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Discussion Starter · #1 ·
I have a project that the customer is requiring us to have the enclosure meet NEMA 12 standards. The control transformer we selected is rated NEMA 3R. It is mounted to the side of the enclosure. Our panel shop is saying that due to C22.2 486-17 4.7.1, the transformer forces the panel to be derated to NEMA 1. The way I see it, only the penetrations for the transformer need to meet NEMA 12.

Is this true? Would this change if the transformer were mounted independent of the enclosure and the only connection between the 2 was conduit?
 

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You do not mention where the transformer is located. On top I might agree.
On the bottom probably put up a fight on the issue.
To me a penetration is just that a place to leak, weather that be dust, fumes, water or some other liquids.
I looked up your spec and there was a exception for power supplies as I read the text.
What are you going to do about the other penetrations?

There are several methods of maintaining the integrity of the cabinet.
Sealing lock nuts, inside and out.
Meyers hubs come to mind
I saw a guy weld nipples on the bottom of a cabinet once. Welded inside and out.

I believe Hoffman used to have a chart for power supplies inside the cabinet. X kva required so much bigger for the heat.
Coming from the mining industry were it had better be bullet proof. I used to design control cabinets frequently for different environments. We found keeping the penetrations on the bottom and Meyers hubs gave us the best chance at survival. We installed the power supplies inside on feet on a back plane. Never mounted a cabinet solid on a wall, always used unistrut so the back had some ventilation. I live in Arizona which is brutal on temperature and general environment.

We built 4 SS monitoring cabinets for the evaporation ponds. Required by EPA.
Cabinet, battery, solar panel, sensors and radio for the telemetry
Used the best stainless I could find, put the thing together with plastic unistrut and nylon screws. Best we ever got was 6 months before the solar panels died. Everything was eaten and we tried again. Became a constant build project as the customer wanted these installed next to the waters edge.

So you want to know what an evaporation pond is. After the leaching solution has reached its life. It is pumped into a pond for evaporation.
Leaching solution commonly called "water" in the mining industry is made up of H2SO4, water and secrete sauce. I say secrete sauce because depending on the ore, it would change. We had a rail head and would go through 40 tank cars a month of H2SO4. Not counting the semi's that delivered it around the clock.
All of this is for the SXEW building where the copper is plated on cathodes, solvent extraction electro winning.

the big blue space is pond. I am not sure if the zoom I chose will work so the pond is to the east and close to the freeway near the words Green Valley, a retirement community

This is not the largest open pit mine for that look up Morenci Mine which was the largest in the USA when I worked for them.
 

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Technically I think they are right no matter how or where you mount it. You have taken a 3r device and installed it in a NEMA 12 system. Most times a nema 12 panel is installed to Nema 12 enclosures so the 3R blew your dust tight rating.
 

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What if we seal the conduit so there's no airflow?
What do you need the NEMA 12 rating for first?
Is it really the panel shops call, they are building the panel not the system?
Never heard of a panel rating changing due to improper installation, just system rating changing and that should not be the panel shops concern.
 

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Discussion Starter · #6 ·
Our customer is requiring our delivered panels to have a NEMA 12 rating. We don't get it, but it is in their spec.

To be a certified panel shop, they have to call us out on things like this, or else they can lose their certification. We have already purchased transformers or else we would substitute NEMA 12 and not worry about it. NEMA 12 transformers have a 6-8 week lead time, so we need to figure something out with what we have on hand.
 

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Can you move the transformer out of the area or use a gas seal-off between them. Not sure how i would explain to the customer that im using a 3x in a area they want nema 12.
 

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Not sure how i would explain to the customer that im using a 3x in a area they want nema 12.
Bingo. Back to system issue.
I have seen this many times, when someone thinks Nema 12 is better for minor dust, but don’t realize you can’t add fans, need air conditioning for drives and whole system needs to be NEMA 12
 

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We see a lot of N12 over speced just cause, lot of times just cause that's what you get when you get a Hoffman Concept or SCE Enviroline enclosure is a N4/12 and some just start assuming every control can has to be.
 

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The problem is that you delivered parts to the panel shop forcing their hand. Have them deliver the panel with the transformer as a field mounted assembly. Now they are rating the panel not the assembly and it’s your responsibility to meet the N12 spec with your conduit penetrations (or not).

So what you need to do is buy and install a fused disconnect to feed the transformer primary and secondary. The panel shop starts with your feed (via Meyers hub). They can even deliver the panel without opening. From there it’s the installers job.

Transformers do NOT follow the NEMA enclosure rating system at all. They have their own IEEE rating system. Dry transformers above about 10 kVA MUST have air flow. Below that you can get a totally sealed and potted design. Above that if you want “sealed” it’s oil filled. You need to give your customer the transformer ratings and have them pick one out.

Buying parts does not mean going to the supply house for everything. In four weeks I could have had one custom made in that time. And if you need fast write a big check and buy an epoxy encapsulated transformer. The coils are molded assemblies. When put order they stack the primary and secondary on a core, bolt everything down and ship within 24-48 hours.

Don’t be afraid to call Sunbelt Transformer either. They can source anything.

I just built and installed a NEMA 4/12 system for a garbage sorter with drives. The transformer is external and it’s sealed.

I used to write the N12 on my specs. I had a clause using the IEEE C series terms for transformers. I’d go back and tell the customer you can’t meet their spec because transformer enclosures don’t follow NEMA enclosure ratings. Give them options and ask for clarification. I’ve also similarly had to deal with comical plant engineers that write NEMA 4XSS into all their specs not considering SS conduit never mind SS transformers and all the problems it creates.
 
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