Grounding House Electrical Question

[WhiteWhale]

Should I bond negative side of house battery bank to bus chassis? I am running 2 wires to all DC accessories from DC load center, so I wont be trying to use body or chassis for individual negative connections. Is it still necessary/recommended to bond negative battery connection to chassis for any reason? And if so, would the steel chair rail on the interior of the bus be adequate? My battery bank is inside the cabin so Id rather not have to go through floor to chassis if I dont have to. I would think the metal body would be adequate and is tied to chassis anyway?

My Aims inverter does say to bond safety ground to chassis as well. Can this be bonded to body instead? Is it bad to bond inverter ground and battery negative at same point or near each other?

Thanks for the help.

[roach711]

If you'll be charging your house bank with the alternator you'll have to ground to the body/frame or run a negative cable back to the starting batteries. With no alternator charging and all house DC grounds hardwired back to the house bank you could forgo the chassis ground.

Many here have grounded to the metal body. The body & frame will be bonded together with a ground cable. Corroded connections can limit its effectiveness though, so it's a good idea to check and clean up any corroded ground cables/straps you find.

Your 120v AC service should be grounded to the bus also to avoid the dreaded "hot body" condition. Make sure your AC breaker box has separate neutral and ground bus bars and that the panel itself is grounded to the body/frame. The neutral and ground should only be combined back at the shore power panel.

To check your battery-to-frame-to-body ground connections set your voltmeter to 200 OHMS (not 200K ohms) Touch the leads together to check that the meter is working properly (should read 0 ohms) then put one lead on the battery ground post and one on a clean (paint/rust free) spot on the body. You should see zero ohms with a good ground. Anything over .5 ohms and you should check your connections.

[leadsled01]

Roach, I like the way you explain things, simple and to the point. I'm an electrician but can't find the words like you can. Thanks for all you do.

Originally Posted by roach711

If you'll be charging your house bank with the alternator you'll have to ground to the body/frame or run a negative cable back to the starting batteries. With no alternator charging and all house DC grounds hardwired back to the house bank you could forgo the chassis ground.

Many here have grounded to the metal body. The body & frame will be bonded together with a ground cable. Corroded connections can limit its effectiveness though, so it's a good idea to check and clean up any corroded ground cables/straps you find.

Your 120v AC service should be grounded to the bus also to avoid the dreaded "hot body" condition. Make sure your AC breaker box has separate neutral and ground bus bars and that the panel itself is grounded to the body/frame. The neutral and ground should only be combined back at the shore power panel.

To check your battery-to-frame-to-body ground connections set your voltmeter to 200 OHMS (not 200K ohms) Touch the leads together to check that the meter is working properly (should read 0 ohms) then put one lead on the battery ground post and one on a clean (paint/rust free) spot on the body. You should see zero ohms with a good ground. Anything over .5 ohms and you should check your connections.

[WhiteWhale]

Originally Posted by roach711

If you'll be charging your house bank with the alternator you'll have to ground to the body/frame or run a negative cable back to the starting batteries. With no alternator charging and all house DC grounds hardwired back to the house bank you could forgo the chassis ground.

Many here have grounded to the metal body. The body & frame will be bonded together with a ground cable. Corroded connections can limit its effectiveness though, so it's a good idea to check and clean up any corroded ground cables/straps you find.

Your 120v AC service should be grounded to the bus also to avoid the dreaded "hot body" condition. Make sure your AC breaker box has separate neutral and ground bus bars and that the panel itself is grounded to the body/frame. The neutral and ground should only be combined back at the shore power panel.

To check your battery-to-frame-to-body ground connections set your voltmeter to 200 OHMS (not 200K ohms) Touch the leads together to check that the meter is working properly (should read 0 ohms) then put one lead on the battery ground post and one on a clean (paint/rust free) spot on the body. You should see zero ohms with a good ground. Anything over .5 ohms and you should check your connections.

Thanks! I won't be charging house bank from alternator so it sounds like no need to ground batteries then.

As for AC my inverter/charger is equipped with a relay that uses the chassis ground from the inverter when running off batteries, but switches to shore power ground only when plugged in. I was under the impression that the relayed ground from the inverter is the only place I should bond to chassis. This will serve as ground when inverting, and the shore ground should be the only ground when plugged in. If I were to bond AC panel to chassis as well wouldn't that create two separate grounds when plugged into shore power?


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[roach711]

I've never installed an inverter/charger so I'd go with the manufacturer's instructions. That said, I can't imagine how multiple AC grounds would be a problem. The relay may be there to switch between a utility ground and a generator ground. When in doubt a quick call to the manufacturer's tech support should be the final word. In this case, do not rely on my advise.

Remember that an AC ground is a safety circuit only and doesn't normally carry any current. A DC ground is the return circuit. A DC ground has the same purpose as an AC neutral.

[roach711]

Leadsled - You're like my nephew who's also an electrician. He knows the subject instinctively but when he tries to explain in mugglespeak it's hard for him. It's like explaining how to walk, he doesn't have to think about it anymore so the words are irrelevant.

I have to rethink (sometimes relearn) the subject each time I post so I have to make it understandable to myself first.

[roach711]

I had a look at an AIMS inverter/charger manual and you may be thinking about the automatic neutral to ground switching feature. When plugged in, the shore power main panel AC ground and the inverter AC ground are connected as they normally would be. At the main panel (and only at the main panel) the neutral and ground are connected together. This makes the breakers work properly. Don't ask me why.

When on inverter power there is no "main panel" so the relay connects the AC ground and neutral at the inverter so the breakers will work as they should. This, in effect makes the inverter the main power panel.

It's best to think of all this as magic.

At any rate, there is a ground lug on the inverter case that should be cabled to a good body ground.

[WhiteWhale]

Originally Posted by roach711

I had a look at an AIMS inverter/charger manual and you may be thinking about the automatic neutral to ground switching feature. When plugged in, the shore power main panel AC ground and the inverter AC ground are connected as they normally would be. At the main panel (and only at the main panel) the neutral and ground are connected together. This makes the breakers work properly. Don't ask me why.

When on inverter power there is no "main panel" so the relay connects the AC ground and neutral at the inverter so the breakers will work as they should. This, in effect makes the inverter the main power panel.

It's best to think of all this as magic.

At any rate, there is a ground lug on the inverter case that should be cabled to a good body ground.

Roger that. So the inverter ground lug to body only. No need to bond my breaker panel to body as well?


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[roach711]

The sub panel would ground back to the inverter so a ground from the panel to body wouldn't be necessary.

Wrapping my head around the AC and DC wiring in our bus was easily the hardest part of our conversion.

[Chevydude01]

Originally Posted by roach711

Wrapping my head around the AC and DC wiring in our bus was easily the hardest part of our conversion.

I hear that. That's what I'm working on right now

[WhiteWhale]

Thanks everyone. Hopefully wrapping my electrical up soon!

[turf]

i set my bus up with a "floating" 12v house circuit. i do not use the bus body to ground it at all.

there are some advantages to have the systems separate, and some advantages having them tied together.

some of the comments are right on like you can't charge your house bank with the alternator. they'll need their own charger. on the plus side, it wouldn't drain your truck battery, no matter what. and its probably safer, if you're willing to run 2 wires everywhere.

safer because the 2 systems will not short out each other. i can take a hot wire from the house battery, and accidentally brush it against the body and nothing happens.
my battery charger for the house battery does ground to the chassis. but its only the 120v side that grounds, the output from the battery is "floating".

[KerryBeth1985]

... but you guys seem to know your stuff. we are starting rough in framing and electrical on our conversion. i want LOW EMF as much as possible. (yes, yes, i'll get my tin foil hat right after the conversion). moving on, our low EMF protocols (metal conduit from battery array to electrical cabinet, isolated ground MC wiring, etc. all require separate grounds.

i am paying an electrician with solar and bus conversion experience to install the electrical but i like to ensure that things are done correctly.

the multiple grounds all specify separate grounding "earth ground". how will this be done in a bus conversion?

[lanegordon]

Can we get clarification that the chair rail or steel "ribs" of the bus are an adequate for "grounding to the chassis." It seems like a logical place to ground to so cutting holes in the floor could be avoided. I was wondering the same hitting. Any insight?

I will need to ground my 110 box, my battery bank (because I am running a battery isolator for charing while going down the road too) and I have an AIMS 3000W inverter. Does the AIMS inverter need to be grounded (and can it be done on the chair rail or a metal rib)?

Thanks everyone!

[CaptSquid]

Ground is ground. The lower chair rail seems to be an obvious point, but how do you propose getting electricity from the battery bank to your inverter without drilling holes? Scotty can't beam the electricity up to your inverter.

On a side note, try to make the cable run from the batteries to your inverter as short as possible.

[ol trunt]

I can agree with Cptn S that ground is ground----with the stipulation that regardless of the source of the electricity, shore, genny, inverter or battery the ground must be directed back to its original source. If you are using a genny the ground must go back to the genny. If you are using Ma Edison's electric then the ground MUST go back to Ma Edison, if you are using an inverter the ground must go back to the inverter. The chair rail is not the issue.

Take the time to Google grounding issues Skoolie.net. You will find this method of searching Skoolie to be better than using Skoolie's own search mechanism.

Improper grounding can lead to your bus having a "hot skin". If this happens, YOU become the ground rod when you step on or off the bus--a real killer deal.

Jack

[family wagon]

It isn't totally clear from the context what's meant by "grounding" (ac safety ground, or dc negative/return). I'd humbly submit that the negative wire on the dc supply side of a 3kW inverter really ought to have its own cable back to the battery negative -- don't send ~300 amps back via jumpers to the chassis/body. For the ac safety ground: choose a place that's accessible for inspection later and clean it down to bare metal.

[ol trunt]

Here is a easy to understand article on RV electrical.
Are “Little” Shocks OK? | No~Shock~Zone.

Its author is Mike Sokol. Mike provides both text and wiring diagrams that cover the AC circuit in your bus. He explains line, common and (safety) ground and where each must be hooked up.

Jack

[CaptSquid]

The 10 Commandments of Electrical Safety - Navy Version

I Beware of the lightning that lurketh in seemingly uncharged capacitors, lest it cause thee to bounce upon thy buttocks in an unseamanlike manner and cause thy hair to stand on end, thereby exceeding regulation length.

II Cause thou the switch that supplieth large quantities of juice to be opened and thusly tagged, that thy days may be long in this earthly vale.

III Prove to thyself that all circuits that radiateth and upon which thou worketh are grounded and thusly tagged, lest they lift thee to radio frequency potential and causeth thee to radiate with the angels.

IV Tarry thou not amongst those fools that engage in intentional shocks, for they are not long of this world and are surely unbelievers.

V Take care thou useth the proper method when thou taketh the measure of high voltage so that thou dost not incinerate both thee and thy test meter. For verily, though thou has no NSN and can be easily surveyed, the test meter has one, and as a consequence, bringeth much woe unto thy supply officer.

VI Take care thou tamperest not with interlocks and safety devices, for this incurreth the wrath of thy department head and bringeth the fury of thy commanding officer on thy head.

VII Work thou not on energized equipment without proper procedures, for if thou dost so, thy shipmates will surely be buying beers for thy widow and consoling her in certain ways not generally acceptable to thee.

VIII Verily, verily, I say unto thee, never service equipment alone, for electrical cooking is a slow process, and thou might sizzle in thy own fat upon a hot circuit for hours on end before thy maker sees fit to end thy misery and drag thee into his fold.

IX Trifle thee not with radioactive tubes and substances lest thou commence to glow in the dark like a lightning bug and thy wife be frustrated and have no further use for thee except for thy wages.

X Commit thou to memory all the words of the prophets which are written down in the 300th chapter of thy Bible which is the "Naval Ships' Technical Manual", and giveth out with the straight dope and consoleth thee when thou hast suffered a ream job by thy division LPO.

[meteoricide]

Originally Posted by CaptSquid

The 10 Commandments of Electrical Safety - Navy Version



I Beware of the lightning that lurketh in seemingly uncharged capacitors, lest it cause thee to bounce upon thy buttocks in an unseamanlike manner and cause thy hair to stand on end, thereby exceeding regulation length.



II Cause thou the switch that supplieth large quantities of juice to be opened and thusly tagged, that thy days may be long in this earthly vale.



III Prove to thyself that all circuits that radiateth and upon which thou worketh are grounded and thusly tagged, lest they lift thee to radio frequency potential and causeth thee to radiate with the angels.



IV Tarry thou not amongst those fools that engage in intentional shocks, for they are not long of this world and are surely unbelievers.



V Take care thou useth the proper method when thou taketh the measure of high voltage so that thou dost not incinerate both thee and thy test meter. For verily, though thou has no NSN and can be easily surveyed, the test meter has one, and as a consequence, bringeth much woe unto thy supply officer.



VI Take care thou tamperest not with interlocks and safety devices, for this incurreth the wrath of thy department head and bringeth the fury of thy commanding officer on thy head.



VII Work thou not on energized equipment without proper procedures, for if thou dost so, thy shipmates will surely be buying beers for thy widow and consoling her in certain ways not generally acceptable to thee.



VIII Verily, verily, I say unto thee, never service equipment alone, for electrical cooking is a slow process, and thou might sizzle in thy own fat upon a hot circuit for hours on end before thy maker sees fit to end thy misery and drag thee into his fold.



IX Trifle thee not with radioactive tubes and substances lest thou commence to glow in the dark like a lightning bug and thy wife be frustrated and have no further use for thee except for thy wages.



X Commit thou to memory all the words of the prophets which are written down in the 300th chapter of thy Bible which is the "Naval Ships' Technical Manual", and giveth out with the straight dope and consoleth thee when thou hast suffered a ream job by thy division LPO.

Amen. Oh and never place a 3 dimensional radar array in pencil beam mode, crank output power to 1 billion watts - and attempt to flame seagulls flying around your port of call. It may interfere with local ATC radars and cause great backlash on your command!


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