Bus Electrical (house) problems

[86102A3]

The code is concerned with insulation values. If you run your 12v with wiring that has an insulation rated at the same or greater than your 120v that will meet the NEC. This is for insulation of wiring in shared raceways. The distribution panels should be separate.

[robertglines1]

I reviewed my original post and response on continuity between green wire and white at campground post. You say  yes.. Then in effect when you plug in you complete the the connection of green Safety and white common you so carefully kept separate in in bus. So ? keep separate in coach but defeat at pedestal? Also complete ground Chassis of bus DC to AC when you plug in. I will leave this discussion to those whom are expert.One advise to guys whom have to do their own.. Keep your color code standard so you know what wire does what.  Rolls of wire are cheap when in the future you are someone trying to read your mind has to figure it out.  Example 12 Volt DC= yellow  DC grounds =Black  24Volt dc +=red.    120-240 volt ac  Green =safety ground  white = neutral/common  red=line 1   black = line 2 . I use tatoo # on wires to identify circuits.  So I'm totally wrong?  I stay confused about the grounds because If they are bonded anywhere the whole system becomes one. Yes I do understand if one ground(say white) fails in a outlet the 2nd(suppose green safety) will complete circuit.

[robertglines1]

My response: I noticed original poster withdrew his picture and is probably dismayed. Please don't feel like that! Know you are not alone... This subject has been a discussion for years and many time on the board. If you want to have a idea of what you have plug it into a proper outlet and have someone test it for you.     Respect to all.  Bob

[bevans6]

The reason you keep ground and neutral separate on the bus is that neutral is the return path for the load current.  Current goes out to the load, and returns on the neutral conductor, all the way back to the bond between neutral and ground at the source.  What that means is that no current is present on the grounding conductor, because it's not connected to neutral until the source panel.  So no current can be present on the chassis of the bus (unless there is a fault, which would trip a GFCI device).  If you connect ground to neutral anywhere other than the source the return path from the load is split, and in a reasonable installation the return current will be shared between the two paths.  It's reasonable to presume that the cabling will be about the same, so roughly half of the return current will flow on the bus chassis.  Normally, no one cares because all the current goes to ground eventually, but in many failure or fault situations you could get that "hot skin" situation where someone could be electrocuted.

There is a truism that electricity seeks the path of least resistance.  That's true but people take it as an all or nothing statement, which is not true.  Electricity will flow through all paths based on the ratio of the resistances of the paths.  If you have a bond between neutral and the grounding conductor in a load path, for ever after the current will flow based on the ratio of the resistance to ground of the two paths.  That's why it's so important to keep neutral (also called the grounded conductor) and "ground" - properly called the grounding conductor - separate until they are bonded at one place.  The real thing that all this does is ensure that circuit breakers pop when there is a short circuit to "ground".  And that all return path current flows in the proper conductor, not the chassis of the bus...

Edit;  A better way to think of "ground" is as a zero voltage reference that you utilize to provide an effective ground-fault path to clear a fault.  That's why a generator that sits in a bay in your bus has a "ground" that you bond to neutral so that you are safe in your bus when your generator is running.

Brian

[86102A3]

Good job explaining Brian, are you a fellow electrician?
It is also important that when you transfer from generator to shore power that you break the neutral in your transfer switch, otherwise then you will have multiple paths situation.

[bevans6]

I'm neither an electrician or electrical engineer by license or degree, but I spent 35 years in data communications.  I designed equipment rooms, I designed networks, I did protocol analysis and network engineering.  I was an electronics technician and did my stint on a bench doing chip level repair and analysis of 1980's computer and digital circuits.  I was part of a very small company that built the first national Internet backbone network in Canada.  That network is now owned by Verizon...(geeks, it was part of Alternet).  I spent 30 of those 35 years in sales, so my key competency was explaining all this new-fangled crap to executives who really didn't want to know...  At the end of the day I was an interpreter and teacher, I just got paid commission...

Brian

[jmsokol]

I reviewed my original post and response on continuity between green wire and white at campground post. You say  yes.. Then in effect when you plug in you complete the the connection of green Safety and white common you so carefully kept separate in in bus. So ? keep separate in coach but defeat at pedestal?

Yes, that's correct. You have to maintain separation of the neutral and chassis ground on the bus/RV, and it get's bonded together when you plug it into the pedestal. However, the pedestal doesn't do the G-N bonding.... the main entrance service panel does it. The reason for this is that the "ground wire" which is technically called the EGC (or Equipment Grounding Conductor) is not allowed to carry any of the return currents. It's only supposed to carry ground fault currents (short circuit from your hot wire to the bus chassis) and that's supposed to trip the Circuit Breaker (technically called the OCPD / Over Current Protection Device). So you're technically not "grounding" your bus chassis to the shore power cord, you're "bonding" it to the entrance service panels connection where the Neutral, EGC Ground, and Earthing Ground Rod all connect (bond) together. That's also why a ground rod next to your bus doesn't actually "ground/bond" your vehicle. The ground rod likely has an impedance to the earth of around 100 ohms. That implies that a 120-volt short circuit to your bus chassis from something like a pinched wire will only produce about 1.2 amps fault current to the earthed ground rod next to your bus. But the EGC must have an impedance of less than 1 ohms all the way back to the service panel, so it will attempt to push at least 120 amps of current, which will certainly trip any 20, 30 or  50 amp breaker in the circuit.

Don't feel bad if you're confused about this. I'm the moderator on the AC Power & Grounding Forum at ProSoundWeb.com and the subject of grounding vs. bonding comes up all the time. Also, I find myself explaining this concept to electricians and inspectors more than I should have to. It's just not obvious how it all works, and the NEC book doesn't explain theory... it just tells you how to wire stuff.

One of the things I'm fishing for is a grant that would allow me to teach classes on this at campgrounds and RV dealerships around the country. I have a bunch of table-top and full-size demonstrations on how this all works. But I just can't afford to quit my day job and teach this full time, as much as I would like to.

[86102A3]

Well I hope you are able to get your grant. You definitely are able to explain it well. I run across many people and have been many places where I have had to fix grounding and bonding issues. I cannot say I know every aspect of it but I try to research anything if I am not familiar with it. I have a fairly good knowledge of grounding and bonding because we do a lot of work for the telecom industry and they are fanatical about having grounds with less than 5 ohms. They typically have a ground system.

[Midwilshire]

Three questions, because I'm curious:

1.  Is it unsafe to have no 120v chassis ground?

2.  Where should the 120v chassis ground be (main panel)?

3.  Is it okay to have multiple 120v chassis grounds?

Thanks,

Mike

[jmsokol]

1.  Is it unsafe to have no 120v chassis ground?

Yes, it is unsafe to have an "ungrounded" chassis that's isolated from the 120-volt EGC (Equipment Grounding Conductor). Plus it's both an NEC and RVIA code violation.

2.  Where should the 120v chassis ground be (main panel)?

Yes, the RV's main panel is the approved bonding/grounding spot for the EGC

3.  Is it okay to have multiple 120v chassis grounds?

Yes, a secondary chassis bonding/grounding point is allowed and probably desirable.

[yvan]

I traced every wire in the bus and have a few additional questions.

All my house 12v has both positive and ground runs back to the distribution panel.

There is no continuity between house 12v and Chassis 12v system, nor between 120v and chassis or house 12v.

Should I all interconnect them, and how? 

[bevans6]

I call that "home-run" wiring for the DC grounds.  I pulled all of mine back to a bus bar, and tied that bus bar to chassis ground.  I then tied my batteries to chassis ground.  That lets the few 12v loads I have that are not home-run wired to work just fine (dash radio and fans).  That also lets me bridge the house batteries with the start batteries for charging from the alternator and for starting assist.  So yes, I would tie your house battery system and wiring to chassis ground.

The answer on bonding the house 120VAC system to ground is above, from Mike.  Yes, the 120VAC system should have it's ground connected to the chassis.

Brian

[yvan]

I am glad I sparked( pun very much intended) this discussion. I have this as my plan, please correct as needed.

The only time we pony up to shore power is at home to cool the fridge down before taking off, we camp just on week-ends at race tracks.

In our Winnebago ( a classic 1973 Indian ) we got by with a single house battery and a 4000w generator for the coffee maker and Microwave( used the AC once last summer)

I would like to camp for longer periods( I am trying to convince my wife we should be full timers)

So the set up as I see it, 4 or 6 6v deep cycle batteries, a 2000w inverter( for microwave and coffee maker) and a generator for those times when AC is a real need.

To save money I will forgo an automatic transfer switch and just plug my shore power cord into the inverter, or generator, or shore power. When running the generator I will also run a charger to maximize efficiency, and while driving have a switch  to allow the bus alternator to give a helping hand to the house batteries.

Eventually solar power will be added( when I convince the wife that full timing is a good idea) , what size wire should I take from roof to basement since I have the possibility of running them since it's almost gutted.

What's missing in my plan, what else should I plan for in the future, and what should I change. For those of you that did or re-did a conversion here is a pic of some of my wiring.

[bevans6]

What racing do you do?

Brian

[yvan]

We race vintage Dirt Modifieds

This one is mine, the 2 others are my cousins cars.