MEP-002a wiring sizing question

[AndrewOH]

Hello all, FNG here. I am trying to figure out how to hook up my newly acquired MEP 002a's to my house and am stumped on the cable sizing question. I have decided to use the SOOW type and am trying to figure out the gauge. I see many recommendations to use 10/4.

If I understand this correclty, 5000 watt genny, .8 PF, yields 26 amps. for each 120v Section: ((5000/./2)/120=26 amps per wire. At a 50' run of it, the voltage drop will be just under 3% (however, I believe I should be able to make this up with adjusting the voltage on the generator).

However, after going through the NEC 2008, Table 400.5 says for 10/4, with three conductors (unfortunately the neutral counts towards this) at 30 degrees C ambient , ampacity is 25 amps.
Now, that being said, will my neutral really be carrying that much current? I doubt it, especially if the panel is properly load distributed. Also, what are the chances I will be running my generator at maximum capacity with a PF of 1...

I should probably just shut up and drink the cool-aid and just use what everyone else is using. I apologize if my math is wrong (math in public, .doh) or if my logic is whacked. I read through everything I could find and just think I need someone double checking my work.

Thanks in Advance!

 

[AndrewOH]

I meant to type in .8 for the power factor in my equation, instead it made a smiley face. My bad, I'm new to this kind of stuff. ((( 5000/.8 ) /2 ) /120 ) = 26

 

[Ken_86gt]

There are different insulation types- you must be looking at one rated at a low temperature. You can buy 10/4 30Amp generator power cables rated for 7500W generators at any RV store all day long. I would see no issue using this cable with a 5KW generator.

 

[mistaken1]

Insulation is the key. The current limits are designed to protect the insulation. #10 wire can carry much more current before the wire melts however the insulation will melt/catch fire long before the copper melts.

As Ken_86gt suggests select the proper combination of wire size and insulation type to avoid a fire. http://www.steelsoldiers.com/members/ken_86gt.html

 

[Isaac-1]

Without saying if it is safe, or not, a couple of things to keep in mind when it comes to the NEC ratings,

1, Flexible extension cords are rated lower than other equal size cords in amps because of an expectation of abuse, so it is assumed a certain percentage of the strands in the wires will be broken (I don't remember the amount, but around 10%)

2, All the ratings in the NEC have multiple levels of conservatism applied with the expectation that they are being fed from an unlimited bus (nearly unlimited amps available from the power line), a generator is a limited bus. This makes a difference when you are looking at the amount of heating a wire must withstand during direct shorts until the breaker trips.

3, As you say what percentage of the time do you expect to be running at 100% load. Now to be ultra safe you could go out and get 8 gauge SOOW, which would be better all around, other than being heavier and costing a LOT more. Note that 10 Gauge wire is rated at 30 - 35 amps in all other types of wire other than flexible cords.

Ike

 

[ETN550]

On a single phase system the neutral carries a full load equal to hot leg #1 if hot leg #2 is zero load and vice versa. The current in the neutral decreases in proportion to the increase in current in hot leg #2. This is because the two hot leg phases are 180 degrees apart and as current travels in the neutral in one direction from one hot leg it travels in the opposite direction at the same time from the other hot leg, thus cancelling.

Therefore: The most current in any one hot or neutral leg at any time is the 26 amps. The most current in the sum of the three wires hot, hot, neutral is 52 amp. The neutral leg will have zero current whenever both hot legs are equal.

For example:

Hot 1 = 26a, Hot 2 = 26a, Neutral = 0.0a, total delivered amps = 52a
Hot 1 = 26a, Hot 2 = 15a, Neutral = 11a, total delivered amps = 41a
Hot 1 = 11a, Hot 2 = 17a, Neutral = 6a, total delivered load = 28a
Hot 1 = 0.0a, Hot 2 = 26a, Neutral = 26a, total delivered load = 26a

So the neutral is the difference between the hot leg loads and the total delivered is the sum of the hot leg loads.

And, interestingly, the only way to make full load with a 240/120 reconnection setting on the generator (without overloading a winding) is to have a perfectly balanced load with Hot 1 = Hot 2 and Neutral = zero.

The above statements are true for 100% power factor applications and for utility distribution power. The neutral may carry slightly more current if the power factors in each leg differ, say one leg is all resistance and the other is all motors. The effect would be slight. Additionally, depending on the voltage regulator in the generator (sensing one or all three coils) and other effects in the generator relating to field imbalance there may be additional neutral loads, but they would probably be slight.

 

[AndrewOH]

Thanks guys, it clears it up perfectly. 10/4 will be no problem.

 

[Chrispyny]

This was a great thread. I love the knowledge on this board.

I have one question. Where is the most affordable place to get about 40-50 feet of 10/4 soow ? Fleabay, local shope etc ? Who's got best prices?

And lastly, what are you guys doing to ensure the ends of the 3 wires on L1, L3, amnd L0 are staying put in the split lugs? I built a little table with 2 quad outlets on it, each fused with 20 amp fuses, when load testing, i find i have to REALLY crank down on the split bolts to keep the 10 gauge wire tight and solid. Seems like the split bolts were designed to hold far larger wire ? Anyone solder something to the end of the bare wires to then stick into and clamp down in the split bolts ?

 

[Isaac-1]

I can't help with 10/4 SOOW, but for the lurkers out there if your looking for 6/4 for your MEP-003a, check out used 50 amp RV cords on ebay, these often sell dirt cheap, particularly ones with crushed or damaged ends. 50 amp RV cords can either be 6/4 SO cord, or sometimes a 4 conductor SO cord with 3 #6 conductors and 1#8 ground. (unfortunately 30 amp RV cords are 120V 3 conductor not 4 120/240V)

 

[Keith_J]

Do NOT solder lugs onto the wire, crimp only. What I do is make crimp T lugs from 1/4" copper tube, drilling a cross hole and using a short length of 10 gauge solid wire as the tee. This prevents pulling it out of the terminal clamp.

Solder melts at at a low temperature, this can cause issues.

 

[Chrispyny]

Do NOT solder lugs onto the wire, crimp only. What I do is make crimp T lugs from 1/4" copper tube, drilling a cross hole and using a short length of 10 gauge solid wire as the tee. This prevents pulling it out of the terminal clamp.

Solder melts at at a low temperature, this can cause issues.

I'd love to see a picture please ?!? Having a hard time picturing it.

 

[Keith_J]

Sure, this is one. The cross bar is staked in place, forgot what size of drill. The big copper piece is the tube. Sorry for the delay, iPad was being like a typical apple product.

 

[Chrispyny]

Any chance you have a pic in action ?

Im trying to imagine how this works in place. Do i slip a 10g wire into the 1/4" copper tube and crimp down?

 

[Keith_J]

Exactly, put e wire into the tube, crimp it down. Now you have a better connection that will not pull out. Regular wire crimper tool for 10 gauge works fine, crimp it 4 times or more. It will still fit 002a terminal lugs fine.

 

[Chainbreaker]

I have one question. Where is the most affordable place to get about 40-50 feet of 10/4 soow ? Fleabay, local shope etc ? Who's got best prices?

In Sept. 2013 I picked up 30' 6/4 SOOW (UL/CSA) for $120 with shipping. I found it on eBay; seller was "RSM1". Shipping receipt indicated:

Lou Marks & Sons, Inc. aka: www.extensioncords.com
Louisville, KY
(502) 969-5116

They specialize in bulk wire, etc. Might be cheaper to go direct, give em a call and see what they can do.