Surface mounted panelboard inside outdoor control cabinet

[jtinge]

For a steam tunnel exhaust fan application, a contractor will locate an outdoor rated control cabinet for the fan controls and VFD's. He wants to install a NEMA 1, surface mounted panelboard inside of the control cabinet to avoid having to separately mount an outdoor rated panelboard. Is there any code requirement that explicitly permits or prohibits this type of installation? For panelboard circuits that route outside of the control cabinet to the panelboard, would terminating conduits to the control cabinet and then routing conductors in a chase between the control cabinet enclosure and the panelboard enclosure be preferred over routing conductors in free air between the control cabinet and the panelboard? What other options are available?

 

[SceneryDriver]

For a steam tunnel exhaust fan application, a contractor will locate an outdoor rated control cabinet for the fan controls and VFD's. He wants to install a NEMA 1, surface mounted panelboard inside of the control cabinet to avoid having to separately mount an outdoor rated panelboard. Is there any code requirement that explicitly permits or prohibits this type of installation? For panelboard circuits that route outside of the control cabinet to the panelboard, would terminating conduits to the control cabinet and then routing conductors in a chase between the control cabinet enclosure and the panelboard enclosure be preferred over routing conductors in free air between the control cabinet and the panelboard? What other options are available?

I see nothing wrong with this, and it has many advantages. I considered it for a recent project that fell through for unrelated reasons.

First and foremost, you get the ratings that come with a NTRL-tested panelboard; high(er) SCCR ratings are much easier to come by with an off the shelf panelboard than with breakers and distribution blocks mounted on DIN rail.

Likely much easier to swap out a breaker if its ever needed, or to add a breaker to the panelboard should future expansion require it.

Faster to mount / install.

Possibly easier to source parts these days. Eaton, for instance, seems incapable of fixing its supply issues with DIN rail -mounted breakers and it looks like it will continue that way for some time.

If the panelboard is rated as NEMA1, but enclosed in an enclosure rated for the exterior conditions encountered, it will never know. The only concern I might have is that 3R is not necessarily guaranteed to keep out all water, just that water won't affect anything inside. I would request/require a NEMA4 / 4X enclosure (and proper fittings) to ensure that water is excluded.



SceneryDriver

 

[petersonra]

Sounds like a good idea to me.

 

[jtinge]

I see nothing wrong with this, and it has many advantages. I considered it for a recent project that fell through for unrelated reasons.

First and foremost, you get the ratings that come with a NTRL-tested panelboard; high(er) SCCR ratings are much easier to come by with an off the shelf panelboard than with breakers and distribution blocks mounted on DIN rail.

Likely much easier to swap out a breaker if its ever needed, or to add a breaker to the panelboard should future expansion require it.

Faster to mount / install.

Possibly easier to source parts these days. Eaton, for instance, seems incapable of fixing its supply issues with DIN rail -mounted breakers and it looks like it will continue that way for some time.

If the panelboard is rated as NEMA1, but enclosed in an enclosure rated for the exterior conditions encountered, it will never know. The only concern I might have is that 3R is not necessarily guaranteed to keep out all water, just that water won't affect anything inside. I would request/require a NEMA4 / 4X enclosure (and proper fittings) to ensure that water is excluded.



SceneryDriver

Thank you for the feedback. I had a similar opinion. Any thoughts on wiring method between the NEMA 4 enclosure, which is where I believe the conduits will be terminated, and the panelboard enclosure? I'm not a fan of open, single conductor wiring between the two enclosures as the contractor proposes. I would think some type of chase or wireway between the two enclosures would be preferable such that you could nipple in from the chase to the panelboard enclosure and keep the conductors guarded.

 

[petersonra]

Thank you for the feedback. I had a similar opinion. Any thoughts on wiring method between the NEMA 4 enclosure, which is where I believe the conduits will be terminated, and the panelboard enclosure? I'm not a fan of open, single conductor wiring between the two enclosures as the contractor proposes. I would think some type of chase or wireway between the two enclosures would be preferable such that you could nipple in from the chase to the panelboard enclosure and keep the conductors guarded.

You don't think the enclosure is guard enough?

 

[kwired]

Thank you for the feedback. I had a similar opinion. Any thoughts on wiring method between the NEMA 4 enclosure, which is where I believe the conduits will be terminated, and the panelboard enclosure? I'm not a fan of open, single conductor wiring between the two enclosures as the contractor proposes. I would think some type of chase or wireway between the two enclosures would be preferable such that you could nipple in from the chase to the panelboard enclosure and keep the conductors guarded.

IMO open conductors within the larger cabinet is fine, chances are you already have other open conductors in there before adding the "panelboard".

I have also mounted N1 load centers inside of non metallic enclosures when in corrosive locations. Some with the entire cabinet and cover inside, some with just the panelboard component and maybe find a way to put the dead front cover in to block ready access to live components. Would possibly do this even with a stainless general purpose enclosure if needed, those kind of more readily available than getting one from panel manufacturer in most instances, and isn't happening with load center series anyway would need to be a real panelboard.

 

[jtinge]

IMO open conductors within the larger cabinet is fine, chances are you already have other open conductors in there before adding the "panelboard".

I have also mounted N1 load centers inside of non metallic enclosures when in corrosive locations. Some with the entire cabinet and cover inside, some with just the panelboard component and maybe find a way to put the dead front cover in to block ready access to live components. Would possibly do this even with a stainless general purpose enclosure if needed, those kind of more readily available than getting one from panel manufacturer in most instances, and isn't happening with load center series anyway would need to be a real panelboard.

Feedback is most appreciated.

 

[SceneryDriver]

Thank you for the feedback. I had a similar opinion. Any thoughts on wiring method between the NEMA 4 enclosure, which is where I believe the conduits will be terminated, and the panelboard enclosure? I'm not a fan of open, single conductor wiring between the two enclosures as the contractor proposes. I would think some type of chase or wireway between the two enclosures would be preferable such that you could nipple in from the chase to the panelboard enclosure and keep the conductors guarded.

Since you said you will have VFDs and fan controls in the enclosure, I assumed it would be control panel. The panelboard would simply be another component mounted to the backplane. Panduit run around the sides of the panelboard should serve nicely to keep the wiring neat. Just make sure to use bushings on the KOs of the panelboard so no wiring chafes. Additionally all circuit conductors - including the neutral if present - for a partcular circuit MUST enter/leave the panelboard enclosure through a common KO, or you will have inductive heating issues (higher amperage circuits are much more of a concern) with the panelboard enclosure.

If you're mounting controls in the enclosure, and especially VFDs, make sure your vendor does a heat calc and has a good grasp of enclosure cooling. If its a sealed (NEMA4) enclosure, you can't simply add a cooling fan. You also said Steam Tunnel as the location; that says HOT!!! to me. Watch your temperatures and the temp ratings of the components.



SceneryDriver

 

[jtinge]

Just make sure to use bushings on the KOs of the panelboard so no wiring chafes. Additionally all circuit conductors - including the neutral if present - for a partcular circuit MUST enter/leave the panelboard enclosure through a common KO, or you will have inductive heating issues (higher amperage circuits are much more of a concern) with the panelboard enclosure.

If you're mounting controls in the enclosure, and especially VFDs, make sure your vendor does a heat calc and has a good grasp of enclosure cooling. If its a sealed (NEMA4) enclosure, you can't simply add a cooling fan. You also said Steam Tunnel as the location; that says HOT!!! to me. Watch your temperatures and the temp ratings of the components.



SceneryDriver

You described my exact feedback to the contractor regarding running all conductors for a circuit through the same knockout to prevent inductive heating.

The control enclosure will be located on an equipment pad at grade level while the FDC controlled fans will be located in an exhaust tower that exhausts hot air from the below grade steam tunnel to above grade, at a significant distance from the control cabinet. Heating of the control cabinet by the steam tunnel is not an issue.

 

[tom baker]

I have designed and installed many panels similar to what you describe. Typical size was 5ft wide, 4 ft high, 1 ft deep with a hinged door. They were open bottom mounted on a raised concrete pad. Multiple rigid conduits stubbed up through the pad and were connected to a NEMA 1 wireway that ran via LTMC. I used chase LTMC fittings into the wireway. From the top of the the wireway conduits stubbed up to equipment. All the wiring in the cabinet was enclosed, no open wiring. This was because non electricians would access the equipment
The cabinets were pre wired before installation seton the pad and field wiring pulled in. When I can I will see if I have any pictures

 

[SceneryDriver]

You described my exact feedback to the contractor regarding running all conductors for a circuit through the same knockout to prevent inductive heating.

The control enclosure will be located on an equipment pad at grade level while the FDC controlled fans will be located in an exhaust tower that exhausts hot air from the below grade steam tunnel to above grade, at a significant distance from the control cabinet. Heating of the control cabinet by the steam tunnel is not an issue.

If the cabinet is outdoors and especially if it's exposed to the sun, expect to have heat issues with the VFDs unless you have an active cooling solution. Since you want NEMA4, that probably means an AC unit.

Having done this several times, I would consider insulating the inside of the cabinet to cut down on heat gain. We used 3/4" closed-cell peel-and-stick foam to insulate several cabinets, and it worked extremely well.


SceneryDriver

 

[petersonra]

If the cabinet is outdoors and especially if it's exposed to the sun, expect to have heat issues with the VFDs unless you have an active cooling solution. Since you want NEMA4, that probably means an AC unit.

Having done this several times, I would consider insulating the inside of the cabinet to cut down on heat gain. We used 3/4" closed-cell peel-and-stick foam to insulate several cabinets, and it worked extremely well.


SceneryDriver

Insulation works, so does using aluminum which does not absorb heat like steel does. painting steel cabinets white is a huge help too.

 

[jtinge]

I have designed and installed many panels similar to what you describe. Typical size was 5ft wide, 4 ft high, 1 ft deep with a hinged door. They were open bottom mounted on a raised concrete pad. Multiple rigid conduits stubbed up through the pad and were connected to a NEMA 1 wireway that ran via LTMC. I used chase LTMC fittings into the wireway. From the top of the the wireway conduits stubbed up to equipment. All the wiring in the cabinet was enclosed, no open wiring. This was because non electricians would access the equipment
The cabinets were pre wired before installation seton the pad and field wiring pulled in. When I can I will see if I have any pictures

If someone other than qualified maintenance techs would access the cabinets, I'd probably push for the configuration you described, but since we have an in-house qualified maintenance crew, I'm not as concerned about the open wiring of the branch circuit conductors any more than I would be of the other control wiring inside the NEMA 4X control cabinet. Thanks for describing much better than me what I was alluding to in my initial post.

Also, good feedback on heat concern for VFD and measures for controlling via active measures, insulation, and painting.

 

[tom baker]

I also used foam insulation on an outside cabinet, that worked well.

 

[petersonra]

I also used foam insulation on an outside cabinet, that worked well.

Shading helps too. Hoffman actually makes a doohickey for this.

 

[kwired]

I have designed and installed many panels similar to what you describe. Typical size was 5ft wide, 4 ft high, 1 ft deep with a hinged door. They were open bottom mounted on a raised concrete pad. Multiple rigid conduits stubbed up through the pad and were connected to a NEMA 1 wireway that ran via LTMC. I used chase LTMC fittings into the wireway. From the top of the the wireway conduits stubbed up to equipment. All the wiring in the cabinet was enclosed, no open wiring. This was because non electricians would access the equipment
The cabinets were pre wired before installation seton the pad and field wiring pulled in. When I can I will see if I have any pictures

Sounds more like you essentially are using the enclosure as a closet, room, or even building if it were outdoors in those cases. Nothing wrong with that and may actually cost less than field constructing said room or building via some other method.

 

[jtinge]

Thanks again everyone. Good discussion and it expanded into areas I hadn't thought of. Very useful nuances for future installations.