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MEP-802A questions

robert248

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Texas
I'm building a concrete slab where the generator will sit. Do you guys bolt yours down to the concrete? How thick should I make the concrete slab?
 

Mainsail

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Puget Sound, WA
I'm building a concrete slab where the generator will sit. Do you guys bolt yours down to the concrete? How thick should I make the concrete slab?
I tried bolting mine down and the vibration of the generator was amplified by the slab and vibrating the whole house. Of course my slab was not very thick and only a little bigger than the footprint of the 802.

So I moved the generator forward a few inches and used the j-bolts in the concrete as pins, fitting into a hole in the wooden block. That keeps it from creeping around. The skid is lag-bolted to the blocks.

The blocks are sitting on air compressor isolators. This is working to keep it quiet and keep it from vibrating the house. I will eventually swap out the 2x6s for solid blocks as I think that will do a better job.

PadConfig3.jpg
 

Ray70

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West greenwich/RI
I tried bolting mine down and the vibration of the generator was amplified by the slab and vibrating the whole house. Of course my slab was not very thick and only a little bigger than the footprint of the 802.

So I moved the generator forward a few inches and used the j-bolts in the concrete as pins, fitting into a hole in the wooden block. That keeps it from creeping around. The skid is lag-bolted to the blocks.

The blocks are sitting on air compressor isolators. This is working to keep it quiet and keep it from vibrating the house. I will eventually swap out the 2x6s for solid blocks as I think that will do a better job.

Definitely don't want to bolt it down tight, you need some kind of vibration isolation in there.
Those rubber isolation blocks Mainsail used are pretty cheap and available at plumbing supply houses or https://www.supplyhouse.com/Diversi...on-Pad-4-x-4-x-7-8?_br_psugg_q=vibration+pads
They are rated for 50 Psi.
Note that Mainsail's bolts are not going straight through the skid frame and into the concrete, that is a very important detail.
I'd use something like that or squares of 3/4" rubber horse stall mat both above and below the skid frame and I'd use threaded rod ( bent into a "J" ) in the concrete or bolts with the head and a washer buried in the concrete, then use a fender washer or a plate ( above the top rubber isolator ) and double jam nuts on top to snug it down slightly but not cranked down tight.
You want the rubber to be able to absorb the vibration without transmitting it through the bolt or tightly compressed rubber.
 

robert248

Member
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Location
Texas
So basically the four 6x6 blocks that are bolted to the skid base are just sitting freely on the air compressor isolators? It wont vibrate off the slab and isolators when its in operation right? Its too heavy? So what your saying is there is absolutely no direct hardware that is put into the concrete for the optimal set up.
 

Ray70

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West greenwich/RI
Almost... I believe Mainsail bolted the lower blocks to the pad then lagged the upper block through the frame and into the lower blocks.
This will work fine, but gives you a bunch of unnecessary added height.
I would put your bolts into the concrete with the thread up. Use bolts with washers, j-bolts , threaded rod or drill in concrete studs after the concrete is cured.
Sit the generator on 4 isolators, then put another isolator above the skid frame with a large washer then 2 nuts.
snug down the first nut but don't crank it down hard, then tighten and jam the 2nd nut against the first to prevent the nuts from loosening, but not cranking on the pads hard enough to transmit vibrations through the bolts and crushed isolators.
 

2Pbfeet

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Mt. Hamilton, CA
My rule of thumb is that you want the base to weigh significantly more than the installed machine. That forces (pun intended) the vibrational energy to be absorbed in the absorbers. If the base is too light, it becomes a transducer for the vibrations.

I agree with @Ray70's advice above. If you want to spend big bucks, you can get spiral spring isolators that have a longer lifetime, but unless it is a commercial or you want a gold plated install, I don't think that it is much value add, just more durable. Just check your bolts, tighten when needed, and replace the vibrational isolation material as they start to compress. I try to make a few measurements of the height of the isolator at the installation, and then keep an eye on it over time. Depending on the material, the site conditions, and usage, they can have very different decay rates. After less than three years, I recently replaced some cheap, supposedly UV resistant, rubber, that was mostly stored in the shade, but as the rubber was dirt cheap, and the swap took only a few minutes, it works for me. YMMV...

All the best,

2Pbfeet
 

FarmingSmallKubota

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Wapakoneta, Ohio
Here is the frame. All ready for concrete.
Looks like it will be a nice pad i usually throw plastic down if i dont have stone to go over the dirt, but wet the dirt down well before the pour and it should be fine. Glad someone has dry weather. another several inches here in ohio cant do anything.
 

Ray70

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Location
West greenwich/RI
Shouldn't have the remesh wire touching the form, it should be fully encapsulated in the concrete, 2" min away from the form, but.. this is a generator pad, not the Washington Bridge.... :ROFLMAO: ( not sure how many of you are aware of the problem with the bridge on 195 in RI ) so it will be fine.
 

robert248

Member
36
23
8
Location
Texas
Shouldn't have the remesh wire touching the form, it should be fully encapsulated in the concrete, 2" min away from the form, but.. this is a generator pad, not the Washington Bridge.... :ROFLMAO: ( not sure how many of you are aware of the problem with the bridge on 195 in RI ) so it will be fine.
I appreciate all of this feedback. Thank you for the replies and tips!
 
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