Shore power

[Heavymetal]

Need some help adding shore power. I am in the process of putting in my 120v circuits and the new generator and am wondering were is the best place to ground it to?

Any help would be appreciated, I don't want to interfere with any off the other electronics. 

[brunsje]

The frame is the grounding point.  JohnnyB

[Heavymetal]

2 hours ago, brunsje said:

The frame is the grounding point.  JohnnyB

I figured that! I just wanted to double check about grounding 120v  to the frame. Thanks.

[NeverEasy]

Ground has been a topic in the past.  RandyA has a great paper on it.  The basic point is that our campers and trucks are big toasters plugged into shore power.  Therefore, you should not ground to the frame when using shore power.  The ground comes from the source pedestal.  Grounding generators is a whole other thing and I would not venture there.  Ask RandyA.  I cannot locate his paper right now.

[NeverEasy]

I found the file and a link to it but the link is defunct.  Not comfortable forwarding Randy's work but if you cannot get some help, I will share.

 

[Mark and Dale Bruss]

One of the jobs of the Transfer Switch that connects the generator output to the RV is to cause the Generator Ground to be connected to the RV Ground, when connected.

[Yarome]

Brunsje probably just misunderstood and thought you were talking 12v. You do not want to ground shore power to your frame. Use an isolation post or bus bar from your distribution panel to your incoming power cords ground. 

[JPL]

Chet   Getting close to Race Day! Where would you ground it? Back to the shore power? Because i'm not even close to a electrician I'll watch this!   Pat

 

 

The Old Sailor

[Chad Heiser]

The 120 volt panel should not be grounded to the trailer.  It is in effect a sub panel of the shore power connection.  It should have two separate bus bars within the panel.  One should be ground and one should be neutral.  These bus bars should not be bonded like they are in a residential panel.  The trailer will get its 120v ground from the source of the power (shore or generator).  There should be no neutral/ground bonding within the trailer and no frame grounding of the 120v system in the trailer.

For a 50 amp trailer, your power supply cord will have four wires coming into the power panel.  Line 1 (black wire) goes to one side of the 50 amp double pole supply breaker.  Line 2 (red wire) goes to the other side of the 50 amp double pole supply breaker.  The neutral wire (white) goes to the stand alone neutral bus bar.  The ground wire (green) goes to the stand alone ground bus bar.  All other circuits in the trailer will be wired the same; positive wire (typically black in Romex wiring) to the breaker, neutral wire (white) to the neutral bus bar and ground (bare copper) to the ground bus bar.  Nothing else should come in or out of the trailer power panel connecting it to any part of the trailer framing.

The only difference with a 30 amp panel is there will be no red wire (line 2) and the supply breaker in the panel will be a 30 amp single pole.

[alan0043]

11 hours ago, NeverEasy said:

Ground has been a topic in the past.  RandyA has a great paper on it.  The basic point is that our campers and trucks are big toasters plugged into shore power.  Therefore, you should not ground to the frame when using shore power.  The ground comes from the source pedestal.  Grounding generators is a whole other thing and I would not venture there.  Ask RandyA.  I cannot locate his paper right now.

2X on RandyA paper.

[RandyA]

Terminology for a 3-wire AC power system:

Neutral or Ground - Conductor in an AC system that has a common connection to earth.  The neutral does carry current back to earth and is not a safe wire. If broken from earth ground it can supply a full voltage and current shock if touched while one is in contact with earth ground.

HOT - Main current carrying conductor that is not connected to ground.  Touching this conductor at any point while in contact with ground can cause a painful or deadly current to flow through your body.

Grounding Wire (sometimes called "safety wire") - This is a NON-current carrying wire connected to a specific ground point.  It's purpose is to shunt any potential current fault from the neutral or hot to earth ground and, in most cases, blowing a fuse or opening a circuit breaker if the current is higher than the device's over current rating.

Bond - A physical connection between neutral and the grounding wire.  For shore power this is ONLY suppose to occur at the Main Service Entrance Panel (SEP) where commercial utility lines come in.  It should not occur anywhere else in a branch circuit before the main supply SEP.

 

With a shore power connection in a RV the grounding wire (green, green-yellow or bare copper) is attached to the same ground as the batteries use, which are also bonded to the vehicle's metal frame.  Typically this is done in an added vehicle breaker box for alternating current that is frame mounted or bonded to the frame if it should be mounted on an insulated surface.  The neutral (also called ground - note no -ing on the end) is NOT bonded to the vehicle frame - ever.  In your breaker box for shore power input you will need two buss bars, just as in your trailer.  Neutral and grounding will NOT go to the same buss bar as you might find in a residential service entrance panel.  This means using a box specifically designed for sub-feed circuits from a SEP or one made for RV's that have separate buss bars for neutral and grounding.  If the box does not have this, you can add another buss bar for neutral that is NOT bonded to the frame or the breaker box metal (often mounted on a plastic insulator).  These are usually sold in home stores packaged separately from a breaker box.   Per the NEC (National Electric Code) the bond to true ground is only made at the service entrance panel where the commercial power connection is made and the shore power circuits originate.  The neutral in your RV will "float" until it is connected to shore power.  Multiple grounds or "ground loops" as they are called can actually create dangerous conditions, not to mention weird problems and "noise" in electrical devices.

Installing a generator or inverter can be a different story.  Many generators are internally bonded, meaning the designated neutral (there is no true neutral since there is no earth ground) and the genny frame, which is the typical grounding wire point, are common connections and are often connected to the vehicle frame.  The NEC has yet to modify their requirement calling for generator (or inverter) bonding in a vehicle because they want a circuit breaker or fuse to blow if there is a short - thus the practice persist.  Unfortunately this is not true protection for humans as many generators use breakers that can take several seconds or minutes to open.  In contradiction to the NEC and CSA advice, the safest way to wire in the generator is with a "floating neutral" which means it is not bonded to the vehicle frame or grounding connection.  In this case it is imperative that power is then distributed to outlets in the vehicle via a Ground Fault Protection outlet(s) or a GFCI main breaker.  Many generators now come with a floating neutral or the ability to separate neutral from grounding but they may not have a GFCI outlet since GFCI's do not always hold up well when mounted to a generator panel due to the higher frequency vibrations caused by the genny engine.  GFCI's are a good idea for all shore power branch circuits in your truck as well - the NEC requires GFCI protection where one may contact ground and a powered device at the same time (i.e. outside, kitchens, bathrooms, garages, swimming pools, hot tubs, etc.).  Many folks do not like them because they say, "They trip all the time".  Well... yeah...... when they do trip it is for a reason - there is a ground fault somewhere in the circuit that can cause electricity to flow through your body if you contact the circuit before the GFCI device cuts off both neutral and hot sides of the circuit.  Just a circuit breaker or fuse can allow a fault to exist and not trip or blow.  A GFCI disconnects power fast if a fault occurs - fast enough to save your life.  A fuse or circuit breaker may not open fast enough to keep deadly current from turning your heart to something like a bowl of Jello.  If a GFCI constantly trips, the fault in the circuit or appliance needs to be located and fixed.  Power surges may occasionally trip a GFCI, especially lightning strikes - we learn to live with that minor inconvenience.  GFCI's require protection from rain and water - when they get wet they are usually toast and will require replacement.  Always replace a GFCI with another GFCI - don't replace it with a conventional unprotected outlet.  And yes, there are portable 30 and 50-50 amp rated GFCI's for larger generators or shore power connections.  Just don't expect to find them in your home store.  Sources are RV stores or Amazon with devices made by Iota, Progressive Dynamics, etc.  They are more expensive than the residential 15 or 20 amp GFCI devices you wire into an outlet box, but what is a life worth?  Incidentally, a transfer switch for a generator or inverter may disconnect both the neutral and grounding circuits on a bonded device from the vehicle when open.  This will prevent the rouge connection created by giving a current path between the grounding wire and neutral back through the generator frame to the vehicle frame that is  caused by transfer switches that do not lift both connections.  But, even a transfer switch that breaks both neutral and grounding wires when open for shore power input will put the vehicle frame at voltage potential when closed if a generator is bonded.  A portable or frame mounted generator has NO TRUE NEUTRAL that is connected to earth.  Unlike shore power, both the hot and designated neutral will be at the same voltage potential.  Repeating myself - I do not advocate bonding with a portable generator or inverter, period.  And always install GFCI circuit protection when wiring your truck for 120 VAC power.  Safety First .

[HERO Maker]

As always, the prof here has given a great explanation of the subject matter!  Probably something we need to put in the resource guide.

Thanks Randy.

[Heavymetal]

On April 6, 2017 at 11:15 PM, Chad Heiser said:

The 120 volt panel should not be grounded to the trailer.  It is in effect a sub panel of the shore power connection.  It should have two separate bus bars within the panel.  One should be ground and one should be neutral.  These bus bars should not be bonded like they are in a residential panel.  The trailer will get its 120v ground from the source of the power (shore or generator).  There should be no neutral/ground bonding within the trailer and no frame grounding of the 120v system in the trailer.

For a 50 amp trailer, your power supply cord will have four wires coming into the power panel.  Line 1 (black wire) goes to one side of the 50 amp double pole supply breaker.  Line 2 (red wire) goes to the other side of the 50 amp double pole supply breaker.  The neutral wire (white) goes to the stand alone neutral bus bar.  The ground wire (green) goes to the stand alone ground bus bar.  All other circuits in the trailer will be wired the same; positive wire (typically black in Romex wiring) to the breaker, neutral wire (white) to the neutral bus bar and ground (bare copper) to the ground bus bar.  Nothing else should come in or out of the trailer power panel connecting it to any part of the trailer framing.

The only difference with a 30 amp panel is there will be no red wire (line 2) and the supply breaker in the panel will be a 30 amp single pole.

Thanks guys. I have read through all the post and I guess I did not make myself very clear in my opening question. I am not talking about my RV I am talking about my truck. I have just installed a 2 circuit 4 breaker panel and a 2000 watt inverter in the truck and am in the process of running the shore power plug to the rear of the sleeper. I have mounted a MEP-802A 5kw military generator to the bed and plumbed to my fuel tanks. I plain to use the genset as a APU when stopping so it will be plugged into the shore power plug. My concern is the grounding all all the electrical inputs that I now have, I don't won't to fry the electronics on the truck. I don't think it would happen but for the cost of the ECU I had rather be safe then sorry, if it was a house no problem but the truck is different. 

 

Thanks

[Heavymetal]

Ok. I know the difference detween the neutral and a ground and I know how to wire a house with a/c and a RV with d/c. When it comes to having a/c and d/c in my truck is it safe and standard to ground the a/c to the truck frame as you would you d/c?  

[Heavymetal]

Randy A. 

The generator I am using is a MEP-802A military genset it sit up to be ground via a standard grounding rod and cable. The unit is basically a faraday cage, the frame is all aluminum and works to imped EMP's this is the reason I want to know about ground to the frame. 

[Jim & Wilma]

I have a couple Honda EU2000 generators installed in one of the truck bed boxes. They're wired to a 30 amp breaker which feeds a 30 amp rv receptacle at the rear of the bed.  The neutral, ground and truck frame are connected together within the 30A breaker box.  This setup works for me since loads are connected via receptacle.  The RV shore power cable is plugged into a source which has the neutral and ground tied together at ONE point, be it the RV park distribution system or my truck.  At no time are both the truck power distribution system and RV park distribution system tied together.  

[Heavymetal]

11 hours ago, pratten said:

I have a couple Honda EU2000 generators installed in one of the truck bed boxes. They're wired to a 30 amp breaker which feeds a 30 amp rv receptacle at the rear of the bed.  The neutral, ground and truck frame are connected together within the 30A breaker box.  This setup works for me since loads are connected via receptacle.  The RV shore power cable is plugged into a source which has the neutral and ground tied together at ONE point, be it the RV park distribution system or my truck.  At no time are both the truck power distribution system and RV park distribution system tied together.  

So your ground and neutral are bonded together in your truck Deb. 

[I'mdonewiththis forum]

2 hours ago, Heavymetal said:

So your ground and neutral are bonded together in your truck Deb. 

Correct me if I am wrong, but I was under the impression that you did not want the neutral and ground bonded there. I thought it was to be bonded at the source.

[RandyA]

8 hours ago, Mntom said:

Correct me if I am wrong, but I was under the impression that you did not want the neutral and ground bonded there. I thought it was to be bonded at the source.

Yes, the source is correct. 

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Heavymetal said:

Ok. I know the difference detween the neutral and a ground and I know how to wire a house with a/c and a RV with d/c. When it comes to having a/c and d/c in my truck is it safe and standard to ground the a/c to the truck frame as you would you d/c?

You should ground the metal frame and cage of the generator to the vehicle frame and remove any bond that may exist to the generator neutral and the metal frame and cage.  This is usually a quick snip of a jumper wire between neutral and the genny frame that is found behind the control panel where the power outlet(s) is/are.

Truck, RV, car - all the same.  120 or 240 volts alternating current for a truck or RV is NOT wired like a house.  You should only put the non-current carrying wire, which is the grounding wire, to the frame.  You should not connect the neutral or white wire to the frame. That is the way RV's (or your truck) are/should be wired.  It is NOT safe to put the neutral or ground wire (white wire) to the frame - a practice called a "bonded neutral".  Neutral and the grounding wire are not bonded in the breaker box like in a residence.  If you attach the white wire or neutral to the frame of the vehicle you will create a voltage potential to earth ground.  This is often referred to as a "hot skin" and can give you a significant jolt if you touch the metal part of the vehicle while standing on earth ground without the benefit of the grounding wire going to earth ground.  When you add a generator or inverter that is bonded (designated neutral and grounding connected) you will not have the safety benefit of an earth ground as you have with shore power.  We live in an AC world.  Positive electrons and negative electrons are attracted to each other.  A wire is not required for the electrons to move.  There will be an electron attraction between a bonded vehicle frame and earth ground.  Think of the relationship between the bonded vehicle frame and earth ground like a big capacitor which, BTW, is why we have lightning.  If the electron charge is higher on one surface than the opposing surface electrons are going to try and move.  The air space between the vehicle and the rubber tires on the vehicle will act as insulators and 120 volts is not high enough to make a visible electron jump between the bonded vehicle frame and the opposing surface - it would take about 120,000 volts or more for this to happen.  But, the human body easily conducts electrical charges over 32 volts.  Touch the vehicle frame and ground and you can become the pathway for the movement of electrons.  True, this does not always happen.  A lot depends on humidity and how wet or conductive the earth is as well as how well you may be insulated from earth ground and how moist your skin may be.  I have measured the voltage between a metal vehicle frame that has a bonded generator and nice wet conductive earth ground.  Measured voltages of as much as 60 volts have been observed - enough of a shock to put the unlucky person into V-Fib. I can't tell you the odds of this happening - maybe 1 in a 1,000 or even 1 in 100,000.  Most of the time we get away with it with no electrical shock - anyway, the odds of getting zapped are less than winning the lottery or getting hit by lightning.  My position is why risk it?  It is so simple to wire a floating neutral and put in a ground fault circuit interrupter.  The odds of getting a shock if wired this way will be higher than winning the lottery.

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Pratten wrote:   I have a couple Honda EU2000 generators installed in one of the truck bed boxes. They're wired to a 30 amp breaker which feeds a 30 amp rv receptacle at the rear of the bed.  The neutral, ground and truck frame are connected together within the 30A breaker box.  This setup works for me since loads are connected via receptacle.  The RV shore power cable is plugged into a source which has the neutral and ground tied together at ONE point, be it the RV park distribution system or my truck.  At no time are both the truck power distribution system and RV park distribution system tied together.  

Jim - your Honda 2000 generators do not have a bonded neutral to the grounding wire even when paired unless they were sold in Canada and are subject to CSA requirements.  Creating a bond externally between the designated neutral and the grounding wire is often done because it may cause the circuit breaker to trip if a short between the hot and vehicle frame should occur. The NEC has unfortunately hung on to this procedure so many installers perpetuate the practice of bonding out of fear of litigation.  OSHA rules do not apply to our vehicles.  Adding a 30 amp GFCI breaker between the generator and truck AC distribution system where the neutral is not bonded will open more quickly than a fuse or circuit breaker will if a short should occur.  It also makes your vehicle AC system safer to you and your loved ones.  Your observation that, "The neutral, ground and truck frame are connected together within the 30A breaker box. This setup works for me since loads are connected via receptacle."  Connecting loads via receptacle does not negate the issue of the neutral  being bonded the way you described your system.  I assume the receptacle is used to plug in your trailer?  Grounding and neutral will no longer be isolated in the trailer.  Remember.... a generator has the same voltage potential for both the hot wire and so called neutral.  The neutral is designated but it is not a true neutral.

[SuiteSuccess]

Mike Sokol at noshockzone.org has some great info on all this although Randy's is just as good.

[Jack Mayer]

Mike and I have talked about this off and on for many years. It causes peoples eyes to  glaze over. But it is VERY IMPORTANT to do things the right way. Shortcuts can kill you. Not outright, but they up the odds of death.  Please read Randy's excellent explanation and try to understand the right way....you do not have to understand the theory...but understanding the tactic is important. 

Randy, as always, you explain this far better than I can/do. Maybe it has to do with being a teacher....(yes, once a teach, always a teach   )

 

[I'mdonewiththis forum]

1 minute ago, Jack Mayer said:

Randy, as always, you explain this far better than I can/do. Maybe it has to do with being a teacher....(yes, once a teach, always a teach   )

 

Either that or some people are way more articulate on the keyboard than some of us............

[RandyA]

Thank you Mntom, Jack and Carl,

Back in the mid '50's I remember watching my grandfather put penny's behind fuses that would frequently overload and blow in his early 1900's era North Augusta home.  Kim, his oldest son, warned him that he needed to upgrade his house wiring from the original knob and tube to Romex and that he could burn the house down by putting penny's behind fuses.  Grandfather was very stubborn and reluctant to spend money on what "he didn't think he needed".  He was convinced he knew what he was doing and would come to no harm.  Two weeks later, while using electric hotplates in his kitchen, the fuse box caught fire and the house quickly burned to the ground.  His dog died in the fire.  He escaped but lost everything in the house - even his Lincoln Continental parked in a driveway next to the house.

When I was 16 I was the proud owner of a '54 Studebaker Starlight 2-door hardtop.  I was standing on damp concrete using a metal cased electric drill working on the car.  This was back in the days when most everything was 2-wire with no grounding and GFCI's did not exist.  Double insulated power tools had yet to make it to the hardware store shelves.  Without warning my hands clamped around the drill and I could not let go.  I was screaming bloody murder and pissed my pants.  I was lucky, my erratic movements pulled the plug from the wall and the drill let go.  My Dad took the drill, cut the cord off, and threw it in the trash.  I had minor burns on my hand and my muscles hurt for days - but I recovered.  I later learned that Dad had recently taken the drill apart because it stopped working.  He had soldered a wire and insulated it with friction tape before putting it back together.  No doubt the tape came off and contacted the metal case.

Many years later I was working on a TV set in my basement workshop and needed to pull the chassis (tube type TV).  I took a screwdriver and began to pop the HV lead from the picture tube thinking it had been sitting there for a week or more with no power so I was safe.  Even unplugged there was a 20,000 volt capacitance charge that remained between the tube's metal grid and the dag coating  - I did not bother to discharge it to ground before popping off the lead.  The charge found a path to ground through my body, my elbow reflexively rapidly jerked back and I fell hitting a metal file cabinet on the way down.  Four stitches in the back of my head and a chipped bone in my right elbow that required a sling for a couple of weeks.  Kind of awkward when your only car has a floor mounted 4-speed stick.

Around the same time I had built a linear amplifier for my ham radio.  The amplifier used a 2,000 volt power supply that would provide 1 full amp of current to a pair of 813 tubes.  The power supply was connected to the amplifier by a solid core spark plug wire.  The connector to each was insulated and rated for 10 KV.   One day I reached behind the amplifier to check and see if the antenna connection was tight.  My forearm touched the 2,000 volt lead where the connector attached to the amplifier.  I burned a hole completely through my forearm.  It looked like someone had poked me with a red hot nail.  Since it was cauterized it didn't bleed, but it was extremely painful and several of my fingers wouldn't work.  I still carry the scar on my forearm.  That one should have killed me.

Back in the early 70's I was teaching Electrical and Electronic Trades at our County Vocational Center.  The more senior students would take a capacitor and quickly poke and then remove the wire leads from an electrical outlet.  They would set the charged capacitor on a table where a unknowing student was sure to pick it up or they would hold the capacitor so they did not touch the leads and toss it to an unsuspecting student with a "Here catch".  Anyway, I rarely need to teach how capacitors could hold a charge for quick release after these shenanigans.

I can tell literally hundreds of stories from first-hand experience about how failure to follow the "rules" resulted in personal injury, loss of property and even death.  Over my 50+ years as a volunteer EMS provider, teaching, designing, servicing and generating electric power I have gained a tremendous respect for what electricity can do - or not do.  It is kind of like a wild tiger - if you don't keep it in it's cage and treat it with respect it is bound to bite you badly one day.  Mistakes are much easier to make than they should be.

[Jim & Wilma]

Thanks Randy, good discussion and I got a little smarter today.  Looks like I'll be changing my wiring by removing the neutral to ground tie.  

Randy, I'm not clear though on how the GFCI functions If there's no connection between ground and neutral.  Can you help me understand how it works.

[NeverEasy]

The GFCI monitors the current on the hot wire and the neutral wire.  Normally, what goes in must come out.  If there is a difference, it trips, sensing that some of the current is being sent down a path (you or a faulty device) other than the one it is supposed to. 

On edit, I looked it up.  The difference between hot and neutral must exceed 5mA