mep-803 terminal output question

[Kvl00ej]

I have what some might think is a pretty dumb question, in 240v single phase operation on an 803 is each hot leg rated at 52 amps or is that both legs combined 52 amps? I have seen some people's YouTube videos showing an amp meter and some are pushing anywhere from 25-49 amps on a single leg. Just wondering what rated wire to use when hooking up the auto-transfer switch.

 

[TrailLifeBill]

I have mine hooked to a 60A breaker in the panel - and use #6 wire (rated 65A). Interlock installed between main breaker and gen breaker so that they can't both be on simultaneously. One day I might spring for the auto switch route, but right now can't afford a 200A ATS plus circuitry.

 

[rhurey]

Same. I have #4 cord between the gen and the house, then #6 to the panels that have interlocks in them.

And that's 52A per leg.

 

[TrailLifeBill]

One factor I forgot to ask - how far is your run?? You would oversize to compensate for voltage drop if you have a very long run.

http://www.southwire.com/support/voltage-drop-calculator.htm

 

[DieselAddict]

Thanks for starting a new thread.

The total output is about 50A between the two hot wires (L1 & L3). Where this is a little tricky is that you can have 240v and 120v loads. The 120v loads won't distribute amps equally between L1 & L3. This unbalanced 120v load is carried back on the neutral (N) and won't show up on BOTH hot wires (L1 or L3). Unbalanced load will show up on only one of the hot wires. What that means in practical terms is that you need to measure both L1 and L3 wires to know the complete picture of load. The difference in amps between the hot wires will equal the amps on the neutral. You will reach full load on the generator (wiring limit, not engine power limit) when you reach either 50A of balanced load or at about 25A of unbalanced load. Lets take a look at a couple of example to better explain it.

Here are some examples (I'm sure this is going to look bizarre):

L1 = 50A
L3 = 50A
Load = 100% (of L1 AND L3, You'll have Zero neutral current)

L1 = 25A
L3 = 0A
Load = 100% of L1, Your constraint is the 25A of neutral current (unbalanced load), In this situation you can only get half of the generators rated power out of it. You can add load to L3 but for L1, you're done. This is why its not good to use a 3 phase generator for single phase loads. Your neutral current will always be high.

L1 = 25A
L3 = 10A
Load = ~60% of L1, You'll have 15A of neutral current.

L1 = 35A
L3 = 10A
Load = 100% of L1, Your constraint again is the 25A of neutral current, The generator is at max allowable unbalanced load.

This is simplified a bit but hopefully communicates the concept. The true way to do it is to know the manufacturers load factor for the alternator and use that for calculating the limits of unbalanced loads. But this will work and air on the side of safety for the equipment.

 

[Haoleb]

When it comes to wiring it depends on your distance and type of wire etc. My setup consists of 20' of 4/4 SOOW cable from my generator to my inlet box. From there I have 4AWG THHN run about 10' inside of conduit from my inlet box to my generator transfer switch which then uses 2-2-2-4 service entrance cable to run 35' back to my second transfer switch that switches between the utility or generator. The 2-2-2-4 is aluminum cable which I am not fond of personally but it is typically used for 100A service hookups. I selected it because it is aluminum I went with a 60 degree column for sizing and that put it right at 75A capacity If I remember correctly.

I sized everything to safely be able to carry 60A of current. Personally 6AWG wire is a little small to safely carry 60A but YMMV.

 

[DieselAddict]

The question about cable size got inserted in more as a comment than a question if I read the above posts correctly.

As a general rule of thumb you use the ampacity table for wire lengths up to about 100'. For lengths between 100' and 250' you would go up one wire size to keep voltage drop within spec.

As an example for a MEP003a you could use 6 ga (copper) wire up to about 100'. Over 100' and under 250' you should drop to 4 ga.

 

[DieselAddict]

When it comes to wiring it depends on your distance and type of wire etc. My setup consists of 20' of 4/4 SOOW cable from my generator to my inlet box. From there I have 4AWG THHN run about 10' inside of conduit from my inlet box to my generator transfer switch which then uses 2-2-2-4 service entrance cable to run 35' back to my second transfer switch that switches between the utility or generator. The 2-2-2-4 is aluminum cable which I am not fond of personally but it is typically used for 100A service hookups. I selected it because it is aluminum I went with a 60 degree column for sizing and that put it right at 75A capacity If I remember correctly.

I sized everything to safely be able to carry 60A of current. Personally 6AWG wire is a little small to safely carry 60A but YMMV.

THWN-2 (90C) 6 ga copper wire is good for 75 amps. That is more than enough for a MEP803a.

75C wire is good for 65A. Still OK but closer. There is no difference in cost so why not go for 90C wire.

 

[Daybreak]

Howdy,
Like others have stated, it really depends on what the generator capacity is, how long the run is, what type of wire you want to use.

Standard #6 AWG THHN 90C will be fine at 75 amps (4 wires needed, 2 hots, a neutral, and a ground)

A flexible type wire cord, like a extension cord, rubber coated and flexible and weather resistant. There are some options here. The naming conventions is kinda important to the outside covering and the internals construction.

Standard 6/4 SOOW cord is a bundle of 4 wires sized #6AWG stranded, covered in EPDM Rubber gets you 45 amps

A more expensive way would be with Type W cord. a 6/4 Type W cord is constructed differently than SOOW, it cost more, but is industrial flexible and covered in EP Rubber and gets you 87 amps.

Anytime you start going a long distance, you start getting voltage drop. So a 50ft run is not a issue. You start going over 100ft, you need to watch what your amperage needs are. A 250ft run will need to be bumped to the next larger gauge wire etc...

OK, say a flexible cord is needed from generator to house inlet, rubber coated cord works here. From the inlet to your electric panel, different ways to accomplish this. In conduit, 4 #6 THHN wires works here. Gets you 75 amps. You also can use copper service entrance 6-6-6-6 ( known as 3 conductor wire with bare ground) gets you 75 amps.

Yes, on one of my video's with the MEP-803A and load bank, I was loading 67 amps. I was not loading 67 amps all day long either. That is using 4 #6 awg THHN wires, rated for 75 amps.

 

[Guyfang]

Kv100ej,

See, got what you wanted! Got mucho info. You can learn something new every day.

What we do here in germany, is whip out our slide rule looking "cabe helper". Move the little window to say, 70 amps and listed below, is a table with lengths, cabe size and other such info every good "elektriker" needs to know. And then cable types. Inside. Out side. Fire resistant. And on and on. But then we do mostly industrial installations. As a simple "Strippenseiher, or "cable puller" I rarely do any of that. The "Meister" or master electrician figures out what we need, then sends us matrial and says "Ain't done yet?"

Oh, remember? There are no dumb questions.

 

[Haoleb]

All good points above. One other thing that must be considered is the rating for the terminals in the equipment you are hooking into. For example you cannot use the rating for wire at 90 degrees when the terminals are rated at 75 degrees... you need to step down to 75 degree rating.

From my standpoint if #6 will do the job... #4 is not really that much more expensive in the big scheme of things so why not run #4 and and have an even greater margin of safety.

 

[zarathustra]

If L1 is rated at 52 amps then it is 52 amps. The L1 52 amps is the same as the L3 52 amps and is NOT additive. Think of it this way... if in a 110 volt circuit the L1 is drawing, say 10 amps, then the neutral is carrying 10 amps as well, and you wouldn't add the 10 +10 to make it 20. Since, in a perfect world the neutral and ground are not needed in the 220 volt circuit to make it work, the L3 in a 220 volt circuit is "effectively" the "return" line and is carrying the same amperage as the L1.

The white neutral in a perfect circuit will carry 0 amps in a 220 volt setup. In practice it can carry a little current, but that means that the circuitry isn't fully balanced.

So, y'all should be able to read the L1 amperage and subtract the L3 amperage and add/subtract any amperage traveling on the white wire and it should equate to 0.

That concept took me a little while to wrap my head around, but it makes sense if one realizes that the white and ground wires are not necessary in running a 220v circuit. It goes without saying that grounding the circuit is necessary for safety reasons.....

 

[Kvl00ej]

For those of you who asked me to start a new thread "Thank You". My run will be about 60 foot at the longest. My electrician recommended aluminum wire and I'm not a big fan that's why I'm asking. Also I wanted to have overkill built in so I don't bun down my new house lol

 

[Guyfang]

If L1 is rated at 52 amps then it is 52 amps. The L1 52 amps is the same as the L3 52 amps and is NOT additive. Think of it this way... if in a 110 volt circuit the L1 is drawing, say 10 amps, then the neutral is carrying 10 amps as well, and you wouldn't add the 10 +10 to make it 20. Since, in a perfect world the neutral and ground are not needed in the 220 volt circuit to make it work, the L3 in a 220 volt circuit is "effectively" the "return" line and is carrying the same amperage as the L1.

The white neutral in a perfect circuit will carry 0 amps in a 220 volt setup. In practice it can carry a little current, but that means that the circuitry isn't fully balanced.

So, y'all should be able to read the L1 amperage and subtract the L3 amperage and add/subtract any amperage traveling on the white wire and it should equate to 0.

That concept took me a little while to wrap my head around, but it makes sense if one realizes that the white and ground wires are not necessary in running a 220v circuit. It goes without saying that grounding the circuit is necessary for safety reasons.....

When I was in electrician school here, it took me a long time to grasp that concept. Then one day on a job, I was working on lights. Hundreds of neon lights. No voltage was applied to the circuits. I was just sticking cables through the light, and hooking up cables. As soon as I stuck the cables through the METAL lights, I could hear screaming and all kinds of carrying on, up on the next floor. And then I cut the cable to length, before hooking it up. And for some reason lots of screaming and cursing was still going on up stairs. It went on for ever. Then came my mentor, and asked me in a silky, smooth evil way, if I had been cutting the cables with my side cutter. I, in my ignorance, replied, "yes, of course. Why." I thought everyone in the building was going to kill me. When you have an unbalanced load, (real world) the N will always have some small amount of waste voltage on it. As all circuits here run through a GFI, when ever the N wire touched something grounded, it popped. Whenever I cut a cable, and my side cutter made contact between the N and the ground wire, the GFI popped. I had turned off the lights in the building about 200 times during the day. Someone had to reset the lighting GFI, after every "incident". At that point, my master electrician made me study phases, phasing and how in a perfect world, a N is not needed. We use lots of three phase motors here in germany, and in an industrial setting, you save big money when you hook up miles of (copper) cable that only have 4 wires, instead of 5. But the fact that no N was needed on a motor, just didnt sit right in my head for a while!

 

[Kvl00ej]

Your story is so funny, I understand the concept now. It's weird at first cause you don't want to believe it but it's so true about balanced loads.