Generator Connection. How Would You Do It?

[Tscott]

I bought a trailer mounted 10kw military surplus generator for the farm and now I need to figure out how to connect it to the house. Based on my research, these units are very underrated and are closer to 15kw capacity. I plan to leave it on the trailer so I can move it around the farm if needed but its main purpose will be as a backup for the main house. Since it will be mobile I'm not sure the best way to connect it.

Would you give up some generator capacity and wire a 60A plug and breaker or possibly even a partial house transfer switch mounted in the garage? Or would you size the circuit for the generator max output of approximately 70A and hard wire it in every time you needed to use it?

A third option would be to use a 70A or 80A pin and sleeve type socket but they are pretty pricey so I'd like to avoid that if at all possible.

I think the simpler solution is to use the 60A plug but I do want to make sure I can power the air conditioner (30A circuit) as well as the refrigerators and all the smaller appliances at the same time without tripping the breaker. I'll give up the use of the washer, dryer, and oven for the use of the AC. We will exercise load management so in an extended outage we will have to switch loads around if we want to run the washer and I'm pretty sure we would have to shut most everything else down to run the dryer so we would probably just leave that off line and rig up a cloths line.

After typing this, I'm definitely leaning towards the 60A circuit with a plug but I'd still like to hear your input.

Tom

 

[theoldwizard1]

Aren't those military generators 3 phase, or is that the bigger ones ?

The easiest way to wire any generator that does not have an automatic transfer switch is with a generator interlock. I an not 100% certain, but the biggest straight blade plug and receptacle I can find for your application would be a 14-50. Above that, I think you have to go pin and sleeve ($$$).

I think you are good running the A/C off of that (you need to check the "locked rotor amps", LRA, on the compressor) if you have no other "big" loads (oven, water heater, clothes dryer).

Worst case, swap out the existing A/C disconnect box for a small breaker panel with a generator interlock. Then you can run a second, separate power cord just for the A/C.

 

[Tscott]

Aren't those military generators 3 phase, or is that the bigger ones ?

The easiest way to wire any generator that does not have an automatic transfer switch is with a generator interlock. I an not 100% certain, but the biggest straight blade plug and receptacle I can find for your application would be a 14-50. Above that, I think you have to go pin and sleeve ($$$).

I think you are good running the A/C off of that (you need to check the "locked rotor amps", LRA, on the compressor) if you have no other "big" loads (oven, water heater, clothes dryer).

Worst case, swap out the existing A/C disconnect box for a small breaker panel with a generator interlock. Then you can run a second, separate power cord just for the A/C.

This generator does has 3Ø capability but I will be using it 1Ø only.

Tom

 

[tyme2par4]

I would do the first option. The air conditioner isn't going to be pulling 30A continuously, so as long as it doesn't kick on at the exact same time that every other appliance does, you won't see an issue.
My parents run just about their whole house off of a 30A generator inlet when they lose power. Granted, that's mostly in winter, so we don't have to worry about A/C or the pool pump. It will even run the electric range, as long as you only use 1 or 2 burners at a time.

 

[grantw]

I'm planning on adding a L14-30 inlet to my house panel for a future generator. I have the generator interlock kit fo rmy panel, and will install it when my panel arrives, before it's installed on the wall.

The kit is listed and rated. At some future point, I would love to go with an automatic transfer switch, but a manual interlock is fine for now. During the manual interlock process, the large appliance breakers can be flipped manually to keep load off the generator.

(oven / dryer / A/C / whatever)

 

[Tscott]

The only thing giving me heartburn about the 60A plug is the fact you can't buy it in a twist lock with a male socket like you can for the 30A units. It just makes me nervous to think someone can pull a live male prong plug out of the cataleptic as the generator is running.

Tom

 

[ishiboo]

The cheapest way to do those high-amperage connections are with Anderson connectors.

The best is probably a pin plug, you can find used/surplus/etc. ones on eBay pretty inexpensively at times.

Being a 10kw rated generator, I would probably use a 4-wire 50A plug on a pigtail because it'd be clean, easy, and you could get it easily at a local store.

 

[Brandon314159]

Keep in mind most generators (military included) that are 3-phase are rated evenly (or within 20%) loaded on all phases.

There is some significant de-rating if only running single phase.

 

[theoldwizard1]

I am not a pro, but depending on what type of 3 phase you have, you may or may NOT be able to get 240V split phase.

Of course, there may be multiple windings and transformers inside one of those beasts !

 

[wyliesdiesels]

This generator does has 3Ø capability but I will be using it 1Ø only.

Tom

Are u sure it can be ran in single phase mode?

Or are u just planning on using 2 legs and neutral out of the 3?

What voltage is it?

If its 240v delta, u need to make sure u arent using the stinger/high leg as that is 208v line to neutral and WILL burn up 120v equipment.

 

[ard]

This generator does has 3Ø capability but I will be using it 1Ø only.

Tom

Hats off for the character usage....

 

[Tscott]

Are u sure it can be ran in single phase mode?



Or are u just planning on using 2 legs and neutral out of the 3?



What voltage is it?



If its 240v delta, u need to make sure u arent using the stinger/high leg as that is 208v line to neutral and WILL burn up 120v equipment.

Everyone relax. It has 3 phase and 1 phase windings. Output is either 120/208 or 120/240. I'm an electrical engineer and work for a utility so I'm quite familiar with generators. I just need to know all my connection options.

Tom

Ps can't use phase symbols on my phone.


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[theoldwizard1]

It has 3 phase and 1 phase windings. Output is either 120/208 or 120/240.

Most modern A/C can run on a wide range of voltages. (200V - 250V)

If you did a SEPARATE load center with a generator interlock for the A/C you could actually run the A/C off of 208V !!

 

[brewchief]

How about cam lock connectors? https://www.gencable.com/product/cam-locking-devices/

 

[CNGsaves]

GJ member Sewerzuk is a guru on military generators. See some of the cool YouTubes he has made bringing them back to life.

If I were you, I'd utilize ALL the great capability of that genset. Have it run your ENTIRE electrical needs when power is out. As you say, those gensets are built for 100% duty in worst case scenario like desert heat !! Output is often 125% or more of the rated Kw. Thus, either setup large automatic transfer switch, or Interlock so that the genset handles ALL electrical of both house and shop . . . ie have your genset hookup to the MAIN panel. No use in having 10Kw genset (really more like 13Kw to 15Kw) and just babying it with minimal load.

See forum www.steelsoldiers.com where whole slew of those guys have military gensets handling all their electrical needs during outage.

 

[bjcouche]

Before buying a bunch of connectors and spending a lot of time thinking about it, how about wiring it to your house temporarily and testing to see if your air conditioning will actually start when on generator power? I say this because air conditioners can draw 6X rated current during the 1 second it takes for startup. I had a generator that was rated 2X the full load current of the air conditioner and it wouldn't start the compressor. When the compressor kicked on, the huge inrush current caused the voltage to sag, which caused the compressor to not start, which caused the generator to bog down, voltage to dip further and then the compressor breaker tripped. My problem wasn't the engines horsepower, but the impedance of the generator windings. When the compressor kicked on, the high impedance of the generator (compared to the low power company impedance) caused an instant voltage sag way before the generator (due to inertia) had a chance to drop rpm. Some of the newer inverter driven or soft started compressors might work better on generator power.
Just saying, try it first, if it doesn't start your compressor, then there's no need for a higher current plug....

Brian

 

[theoldwizard1]

I say this because air conditioners can draw 6X rated current during the 1 second it takes for startup.

That is the LRA I referred to in post #2. It is typically on the compressor/motor plate.

 

[ant.foste]

Here is my take, as someone who has been in the large generator rental industry for 12 years. By large, I mean we can and do take as many 1,000kw diesel reciprocating machines you can afford to fuel and parallel them together.

If I didn't want to squeak every last amp out of the machine to power every single load in the house simultaneously, I would wire in a 50a twist lock male at the panel and build a 6/4 SO whip as long as necessary, hardwired into the generator lugs with a 50a twist lock female CS6364 on the end.

Keep in mind that 6/4 is an industry standard which would provide me with plenty of cable and connectors to do such a thing for myself, so my cable selection is biased by availability.

50a will provide you plenty of power but you'll have to watch that your a/c isn't running at the same time as the electric dryer and microwave. No big deal.

 

[wyliesdiesels]

That is the LRA I referred to in post #2. It is typically on the compressor/motor plate.

My 2.5 ton condenser has a 100a LRA.

This is the measurement I got with my clampmeter using the 'in rush' current mode when I was trying to figure out why the AC wasnt starting. Turned out to be bad cap...

 

[ctfjr]

I might have the same unit - MEP-003A diesel genset. It's built like the proverbial brick ...

I have a 400 amp service in my house. I found a 400A new xfer switch (manual) on ebay & got it for $200, delivered. I ran 3X #3 wire in from the genset to the xfer switch and a #6 safety ground. Picked up all the wire on ebay in cut lengths (needed ~100' runs) at a fraction of what I would have paid at an electrical supply house.

The genset runs the entire house. In the summer with the ac units running its unusual to see more that 50-60% of capacity on the meter. There are utube videos you can find where users have run these sets at 14kw for an hour at a time on single phase.

If you picked up a good one - mine was rebuilt & completely reconditioned & had 1.5 hrs on the clock - they will last a long long time as in 1000's of runtime hrs.

 

[wyliesdiesels]

Are those turbo-charged?

 

[ctfjr]

Are those turbo-charged?

No, the MEP-003A uses a 4 cylinder Onan, naturally aspirated

The set weighs in at 1300lbs

 

[chrispyny]

Tscott,
Go spend time at steelsoldiers.com. The auxilliary equip forum. You will read exactly how to hook up your genset the 'right way' from guys who do it all the time. I'm a member there myself.

Here's mine. 2 cyl, officially rated at 6300 watts. Half gallon an hour at full load, designed to run a 100% duty cycle until it runs out of gas, or its time to change the oil every 200 hours.

 

[TheEquineFencer]

I'd find a 200a Manual ATS from an old chicken house and use cam lock connections.

It sounds like you have an Onan JC style generator, they are what IMO made Onan.

 

[sberry]

Its only 10K, run it thru a common connector. While its got a low rating its got plenty of poop, running the AC wont be a problem, just don't run dryer at the same time.

 

[LS6 Tommy]

The only thing giving me heartburn about the 60A plug is the fact you can't buy it in a twist lock with a male socket like you can for the 30A units. It just makes me nervous to think someone can pull a live male prong plug out of the cataleptic as the generator is running.

Tom

I agree. Unfortunately, thats just one of the reasons why I would suggest you to lay out the cashola for the proper connectors to use a whip at reduced capacity, or better yet, wire to a transfer switch like ctfjr did to run the whole house. I think as an electrical engineer you don't need to preached to about the other reasons.

Tommy

 

[donpauli2]

Before buying a bunch of connectors and spending a lot of time thinking about it, how about wiring it to your house temporarily and testing to see if your air conditioning will actually start when on generator power? I say this because air conditioners can draw 6X rated current during the 1 second it takes for startup. I had a generator that was rated 2X the full load current of the air conditioner and it wouldn't start the compressor. When the compressor kicked on, the huge inrush current caused the voltage to sag, which caused the compressor to not start, which caused the generator to bog down, voltage to dip further and then the compressor breaker tripped. My problem wasn't the engines horsepower, but the impedance of the generator windings. When the compressor kicked on, the high impedance of the generator (compared to the low power company impedance) caused an instant voltage sag way before the generator (due to inertia) had a chance to drop rpm. Some of the newer inverter driven or soft started compressors might work better on generator power.

Just saying, try it first, if it doesn't start your compressor, then there's no need for a higher current plug....



Brian

I have this problem with a generator I bought when I tried to run a 5 HP Air compressor off it. 13k rated but couldn't start it


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[Tscott]

I might have the same unit - MEP-003A diesel genset. It's built like the proverbial brick ...

I have a 400 amp service in my house. I found a 400A new xfer switch (manual) on ebay & got it for $200, delivered. I ran 3X #3 wire in from the genset to the xfer switch and a #6 safety ground. Picked up all the wire on ebay in cut lengths (needed ~100' runs) at a fraction of what I would have paid at an electrical supply house.

The genset runs the entire house. In the summer with the ac units running its unusual to see more that 50-60% of capacity on the meter. There are utube videos you can find where users have run these sets at 14kw for an hour at a time on single phase.

If you picked up a good one - mine was rebuilt & completely reconditioned & had 1.5 hrs on the clock - they will last a long long time as in 1000's of runtime hrs.

I've got the next generation. It's an MEP-803a. It shows 125 hrs on the clock and when I got it it had all fresh fluids, filters and even had a tank full of JP8. Starts and runs like a top.

Tom




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[fastjohnny]

The cheapest way to do those high-amperage connections are with Anderson connectors.

The best is probably a pin plug, you can find used/surplus/etc. ones on eBay pretty inexpensively at times.

Being a 10kw rated generator, I would probably use a 4-wire 50A plug on a pigtail because it'd be clean, easy, and you could get it easily at a local store.

This! Research here:
http://www.nooutage.com/300134.htm

I did this for my 25k PTO generator, made 1ga power cable bundle from welding cable. My PTO genset had the anderson connectors already on it. I used 2 more anderson connectors for the inlet, then total of 4 more for the cable. Purchasing multiple anderson lugs and connectors can be expensive, but deals can be found if you look.

 

[fastjohnny]

And wouldn't you know it, power is out...generator up and running.