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Les Lampman 12-14-2004 10:47 PM

Bus Electrical Systems - AC
This is the start of the new Bus AC section

This is a modified thread and has been resurrected 10/05/16 starting on page 18

This was edited 12/5/2016

Original wording "How To" section...Under Construction! :lol:

Ryan Grimm 11-17-2005 12:41 PM

General AC Wiring (or, how I would do it)
There are a couple ways to wire the bus, and by this I mean:
Do I put the wires in the chase up by the ceiling;
Do I put them along the floor behind the cabinets;
Do I put them in conduit under the bus?

I'm probably going to do a combination of the three. Most of the main wiring I will run under the floor, going through grey PVC for the main runs from the panel to the runs that will be broken down into the individual areas.
The PVC will be firmly supported, preventing any sag or vibration from operation of the bus which would fatigue wires and cause breakage or shorts.
Any wire connections will have wires twisted together with pliers, wire nuts firmly screwed on, then further secured with colored electrical tapes.
The electrical tape colors will also be an indicator of what the circuit is for; I will be color-coding the wires so I know what goes where for future repairs and additions.
Then I will make up a wiring diagram for future reference.

At that point I will branch up/out to any outlets or switched lights, running under any convenient cabinets or up the wall in a chase to protect the wires.
If any wires proceed up to the ceiling for lighting, cooling etc., those will be protected by ceiling panels that can either have space to run future wires, or a chase installed, or the panel will be removable for repairs, or a combination of any of these.

RV/Vehicle wiring MUST be stranded, NOT solid wire!

15 amp outlets and lighting will be served with 12 gauge/with ground 'SO'-style cable, also known as Extension Cords!
Yep, per my Licensed Electrician friend who gave me the staright poop on this...I will also be tinning the ends of the wires with ROSIN-CORE solder so it makes for better connections.
20 amp outlets, lights and circuits will be served with 10 gauge SO cords.
Sure can't beat the prices, especially if I get them as seconds or on sale at the discount stores.

If larger cuircuits are needed, I will find out what are the appropriate gauges of wire to be used for those applications, and use the appropriate stranded wire.

A circuit panel will be connected to the 'shorepower' cable with a disconnect so that the panel either takes power from the shore supply, OR the genny, but NOT both at the same time...don't want any polarity or backfeeding problems that will turn my wiring to smoke!
If I use GFCI breakers right at the panel, they will protect any circuit directly down-line of that breaker...this will also make installations easier, as GFCI outlets are bulky and somtimes hard to fit all the wires in the box.

Which reminds me:
All electrical boxes, whether for switches, outlets, etc. are stamped with their volume in cubic inches. These are limits on how much stuff you can SAFELY load any box with connections and devices. PAY ATTENTION TO THESE SPECS!!!

The ground for the main panel will ALSO be grounded directly to the bus chassis and bodywork; I want to eliminate any possible chance of electrocution just by leaning on the bus.
The ground and neutral wires from the panel will be kept separate at all times.

I will also keep in the 'shore power cable storage box' a circuit tester to let me know that the shore power I plug into is grounded and connected correctly. These testers plug into a standard 15- or 20-amp outlet, and let you know by indicator lights what's up. IF plugging into a 30-amp outlet, use an adapter to check it, too.

All cables that exit the conduit and run free under panels, etc. will be supported no less than 18 inches apart, to prevent vibration fracturing of the wires. All wires that enter outlet and switch boxes will be supported within 6 inches of the box for strain relief, and to reduce wire flex and breakage.

If the wire is to be in an exposed but dry (interior) space, I will use armored cable with the appropriate gauge cable and fittings. Don't forget the bushings on the end of the cable armor to prevent chafing of the wires on the metal.
If the wires are to be in an exposed EXTERIOR space, I will use waterproof armored cable AND fittings.
If the wire passes through any openings, I wall make sure that there will be appropriate grommets or other measures to prevent chafing of the insulation.

I will be using commercial grade outlets and switches, as they are heavier duty and more reliable in the long run. I think this saves money and time, too.

I will think twice, no, THREE times before I use any USED electrical equipment, as I have no idea if the equipment had been previously installed correctly or subjected to unusual loads that may have done unseen damage.

Circuits that will be protected by the GFCI breakers will include, but are not limited to, the kitchen area, the bath area, and any exterior outlets.
These will be 20-amp breakers.

I will NOT use any "push-connect" wiring on the back of outlets and switches, as they have a tendency to arc if loose or vibrated. I will ONLY use the correct screw connections, and will ground all circuits.
I will leave a minimum of 6 inches of wire in each box, as I will need adequate lengths to ensure I have the connections properly made.
I will also check each circuit I have finished, using an appropriate meter.

That's it for now, more to come (eventually)

GoneCamping 01-06-2007 09:23 PM


RV/Vehicle wiring MUST be stranded, NOT solid wire!
Please clarify the above statement?

If you are referring to Coach 12v wiring that is correct. If you are referring to 120vac wiring that is in error. One quick look at my Travel Trailer and another at a friends Fleetwood Motor Home tells a different story, they have standard 12/2 solid house wiring... My trailer is a 2004 model and his motor home is a 2002 model both with RVIA certificates...

On edit: I also spent a couple of Saturdays this summer tearing apart a Prowler fifth wheel that had the roof cave in, this is where I got many of my RV specific hardware items. I happened to save some of the wiring from that rig too, including the switch system between the Microwave and water heater (shared resource). That unit also had standard 12/2 wiring...

GoneCamping 01-06-2007 09:47 PM

To back-up my statement, I dug out the camera and snapped this...this is under the end table beside the sofa in my trailer....

Les Lampman 01-06-2007 09:57 PM

Hiya Cliff,

Well, there's always a a point of contention with this subject. I think a lot of folks are of the opinion that in something that moves that stranded wire is the way to go but I'll be the first to say that's not universally agreed upon. Since my background is so heavily marine and solid wire is NEVER used in any circuit I'm in the "stranded wire is best" camp but I've also got a classic Class C Beaver motorhome that has house-style (solid) wire in it; it's now almost 30 years old and seems to be doing fine so I can't say categorically that solid wire is horrible.

The issue centers around the solid wire work-hardening and perhaps breaking where it enters connections (like in an outlet box, breaker panel, etc) due to vibration on the road and constant movement.

Technically I think there's a better arguement for using stranded wire than not and I'll use it myself but I don't think that means that everyone has to given that solid wire is used in production RVs. To a large degree I think a lot of converters believe that stranded wire is better and feel that production builders are more interested in keeping costs down and profits up and therefore that's why they use the cheaper solid wire (custom coach companies all use stranded wire to the best of my knowledge).

I think you have to look at the use you're going to give your conversion and make a decision that's best for your needs.

GoneCamping 01-06-2007 10:13 PM

You gotta keep in mind that the point where the wire is connected is also vibrating right along with the wire, so all things being equal if everything is vibrating at the same rate it's more a question of things vibrating loose rather than breaking. Be that as it may, I had to take issue with the tutorial since it runs counter to what's actually out there. In real life, these RV's are made by the thousands year and and year out and they almost all universally use solid wire. So to say that it MUST be stranded is not doing your readers a real service.

I'm just trying to be objective with information that I know to be consistant with the facts. Not trying to flame anything or anyone....

Les Lampman 01-06-2007 10:27 PM

Re: General AC Wiring (or, how I would do it)

Originally Posted by Ryan Grimm
The ground for the main panel will ALSO be grounded directly to the bus chassis and bodywork; I want to eliminate any possible chance of electrocution just by leaning on the bus.

Just to clarify, since I'm not sure I'm interpreting what I read above correctly, here is some information on grounding.


As required by NEC code and UL specification 458, inverter/charger installations in the U.S. that are used in RV or Marine applications employ ground-to-neutral switching. The purpose for this requirement is to ensure that all the neutral conductors are connected (“bonded”) to a single ground point in a three-wire (hot, neutral and ground) AC system. This prevents a voltage difference from developing between the vehicle/boat’s AC neutral and the external AC source’s (generator or shore power)neutral, which may cause an electric shock or cause nuisance tripping of GFI’s.

When the unit is operating as an inverter, the AC output neutral should be connected or “bonded” to the frame/hull (chassis ground).

When an external AC source (AC shore cord) is provided, the inverter’s AC output neutral should be disconnected from the frame/hull (chassis ground) and allow the “bond” to be provided by the external AC source.

The requirement to switch the neutral can be met by your inverter internally or can be easily met by using an external relay to connect and disconnect the external AC source’s neutral.

If another AC source (on-board generator) is included in the RV or boat, this AC source neutral is required to be connected to ground when it is being used, and to disconnect all other neutrals from ground. An AC transfer switch can be used if it switches both the shore cords and generators neutral.


In other words, if you're connected to shore power your AC system neutral must be grounded through the shore power system and not to your bus frame.

Les Lampman 01-06-2007 11:44 PM


Originally Posted by GoneCamping
You gotta keep in mind that the point where the wire is connected is also vibrating right along with the wire, so all things being equal if everything is vibrating at the same rate it's more a question of things vibrating loose rather than breaking. Be that as it may, I had to take issue with the tutorial since it runs counter to what's actually out there. In real life, these RV's are made by the thousands year and and year out and they almost all universally use solid wire. So to say that it MUST be stranded is not doing your readers a real service.

I'm just trying to be objective with information that I know to be consistant with the facts. Not trying to flame anything or anyone....

I think the point is that things are not moving together; the circuit breaker box, or the outlet box, or the switch are all solidly fastened to walls and such. The agument is that the solid wiring if not completely and securely fastened will move around as the wires bounce and jostle going down the road which puts stress on the connections; this is well proven and universally accepted in the marine industry since that's such a rugged environment I believe that the feeling is if it works there it ought to be even better in an RV.

Your observation that it's accepted production RV practice to use solid wire is true but I also believe that a lot of folks doing their own conversions are doing so in order to end up with something much better than they perceive a production RV to be and that typically means massive upgrades to what are thought to be shoddy practices in the production RV world. This isn't about "facts"; it's about very subjective and personal feelings.

There have been a few books written about coach conversions. I've read several by Dave Galey and George Myers, both of whom are well respected in the conversion community. They don't agree on the wire to use for the AC system; Mr. Galey says "Although I have seen Romex used in bus conversions, I do not recommend it since sold copper tends to work-harden and become very brittle under vibrating loads, hence the risk of breaking". Mr. Myers says "The most serious failure mode of any wire happens when the wire moves relative to something next to it and the insulation wears through. More flexible wiring has a higher probability of moving..." so he doesn't recommend "Boat Cable". He does recommend running your AC wire in steel conduit, second would be plastic conduit, the next choice BX. sure that the Romex you get is Type-NM. [I don't agree with Mr. Myers (although I do on many other subjects); if what he says is true we'd use Romex on boats and that never happens...that's just my prejudice.]

I highly doubt we're going to end the controversy here! Until some definitive tests are done and the results made public (not likely to happen) there will be the Romex camp and the Boat Cable camp ever arguing over which is best! :lol:

There isn't a tutorial here per se; up to this point there was one persons post about how he was going to approach the wiring in his conversion. I doubt he intended a disservice to anyone.

the_experience03 01-07-2007 12:20 AM

12/3 Extension cords which equate out to a 12/2 NM (I don't understand the difference in numbering conventions) were a whole lot cheaper than solid wire when I did my conversion. On top of that, every circuit could then easily be color coded.

paul iossi 01-07-2007 01:23 AM

Just to help confuse the issue, there are different types of stranded wire, industrial AC stranded wire for installing in conduit has much larger strands than automotive or marine stranded wire, and then their is flexable, fine stranded wire used for extension cords and welding cable.
In my opinion the most important thing when wiring is to make sure that you keep everything properly supported and secured in a neat package that can be easily serviced when necessary. Just for the record I'm a stranded wire and busbar kind of technician because if the smoke gets out you need help. :twisted: :shock:

Ryan Grimm 01-07-2007 11:24 AM

My post was pointed at the way I'm doing things. If you have a different method, fine, I just hope you don't have problems during the 'smoke test' (i.e. energizing the circuit).

If folks want to use solid NM, fine. I'm sure RV manufacturers use the stuff based on expense of materials, ease of use (meaning cheaper labor), ease of connection to outlets, switches, etc.; after all, it's all about the bottom line and what they can get away with.

With copper having more than DOUBLED in price in the last year, this will be, again, driven by economics.

I prefer using plastic conduit, followed by EMT, and save BX for exposed places, or where it has to be moved on occasion, say an appliance that is wired in and I want more protection from pinching etc. during re-installation.

Typed in using 100% recycled electrons

nyrockingchairs 08-20-2007 12:58 PM

Re: How To: Bus Electrical Systems - AC
The numbering conventions, not sure how a 12/3 extension cord equates to a 12/2 NM but the 12 is the wire guage size and the /3 is the number of insulated conductors, usually not including the ground wire. So maybe the 12/3 indicates 3 insulated conductors with 1 used as the GND, and the 12/2 NM is a 2-conductor with a ground wire.

When you buy wire in the store it is almost always of the convention 12/2 indicates 2 insulated conductors and then you get it with either with or without a GND. 12/3 is usually used for when you want the multiple switch control over a single circuit or are running outlets and the top halves are switch controlled while the other half is always on, it has a multiple usage life...

the_experience03 08-20-2007 01:12 PM

Re: How To: Bus Electrical Systems - AC
What I can't for the life of me remember is if the bulk SO is numbered like the extension cords where 12/3 means 12 gauge and two conductors plus a ground or if it is named like the NM where 12/2 (w/ grnd) would mean two conductors and a ground. I usually just cheat and look at the cut end of the wire if all else fails.

I don't want to get into the stranded versus solid debate again, but for those of you running solid are you running just regular romex (NM) or are you getting the direct bury, UV resistant UF stuff?

After a year and a half my cut up neon extension cords are still working GREAT. I haven't had a single electrical problem unless you want to count one fluorescent fixture in the bathroom falling down from a stripped screw and occasionally having to tighten a bulb back up.

Ryan Grimm 08-20-2007 08:29 PM

Re: How To: Bus Electrical Systems - AC
OK, here's what I've done over the last two years:

I've parted out five RVs of one sort or another......two 5th-wheels (one top-of-the line), two travel trailers (both lower end), and an older Dodge-powered RV.
The high-end 5th-wheel and the Dodge RV both had STRANDED copper wiring for the 120VAC and 12VDC systems.
The lower end 5th-wheel and both travel trailers had stranded copper for the 12VDC, and solid 12-2 and/or 14-2 NM for the 120VAC.
Seems to me that economics definitely had a hand in the wiring choice!

I checked the systems as best I could by energizing them with the appropriate voltage. I found NO problems with the stranded wiring, and two faults (shorts/popping breakers) with the low-end 5th-wheel. One of the cheapo travel trailers had a no-power fault to the fridge. I did NOT bother tracing down the faults, as I was converting the wire to scrap for the $$$.

And NO, I will NOT publish the names of the vehicles, I don't need the hassles from manufacturers.

I WILL continue to say that you can choose what to use for wiring. Me? I'm going to watch my wire gauges for proper sizing, and wire it up like I said.

As an aside, I recall an RV that a friend rented a few years ago, virtually new.......he was having trouble with a circuit for the kitchen popping the wouldn't reset, and I tried swapping out a breaker from another circuit; same problem, so it wasn't the breaker.
The 120VAC wiring in that vehicle was all 12-2 NM to my recollection....solid wire.

Your mileage may vary. Please use ONLY 100% recycled electrons at all times for best efficiency!

Xtevan 09-20-2007 12:22 PM

Re: How To: Bus Electrical Systems - AC
Extreme recycling!! :shock:

Don't try this at home or on your bus


Ryan Grimm 09-24-2007 08:31 AM

Re: How To: Bus Electrical Systems - AC
Love that picture! What kind of wire is it? It kinda looks like phone wire in relation to the staples and "wiring box", but I can't be sure.

Yet another excellent example of a terrible that again and you'll see what I mean!

IF it's just a phone connection box, it's just fine.
If it's a 12VDC or worse, 120VAC connection, I don't want to see the video of it burning on YouTube....OK?

Gotta admire that backwoods inventiveness, though...............

Xtevan 09-24-2007 09:09 AM

Re: How To: Bus Electrical Systems - AC
I can across the picture with a bunch of Home inspection nightmare photos on the web. It reminded me of the summer I cleaned air conditioner coils for a property management company in College Station, Texas. On a hazy monday morning I could envision a few of my co workers using this fix after seeing some of their other 'work'.


the_experience03 11-04-2007 09:49 PM

Re: How To: Bus Electrical Systems - AC
Neon extension cord wiring. 8)

timbuk 12-22-2007 01:30 PM

Re: How To: Bus Electrical Systems - AC
when i bought my bus the shore line cable had been removed from the junction box in the shoreline cable storage area i wired in a 12 guage stranded cable to the connection box and hooked the ground to the chassis all was working well untill it rained and the gfci in the house began to trip where thu bus was plugged in Does the ground need to be hooked up to the bus or should it float at this point? thanks in advance

dieselman69 01-07-2009 11:39 AM

Re: How To: Bus Electrical Systems - AC
I was wondering what to use for the electrical transfer switch, 1st option use a rv automatic transfer switch or, option 2 could a person use a generator transfer switch, also what do most people use for circuit breaker panels to control loads. I'm needing to know starting work on our 1993 genesis DT466, MT643 84 pax FC bus . Thank you in advance.

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