ESP Fault with nEu code

[timjet]

I went to the coach this morning and there is no power to the coach. It is in storage and plugged into 30 amp shore power. Both coach battery banks and chassis battery banks are completely dead. There is no AC power to the coach. The Electrical System Protection Panel has the red fault light on and the display reads nEu. I pressed the bypass button and the display changed to 120 volts and the red fault light went out for about 5 seconds and then the red fault light came on and the display again reads nEu.

I switched AC power source to a different 30 amp power pole and got the same thing.
Help please.

[Ilvmygt]

Who is the manufacture and what is the model number of your “Electrical System Protection Panel”?

[timjet]

The Electrical system Protection system is made my Automated Engineering Corp. model # M10040A, M10041. I called their number and it has been disconnected.

[oldnavycdr]

I had this same fault -- open neutral. The ESP system won't let you bypass it and that company is no longer in business. If you can charge up the batteries with a charger, start your generator to see if the transfer switch will engage and power the coach. If so you can swap the electrical inputs to the transfer switch by removing the generator input and replacing those wires with the shore power connections from the power cord. This will allow you to keep the coach batteries charged while you address the underlying problem. In my case the generator did power the coach so this told me the problem was with the transfer switch circuit. There are circuit boards in the switch which detect faults and these can go bad. Also the shore power contactor could be bad as it cycles many more times over the years than the generator contactor does. M&M electronics will repair & refurbish the ESP/transfer switch but it is pricey. I chose to simply replace the transfer switch and I was back in business. I use a portable Hughes Autoformer surge and fault guard to protect the coach. Good luck troubleshooting.

[timjet]

Thanks OldNavy, I'm headed to the coach now to charge up the chassis batteries.

[Gary RVRoamer]

Automated Engineering went out of business long ago, but that's not your problem. That fault is an Open Neutral wire on the power source. Probably a faulty shore cord, faulty transfer switch, or a broken wire in the shore power outlet you have plugged to. An open neutral is a serious problem (voltage in the motorhome hot wires can go to 240v), so the AEC unit shuts off the power to avoid damage.

[timjet]

Thanks Gary,
I plugged into a different power post with no change.
I'm going to check on the batts this morning and see if I can start the genny.

[Gary RVRoamer]

The most common cause is a faulty ATS wire connection or a broken neutral wire in the shore cord, often right where the plug is connected. The latter would be my first place to check.


I had an AEC ESP in my '04 and the module itself failed by giving a false "open ground". It only happened when the box was physically hot from engine heat (it was mounted on a metal wall adjacent to the diesel engine). I replaced it with a Surge Guard unit and put a slab of foam insulation between the unit and the engine-wall.

[timjet]

Originally Posted by Gary RVRoamer

The most common cause is a faulty ATS wire connection or a broken neutral wire in the shore cord, often right where the plug is connected. The latter would be my first place to check.
Snip

When you say connected do you mean at the power pole or where the cord is connected to RV.


I am connected to a 30 amp power pole with a 50 amp to 30 amp adapter. It was old and had one contact that showed some arcing. I replaced that adapter but it was no help.

All the batts are dead, both coach and chassis. The 2 chassis batts showed less than 2 volts and would not take a charge when I removed them from the coach and put a battery charger on them.

I intend to replace them with 2 group 31 and about 1200 cca. Does this sound about right?


BTW, I tested the power pole and it does not show an open neutral so the problem is in the coach.

[Gary RVRoamer]

When you say connected do you mean at the power pole or where the cord is connected to RV.

Could be either end. The wires tend to get flexed a lot at the plugs, so that's where breaks tend to occur. If your shore cord is detachable from the coach, the plug on the coach end is just as likely to be at fault of the shore end. If not detachable (hardwired), the coach end is probably ok. If you have a shore cord reel, that too is a potential source of a bad connection.



Loose wires at the ATS is also a fairly common cause and usually easy enough to check.


Few modern bulk chargers will try to charge a badly discharged battery because it might be shorted internally and cause a fire. A trickle charger (3A or less) may be able to slowly bring them back to life until a bigger charger is safe to use, but once discharged that badly you probably want to replace them anyway. Yes, a pair of 1200 CCA batteries is suitable for cranking a large diesel.

[timjet]

Thanks Gary, I'm sure I'll have further questions.

[timjet]

I was finally able to get to the coach yesterday and do some diagnostic testing. I replaced both the chassis battery bank and house battery bank with new batteries. With no shore power connected I started the generator and after a 2 minute warm up connected it to the coach. It worked normally. All AC and DC electrical components worked normally.


I then shut down the generator and with a multi-tester checked the 30 amp shore power pole again. I am getting 120 volts between the hot and neutral angled slots, 120 volts between the left and round ground slots and no power between the right angle neutral slot and ground slot. So the power pole is wired correctly and working.


I then opened up the AES box in the power reel bay and checked continuity between the coach power plug and the connectors on the AES box as Gary suggested. Using a multi-tester I got good continuity between the coach power plug and the AES box connectors keeping in mind there was no load on the wires.


I then connected the coach shore power cord to the power pole and noticed when I first connected it, the AES panel in the power reel bay displayed “U-01 then after about a second displayed “C-09” then after about another second displayed “124v”. That displayed (the power pole voltage) lasted about 5 seconds and then I heard a click, like a solenoid open or closing sound, and the display changed to “nEu” and the red fault light illuminated and no power to the coach.


I disconnected the negative lead to each battery bank so they won’t discharge and came home awaiting your next instructions.

[Gary RVRoamer]

Sorry to say that it sounds more & more like a faulty AES unit. Many, if not most, owners have already replaced theirs with a Surge Guard or Progressive power monitor and ATS.


It seems clear that the AES unit had determined that the neutral is open and decided to remove power. Your measurements indicate the neutral is fine, so it boils down to whether you trust your meter readings or the circuit board inside the AES unit.

[timjet]

Thanks Gary, based on your comments about a faulty power cord, I remember about 2 years ago the rear jack foot was lowered on the power cord. I raised it when I realized what happened. Everything worked fine until now. Even though I'm getting continuity on all 3 wires I think it's possible when a load is applied to the wires, the damage done by the jack foot pad could have damaged it sufficiently to prevent full power from passing through the wires but does allow a small current to pass as I'm checking continuity. Anyway I will buy a 30 amp plug with a short length of wire and connect the wires to the input on the AES and see what happens.
If I still get the open neutral indication, I have to ask exactly how to replace the ATS and install a surge guard.
Thanks, I'll be back soon.