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Mounting exterior HID fixtures #53631 07/01/05 03:25 PM
Joined: Feb 2003
Posts: 231
RobbieD Offline OP
Hello, we are constructing a building and we mounted 4x4 boxes for the exterior lighting fixtures. They are mounted on the studs and are flush with the exterior sheathing. They plan to side the building with steel. The siding will be flat but will have a raised groove. I am sure that when the siding goes over my boxes there will be some that will have this raised groove in line with them and my fixture won't be flush. What is the best way to mount the fixture in this situation? Should I mount the fixtures and have the guys doing the siding go around them? Any help would be appreciated and I know people here have run into this before. Thanks!

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Re: Mounting exterior HID fixtures #53632 07/01/05 04:16 PM
Joined: Jun 2005
Posts: 124
poorboy Offline
I don't use boxes for wallpacks anymore. I use MC cable in a situation like yours (metal siding). If the fixture has no 1/2" knockouts(the ones I have seen have at least one) I make my own, and I have used duplex MC connectors for two cables or sometimes made my own second KO. I try to duct seal the hole or silicone it before I push the fixture against the wall to waterproof it. Getting it to sit evenly on deeply ribbed metal siding IS a pain, and I too would like to see some input here, as mounting them securely is very difficult on a steel building with beams and purlins and no wood backing.

Re: Mounting exterior HID fixtures #53633 07/01/05 06:03 PM
Joined: Dec 2004
Posts: 1,064
Dnkldorf Offline
Get rid of the box.

Measure the back of the fixture, and cut a piece of plywood that size.

Mount the plywood where you want the fixture, and stub a wire out.

Have the siding guys J-channel around the plywood, and bend a piece of facior(spelling)metal the size of the plywood to cover the plywood, make sure they leave the wire stubed out.

Mount your fixture when they are done. Very clean looking installation.


Re: Mounting exterior HID fixtures #53634 07/01/05 06:30 PM
Joined: Feb 2003
Posts: 231
RobbieD Offline OP
I can't get rid of the box. The inside walls are drywalled. With this situation what would be the best way to mount the boxes without cutting out the inside walls.

Re: Mounting exterior HID fixtures #53635 07/01/05 07:16 PM
Joined: Dec 2003
Posts: 886
hbiss Offline
Around here the outside of a building usually gets finished before the inside is rocked. Easy matter to locate a wall pack so it's not on a rib. We leave a tail hanging out from the inside to be connected later.

You say you used 4x4 boxes. 1900's with rings? I suppose you could use a raised ring high enough to be flush with the top of the rib then cut something the size of the fixture to fill behind it. I can't think of what to use though, I would want it to last as long as the siding.

Any way you look at this you have a mess, the fixtures should have been located so as not to land on a rib. I don't know what you could have done though, sounds like an ass backwards method of construction caused this.


Re: Mounting exterior HID fixtures #53636 07/01/05 07:38 PM
Joined: Jun 2005
Posts: 124
poorboy Offline
The fixtures generally won't fit between 2 ribs, and most of the jobs I've ever been on are not loaded with other trades that want to make my installations easier or better quality. If a metal bldg has 6 or 8 wallpacks the siding installers are looking at it as a big hassle. We do what Dnkldorf(cool name) said with vinyl siding over wood sheathing installers and it does make a nice finished product. Steel bldgs with metal ribbed siding panels are not as easy for the builder to accomodate us...steel beams at great distance apart with horizontal pieces every 6 feet and blanket insulation don't give you many structural members to fasten to and the siding is not strong enough for screws. Toggles are OK if care is taken.

If you still have a chance to do as Dnkldorf said you can add a mud ring to the 4" sq. box to bring it out flush with the plywood piece, and cut the box opening into it instead of stubbing a cable out. Should work fine.

[This message has been edited by poorboy (edited 07-01-2005).]

Re: Mounting exterior HID fixtures #53637 07/01/05 07:48 PM
Joined: Feb 2003
Posts: 231
RobbieD Offline OP
I will put a plaster ring and bring it out to some plywood.Thanks!

Re: Mounting exterior HID fixtures #53638 07/01/05 08:04 PM
Joined: Oct 2004
Posts: 26
zero76 Offline
The problem with stubbing out a piece of mc or flex with thhn/thwn is that the insulation is not rated for the temp. of hid fixtures. I've opened some up where, not only the wire is brittle and cracked but the same for the wirenuts if they're not heat rated.

They make a type of moly that works on sheet metal...i get them at a business that specializes in screws and bolts.


Re: Mounting exterior HID fixtures #53639 07/01/05 10:44 PM
Joined: Jan 2005
Posts: 5,316
renosteinke Offline
Cat Servant
Zero, you are facing a prob that drove me nuts until I found a half-way acceptable solution.

My first prob was, as yo mention, those darn ribs. The second was- how to mount anything with any security? There's not much to the sheet metal.

My best solution so far is to mount a pair of pieces of strut to bridge over the ribs. I attach the fixture to these with strut-nuts. The strut is anchored using toggle bolts- nothing else has any strength.
Where the box, or mud ring, exits the sheet metal I put a "bell box" blank cover. In that cover I have already mounted a connector for a short piece (maybe a foot) of liquid-tite. It is important that there be enough extra so that you will be able to access the box easily, without moving the light. In the liquid-tite I run the hi-temp (appliance wire) specified for the light. Wiring inside the building can be your standard THHN.

As a side note, I have gotten better results by having each light have its' own photocell. These in turn have worked best when aimed straight up.

Re: Mounting exterior HID fixtures #53640 07/02/05 04:01 AM
Joined: Jun 2005
Posts: 124
poorboy Offline
Zero, I'm curious now if I have been "code-busting" as I installed wallpacks with MC. I need to look at what the fixture calls for as far as temp. rating next time. I have seen the brittle wires, too and don't want to leave any more messes behind me. Wallpacks are one of those items that just don't seem like they design them with ANY thought to the installer.

Renosteinke, I really like your idea about the strut and spring nuts. It gives you the chance to get a solid mounting platform without holding the heavy fixture awkwardly up with one hand. Box above/below the wallpack with LT whip is a real good way to get the THHN to high temp wire changeover made, and I like the accessibility of the box part of it , too. Not all customers I have had would want to see anything but the light, though. Want that clean, uncluttered look, and may not even want the strut.

Of course it's never an excuse for poor workmanship,(definately a cause, though) but construction schedules and the "push, push, push" mentality of GC job supers makes it hard to treat many of these projects the way you like to.

[This message has been edited by poorboy (edited 07-02-2005).]

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