A quick trailer electrical wiring question

[clhjsh]

A buddy of mine asked me to help him add a 120 volt system to his car trailer. He wants to be able to plug into a 20 amp outlet and operate some lights a convenience outlet and a battery charger for the trailer battery.
Having done a fair amount of residential wiring it seems straightforward but when checking for diagrams online there are some that show grounding the trailer chassis and others that do not show this ground.
My first thought was to ground the chassis and I feel that is correct but I wanted some advice to make sure that I am correct on this. The main plan is to add a small 4 circuit panel to separate everything to be able manually turn off breakers so we do not overload the incoming circuit.

One last thing, what if he plugs into a portable generator instead of a standard power outlet does that create any issues?

[CHICKDOE]

think about how a rv trailer is wired for 110 volts. three conductors from the pedestal to the distribution box. hot to hot in the box, neutral to neutral in the box, ground is connected to the chassis. do not bond the neutral and ground in the distribution box. plugging into a generator does not affect the trailer wiring. though there are some issues with the grounding at the generator. the generator manual will say to drive a ground rod into the ground and connect it to the generator chassis.

[CedarCreekWoody]

X2 what chickdoe said. Key points:
Use a small distribution (breaker) box, as a sub panel.
Ground the trailer frame to the green wire ground in the box.
Do NOT bond the neutral and ground in the box.

Should work fine with a generator.

[clhjsh]

Thanks for your help you guys.

[mwdilday]

I would vote no on grounding to the trailer but I am not an electrician so don't listen to me.

[WY Husker Fan]

Originally Posted by mwdilday

I would vote no on grounding to the trailer but I am not an electrician so don't listen to me.

I am an electrician and this isn’t a voting situation! Absolutely ground the trailer frame. No reason not to and no issue with a generator. As stated previously - do not bond the neutral in the loadcenter.

[Bama Rambler]

Originally Posted by WY Husker Fan

I am an electrician and this isn’t a voting situation! Absolutely ground the trailer frame. No reason not to and no issue with a generator. As stated previously - do not bond the neutral in the loadcenter.

X2

[mwdilday]

Originally Posted by WY Husker Fan

I am an electrician and this isn’t a voting situation! Absolutely ground the trailer frame. No reason not to and no issue with a generator. As stated previously - do not bond the neutral in the loadcenter.

OK I couldn't find the NEC online that addressers this but I did find some snippets from it that supports bonding the ground the the chassis. So my dilemma is if the ground fails on the main service to the RV somewhere you will not be aware of it unless you have a device that lets you know. If the ground fails and you have a short then the RV will be energized. Anyone touching the chassis will get shocked.

[CedarCreekWoody]

Originally Posted by mwdilday

OK I couldn't find the NEC online that addressers this but I did find some snippets from it that supports bonding the ground the the chassis. So my dilemma is if the ground fails on the main service to the RV somewhere you will not be aware of it unless you have a device that lets you know. If the ground fails and you have a short then the RV will be energized. Anyone touching the chassis will get shocked.

But if you have a short to the trailer frame that is not grounded the frame would then be energized and could electrocute a person when their body completed the path to the ground. But if the frame was properly grounded this ground wire would complete that circuit and trip the breaker.

Ground the frame.

[WY Husker Fan]

Originally Posted by mwdilday

OK I couldn't find the NEC online that addressers this but I did find some snippets from it that supports bonding the ground the the chassis. So my dilemma is if the ground fails on the main service to the RV somewhere you will not be aware of it unless you have a device that lets you know. If the ground fails and you have a short then the RV will be energized. Anyone touching the chassis will get shocked.

The more likely scenario if the chassis were not grounded is that if there was a short anyone could get shocked. If you use this same argument for the refrigerator in your house you are saying you are better off not grounding it because if the ground fails and there is a short in the refrigerator you could get shocked. Not a dilemma at all - ground the chassis! This situation is technically outside the scope of the NEC but common sense tells me that this is essentially the same as any other “appliance” and should be treated the same as equipment called out in NEC 250-114. I should know what I am talking about - I have only been an electrician for 40 years - licensed for over 25 as a master and master of record and owner of a 30 employee electrical contracting firm for over 20 years.

[CHICKDOE]

you could always install an ems system in the power feed coming into the trailer to monitor for an open ground. Just think of it as a rv, minus the body.

[aeblank]

How many other double faults are you trying to overcome?
A short AND a failed ground, and you're being concerned about it?
What if a fuel line ruptures AND a spark plug wire fails and causes a fire in the car?

[Scrapper]

Originally Posted by CHICKDOE

you could always install an ems system in the power feed coming into the trailer to monitor for an open ground. Just think of it as a rv, minus the body.

What nobody has mentioned is the neutral-ground bond plug at the generator, a EMS will need it, otherwise it will detect it and shut down the power.

Campgrounds are neutral-ground bonded at the campground power. That's why RV's are not bonded in the power center/ breaker panel.

[EdnKat]

Originally Posted by mwdilday

I would vote no on grounding to the trailer but I am not an electrician so don't listen to me.

Don't be shocked. I'm not an electrician either, but, I play one on TV.

[danny4127]

I stayed in a Holiday Inn

[aquenichet]

Ok, you guys are raising a question for me. We just bought a 3500W inverter generator for our 2015 255P fifth wheel. When using this generator on our trailer, can we just plug the trailer power cable into the generator and go, or do we have to ground the generator? There is a stud on the front of the generator that says ground.

[Bluepill]

Explainer of why you do not want parallel ground and neutral circuits:

Panelboards – Bonding of the neutral terminal to the case of a panelboard, which is not part of service equipment or separately derived systems, creates a parallel path for return neutral current. The result is neutral current (net current) flowing on the metal parts of electrical equipment as well as the grounding and bonding conductors.

Connection at Separate Buildings – Where an equipment grounding conductor is run with the feeder conductors to a separate building [250-32(B)(1)], a common and dangerous mistake is to make a neutral-to-case bond in the separate building disconnect. This ties the neutral and equipment grounding conductors together allowing objectionable neutral current to flow on the feeder equipment grounding conductor.

Separately Derived Systems – The neutral-to-case bond for a separately derived system shall not be made at more than one location because doing so results in a parallel path for neutral return current.

Transformers – If a neutral-to-case bond is made at both the transformer and at the secondary panelboard, then neutral current will flow through metal raceways and grounding and bonding path on its return path to the power supply.

Generator – If the grounded (neutral) conductor in a transfer switch is not opened, then the grounded (neutral) from the generator will be solidly connected to the utility’s service grounded (neutral) conductor. Under this condition, the generator is not a separately derived system, and a neutral-to-case bond shall not be made at the generator or at the generator disconnect [250.20(D) FPN 1].

If a neutral-to-case bond is made at both the generator and generator disconnect, then objectionable neutral current will flow through metal raceways and grounding and bonding path to the power supply.

What are the dangers associated with improper neutral-to-case connections [250.6]?
Improper neutral-to-case connections can create a fire hazard, electric shock and electrocution, improper operation of protection devices, and power quality issues for sensitive electronic equipment. Particularly when the neutral is open or it has a high impedance path.

[Bluepill]

Originally Posted by aquenichet

Ok, you guys are raising a question for me. We just bought a 3500W inverter generator for our 2015 255P fifth wheel. When using this generator on our trailer, can we just plug the trailer power cable into the generator and go, or do we have to ground the generator? There is a stud on the front of the generator that says ground.

Best solution here:

https://youtu.be/M-bTLdMjuqU

[Bluepill]

Originally Posted by chickdoe

think about how a rv trailer is wired for 110 volts. Three conductors from the pedestal to the distribution box. Hot to hot in the box, neutral to neutral in the box, ground is connected to the chassis. Do not bond the neutral and ground in the distribution box. Plugging into a generator does not affect the trailer wiring. Though there are some issues with the grounding at the generator. the generator manual will say to drive a ground rod into the ground and connect it to the generator chassis.

do not do this


Grounding conductors serve 2 purposes:

1. It can provide a path to earth for voltage spikes from lightning strikes.

2. Most important - It provides a low impedance path for a fault current to trip the circuit breaker or fuse in the branch circuit. This shuts the branch down, so that the fault cannot electrocute someone. An example of a fault would be the "HOT" conductor coming into contact the the metal frame of a toaster, washing machine, or an RV. An external ground rod has an average impedance too high to carry enough current to trip a breaker or blow a fuse.

[Bluepill]

In depth lesson on bonding and grounding:

https://youtu.be/3vvvv5QVZoA