MEP803a tripping overload fault while other unit chugs along no problems.

I'm having a similar issue on one of my MEP-803A's; havent' had a chance to get into the S8 yet as I'm wrapping up my piston replacement / rering project right now. Anyhow, is there a good NSN for a 'better' S8 reconnection switch? I can only seem to locate NSN 5930-01-386-0543 which is the Kraus & Naimer C26-C57442ER blue plastic switch. I don't know if cleaning up my S8 is going to be a kill shot fix for it yet, as it gives the overload warning whenever I apply more than 2kw to the unit for a minute or two; but if I get to the point of requiring parts replacement; I'd like to put the better part in.

Also, potentially related, my percent load ammeter doesn't work - does it run through S8? Again, haven't had a chance to crack the books on this issue as well.

devilphrog said:

I'm having a similar issue on one of my MEP-803A's; havent' had a chance to get into the S8 yet as I'm wrapping up my piston replacement / rering project right now. Anyhow, is there a good NSN for a 'better' S8 reconnection switch? I can only seem to locate NSN 5930-01-386-0543 which is the Kraus & Naimer C26-C57442ER blue plastic switch. I don't know if cleaning up my S8 is going to be a kill shot fix for it yet, as it gives the overload warning whenever I apply more than 2kw to the unit for a minute or two; but if I get to the point of requiring parts replacement; I'd like to put the better part in.

Also, potentially related, my percent load ammeter doesn't work - does it run through S8? Again, haven't had a chance to crack the books on this issue as well.

Click to expand...

I don't think there's anything wrong with the old style blue plastic S8 switch, it was used for years on many sets and performed fine.
For as many times as I'll ever switch it (probably never other than to exercise it once in a while once the set is hooked up) I can't justify the additional cost for a newer style switch.

Yes M8 (ammeter) is connected at terminal 44 of S8 and terminal 28 of S6. Cleaning my S8 terminals did get my M8 working but the switch is FUBAR in other places so it's going to be changed. That doesn't mean that your problem resides with S8, it could be many other things but cleaning the S6 and S8 with some contact cleaner and exercising them would be a good start

Get the schematics and read them, it's the only way to familiarize yourself with the wiring and the set in general. The more you look at them, the clearer it becomes as to what goes where and the designations used for the components.

The NSN for the newer style switch is in a thread somewhere in this section, do a search.

Good Luck with your set, lots of great info here and lots of great and experienced people too who will help you along to getting your set right.

Thanks Farmitall. I appreciate the help! I've been buried at work and travelling a bunch so haven't been able to get out into my shop at all; I'm still working on reassembling the engine on my first unit so that has put my personal unit on the back burner...

I recently bought a (NOS) load gauge thinking mine didn't work, before it arrived, I sprayed & exercised the crap out of the S8 and it started working again.

I hope the pattern here is becoming obvious. It is a good idea to exercise those switches on a regular basis. If you have one of the earlier versions use caution to avoid breaking the stem of the switch.

I do that with all my stuff. Including the breakers in my home electrical panel. Once a year I kill main power then go through and flip each breaker off and on several times to clean the contacts. I also check to see if any of the breakers are "welded" closed.

DieselAddict said:

I hope the pattern here is becoming obvious. It is a good idea to exercise those switches on a regular basis. If you have one of the earlier versions use caution to avoid breaking the stem of the switch.

I do that with all my stuff. Including the breakers in my home electrical panel. Once a year I kill main power then go through and flip each breaker off and on several times to clean the contacts. I also check to see if any of the breakers are "welded" closed.

Click to expand...

A few weeks ago, I was helping my son fix up an old house he bought. The place was so old, that there was not even ground in the building. Typical 50's installation. I was trying to find out what breaker was for what circuit, and had three breakers that I had no idea for what they were used for. Output wires were there, but when I turned them off, nothing went out in the house. After an hours, I found two, one in the attic, and one in the heater room. Both for a few plugs that were not used. But the last two, nothing. So I flipped all the breakers off and started repairing circuits that had broken plugs and switches. Everything off. Then I reached into a plug box in the attic, that was only for the antenna amplifier. Image my surprise when I got bit! Mad as hel*, I charged downstairs to find out what butt head had turned the breakers back on. But they were all turned off. It hit be like a brick. got my VOM and started checking outputs. Yep, two circuits had breakers welded shut. Never hurts to check old houses every now and then. Easy check, that no one ever thinks about. And the same goes for gen sets. Had K1's weld only ONE set of contacts shut. There is a big accident waiting to happen. Shut off K1, and the equipment stops, because 2 of 3 phases are turned off. And still have one phase hot. Yeah, that is a tough one to notice, until you get bit.

DieselAddict said:

I hope the pattern here is becoming obvious. It is a good idea to exercise those switches on a regular basis. If you have one of the earlier versions use caution to avoid breaking the stem of the switch.

I do that with all my stuff. Including the breakers in my home electrical panel. Once a year I kill main power then go through and flip each breaker off and on several times to clean the contacts. I also check to see if any of the breakers are "welded" closed.

Click to expand...

I agree with exercising the switches.....and also cleaning them which has proven to me that they do get cruddy because they are not sealed and will impede correct functioning of the generator. On both my 803a's cleaning and exercising brought back functions that were not working.

I also exercise my home breakers. Did it last week during an hour long power outage. Mains off and go down the panel, especially the water heater and fridge circuits that are used most.

A neighbor had a garage door that was intermittent. He told me it had been that way for over a year. The same circuit ran a couple of outlets in his garage that he used to plug in a saw and couldn't figure out why the saw was stalling.

Turned out to be a corroded breaker and pole on the bus bar. His weather head at the service entrance was letting driving rain in and the water was following the wire into the panel. You could see a clear path of deposits from the conduit.

I cleaned the bus bar and changed out the corroded breaker and got his door closed and he had an electrician get the power company to turn off the power at the pole and replace the weather head and stop the leak.

Breakers are convenient, but fuses are actually safer.

I hate house installations. My big love is industrial installation. I simply love to install BIG factories. One of my all time best jobs was a Mega million buck Pre-Fab, Pre-Stressed Concrete plant. In the plant, we used breakers for some simple stuff, but for heavy duty machines and plugs, only fuses. Like Farmitall stated, way safer. A fuse works, or not. My boss, when I first started told me that since he started doing it only that way, the amount of maintenance work, (and cost) dropped way down. Yes, breakers are convenient. But you can buy a bunch of fuses, for the price of a breaker. And you never have to worry about a contact being welded shut.

Well, my new S8 is in the PO BOX. I'll be picking it up tomorrow and attempting an install if the weather isn't blowing snow and rain. This winter weather just keeps lingering on and on here.

Will post back with my results of next load test.

Update:
Picked up the switch but too late in the day and a bit too windy to work on the set outside.....also had to make a run to the tax accountant's to get my taxes in before the post office closed.

So, tomorrow is another day. Anxious to see if the new switch resolves my loading problem. Given the condition of the switch that's in there, I'm very optimistic that it will.

Just to keep the thread up to date, I installed the new S8 on the 803a but still getting an overload condition and load disconnect after 12 minutes of load using two 5400w dryer elements. This is with battle short OFF. I have not tried with battle short ON and really don't want to as the set should function properly without it.

Going to go through the terminal blocks, check wiring for accuracy, remove and clean connections then remake the connections and make sure they are tight. While I have the winding connections off of TB-3 I will check them per the TM procedure.

Next will be swapping out the overload relay from a good working set. If problem persists, then I'm removing and opening up K-1 to inspect the contacts. Seeing how the old S8 had burned terminals, there is a possibility that one or more of the three contacts inside could be burned causing a higher current in one leg of the load.

My clamp on ammeter is due this week so I'll be able to monitor the current per leg and log it for diagnostic purposes. It has the peak hold features.

Been working around the weather here and other things so progress is a bit slow, but is going forward in the right direction.

Update: So far, I've replaced S6 and S8 on this set ( that was a while ago) Wired each following the schematics,( as recommended by Guyfang) and is the proper way to do it so a problem is not duplicated.

The other day, I replaced the overload/short circuit relay with a different one from a member here that is supposedly in good working order. All connections clean and tight.

This morning, I replaced a couple of the terminal studs on the resistor board, wiring them per the schematics and checking point to point for the connections on each wire. Reflowed a couple of solder joints that appeared to be cold joints. Cut the zip ties on the whole harness and Inspected the wiring for any chaffing....none found.

Sprayed and exercised both S6 and S8 again just for grins and the set has sat for a while, checked the S8 position (120/240 1PH) where it should be for the test.

Put the ground rod in, connected the ground wire. Reconnected the battery negative.

Connected the load ( two dryer elements).

Started the set, let it warm for a few minutes and turned on the circuit breaker. Loads to 40.8 amps @ 220vac runs for about ten minutes under load then trips the breaker with overload fault light coming on.

If I reset the breaker, it goes back under load, runs for ten minutes, trips again. This will go on as many times as I care to reset it.

If I boost the voltage to 240vac it trips in about three to five minutes.

Back to the schematics.......

I'm wondering if K1 could be a problem with possibly a corroded or burned internal connection?

I'm also wondering if a main winding is heating up.

Note: With battle short on, the unit will indicate a fault but not trip the breaker. I only did this momentarilly just to see if held with the battle short on.....it held and continued to produce power steadily.

The quest goes on......back to the manuals.

How about the burden resistors, have you tested them?

And that overload came out of a machine that I swapped overloads on, only to not solve the problem (similar to what you are fighting, but different). So it should be solid... if its not I stand behind it. But I believe it won't be that part.

Light in the Dark said:

And that overload came out of a machine that I swapped overloads on, only to not solve the problem (similar to what you are fighting, but different). So it should be solid... if its not I stand behind it. But I believe it won't be that part.

Click to expand...

Thanks, don't sweat it, I'm sure its solid. I don't think its that part either.

There is something triggering the overload fault/ tripping the breaker.

The winds have picked up here significantly so my work with the set is concluded for today. I will perform further trouble shooting tomorrow.

RE: The burden resistors, I put a volt meter across each one with the set running but didn't record the readings....was distracted with my dogs running loose outside. I will do that tomorrow(weather permitting) and compare it to the readings specified in the TM.

If necessary, I will unsolder one leg and record the resistances of each along with operating voltages.

I rechecked all connections on S6 and S8 again, all correct. Both switches are also new.

Also going to perform a winding resistance check on the main windings and also take readings on the current transformer outputs.

I'll figure it out. Good thing is, I have a properly working unit right beside it to compare to.....AND MANUALS.

If the resistance of R10, R11, & R12 check out good then I'd recommend checking the AC voltage across each resistor when running the set under your load.
At 100% load the voltages across R10, R11 & R12 should be ~5.6 VAC.
At 133% load the voltages across R10, R11 & R12 should be ~7.5 VAC.

If your load applied is <100% the voltages across the burden resistors should be less than 5.6 VAC.
I suspect you may find one or more of the voltages above 5.6 VAC.

If you find a voltage above 5.6 VAC then I'd check the voltages at the overload relay terminals.
Check K8-1 to K8-4, K8-2 to K8-4 and K8-3 to K8-4 when running with your load. See if any of those voltages are above 5.6 VAC.
I suspect you may find one or more of the voltages above 5.6 VAC.


Another thing to check in the number of loops of each wire thru the Current Transformer.
On an 803 each wire should loop thru the CT 4 times.

kloppk said:

If the resistance of R10, R11, & R12 check out good then I'd recommend checking the AC voltage across each resistor when running the set under your load.
At 100% load the voltages across R10, R11 & R12 should be ~5.6 VAC.
At 133% load the voltages across R10, R11 & R12 should be ~7.5 VAC.

If your load applied is <100% the voltages across the burden resistors should be less than 5.6 VAC.
I suspect you may find one or more of the voltages above 5.6 VAC.

If you find a voltage above 5.6 VAC then I'd check the voltages at the overload relay terminals.
Check K8-1 to K8-4, K8-2 to K8-4 and K8-3 to K8-4 when running with your load. See if any of those voltages are above 5.6 VAC.
I suspect you may find one or more of the voltages above 5.6 VAC.


Another thing to check in the number of loops of each wire thru the Current Transformer.
On an 803 each wire should loop thru the CT 4 times.

Click to expand...

Thanks, I will measure and record the voltages as you indicate.

The number of turns through the current transformers are correct, I checked the count but haven't yet measured the output of each while running.

I will check back tomorrow with my findings.

kloppk said:

If the resistance of R10, R11, & R12 check out good then I'd recommend checking the AC voltage across each resistor when running the set under your load.
At 100% load the voltages across R10, R11 & R12 should be ~5.6 VAC.
At 133% load the voltages across R10, R11 & R12 should be ~7.5 VAC.

If your load applied is <100% the voltages across the burden resistors should be less than 5.6 VAC.
I suspect you may find one or more of the voltages above 5.6 VAC.

If you find a voltage above 5.6 VAC then I'd check the voltages at the overload relay terminals.
Check K8-1 to K8-4, K8-2 to K8-4 and K8-3 to K8-4 when running with your load. See if any of those voltages are above 5.6 VAC.
I suspect you may find one or more of the voltages above 5.6 VAC.


Another thing to check in the number of loops of each wire thru the Current Transformer.
On an 803 each wire should loop thru the CT 4 times.

Click to expand...

Made my voltage measurements today. All measurements taken using a Fluke 29 Series II digital multimeter.


My measurements with genset off and resistors isolated: R10= 7.2 ohms

R11= 7.6 ohms

R12= 7.6 ohms

Double checked wires to each resistor and compared them to a working unit right beside it.


Voltage measurements on resistors with set running and 10k load applied L1-L3 @ 220 volts ( current meter reading 75% load)

R10= 4.57 vac

R11= 4.59 vac

R12= 8.78 vac


Current transformer output voltages, 10k load applied as above.

CT1 = 4.74 vac

CT2 = 5.13 vac

CT3 = 9.10 vac

K-8 Voltage measurements, 10k load applied

K1 to K4 = 4.57 vac

K2 to K4 = 4.54 vac

K3 to K4 = 8.81 vac


Questions, comments?

Barring any further information on the above, My next step is to isolate and measure the resistance in the main windings.

The readings across CT3, K8-2 to K8-4 & R12 are all suspect. Those voltages are all above the 100% load level.
In the 120/240 single phase setting R13 is connected in parallel to R12 via S8.
Looks like possible a wiring issue to/from R13 and/or S8-14 & S8-13, bad contact closure between S8-13 & 14 or a faulty R13.

Can you measure the resistance of R13?
Can you measure the AC voltages across R13 and from S8-13 to S8-14 with your load applied?

kloppk said:

The readings across CT3, K8-2 to K8-4 & R12 are all suspect. Those voltages are all above the 100% load level.
In the 120/240 single phase setting R13 is connected in parallel to R12 via S8.
Looks like possible a wiring issue to/from R13 and/or S8-14 & S8-13, bad contact closure between S8-13 & 14 or a faulty R13.

Can you measure the resistance of R13?
Can you measure the AC voltages across R13 and from S8-13 to S8-14 with your load applied?

Click to expand...

Will do.

The amount of work you have done, I'm betting your problem is with a mis wired hookup. I had a unit with a similiar problem and I checked everything like you. I double checked the wiring and everything checked out, then I was taking S8 out of another unit to switch them around and noticed it was hooked up alittle different. So I went and compared the 2 units and sure enough, the unit that was tripping overload had 1 wire on S8 hooked up different. Sure enough that was the issue the whole time, the wire was hooked 1 spot off. When I was verifying the wire hookup, I made the mistake of looking to fast at S8 numbers and was just glancing at the wire numbers and the S8 numbers.