Should a Dry Type Transformer be mounted inside or outside of electrical enclosure?

[SSendra]

I wanted to get some opinions on if a NEMA-3R dry-type distribution small transformer (2- 7.5 KVA) should be mounted on the inside or outside of the main free standing electrical enclosure. I can think of good reason for both locations:

Transformer inside enclosure
Advantage
1. The enclosure will have a cleaner appearance.
2. Easier wiring since all wiring is inside enclosure.

Disadvantage
1. There is more heat dissipated inside the enclosure
2. Takes up more space inside enclosure
3. Temperature inside enclosure is increased which requires larger cooling fans.
4. Component life is reduced due the increase temperature.
5. More difficult to physically install to mount a 100lbs transformer inside enclosure


Transformer outside enclosure
Advantage
1. Enclosure size can be smaller since transformer can be mounted on outside.
2. Less heat dissipation so inside electrical components are cooler which they will last longer.
3. Transformer will be easier to install physically since a lift, etc can be used on outside to hold transformer into position to tighten bolts, etc.

Disadvantage
1. The appearance does not look as nice and clean since you have this large object hanging off the side.
2. wiring a little more difficult since have to put hole through enclosure to run electrical wiring to transformer.
3. People can lean, sit, leave objects: liquid, tools, etc on transformer.
4. Transformer is stick out so someone might run into the transformer and cut there arm etc. on end of transformer.

Any opinions would be greatly appreciated on where control engineers mount their NEMA-3R distribution dry type transformers. Thanks for your time and help in advanced.

 

[SSendra]

Does the location of the transformer matter to protect someone from Arch Flash. Is a person more at risk from arch flash if the transformer is mounted on the outside of an electrical enclosure?

 

[waross]

I would be more inclined to put a 100 lb. transformer outside.
I would be more inclined to put a 10 lb. transformer inside.
It depends. You are in the best position to weigh the advantages and disadvantages of each choice.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[DRWeig]

If you're concerned about appearance, find a hiding place (if possible) for your transformer and run a piece of conduit to your panel.

I almost always keep the transformer outside the panel for heat dissipation purposes. If needed inside the panel, keep it at the top and arrange your vent louvers and fan to blow across it and straight on out.

Best to you,

Goober Dave

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[LionelHutz]

I believe you're talking about an enclosed transformer. I most likely wouldn't mount it with the enclosure inside another enclosure. Now an open transformer without its own enclosure is a different story. I have mounted core & coil transformers >10 times as large as what you're asking about inside a control enclosure with other components. You have to consider the pros and cons and decide just like you are doing. For me, it's easier to ship a single enclosure and it was easy to make room and ventilate the transformer.

Often, smaller enclosed transformers are wall mounted or hung from the ceiling above the main enclosures. You often have 8' to 10' of ceiling height up there not being very well utilized anyways.

 

[Gragas]

If you are referencing something around 3MVA dry type transformers, a couple other items do consider:

- You can typically close couple and save yourself cable/non-seg connections
- No reason to have a NEMA 3R if its inside the building
- Can make connecting HRG very simple.
- No foundations, tray/supports, etc as you would have with an external


Cons:
- Typically space is expensive in a building for new applications/buildings
- Heat loading

In my experience, dry-types 3-5MVA are almost always cheaper to place outside, even with the added cable, etc assuming effecient design.

If you are talking about small power transformers for lighting or similar. Almost always inside due to the efficiency and multiple mounting options.

 

[itsmoked]

Gragas; He stated a "(2- 7.5 KVA)" transformer.

SSendra; All good points mentioned. You should consider other details like;

It's preferable to always have the enclosure warmer than the surrounding air. This will prolong the life of everything in it. That's warmer not hot. If your enclosure is going in a damp humid area this is required. So, if what's in your enclosure is non-heat generating then you might consider keeping the transformer inside.

I stuck a 10kVA inside an enclosure for for an oil field pumping station because the enclosure was already to heavy for humans to lift and I knew 9.5kVA of it's capacity was only for running power tools or instruments on a strictly temporary basis.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[enverd]

If you are locating the transformer inside there shouldn't be a reason to go with NEMA 3R enclosure.
I also have to agree with DRWeig that if you want to locate it outside then find a good hiding place for aesthetic purposes because putting the transformer in another enclosure you are just adding to the heat losses.