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Joined: Nov 2007
Posts: 764
KJay Offline OP
What is the preferred wiring method for inside walk in coolers and freezers?
I generally see a couple of methods used, that being, some wired entirely with liquid tight flexible metal conduit [LFMC] and others with EMT and rain tight fittings. I've even seen Sch.40 PVC [RNC] used in a walk in cooler before. I guess this is okay since it was mounted on the ceiling close where the joint between the ceiling and wall meet and the cooler temp was normally only around 34-degrees. I would think it would be to brittle for a freezer application, although Im not sure that it would be a code violation. Sometimes I see a combination of these methods used.

I have also noticed that some mount their conduits right on the walk-in's surface and yet others use minerallac clamps to maintain a 1/4" air space behind them, which I suspect would probably be more in keeping with the Sanitary Code as well as the NEC 300.6[D] spacing for wet locations. Would this spacing only apply when mounting on "wall surfaces", but not ceiling surfaces?

I normally use WP round boxes in walk-in's at splice points or when changing wiring methods and I have noticed there is a slight air space behind these boxes when installed, but it looks to be less than 1/4". Has this air space issue ever been the basis for failing an inspection for a walk-in unit for anyone?


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Cat Servant
It helps if you FIRST have a chat with the local health department. It matters just what the cooler will be used for.

The first decision you must make is: Inside our outside? It's best if you can run your wire outside the cooler, but that's not always possible. There's less opportunity for crud to accumulate (health issue), or someone to damage it with a hand truck.

Where you DO penetrate the wall, you will probably want to use duct seal to seal the pipes where they pas through the wall - prevents moisture from condensing into the pipes.

Once inside, clean-up us a major concern. While a 'beer cooler,' as seen at the local 7-11, may do just fine with pipe run directly on the walls and ceiling .... if there's unpackaged food handled in there, you'll probably be required to run the pipe suspended away from the walls and ceilings. Mineralacs might satisfy the health department ... or you might need to go into the local plumbing house for those larger plastic stand-offs. They need to be able to clean behind the pipes.

Boxes need to be "bell" type, again for sanitary reasons. You want as smooth an exposed face as possible. Fixtures need to be totally enclosed.

Each evaporator fan needs a disconnect switch. In freezers, there also need to be receptacles for the heat tapes on the door and drain lines.

I would not consider using anything but EMT, with sealtight where making the transition to the evaporators.

I have never even heard of a problem where the boxes are mounted to the wall - the stuff has to contact the walls SOMEwhere. You can't eliminate EVERY place that might accumulate crud ... but you can reduce them.

Any wiring method has to be suitable for the mechanical and other environmental hazards it will encounter - back to Article 110 - so PVC in a freezer might be a violation. I don't like the idea of PVC ... but I'm from Chicago laugh

And ... if you haven't already guessed ... GFCI's and bubble covers on the receptacles are in order.

Joined: Nov 2007
Posts: 764
KJay Offline OP
Im right there with you on the rest of it, but I think you have also touched on yet another popular subject for these installations as well.
For some reason, the disconnect switch, within sight, for the evaporator fans seems to be a contested issue among refrigeration and electrical contractors.
Most reefer contractors that use their own in-house electricians dont seem to put them in.
A lot of them will actually get upset if you do happen to put one in, especially in a freezer application, because of the possibility that an employee could turn it off when restocking the freezer, because they are uncomfortably cold, then forget to turn it back on when finished. I have actually seen this has happen at least a few times in the past on smaller single evaporator walk in freezer units, so it seems like, in some ways, it may be a justifiable gripe on their part.

I have done it both ways myself, but it seems that I have put the switch in for the future convenience and safety of the service tech voluntarily, more so than as a requirement and inspectors just never seemed to say anything about it one way or the other. I suppose a lock on the circuit breaker might be a way around it.
I think it should be there to the letter of the code, but Im not quite sure why it never seemed to be an issue.

Joined: Jan 2005
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Cat Servant
As I read Article 440, not only are you required to have a switch at the evaporator, it has to be 'readily accessible' WHEN YOU'RE IN POSITION TO WORK on the unit. In other words, up on the ceiling near the unit.

If reliability is an issue, I might accept a locking, fused disconnect in place of the simple light switch.

Joined: Jan 2004
Posts: 171
The only cooler that I have done has been a beer cooler. It was located inside the facility. I used non-metallic LT. I entered the cooler through the top near the evaporator. I did not install a disconnect in the cooler. The cooling contractor did not want one as the mechanical room with the main panel was just adjacent to the cooler. All they requested was that the light circuit was seperate than the evaporator so they could still see with evaporator disconnected. The condensor, however, was on the rooftop. I did install a disco next to it of course.

Joined: Jan 2005
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Cat Servant
Well, I suppose it's time to break out the codebook. let's look at the exact language:

"440.14 Location. Disconnecting means shall be located within sight from and readily accessible from the air conditioning or refrigerating equipment."

There are further details, and an exception relating to industrial processes, but I don't think those are relevant here. What is relevant is the 'lock it out at the panel' practice is allowed only in the exception, again, for industrial processes.

"Within sight" suggests that, when the equipment is spread in multiple locations, each location is going to need it's own disconnect.

"Readily accessible from the ... equipment" means I have to be able to reach it while I'm working on the equipment, without having to climb down from my ladder.

This may seem over-done for what is essentially a small fan ... but, remember, this is almost THE textbook example of equipment that may start automatically, and get power from more than one source.

As for wiring methods, I see the NEC as allowing any method that the damp or wet location would allow ... with the qualification that environmental conditions may restrict your choices further. Temperature, humidity, and corrosion are certainly relevant, and vary from site to site. There also might very well be mechanical protection and health department considerations.

Separating the lighting from the evaporator fans is a good idea. Those lights are subject to a fair amount of maintenance themselves.

Joined: Oct 2000
Posts: 2,723
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Broom Pusher and

I may be able to offer you assistance on this subject.

The Company I work for deals primarily in Cold Storage Warehouses / Logistics Facilities & Processing Facilities, along with a variety of other Industrial Projects.

Cold Storage Warehouses, "Box In Box", & Logistics Facilities range from 2,000 Square Feet to 300,000 Square Feet, with areas such as:

  • 40� F Loading Docks,
  • 40� to 32� F Coolers,
  • Freezers, down to as low as -20� F,
  • Dry Storage areas, at Ambient Temperature

We perform Design / Build services for > 90% of the Projects.

My tasks are mostly in the Designs area (Electrical Design / Engineering), but also perform Project Management.

With that being said, let me address your original posted questions. Afterwards I will add some additional things to consider, and a few suggestions.
Will try keeping this posted message as concise as I can!


*** 1: Conduits...

Typically EMT with Compression Fittings is used for Projects without crucial specifications, and in "Non-Washdown" areas.

Evaporators (or Air Units, as sometimes termed) connect with LFMC (Metallic Sealtite) for the Fans' Power Circuits, Defrost Heaters' Circuits, and the Control Circuits.

In areas where Processing is involved + Washdown is daily, either PVC 80 is used, or PVC Coated GRC (AKA: "OCAL" and "ROB ROY").
The Building Department is queried to verify their requirements. Normally, with 480 VAC Circuits, the DBS (Dept. of Building Safety) requires GRC. We use ROB ROY to reduce the issues associated with oxidation.

Lastly, some Clients will specify the use of GRC, ROB ROY, or some "High Dollar" Conduits, such as:

* Rigid Aluminum Conduit,
* Stainless Steel Rigid Conduit,
* Stainless Steel EMT.

As you can see, there are many options for Conduits. All depends on the Client's specifications -vs- the requirements of the DBS.

At minimum, EMT with Compression fittings is acceptable above the lid, or inside the box.


*** 2: Conductor Insulation...

If the controlled Temperature is 34� F or higher, then THHN Insulation may be used, unless specifications call out differently.

For less than 34� F environments, use XHHW Insulation.

For Sub Zero environments subjected to extreme conditions (high levels of vibration, frequent moving, etc.), the use of Cables and Insulation designed for "Low Temperatures, Extreme Conditions" should be used.
In these areas, "FREP" Cable is used instead of Sealtite with XHHW Conductors.


*** 3: Disconnect Switches for Evaporators ...

DEFINITELY install local Disconnect Switches at the Air Units (Evaporators). Use lock-off types.

Check the job specs, and any AHJ to determine if NEMA 4X enclosures should be used.


Some things to consider:

a: Seal-Off any Penetrations between Ambient, Non Conditioned areas, and the areas with Controlled Temperatures - even if the Controlled areas are above 32 degrees F.
This is necessary to avoid building up condensation in the Raceway.

I have a copy of the Seal-Off Details used on our Plans, which may be of great assistance to you. Have some saved as a PDF, and even more Details in .DWG file format.

Seals should be placed on the _WARMER_ side of the penetrated partition.

b: Lighting Fixtures should be designed for Extreme Conditions, and have sealable, gasketed panels.
In areas with Temperatures below 25 Degrees F, best to use an application which heats the Fixture.
With Fluorescent Fixtures (T5 HO), we have the inner 2 Lamps on during working hours, and the outer Lamps controlled via Occupancy sensors.

Avoid using any Instant Start, Cold Cathode Lamp Operations, and "Standard" output Lamps (420 ma).
Go with HO (High Output / 800 ma) Lamps, driven by Programmed Start, Hot Cathode Ballasts.

Additionally, in subzero areas, the output lumens of Fluorescent Fixtures will be dramatically reduced (same as extremely warm areas). When designing a Lighting layout, increase the desired average Foot-Candles by 15 to 20%.

c: In Freezers, there may be Floor Heat applied via Heat Trace Cables. This requires certain design criteria.
Along with Floor Heat, Man Doors + Lift Doors will have Heat Strips internal.

d: Evaporators may be Defrosted Electrically - via internal Heater Elements, or via "Hot gas".
With most Electric Defrost Heat, the Fans and the Heaters are different Circuits, fed separately - but from the same C.U. / Rack.
In these cases, Two (2) separate disconnects will be mounted to the A.U.s (Air Units).

e: Drain Lines from the A.U.s may require Heat tape, with appropriate Circuits.
Normal figures use Self-regulating Heat Tape, rated at 6 Watts per foot, in Voltage ratings of 120, 208, 230, and 277 Volts.
Typical wrap patterns on 2" Drain Lines increases the Linear footage by 141%. This should be verified prior to Circuiting the Drain Heat.

f: Surface mounted Outlet boxes, used in 40 degree and lower areas, should be something with a hub - such as Bell Boxes, FS Boxes, and similar.
If at all possible, mount devices outside the box, and where a NEMA 4X rating does not apply.


That's all for right now.
Let me know if you have specific questions, if you would like some more information, or if you would like a copy of Penetration Details.

Reply either directly to the thread, via P.M., or by E-mail.

Good luck.


Last edited by Scott35; 03/05/21 07:22 PM. Reason: Fixed Paragraphs' spacing

Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
Joined: Nov 2007
Posts: 764
KJay Offline OP
Thanks Scott, lots of really good info there.
Just wondering, when designing a walk-in or other cold storage environment, do you find that there is a need to address the issue of an air space behind conduits for walk-in food storage areas for sanitary washdown reasons or is it generally considered acceptable to attach conduits directly to the walk-ins interior surfaces?

The reason I ask is because I have seen it done both ways before, but was never really sure if it was Health Code related, design specification or just installer preference.

What type of hanger or support method would you normally recommend or require for mounting conduits in walk-in interiors used for food storage and other similar cold storage areas?

Thanks again

Joined: May 2003
Posts: 74
So these are Damp Locations and require compression fittings and Bell boxes? Does the code stipulate that somewhere?

Joined: Jan 2005
Posts: 5,462
Likes: 3
Cat Servant
Not quite .....

They can be damp just from condensation. They are wet if they're washed down regularly. Plust, the health folks frown on things like screws, or holes in boxes, that may let crud fester.

That's why the piping is often stood off the walls - to allow for cleaning behind the pipes.

You need to know more than just the NEC to practice the trade. I strongly advise a chat with your health department before you do the job.

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