mep-003a voltage

[pfazioli]

Hi, looking for an answer. When I set my new units reconnect switch to 120/240V 1PH, unloaded voltage meters as it should. When I apply a 240V load (air conditioner, 5000W) one leg drops out to about 60V and stays there, the other leg stays at 120V.

If I shut the set down, cycle the breaker and reconnect switch and repeat the sequence I get the same reaction.

All connections tight, no overheated wires observed etc.

Kinda feels like a bad contact or something.

I am new. Anyone seen this. THANKS!

 

[derf]

Are you connecting the load to L1 and L3?

 

[Speddmon]

More information is needed. Are you connecting the AC directly to the MEP, or are you going through a plug and cable? As derf mentioned, are you connecting the load properly? When you say that the voltage meters as it should unloaded, is this with the meter in the control box or verified with a good multimeter? Also, the readings when the load is applied, are they done with the unit meter, or with a multimeter?

 

[pfazioli]

Hi, thanks for helping.

Transfer switch is on order but for testing purposes I am feeding my house panel through 20 ft. of 6-4 cable through a 50A breaker. Cable ends at the gen are attached tightly to the output lugs. House feed is through a 240V 50A 4 wire plug:

Gen L0 to house L0
Gen L1 to house L1
Gen L3 to house L2

Gen is grounded to a water pipe 6 ft. away with a pair of jumper cables. Feed cable ground (to house ground) left unattached to gen.

Using a very good multimeter I am metering at the lugs and house bus in all cases.

Your thoughts? Thank you!!!!!

 

[pfazioli]

Forgot some detail.

Unloaded voltage:

L0 L! 120
L0 L3 120
L1 L3 240

Loaded voltage, AND after removing load....before shutdown:

L0 L1 120
L0 L3 65
L1 L3 Can't remember!!

Thanks
pfazioli

 

[Speddmon]

Does the 240V air conditioner run?

I suspected this last evening when I read the original post, but I think you confirmed it with your findings. If your air conditioner ran on 240v but you still have the funky 120 voltages you have an open neutral coming from the generator. I don't know where but it's somewhere.

This is the exact reason that the NEC changed the requirements for sub-panel feed wiring a few years ago. You used to be able to just run 3 wires between your main panel and any sub panels, but they changed the requirement to 4 wires some time ago. The reason being, if you ran 3 wires (2 "hot" wires and the neutral), and something happened to the neutral wire going to the sub panel (broken or cut on accident) you would still get 240 volts just fine and everything was just peachy at the sub, but on the 120 legs you would get all kinds of crazy readings because the path back to the main panel neutral had to go through ground (literally the earth which is a very poor conductor). It also electrified your grounds in your sub panel which is a big NO NO because they were acting as the neutral.

I'm willing to be that you have a very similar situation going on here. Somewhere your neutral (L0) isn't connected, whether at the generator, gen head, reconnect box, a lug in the reconnect box, or crossed in your cable going to the house. Somewhere it's probably open.

 

[pfazioli]

Hi again,

Really do appreciate your help.

No, the airconditioner compressor did not start. It tried but then gave off buzz.......like it was single phasing.

I'll check my connections again and do some tracing. Also, I'll connect my 4th wire (green) to the gen frame so I am only bonded at the panel.

What do you make of the air conditioner symptom. It runs fine on grid power.

Thanks
pfazioli

 

[Speddmon]

Well, the new information blows that theory...LOL

If your AC didn't start on 240 then it is time to start inspecting the generator out really closely. Maybe a bad head, loose connection somewhere in the reconnect switch, faulty reconnect switch, faulty breaker...any number of things can cause voltage drop on one of the legs.

I would suggest starting out by visually inspecting the reconnect switch for loose or corroded wires. Also the main breaker. If those look good you may want to try a different setting of the switch with a different load applied. Find yourself some large 120 loads somewhere and set the switch to 120 volt only connection and see what happens. It would be best if you could find a 208 volt 3 phase load to put on the set. This would check all 3 sets of windings at one time. If you have a bad winding that would help you to diagnose it. Without the proper test instruments it's hard to test the gen head windings yourself.

 

[storeman]

"Gen is grounded to a water pipe 6 ft. away with a pair of jumper cables. Feed cable ground (to house ground) left unattached to gen."

Why the wierd ground? Could that be contributing?

Jerry

 

[pfazioli]

I agree. Good advice and thank you. Having the right voltage before loading, and a drop only when a decent load is applied points to the things you mention. I was hoping one component would be notoriously suspect.

I'll test further and work backward from the lugs. If anyone can point to a historically weak link.....let me know.

Thank you!!!!!
pfazioli

 

[n1oty]

Does this happen with purely resistive loads as well?? Air conditioner start up loads can be very high.

John

 

[ETN550]

I agree. Good advice and thank you. Having the right voltage before loading, and a drop only when a decent load is applied points to the things you mention. I was hoping one component would be notoriously suspect.

I'll test further and work backward from the lugs. If anyone can point to a historically weak link.....let me know.

Thank you!!!!!
pfazioli

2 cents: Those sets are wired double delta for single phase 120/240 so maybe verify with some smaller 120VAC devices to confirm which leg it is then go after the specific screw terminals indicated by the wiring diagram that support the side of the delta that is weak. Temporarily jump the terminals to the corresponding contact. Then you may find the bad connection. Chances are it is a contact or connection. Should be producing full output upstream of the failed component. Use a resistive device like a stove burner to maintain the load while checking, as opposed to damaging the A/C unit that cannot start. Maintaining the load might lead to discovery of a bad contact via heat or burning. Try 2 legs of 3 phase at a time may narrow things down more. Swap leads on the breaker or bypass the breaker with a temp breaker.

 

[pfazioli]

MEP-003a voltage

For what it's worth I found a bad breaker leg. Tried to start the air conditioner as before and L3 dropped to 60V at the lug. Metered the in and out for that leg at the breaker. 120V in, 60V out.....bingo!

Cycled the breaker a dozen times and the voltage drop disappeared. Machine drives the heck out of the whole house...plus some. Makes sense in that the face of that breaker is open to the elements.

Think I'll replace it. Anyone know a good source for a NOS breaker?

Thanks again to the trouble shooters
pfazioli

 

[Speddmon]

NOS? No, Brandy New...Yes. They are available from Newark Electronics. I posted the information some time ago. I'll have to go see if I can find it again.

Keep in mind though that they are pretty pricey.

 

[Speddmon]

Found it. Here is my post...Breaker information

It is located in the following thread...MEP-002A and -003A main breaker

 

[derf]

Definitely replace the bad breaker. You don't want to have to replace your AC or other appliances.

 

[trukhead]

Found it. Here is my post...Breaker information

It is located in the following thread...MEP-002A and -003A main breaker

Went that thread, fascinating! I think i want an 003 genset!

 

[billypop]

I've never seen a 5000W AC that was 240v, only 120??????????????

I guees i can't delete this but i was thinking BTUs ..............sorry.........wasn't thinking