New EMS shows Open Ground ?

Hey guys - was hoping some of you could check my sanity.  Here at the house I have a 30A RV hookup next to the trailer.  I plug the trailer in via an 30/50 amp adapter.

I  just completed the install of the EMS-HW50C 50 amp hard wired system.  I plug in the rig and low and behold, the EMS show EC#2 - Open Ground.

Yikes!  How long have I had that problem? 

I did a bit of reading and busted out the old Fluke.  Here is what I get

Pedestal no load:

Hot to Ground:      123V
Hot to Neutral:        123V
Neutral to Ground:  0V

Input to EMS - no load:

L1 to Ground:        123V
L2 to Ground:        123V
L1 to Neutral:          123V
L2 to Neutral:          123V
Neutral to Ground:  0V

I'm not an electrician, but this all seems normal.  This is where I got a little brave (foolish?? ) and flipped the bypass switch on the EMS.  Trailer lights up and everything works.  I put a little heater as a load and the only different measurement with a load on is:

Neutral to Ground:    1.3V

Again, I think that when you have a load you should read some voltage on that link so it still feels normal?

Before I call Progressive Ind. for an RMA - - can anyone who knows more about electricity confirm my finding?  Or am I stupid and my trailer is going to burst into flames

Thanks all!

-Kyle
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Of course it all works with an open ground.  You don't need a ground wire to make the system functional - it's there to protect your life in case of a short in a hot or neutral.

Your meter readings do seem to show a working ground, though. If you can get a voltage reading between hot and ground, it would appear there is a functioning ground in place.  It is possible, though, that there is sufficient ground connection to give a meter reading but not enough to carry any significant current.  I don't know if the EMS ground test is that sophisticated or not.

The most likely candidate for losing the ground would be your shore cord, i.e. a broken, intermittent or corroded connection between the ground wire inside the shore cable and the plug on the end.
Call tech support and discuss your meter readings vs the diagnostic result and see what they say.

  Thanks Gary!  I'm very aware that you can function without a ground - but it still made me nervous flipping that switch

  At this point I'm not sure what else to check so I'll shoot an e-mail off to Progressive Ind. and see what they say....

-Kyle

I'm wondering if that 1.3v N-->G when under load is indicative of a problem and enough to trigger the diagnostic.  If it was 5-6v I'd be sure of it, but don't know anything over zero is  a fault or not.  I'll yield to the electrical engineers on that score.

I am not an engineer but I can say it is normal to have some N to G voltage when the N wire is carrying a significant current. The N voltage comes from the N Resistance x the N Amps.

  Is this the same Harvard from RV.NET?  Sorry for cross posting, I like this forum better but the other seems to get more traffic....

-Kyle

By code the only physical ground is supposed to be "At the service entrance".

One of the problems however is that sometimes people will put a 2nd ground at the garage (Sub panel) and when you have TWO grounds voltage is possible IN fact if you take two ground rods. Drive one in on one side of your property and the other across the lot or front/back or center back  odds are you can measure voltage between them.

I am beginning to believe the EMS BECAUSE I doubt you have enough Neutral current to generate 1.3 VAC N to G.

So, measure the AC volts from the RV Chassis to the local humid Earth Soil and if it is 1.3 VAC (or more) you most likely/definetly have an open ground.

I don't know how much current it takes pull 1.3VAC on N to G.  I had batteries that were charging and a 1500W electric heater running when I did the test.  When I did the test with NO load (unplugged and at the pedistal)  it read like 0.1x VAC.  I did that "loaded" test just to see if I could see the change from current being pulled down the N line.

I worked with Progressive - they also asked about that piece - but in the end are sending out a new unit.

Before it arrives I'll do some more testing to see if I can find a "weak" ground.....

In addition to the above they had me:

- check continuity through the umbilical and 30/50 adapter (0 ohms)
- Double check all the connectors on the circuit board (reseated them all)
- While in bypass I checked several outlets in the trailer with those little yellow 3 light jobbers - all good

Time will tell - but I am gonna feel bad if the new unit has the same reading.....

-Kyle

I too will be VERY interested to see if the new unit changes anything.

I just realized this RV is a trailer and not a motorhome. It matters because any trailer jacks that touch earth ground are going to provide a parallel ground path to the wired GREEN ground wire. Safety wise this is NOT an issue BUT it may be interfering with the trouble shooting voltage readings IF the GREEN GROUND wire is OPEN and not grounding the trailer.

Harvard said:

I just realized this RV is a trailer and not a motorhome. It matters because any trailer jacks that touch earth ground are going to provide a parallel ground path to the wired GREEN ground wire. Safety wise this is NOT an issue BUT it may be interfering with the trouble shooting voltage readings IF the GREEN GROUND wire is OPEN and not grounding the trailer.

Click to expand...

Could this issue be resolved if the parking spot is concrete or asphalt? Would the use of leveling blocks also break the parallel ground during testing.

Gizmo100 said:

Could this issue be resolved if the parking spot is concrete or asphalt? Would the use of leveling blocks also break the parallel ground during testing.

Click to expand...

Yes that would eliminate the parallel ground path. Now just to take this one step further:

IF an RV is electrically isolated from earth ground AND the GREEN GROUND wire is OPEN the RV Chassis is floating. As a result the RV Chassis to EARTH voltage will cause a tingle to anyone standing on EARTH and touching the RV Chassis. The actual measured RV to EARTH voltage will be anywhere UP TO 120/2 = 60 VAC. This is due to the Electrical Capacitance from N-G and G-H of the RV network.

That will probably liven up the thread.  ;D

Harvard said:

Yes that would eliminate the parallel ground path. Now just to take this one step further:

IF an RV is electrically isolated from earth ground AND the GREEN GROUND wire is OPEN the RV Chassis is floating. As a result the RV Chassis to EARTH voltage will cause a tingle to anyone standing on EARTH and touching the RV Chassis. The actual measured RV to EARTH voltage will be anywhere UP TO 120/2 = 60 VAC. This is due to the Electrical Capacitance from N-G and G-H of the RV network.

That will probably liven up the thread.  ;D

Click to expand...

Ok you lost me somewhere after tingle...Been there

But I get the principal of it. Which brings me to another question...If a 2nd earth ground is present the tester could fail the system although the system is safe?

Gizmo100 said:

Ok you lost me somewhere after tingle...Been there

But I get the principal of it. Which brings me to another question...If a 2nd earth ground is present the tester could fail the system although the system is safe?

Click to expand...

That is a very good question and I cannot say my answer is as good as the question, but here goes:

To determine if a N to G voltage is because of normal N currents OR due to an open ground wire you would need to look at the readings as if they were DC volts.

During the Positive cycle:
If the instant voltage N to G is + volts it is normal N current induced voltage.
If the instant voltage N to G is - volts it is an open ground wire with a parallel ground path.

Could be wrong on this......

Harvard said:

That is a very good question and I cannot say my answer is as good as the question, but here goes:

To determine if a N to G voltage is because of normal N currents OR due to an open ground wire you would need to look at the readings as if they were DC volts.

During the Positive cycle:
If the instant voltage N to G is + volts it is normal N current induced voltage.
If the instant voltage N to G is - volts it is an open ground wire with a parallel ground path.

Could be wrong on this......

Click to expand...

This morning I woke believing I knew just enough about electricity to NOT be dangerous....NOW I"M DANGEROUS ;D

If your are wrong I'm not the one to prove it. But thanks for taking the time to answer.

I think we have strayed from the practical to the hypothetical.  Besides, the EMS is checking ground at the input (from the shore power outlet) and has not yet closed the circuit to send power to the RV when it determines there is an open ground. Of course, later with the Ems bypassed and power on, the voltage could reflect a secondary path.

Hi everyone,

Wanted to let you all know the outcome. New EMS arrived last week and I got them swapped out yesterday. I do not like working with heavy gauge wire - what a pain.

Good news - works as designed. Progressive Ind. support was great, good company from my perspective.

https://photos.app.goo.gl/WPWnQxC6MahXonR2A

) ) ) Thanks for the update

So, the original EMS had an issue?  Thanks for the update!