 10:23 pm Best provide a path to ground.
Raysun, while this is true, how it is done is a function of the system design. Off-grid vs On-grid, GFDI presence, FM60/80 vs FM100, etc. In other words read the installation manual for your system.
raysun
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Re: Grounding the negative terminal..... should I?

Post by raysun »

fcwlp wrote: Wed Oct 06, 2021 12:14 pm
raysun wrote: Tue Oct 05, 2021 10:23 pm Best provide a path to ground.
Raysun, while this is true, how it is done is a function of the system design. Off-grid vs On-grid, GFDI presence, FM60/80 vs FM100, etc. In other words read the installation manual for your system.
Yep.
Shadow_Storm56
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Re: Grounding the negative terminal..... should I?

Post by Shadow_Storm56 »

raysun wrote: Tue Oct 05, 2021 10:23 pm Not knowing anything about the prior system, it would be difficult to comment on the "weirdness". However, back in the day, my Austin Healey and much solar gear had positive ground. Connecting the most power-laden negative potential to positive ground equipment would cause some interesting effects.

Many systems can work quite successfully with a "floating" ground. That is, until something comes along to upset the apple cart, and set it on fire.

The two main reasons to establish a good and consistent ground are:

• To keep exposed metal objects from becoming an accidental conductor in the case of a short circuit in the equipment. Grounding the case to the lowest potential available (earth) is a mechanical, or equipment ground, and is meant to provide a path for errant electrons, other than the hapless victim who might touch an energized metal case.

• To provide a safe exit path for surges and transients. This is an electrical ground. Many pieces of electrical equipment have transient protection circuitry. If they absorb a voltage spike, and have no path to ground, the circuit becomes all stressed up with no place to go. It will end up venting its pent up potential into other circuits, or someone's circulatory system. Both are bad, best to channel that stuff to ground.

Ground means the lowest potential. It doesn't necessarily mean the core of the Earth. If a spike, short, or other errant electron gang doesn't get a dirt nap, however, its likely to congregate on some unwanted circuit corner. Which one is easiest? You guessed it, Battery Negative. Apply a jolt of White Heat to a Pillar of Lead, and what do you get? Molten Slag. That might be a name you'd find in red lights on a Soho Walk-up, but isn't a good look for a battery. Best provide a path to ground.
See to me it seems more dangerous that's why I'm scared to do it..... If I connect the negative terminal to ground in our electrical system the ground an AC neutrel are bonded. So this would link the battery negative and neutrel making everything in the 4 buildings on the farm attached to the same transformer and all metal appliances inside them reference to battery negative. Also means if there was ever a line break and a floating neutrel my entire DC system would have 120v ac on the negative. Myself I would probably drive in a seperate ground rod.... so that battery negative isn't linked to ac neutrel. There would still be a path through the ground between the rods but it wouldn't be such a direct link.
Shadow_Storm56
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Re: Grounding the negative terminal..... should I?

Post by Shadow_Storm56 »

My inverters junction panel has 2 giant ground bus bars and a giant battery negative bus bar so it was as simple as connecting the 2 with a short piece of 2 awg wire which I had. It didn't do weird stuff like last time whare everything runs even if you disconnect the negative connection. The cheap stuff I bought back years ago when I started with solar appears to have had the dc negative linked to the case. So as long as the ground was connected then things ran without the negative connection.

I checked before linking them and there was no other point in the system whare ground and negative were linked but there was a 1.1v dc between the negative and ground. Theres a 3v potential between N and ground on that line which is leakage from the heat pumps inverter. I expect that the 1.1v is from the same source but different potential.
raysun
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Honda EU7000is gas fuel generator

Re: Grounding the negative terminal..... should I?

Post by raysun »

The battery negative should now be at ground potential. The positive terminal now defines the highest potential above ground for the DC side of the system.

Equipment grounds and neutral on the AC side should likewise connect and be at the same potential.

Any higher potential, shorted to a grounded component, can cause damage, but the voltage at least has a place to go, other than through a body.

Protection devices like circuit breakers, GFDI and Arc Fault circuits, surge suppressors, etc., all provide methods to interrupt the errant potential.

Keeping equipment in good shape, good electrical connections, proper power handling capacity, all contribute to the avoidance of a ground circuit ever carrying current.
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