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Old 05-21-2018, 12:07 AM   #1
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Grounding necessary? question for extension cord style electrical system

Hi all,
I'm sure this question has been answered but I haven't a clue for to search for it and don't believe I've stumbled across the answer in my prior research.

I am currently installing a secondary "shore power" system for my bus. This will have a separate 120v circuit for powering appliances which my 1000watt inverter can't handle, aka my wife's favorite hair dryer and our convection oven. It will not go through my primary system at all and will basically act as an extension cord outlet splitter in the bus. Since this technically will be grounded from the source of where we are plugged in, am I okay leaving it ungrounded in my bus? Also will I be causing problems for myself if I have them wired through a GFCI?


Just to clarify all my outlets in my primary system will go through a GFCI and are grounded to the frame of my bus, which I believe is proper practice encouraged based off Mike Sokols no shock zone.. Which I haven't read recently.. I am only inquiring if it is safe to skip the ground in my secondary "shore only and maybe occasional generator use" system.

Thank you all in advance;
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Old 05-21-2018, 12:51 PM   #2
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To be clear,

Are you asking if you can skip the ground wire completely or if you need to bond ground and neutral?
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Old 05-21-2018, 01:08 PM   #3
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What does the "primary shore power" connection look like? To most people "shore power" means a cord going from the vehicle to a power source that's part of the permanently installed electrical system at a home/RV park/storage/wherever. Does your primary system plug to some external source like this, or is it limited to being powered only by an on-board inverter?
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Old 05-21-2018, 01:22 PM   #4
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Love to hear the answer both ways: I'm in the same boat.

12v Marine battery, 2000W inverter: connect green wire to bus chassis and call it done?

Extension cord: connect green wire to bus chassis and call it done?
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Old 05-21-2018, 05:43 PM   #5
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If your source of power is from off the bus (earth) you need to be grounded to that source of power. Otherwise any potential which develops in the bus skin could potentially use a person to find the sources ground
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Old 05-22-2018, 02:57 AM   #6
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Hi guys,

Thank you so much for taking the time to respond to this. In a sense I owe you my life, but maybe we'll have to settle for a brew or two.

Quote:
Originally Posted by family wagon View Post
What does the "primary shore power" connection look like? To most people "shore power" means a cord going from the vehicle to a power source that's part of the permanently installed electrical system at a home/RV park/storage/wherever. Does your primary system plug to some external source like this, or is it limited to being powered only by an on-board inverter?


I apologise this diagram is hideous, but I got distracted at work and didn't get around to making this on my computer. I hope this illustrates my primary and proposed secondary system

There are also solar panels in there I forgot to add but I don't think that matters for this.

Here are some pictures of my system if relevant, there is black heat shrink acting as a stripe mark to separate the neutral (left one is striped)and ground wires


Based off this diagram



@pnwsteve, thank you for asking such a relevant question which I didn't consider... I haven't set up anything AC other than my battery charger, currently neutral is not grounded. Would you recommend I bond it before the AC in or after the ac out ? Is it okay if I just wire it into the ground bus bar? I believe I have a second insulated bar in my box for my unbonded neutral. I'll be consulting 2-3 electricians (one to assist with installing my outlets before my move, one family member who I'll be seeing once I move, and a friend I haven't seen in awhile) over the coming months to verify since I'm clearly not qualified to do this solo. You're welcome to stop by too if you want! *Wink

So I guess now I have two questions about

1. If I need to ground my secondary shore power only electrical system to bus?(I think mgulley says I best not ground this to the bus to avoid a hot skin condition)
And
2. where to bond my neutral and ground for my "primary system".

Thank you again everyone for your input, it is very much appreciated!!
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Old 05-22-2018, 07:29 AM   #7
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I wish I was qualified to give a really great technical answer. I'm not... only a tiny bit of real world experience.

I did the research back when I was hooking up my system and I felt the answer was to ground everything - which I did and it is all working as expected. The breaker panels, inverter, etc... are all grounded to the chassis.

All of my outside power comes thru a Progressive Dynamics PD52DCSV. I've never connected to a generator.
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Old 05-22-2018, 08:05 AM   #8
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Yes, ground always. Think of your bus like it's an appliance - a washing machine for instance. With any connection to mains you should ground because there's always the ever so unlikely possibility that a wire could be frayed (most likely outside) and will touch the bus metal. Without grounding the breakers and/or GFCIs will not trip and the skin will be electrified.
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Old 05-22-2018, 09:28 AM   #9
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In the pic of the breaker box, why haven't you connected the neutral incoming wire to the neutral bar, directly opposite the ground bar. I see 2 wires on the ground with one having black heat shrink on it. Is that what you consider your neutral?
You have me confused as to what you are doing because I also see a white wire with black heatshrink going nowhere.
Wondering who is confused, you or me?

John
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Old 05-22-2018, 12:57 PM   #10
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Quote:
Originally Posted by jazty View Post
Yes, ground always. Think of your bus like it's an appliance - a washing machine for instance. With any connection to mains you should ground because there's always the ever so unlikely possibility that a wire could be frayed (most likely outside) and will touch the bus metal. Without grounding the breakers and/or GFCIs will not trip and the skin will be electrified.
Thank you Jazty! So I will ground my secondary system to my bus frame.

Quote:
Originally Posted by BlackJohn View Post
In the pic of the breaker box, why haven't you connected the neutral incoming wire to the neutral bar, directly opposite the ground bar. I see 2 wires on the ground with one having black heat shrink on it. Is that what you consider your neutral?
You have me confused as to what you are doing because I also see a white wire with black heatshrink going nowhere.
Wondering who is confused, you or me?

John
That would be me. And perhaps my electrician friend. I have no reason to have not connected the incoming neutral wires to the bar other than ignorance. You are correct that the outgoing neutral wire goes to nothing at the moment. I will ask him about these next time he comes to help.

Thank you for for looking out for my safety.
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Old 05-22-2018, 01:23 PM   #11
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What really puzzles me is your incoming wiring.

I see two grounds, 3 neutrals, and a red and a black.

Have you used the conduit for both incoming service and outgoing branch circuits? They really should be separate to avoid confusion down the road at some point should you have to troubleshoot.

I think what I see is that you have tried to combine two different service cords which is not a standard practice. You need one hot wire, one neutral and one ground wire in your main service cable minimum.

The way you have it, one circuit could be on,the other off and a backfeed can occur onto the neutral which is not a good thing.

I hope this helps but not knowing what you are doing, I am likely just guessing as to what you are doing. I'm sure your electrician buddies will set you straight.

Good luck,

John
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Old 05-24-2018, 02:47 PM   #12
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Quote:
Originally Posted by Mgulley82 View Post
If your source of power is from off the bus (earth) you need to be grounded to that source of power. Otherwise any potential which develops in the bus skin could potentially use a person to find the sources ground
THIS.

If you ground your "external source" AC to the bus chassis, you walk outside and touch the bus, YOU could be the shortest path to ground. The ground wire leading into the bus from the external source should float.

Now with the inverter, I really don't know the answer to this one, but I'd still assume you'd want it to float. If you have any chance of touching a surface that electrically leads to ground, I'm not sure how it helps you to ground to the chassis.

I think one of if not the primary reason why the chassis is used by the DC system is that you only need a single conductor going to each appliance.
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Old 05-24-2018, 02:51 PM   #13
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??? What?? no. You should always ground the chassis+skin and continue that ground to whatever you plug into. When plugging into a power pedestal you should also check that it is grounded properly to finish the ground.
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Old 05-24-2018, 02:58 PM   #14
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Quote:
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??? What?? no. You should always ground the chassis+skin and continue that ground to whatever you plug into. When plugging into a power pedestal you should also check that it is grounded properly to finish the ground.
Are there not edge cases where this is highly undesirable? If you come into physical contact with the chassis and an energized surface, YOU could become the path to ground.

I also would think that for with buses with inverter setups this would also require some more thought. Since you're potentially mobile, I would think that you wouldn't want for your chassis to be grounded while you are not plugged into a pedestal.

If the assumption is that you're always plugged in, I could see that you are right. This is how its done in building code. But think about what that grounding is actually going to do if either you're not plugged into shore or your shore has a bad/missing ground.
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Old 05-24-2018, 03:03 PM   #15
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No edge cases. Ground it properly and test outlets before plugging in. Don't build your platform around 1 or 2 miswired outlets that you know of. Build it for the 99% of properly wired outlets and test all outlets before plugging in.
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Old 05-24-2018, 03:11 PM   #16
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Quote:
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No edge cases. Ground it properly and test outlets before plugging in. Don't build your platform around 1 or 2 miswired outlets that you know of. Build it for the 99% of properly wired outlets and test all outlets before plugging in.
When I say "edge case", I mean an unlikely scenario or scenario on the border of possibility where the system you're designing could behave differently than you intend. Its programmer-lingo, I don't mean "exceptions to the rule".
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Old 05-24-2018, 03:16 PM   #17
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No edge cases. This is an electrical question that has definitively, objectively been decided by smarter people than I and I fully agree with them. Ground the chassis. If you don't ground the skin you introduce more risk than if you don't. And test your outlet.


AC electrical systems are not dynamic. You won't be introducing an if-else statement for whether or not there is a working ground. Edge case electrical programming can be done, but it's unnecessary. Do it right. Check your power outlets.
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Old 05-24-2018, 03:20 PM   #18
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To some degree you're correct that a person might pick up a faulty appliance and become energized, then touch some grounded metal structure and receive a shock. That's no different in a vehicle, a metal building, or a bathtub.

The solution to this case is not to float the structures, but rather to use GFCI to detect and interrupt that shock current.
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Old 05-24-2018, 03:24 PM   #19
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Quote:
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No edge cases. This is an electrical question that has definitively, objectively been decided by smarter people than I and I fully agree with them.
An argument from authority is not an argument. If you're not willing to do the mental exercise of attempting to reach the truth, I'm not interested in your reply. I'm not willing to delegate my decisions to others blindly, I want to understand the logic.

Quote:
Originally Posted by jazty View Post
Ground the chassis. If you don't ground the skin you introduce more risk than if you don't. And test your outlet.
"Test your outlet" doesn't address the problem case I'm raising. You haven't said anything about why not grounding introduces risk, you're just saying it does. Try saying why it does, that would help.

Quote:
Originally Posted by jazty View Post
AC electrical systems are not dynamic.
In a house, yes. I just gave you a scenario where the conditions are dynamic- buses that are mobile with inverters. They are not always going to be grounded or even connected to a pedestal, period. In those cases, what is the behavior of a system that grounds to chassis versus does not?

Quote:
Originally Posted by jazty View Post
Do it right.
Which is precisely why I'm interested in talking to something more than a parrot. Can we address the raised scenario?
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Old 05-24-2018, 03:28 PM   #20
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The solution to this case is not to float the structures, but rather to use GFCI to detect and interrupt that shock current.
This seems right until I get to the inverter case: if you're on inverter power and boondocking, for example. In that case, it truly seems like it may be unwise to ground to the chassis, unless you have your own lightning rod in the ground.
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