Q about NEMA Ratings

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GlennH

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So I needed an outdoor rated junction box, called supplier and he said sure I"ve got a NEMA 12 box right here.

Fine I said , send it out.

Got the box and then started thinking about the NEMA 12 rating and looked it up in my trusty Electrical Pal book and it says a 12 is rated for indoor use.

Hmmm, supplier says no its fine to use outdoor.:?

Here is a pic box.jpg

box has no knockouts, has a nice gasket and lip at door, there is no way any water is getting in this box.

Would you have a problem using this box??
 

qcroanoke

Sometimes I don't know if I'm the boxer or the bag
Location
Roanoke, VA.
Occupation
Engineering
So I needed an outdoor rated junction box, called supplier and he said sure I"ve got a NEMA 12 box right here.

Fine I said , send it out.

Got the box and then started thinking about the NEMA 12 rating and looked it up in my trusty Electrical Pal book and it says a 12 is rated for indoor use.

Hmmm, supplier says no its fine to use outdoor.:?

Here is a pic View attachment 5672

box has no knockouts, has a nice gasket and lip at door, there is no way any water is getting in this box.

Would you have a problem using this box??
yes, it won't pass.

http://www.nemacotech.com/nema-definitions-list.html
 

augie47

Moderator
Staff member
Location
Tennessee
The problem, as I understand it, is that the outdoor weather conditions will deteriorate the gasket especially when subject to water and freezing. Rain water/snow will settle around the gasket then freeze damaging the material and "breaking" the seal. The little added lip for NEMA 3R prevents that.
It's not unusual for supply folks to sell 12 as 3R.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Retired Engineer
Most Hoffman style boxes are rated NEMA 4/12.
Not true.

Hoffman makes design and Concept lines that are usually dual rated, these are normally 'tan' colored boxes.
Their screw cover, lift off, and continuous hing versions are not regularly dual rated, these are normally 'grey' colored.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Not true.

Hoffman makes design and Concept lines that are usually dual rated, these are normally 'tan' colored boxes.
Their screw cover, lift off, and continuous hing versions are not regularly dual rated, these are normally 'grey' colored.
The Concept boxes I use are all gray. In fact, I have not seen any tan Hoffman box to my recollection. Certainly have never used one.
 

renosteinke

Senior Member
Location
NE Arkansas
So maybe the parts guy is only guilty of bad grammar. That should be no surprise to this forum.

It is correct to say that NEMA 12 and NEMA 3R are completely different ratings, each with its' own criteria. I suppose, in theory, that it might be possible to make an enclosure that would pass one and not the other.

In practical terms, I can't imagine how one would make such an enclosure. I suspect that a little research will show that the enclosure carries both ratings.

The NEMA tests have virtually no consideration of the aging of gaskets, etc. There as some rather mild corrosion tests. Indeed, were I to try to make something that really was 'indoor only,' this is where I would try to do it - though that has become more difficult since the standards were revised to require even indoor enclosures to be galvanized.

Rain hood? Probably not necessary with that gutter flange. I'd go with the manufacturers' recommendations. Likewise, it's possible that the manufacturer would suggest the addition of a small 'weep hole' in the bottom face.
 

jim dungar

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Retired Engineer
In practical terms, I can't imagine how one would make such an enclosure.
All of the major manufactures list 'indoor only' enclosures.
Hoffman - Continuous Hinge - UL 508A Listed; Type 12, 13; File No. E61997,
Hubbell-Wiegmann - NEMA 12 single door wall mount - UL 508 Types 12 & 13
Rittal - Single Door Large Wallmount - UL Type 12
Saginaw - Clamp Fastened Single Door - UL Listed Type 12

I did not find one manufacturer that lists information that their 'drip hood' changes the basic enclosure rating. In fact Saginaw says this about their drip shield: "Industry Standards - (N/A)".
 

steve66

Senior Member
All of the major manufactures list 'indoor only' enclosures.
Hoffman - Continuous Hinge - UL 508A Listed; Type 12, 13; File No. E61997,
Hubbell-Wiegmann - NEMA 12 single door wall mount - UL 508 Types 12 & 13
Rittal - Single Door Large Wallmount - UL Type 12
Saginaw - Clamp Fastened Single Door - UL Listed Type 12

I did not find one manufacturer that lists information that their 'drip hood' changes the basic enclosure rating. In fact Saginaw says this about their drip shield: "Industry Standards - (N/A)".
Judging from Hoffman and the photo, I's guess that enclosure is a NEMA 12/ 13 only, and not a combination NEMA12/NEMA 4.

Hoffman NEMA 4 boxes with that style latch also have latches on the top and bottom of the door. Even the small boxes have 4 latches.
 

GeorgeB

ElectroHydraulics engineer (retired)
Location
Greenville SC
Occupation
Retired
It is correct to say that NEMA 12 and NEMA 3R are completely different ratings, each with its' own criteria. I suppose, in theory, that it might be possible to make an enclosure that would pass one and not the other.

In practical terms, I can't imagine how one would make such an enclosure.
Walk outside and take a look at your POCO meter. I'll almost guarantee it is a 3R enclosure. I'll with even more certainty say it won't pass 12.

Same with an outdoor breaker panel ... 3R, not 12.
 

renosteinke

Senior Member
Location
NE Arkansas
Let's forget the catalog listings, where they simply might not mention every possible enclosure type. Let's also forget what we have 'heard,' or what manufacturers have said in their catalog summaries of different enclosure types. Instead, let's look at what NEMA says:

NEMA defines NEMA-3R as: Enclosures constructed for either indoor or outdoor use to provide a degree of protection to personnel against access to hazardous parts; to provide a degree of protection of the equipment inside the enclosure against ingress of solid foreign objects (falling dirt); to provide a degree of protection with respect to harmful effects on the equipment due to the ingress of water (rain, sleet, snow); and that will be undamaged by the external formation of ice on the enclosure.

NEMA defines NEMA-12 as: Enclosures constructed (without knockouts) for indoor use to provide a degree of protection to personnel against access to hazardous parts; to provide a degree of protection of the equipment inside the enclosure against ingress of solid foreign objects (falling dirt and circulating dust, lint, fibers, and flyings); and to provide a degree of protection with respect to harmful effects on the equipment due to the ingress of water (dripping and light splashing).

Now ... what does this mean in terms of testing?

"Indoor use" used to infer a different level of corrosion protection. This is no longer the case; all enclosures now face exactly the same corrosion tests, unless they are specifically rated for some particular environment (such as "marine.") Indoor and outdoor enclosures have the same exposure test.

Please note that the NEMA-12 definition makes no mention of oil, or 'oil tight,' or 'oil seepage.' It does mention 'light splashing.' I can categorically state that the rain test for NEMA-3R, and the implied drainage requirement, are far more severe than any 'light splashing.' From that regard, NEMA-3R exceeds NEMA-12 requirements.

This leaves us with the issue of knockouts. Since NEMA-3R requirements place all knockouts below any live parts, and require the enclosure to not retain 'excessive' water after the rain test, I have to wonder if this difference in the specification is a cause for concern- especially if there are no factory KO's left unused after installation. Or, if the KO's are replaced with gasketed plugs.

Now, some have made reference to NEMA-4, whose enclosures often look very much like NEMA-12 enclosures. Note that NEMA-4 has a test where a pressurised stream of water is directed at the enclosure from every angle. It's safe to say that an enclosure that will keep hose directed water out from any angle will also keep out 'light splashing' or falling rain.


My point is that one cannot simply adopt the small-minded, petty attitude of 'if the sticker doesn't say just the right things, then it won't do.' One must think, as well. Nor is it the responsibility of the customer to address your ignorance.

The same can apply in the opposite direction; for example, one would be obligated to require additional protection in certain circumstances. For example, even a stainless steel enclosure will corrode away in a sewage pit, while a 'not corrosion resistant' cast iron one will do just fine. Go figure!
 

iwire

Moderator
Staff member
Location
Massachusetts
My point is that one cannot simply adopt the small-minded, petty attitude of 'if the sticker doesn't say just the right things, then it won't do.' One must think, as well.
Actually considering those boxes would be listed 110.3(B) requires us to go by the labeling on the box.
 

pfalcon

Senior Member
Location
Indiana
from NEMA 250
3R: Protected from fingers (3.2mm)
3,4,12: Protected from wires (1.0mm)

3: Protected from 45 degree rain with absolutely no ingress
3R: Protected from 45 degree rain (presumably some ingress allowed); No harmful effects
4: Protected from hose down from any angle
12: Protected from vertical dripping and splashing
 

renosteinke

Senior Member
Location
NE Arkansas
Is that really 45 degree rain? I seem to recall the rule being 15 degree. Indeed, having performed the tests (there are a couple different 'rain tests' around), it takes quite a wind to make even a 15 degree rain.

Indeed, one of the rain test does not specify a 'degree' of angle, but instead specifies the airflow to be applied to the falling droplets. "Eyeball" measurement showed this test to be similar to the '15 degree' that I recall the electrical folks specifying at the time.

(I will concede that my experience is not only dated, but comes from the time before UL admitted even the existance of NEMA, and had their own tests).
 
Last edited:

pfalcon

Senior Member
Location
Indiana
NEMA Standard Publication 250-2008 said:
Enclosures for Electrical Equipment (1000 Volts Maximum)

Table 5-1C Degrees of Protection against Water
Enclosure Type 3R: Water sprayed at an angle of 45 degrees shall not enter: See 5.4

5.3 TEST FOR PROTECTION AGAINST INGRESS OF WATER (DRIPPING AND LIGHT SPLASHING)
5.3.2 Method B
... at any angle up to 15 degrees from the vertical.

5.4 TEST FOR PROTECTION AGAINST INGRESS OF WATER (RAIN)
Meeting 5.4 proves you have met 5.3
5.4.1 Method
See diagram
Spray head is positioned to spray 45 degrees below the horizontal.
So NEMA 12 is dripping and light splashing for about 30 minutes from +/- 15 degrees of vertical above the enclosure.
NEMA 3, 3R are protected from 5psi spray +/- 45 degrees from the vertical above the enclosure.
 

renosteinke

Senior Member
Location
NE Arkansas
Thank you for the reply.

It does appear that the test methods have changed. When I was doing the testing, there was no such thing as a water 'spray head' for the rain testing. Rather, there were defined means of making water droplets, which then began a vertical fall but were then diverted by flowing air.
 
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