• If you like what you see here and your interests are compatible with our 30,000 other users, Welcome. Fill out the registration form with your interests, your real name (seen only by moderators) and your city, state or country. Be certain that you have spelled your email address correctly! Your account is then manually checked and approved.

Cummins Onan 6.5 NHDFB 1M Commercial 6500 home backup power project: Advice Welcome

Zephyr7

Registered
A bit of shudder on shutdown isn’t uncommon. Even big sets do that a little. The engine kinda acts like an air brake a little bit from the cylinder compression, and the rotating mass of everything going into that braking action can make a shudder at shutdown. If it doesn’t vibrate like crazy while it’s running it’s probably ok.

Bill
 

len k

Subscriber
Last Subscription Date
12/12/2018
Better test of gen: Use RESISTIVE load like hair driers , space heaters, light bulbs to put 3250 watt load on one winding at a time and measure voltage. Post results here please.

Not bad idea to measure hz too in case it's way off. $25 kill-a-watt meter (home depot) is good to measure volts, amps, watts, hz
 

Warwagon

Subscriber
Last Subscription Date
05/12/2020
Grounds?

Aside of the ultimate answer of: the mess that is "code" because it varies... What 'else' can I do the make this setup as safe as possible? Clearly the big metal doghouse with metal legs sitting on the "ground" is another "ground".

Gasoline tank? The one I have now is plastic. What if I used a metal gas tank? Does it have to be placed on the metal doghouse or can it be on the ground next to the doghouse with a grounding wire to the doghouse?

Same question would apply to a metal propane tank if I eventually switch it propane.

The house is grounded via a water pipe and the best location for the genset is on the other side of the home from the service entrance breaker box. I have a nearby water pipe for an outside hose available for a genset ground if it will help? Best location is figured as: out of sight, has some extra walls around to help with noise / keeping weather off it, and closer to tools aka the garage.

I expect it will be raining during some power outages where the genset is needed. I would like to stay "dry". However I suspect the "doghouse" will be a ground no matter what esp. during/after the rain. I am considering a remote start switch setup.

I planned to manually plug in the 240v 4 wire plug only when needed. Generator entrance box by genset then run to sub panel with a 30A cable through attic. Manual transfer switch located by service entrance. The manual transfer switch will switch the hot and neutral going to a sub panel that only has critical circuits on it.
 

Zephyr7

Registered
The metal building doesn’t count as a ground for electrical purposes. If the water pipe in your house is your principal grounding point (the ground for your electrical service) then that is the “ground”.

Run a suitable size (per code) grounding wire from your service entrance ground to the generator building along with the power wires (probably two hots and a neutral). In that building, bond (connect) the frame of the generator and any metal tanks to the ground wire you brought into the building. Bond the building to ground too, ideally part of the steel structure (not sheet metal panels). The goal is to make sure there can never be a voltage differential between any two metal objects in the area of the generator.

Your ground/neutral bond stays where it is, in your main panel. Since you’re using a 3 pole transfer switch on single phase service, you’re throwing over both hots AND THE NEUTRAL when you transfer to generator. This means two things are critically important in your application:
1- your subpanel MUST have seperate ground and neutral
Busbars. This is typical for most subpanels.
2- your genset MUST have a ground/neutral bond, so the ground and neutral should be connected together AT THE GENSET and IN THE SAME BOX AS THE GENERATOR BREAKER.

It’s not a problem to oversize the ground wire if you want to. The ground wire does NOT have to be the same size as the power conductors though. For example, with copper wire and a 100A breaker, you need at least #3 wire for the hots and neutral, but you’re OK with a #8 ground wire.

I would run all the wires in PVC conduit underground to the metal shed. I’d install a second PVC conduit for control wires. You don’t want the ground wire to disconnect with the plug to the generator. There is no benefit to leaving the plug disconnected, either. You can add an extra ground rod or two at the shed if you want, but if you do, you MUST make sure they are bonded to the main ground for the building — and that means the building where your service entrance is, probably your house.

Bill
 

len k

Subscriber
Last Subscription Date
12/12/2018
I plan on installing my similar 7NHM outside on a steel table ~ 2ft off the ground with a weatherproof box covering it. Cooling air in/out the bottom just like RV installation. 2 ft off ground will make it easier to work on and get gen up almost out of rain splash up zone. 2ft up also helps let rain and snow fall out of air flow before going into gen as cooling air. Below gen 2" thick cement panels sides (2'x2') covering steel table to help with cosmetics and maybe noise too.

This cement block table is just temporary, it's wide and doesn't have enough width between the blocks to match up with gen's cooling air openings, so I need a steel table.
https://www.smokstak.com/forum/attachment.php?attachmentid=321842&d=1540935225
 

Warwagon

Subscriber
Last Subscription Date
05/12/2020
Looking for a genhead brush cover for this set: Cover-BRU 212-1284. No one online has it in stock anymore.

Any used ones out there?
 

len k

Subscriber
Last Subscription Date
12/12/2018
That # 212-1284 looks like the right #......looking at NHD parts manual 940-0229, item # 34, paper page 58-59
 

Warwagon

Subscriber
Last Subscription Date
05/12/2020
For it's monthly test run I added a 240V 4800W heater to a base load of a 120V 1500W heater. I don't think it's seen this much load in years. I have to tighten that cover panel up some looks like.

And because I was bored made a video of the 4800W load kicking on.

 

armandh

Registered
Last Subscription Date
09/02/2010
if the generator is set up 120/240, your [yellow] cable and outlet appears to only be using one side.
from what I can see of the 4 conductor outlet, it looks that way too
 

Warwagon

Subscriber
Last Subscription Date
05/12/2020
if the generator is set up 120/240, your [yellow] cable and outlet appears to only be using one side.
from what I can see of the 4 conductor outlet, it looks that way too
The cable I made uses the regulated 120V winding (yellow plug assy) and then the 240V heater (black cable) is also wired in. So it's 4800W on 240V and then 1500W on one 120V leg.

Need another 120V plug off the other winding to get full 120V power out of this set for sure.
 

len k

Subscriber
Last Subscription Date
12/12/2018
3900 watts /120 volts = 32.5 amps

If your gen had a 20 amp breaker it should definitely have tripped at 125% of rated amps, as per breaker spec here.
(In my linked info I had a link in begining to breaker info, link died, so I uploaded manual at it's end)

I assume you have a 20 amp breaker, so that should definitely have tripped at ~ 20 amp x 125% = 25 amps

If you had a 25 amp breaker it should definitely have tripped at 25 x 125% = 31`.25 ( close but.....)

You might want to measure your voltage and possibly test the breakers at more amps to see if they trip. To do the test I'ld rewire gen to make 120 V only (both windings in parallel so you don't over heat them
 
Last edited:

Zephyr7

Registered
A 25% overload won’t necessarily trip a breaker very quickly, it depends on the time curve. Medium-size overloads can be dangerous for that reason. It often takes a 100-200% overload to cause an instantaneous trip.

Bill
 

len k

Subscriber
Last Subscription Date
12/12/2018
Onan generally used a #62 breaker trip delay curve.
More info here , in link, in particular see it's post # 2 and #14 for delay amp/time curves

In #14 see page 5 for #62 trip delay curve,
page 7 also gives very interesting comparison of trip amp/time curves to motor starting amps/time
 
Last edited:

Warwagon

Subscriber
Last Subscription Date
05/12/2020
Good catch on the load balance. I will have to watch this when I hook it up to a transfer switch. Still figuring on powering a 240V Air Conditioner. (Want to leave the fridge and freezer balanced on utility.)

Needs a little adjustment unless I am de-rated to it going WOT. I am at 1000' and it was 100 degrees F out. Measured 58 HZ with the full load on. However, because of the 100 degree heat the 4800W heater kept tripping off and then back on. It's possible it didn't stay on long enough to trip the breaker. I think it was 15 -25 seconds on and 15 seconds or more off.

Looks like two 120V heaters on half power, 750W, on each 120V leg would balance the load out better. I would need to break out another 120V plug for that.

If I do reconfigure it to 120V only: Do I need to replace the breaker on the genset with one rated for the 120V configuration?
 

Vanman

Subscriber
Last Subscription Date
06/10/2020
Interestingly, 3900 watts on one line and 2400 watts on the other line results in almost exactly the same total armature copper loss as full rated 6500 watt (balanced) load. So not harmful.

I wonder if that regulator can be reconnected for 240 volts. That is a MUCH better arrangement for a three wire generator!

Keith
 

Top