MEP-016D voltage and wiring

[stoneburner]

Hi, All! I have been gathering tons of info from this site for the past month or so, done tons of searches, and I'm still coming up empty-handed on answers to my particular question.

I recently got an MEP-016D with 1 hour on the engine. I have been planning to run this generator as an emergency back-up in 120 volt 1-phase only. I just had an electrician friend help wire up my transfer switch, and I was hoping he could help me figure out which of the L-1 L-2 terminals was my neutral for house wiring.

We ran the generator in 120 1-phase mode (with the frame grounded) and measured 120 volts from L-1 to L-2, but then both of the terminals measured around 60 volts to ground. Does anyone know if this is "normal" behavior out of this generator? We were expecting 120 volts form one of the terminals to ground (which would have determined which terminal goes to ground).

Has anyone had any luck wiring one of these up to a transfer switch? I was hoping to keep it at 120 volts so that I wouldn't have to bother with load balancing...but, if it comes down to it, I will just add the jumper and use it in 120/240 mode.

Any help would be appreciated!!

Thanks for a great site.

Mike

 

[Isaac-1]

Are you sure you did not have the switch in 120V only 3 phase mode?

 

[stoneburner]

We also tried it in 120 3-phase. We got 120 volts between L1-L2, L1-L3, L2-L3, and then around 60 volts from L1-L0, L2-L0, and L3-L0.

I am assuming from your reply that I should have been getting 120 volts from one of the terminals to ground in 120 1-phase mode?

 

[Isaac-1]

I would suspect so, as that is the way it works on my MEP-701a (MEP-016b in ASK) when in 120V mode, I just got my MEP-016d running a couple of weeks ago and have not set up wiring an outlet to it yet, I had planned to work on it today, but my back is bothering me a bit too much.

Ike

p.s. if my back feels better in a bit I will try to run out and check to see what mine does.

 

[stoneburner]

Thanks, Isaac.

I was going to run to the hardware store yet tonight to get some terminals so I could wire in the mod for 120/240 on the 240 1-phase switch setting (jumper between L0 and TB-6.

If you do get around to messing with yours, please let me know what you find. I suppose that it could have somehow been wired incorrectly. However, I love this thing and I am determine dot get it to work.

Mike

 

[ETN550]

60vac from L0 to L1 or L2 in the 120 vac single mode is normal.

Before connecting the generator to a home you need to know how the generator output is grounded to the frame.

Measure the voltage between L0, L1, L2 and L3 each to the frame ground on the generator. The generator is fully floating with no internal ground. If you get one of the L0, L1, L2 or L3 showing same as ground then that is how the generator was last configured to ground.

For the house setup the L2 needs to be the one to ground on the generator, and will become the neutral. Remove any other output lead to ground. Only one of the outputs L1, L2, L3, L0 can be grounded at any time. More than one output grounded creates a direct short in the generator. Most of the time the ground is made inside the box on the backside of the output lug.


Either L1 or L2 may be grounded to match the house system but normally the L2 is grounded.

After removing the wrong grounds and grounding L2 the generator may be connected to the house through the transfer switch. L1 = Hot, L2 = Neutral and frame is ground, same as L2.

The unused L0 will continue to be 60vac to either L1 or L2. This is normal.

 

[Isaac-1]

Thanks ETN550, I thought of that after I posted my message, I guess that is what taking pain killers do to ones thinking ability.

Ike

p.s. does anyone else have a small ground wire that connects to the top of the Yanmar engine on the generator side? I have one there that goes nowhere (ends in a bullet connector near the fuel pump)

Also ETN550 is referring to running it in 120V only mode when L2 is grounded, this is way I have my MEP-701a configured. This gives you the full 3+KW in one 2 wire connection, instead of 120/240V split single phase as a pair of about 1.5KW connections over 2 hots and a neutral.

 

[stoneburner]

I am not completely following, but sounds like I need to so some more homework. Thank you for the lesson. I am a Civil Engineer, and it's been a few years since my last EE class (almost 20, to be exact). Goes to show that two college degrees are not a substitute for experience. Hopefully my electrician pal can provide some additional guidance.

FYI...I am not dumb enough to attempt a connection until I have a full understanding. However, I am still not clear on the grounding/L2 relation. If I am following this right, I would connect L2 to the frame ground terminal and ground rod, and that to the neutral bus in my transfer switch? Don't anybody yell at me. Just want to prompt a bit more elaboration.

We did take readings between all terminals, but I can only remember L1 and L2 to ground (60+v) and L1-L2 (120+v).

Thanks.

Mike

 

[Isaac-1]

Ok, I will try to keep this simple, and this only pertains to wiring in 120V single phase only mode, other modes like 120/240V will be different

First thing to remember is that L-0,L1 and L2 on the generator are NOT the same as on your home panel (for your home panel L0 is neutral, and L1 and L2 are your two "hot" lines, for the generator in 120V single phase only mode, L1 is hot and L2 is neutral)

Second thing to remember is any of these may be jumpered to frame ground on the generator, most likely on either the front or back side of the connection lugs, you need to clear this and set it right for the mode you choose. (note someone may have done this creatively elsewhere like on the terminal block or the panel outlet)


So using a multi meter check to see if you have continuity to ground from any of the output lugs, if it is other than L2 you will want to find and remove the jumper.

If it is on L2 and your are using it as a stand alone power source or if you are using a switched neutral transfer switch wiring it as a separately derived source per the NEC everything good.

If you are wiring it to your house with a non-switched solid neutral transfer switch (this is the most common type), you will be required to unbond the neutral from the frame at the generator, you will still want a ground rod connected to the generator frame at the generator, but NEC code requires there only be a single neutral ground bond point, usually at the service entrance. NEC grounding for transfer switches is a complicated poorly worded mess and I would be willing to bet that a large percentage of professionally installed backup generators are not wired to code. At one point a few years ago I was tasked with hiring an electrician to connect a backup generator at a small business, I interviewed 4 that all claimed to have experience installing generators before getting to one that half way understood the NEC code requirements for grounding and transfer switch installation. The 4th one was the closest to getting it right, but he still had things wrong confusing requirements for legally mandated emergency generators with optional standby systems.

Ike

 

[stoneburner]

Thanks, guys. I'm going to mess with it some more through the week. I'm sure I will have more questions.

Mike

 

[stoneburner]

Alright, so I played around with this for a few minutes this morning. I grounded the unit at the frame ground lug, flipped the main breaker on, and checked continuity at all terminals - to each other, and to ground.

Only L1 - L2 showed continuity (to each other). None of the other terminals showed continuity to ground or to any other point. I checked this without starting the generator. I am still going to discuss this with my friend, but I believe that this is what you were talking about with a standard transfer switch (Gentran 3028 with L2 to neutral.

Or, maybe I'm nuts.

 

[stoneburner]

Ike and ETN550:

I've spent some time looking into this matter some more, and it appears to me that the "floating neutral" of the MEP-016D in 120v mode is for stand-alone only, and can't be used for house wiring. Since I did not get continuity between ground and L1 or ground and L2, but am still getting 60 volts between L1-ground and L2-ground, I don't have a neutral/ground bond at the generator to break.

My understanding is I should get 120 v between L1 and L2, 120 v between L1-ground, and 0 voltage between L2-ground.

Is this correct? Hopefully, I'm still missing something.

 

[Isaac-1]

I think we may be having a terminology issue, in particular for the terms ground and floating. Another term that may come up is bonding.


Just so we are all on the same page, you are wanting to set up this generator so it will be connected to your house in 120V only mode through a solid neutral transfer switch (the most common type) wired per the NEC non-separately derived source section, correct?

You are currently getting about 60 volts from L-1 to the frame of the generator and from L2- to the frame of the generator?

(this is likely caused by a jumper from L-0 to the frame, which may be in the control box on the back side of the output lugs, which you need to remove for any 120V only operation)

You say you are not getting continuity to the frame, how are you testing this? note there will be some resistance on this connection since it runs through the generator windings, but should ohm out fairly low (10 ohms or so, I checked mine and it is doing the same thing, getting about 9 ohms to the frame from L1 or L2 on my Fluke 87V), certainly low enough to light a continuity light, or should read continuity on most meters, (you should also be doing this test with the output breakers on and the generator stopped)


Ike

 

[stoneburner]

Ike:

Yes, I want to connect to my house in 120 volt only mode. Solid neutral transfer switch (neutral unswitched). (Not sure of NEC article, I deal almost exclusively with Articles 240, 250, 310 and 690)

Alright...I don't know why my meter reads differently from my electrician friend's (I have a Sperry DM-4100A).

I studied the wiring again on the generator, and I cannot find any jumper from L0 to frame ground. But, I ran the machine again, and got different results than my friend did with his meter.

In the 120 1-Phase mode, I got approx 30 volts L2-L0, 100 volts L1-L0, 2 volts from both L1-ground and L2-Ground, and 0.2 volts from L0-ground, and 120 volts from L1-L2..

Again, no continuity except L1-L2 (checked with generator off and main breaker on). Continuity checked with Ohm meter and probe placed on L0...L4 and other probe on frame ground lug. My meter (supposedly) will read to the thousandth of an Ohm.

I am not sure if my meter is right or if my friend's is. But, we were both right there and saw the 60 volts!! I don't know what make his meter is, but I remember some of my coworkers using it on a PV module, and I had to change some setting on it for them. Perhaps my friend had his set wrong. Mine is pretty dumb-proof. Sorry for the conflicting info.

Does my new info make any more sense and explain what is going on better?

 

[Isaac-1]

It may, try checking the voltage while running the lead through a small resistor of some type and see if you get unexpected amounts of voltage drop.

Also a 120V incandescent light bulb would make great to test wired between the various points, if it lights / glows you have real voltage, as you may be getting a phantom voltage on the meters (induced capacitance, digital meters are particularly bad about this, it has to do with how they sense voltage)

Ike

p.s. here is a write up on the concept, of course they are trying to sell a meter that detects it, but you get the idea http://www.supplylink.com/article/new-multimeter-detects-ghost-voltages

 

[stoneburner]

Alright...so I got a light fixture and wired on some #12 THHN to both leads. The 60 W bulb only lights between L1-L2. I checked all other combinations between terminals and ground.

I then twisted the ends of the wire to my multimeter leads, and continued to check. 0 v between L1-Grd, 0 volts between L2-Grd, and 0 v between L1-L0 and L2-L0 (all with the bulb wired in parallel). L1-L2 continued to show 120 volts with bulb lit.

Next, I wired the meter in series with the bulb (thinking this would be my "resistor", as you had suggested. 100v between L1-L0, 30 v between L2-L0, and 4 volts between L1-Grd and L2-Grd (just like before).

Surely, that bulb would light with 100 volts between L1 and L0?

Mke

 

[Isaac-1]

Sounds like ghost voltage to me

 

[stoneburner]

So, with that said, does it sound to you like it's good to go as a 120 volt house back-up?

My garage has a separate service entrance, so I was thinking of tying in L1 to one of the hot bus bars and L2 into the neutral bus bar (with main shut off and only one breaker on that has a few 120 volt duplex outlets on it). Then, check voltage form hot to neutral, hot to ground, and neutral to ground at an outlet. I am assuming that will give me the info I need.

Thanks a ton for your help, Ike!!!

 

[Isaac-1]

If you do that for testing I would suggest pulling the main breaker to make sure no one flips it back on while your testing.

 

[stoneburner]

Not a problem...that's my man cave, and no one ventures out there but me. I will be within 10 feet of and in line of sight of the load center anyhow (it's a separate pole building across the road next to the chicken coop).