Receptacles at Tree Grate - Electrical Contractor's Help Requested

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jrohe

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Omaha, NE
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Professional Engineer
My company has designed some WP, GFCI receptacles to be pedestal mounted in tree planters outside a mall. We designed these to have a small concrete footing poured in the planter to secure the conduits. It turns out that they can not pour the small footing because it may interfere with the tree?s root ball. We are looking into possibly drilling holes in the tree grate to pass the conduits through, but are having trouble determining how to secure the conduits to the tree grate. Does anyone have any suggestions on what types of clamps or other fittings could be used to secure the conduits to the grate? I have attached a .pdf file of the section through the planter and a photo of the tree grate. If it matters, the tree grates will be made of bronze.

Thanks in advance for any expertise anyone can lend.

View attachment Tree Grate Section1.pdfTree Grate Photo.jpg
 
Remeber that you can consider the box supported if you use two rigid conduits threaded into bell box hubs. So I would make my turn up and then put a PVC female adapter on and run a couple of rigid nipples up through the grate.

I'll take my prize in cash.
 
cowboyjwc said:
Remeber that you can consider the box supported if you use two rigid conduits threaded into bell box hubs. So I would make my turn up and then put a PVC female adapter on and run a couple of rigid nipples up through the grate.

I'll take my prize in cash.
Click to expand...

I was going to suggest a rigid nipple threaded into a floor flange and one of those set screw type holders that threads into the back of a bell box.
 
How tall are they?

We don't want too much cantilever going on.

And will they have to remove the grate from time to time?

If they have to remove them, can you mount to the concrete wall and slightly notch the edge of the grate?
 
cowboyjwc said:
Remeber that you can consider the box supported if you use two rigid conduits threaded into bell box hubs. So I would make my turn up and then put a PVC female adapter on and run a couple of rigid nipples up through the grate.

I'll take my prize in cash.
Click to expand...

That was my first thought also, but this does not address the requirements from 314.23(F) that the conduit be secured within 18 inches of the enclosure.

Joethemechanic said:
How tall are they?

We don't want too much cantilever going on.

And will they have to remove the grate from time to time?

If they have to remove them, can you mount to the concrete wall and slightly notch the edge of the grate?
Click to expand...

The bottom of the receptacle box will likely only be a couple of inches above the top of the grate. The grates are designed so the inner rings can be removed as the tree grows and the trunk outgrows the hole in the middle. As this happens, the Owner would have to move the receptacle if it was mounted on a ring that was being removed. The Owner has already been made aware of this and they seem willing to accept this comprimise. There is no wall to mount the receptacle boxes on. The top of the planters is actually flush with the adjacent pavement.

The landscape designer has suggested driving a "metal stake" through the tree's root ball and locate the receptacle within the tree trunk opening like in the attached .pdf. If this were a piece on strut, this would likely work. However, I think we would want the strut driven at least 36 inches into the undisturbed earth below the planter to ensure it is solid.

View attachment Tree Grate Section2.pdf

Thoughts?
 
My opinion after having had to deal with this at other shopping areas is this.

It can't be done and accommodate all wishes

  • Comply with the NEC
  • Look good
  • Not kill the tree
  • Still allow the grates to be opened
  • Allow tree replacement without an electrician
 
jrohe said:
We are looking into possibly drilling holes in the tree grate to pass the conduits through, but are having trouble determining how to secure the conduits to the tree grate.
Click to expand...

If you are willing to cut say a 2" hole in the tree grate it should be simple. Pour some concrete under the tree grate ( not deep enough to affect root growth ). Use an "L" type mounting bracket secured to the concrete or in the concrete to mount the box and and also secure conduit straps.

The bigger the hole you are willing to cut in the tree grate should help. You could use a bronze bracket and bronze box to match ( even pain the conduit bronze).

If you don't run out of money I'm sure we can come up with something you will like.
 
Under ground pvc to"Sealtite" to rigid, LB, nipple to box, dead man, strap rigid to grate.
I like beer say Sam Adams, say 288oz.?
 
Mount it to the tree. Have some sealtite down the bottom somewhere to allow for growth

Paint it to match the bark
 
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Joethemechanic said:
Mount it to the tree. Have some sealtite down the bottom somewhere to allow for growth

Paint it to match the bark
Click to expand...

I was about to half suggest that (minus the painting part) :).

We had a long discussion here once, and the concensus was that the bottom of the tree won't grow up- the bottom will always stay in the same place.

So the only movement the sealtight needs to allow for is for an increase in the width of the trunk.
 
If you ever built tree houses and stuff as a kid, you know they don't gain elevation as the tree grows. Although the tree houses do push apart from ring growth.

What do you think hurts the tree worse, fastener into the trunk? Or some kinda band around it?

Can you hard wire a good piece of cord in the hole, and use something like this on the end?
 

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Could you not set the rootball of the tree 6" or so lower and mount the recep box horizontally to the slab, just under the grate?
 
Go to the tree grate manufacturer and include him in the discussion. You would be amazed at what solutions may be available to improve the installation with their help in changes they can make on their end. Tree grates are designed to be removable and have the growth rings broken or cut out as the tree matures and you want your penetration to be notched so the grate is removable and it should not be strapped to the grate itself. You may need to bite the bullet and increase the size of your weather proof box to accomadate larger conduit for structural strength if installed in a public space. 1/2" and 3/4" will be toast in a matter of months from abuse.
 
I want to thank you all for your expertise, insight, and recommendations. After going back and forth with the Architect, Owner, and Landscape Architect, we have decided to go with the option mentioned in post 6. The difficulties noted by iwire echo my sentiments exactly and these were conveyed to the Owner. However, the Owner was adamant about the receptacles at the trees because they plan to put holiday lighting on the trees, as they line a very prominent street in Honolulu. Thanks again for all your help. I love this forum for the wealth of knowledge that everyone so openly shares.
 
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