Din Rail Mount Breakers

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Dennis Alwon said:
Excuse my ignorance but what would they be used for..?
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I am not sure, they say they are for AC but 'solar breakers'

Check out the ratings of them

MNEAC10 10 amp, 120VAC UL489A din rail mount, 10,000 AIC $12.90
MNEAC15 15 amp, 120VAC UL489A din rail mount, 10,000 AIC $12.90
MNEAC20 20 amp, 120VAC UL489A din rail mount, 10,000 AIC $12.90
MNEAC40 40 amp, 120VAC UL1077 din rail mount, 3,000 AIC $12.90
MNEAC50 50 amp, 120VAC UL1077 din rail mount, 3,000 AIC $12.90
MNEAC60 60 amp, 120VAC UL1077 din rail mount, 3,000 AIC
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A 10 amp?

40, 50 and 60 amp only rated 3,000 AIC :huh: ... that cant be connected to a utility. It must be for the AC output of a PV system.
 
If it is a UL489 CB, it can be used for branch circuit protection. These small breakers tend to be the same frame size upto 63A so it may make economic sense to make them all 100% breakers. They seem to only be slash rated at 480V though.

I have never seen any indication that they are not all rated 100%. And the only AIC rating I have seen for them is 10kA.
 
These breakers, made by CBI in South Africa, are Hydraulic-Magnetic, not Thermal-Magnetic. Ultimately it doesn't make much difference as long as they work and carry a UL489 listing as a branch circuit breaker, and it's true that H-M breakers are always rated for 100%. That'
s because the breakers don't change tripping characteristics when hot. The common H-M breaker used in the US has been Heineman for years (now owned by Eaton I think). The only issues with H-M breakers are that they tended to be more expensive, they must be mounted vertically because the plunger mechanism can be influenced by gravity, and the trip times vary with LOWER temperature more than a basic T-M breaker will. That's because the silicon oil used to dampen the magnetic trips will change viscosity when really cold, so the breaker may take longer to trip. The up side to that is that they do NOT nuisance trip when hot, so in a lot of applications where heat is a potential issue, people tend to use them instead of the cheaper T-M breakers.

However, ALL UL listed breakers are tested for use at 100% current, the "80% rating" is kind of an urban myth. UL489 testing of the breakers themselves says absolutely NOTHING about only loading them to 80%, the continuous rating of a UL489 listed branch circuit breaker is officially 100% of the rating under the breaker test procedure, which is all by itself in free air. The so-called "80% rule" for a breaker is based on how they are MOUNTED and terminated as part of a SYSTEM that includes the box you put them in. If you want to USE the breakers at 100% rated current continuously, the way they are mounted and wired is part of that listing.

So here's the kind of "iffy" part of this; If you look carefully, that web page for Midnight Solar says the following, parsed out with my comments in red;

Note: Branch circuit rated 489A
True; the breakers themselves are UL489 listed.

All MidNite circuit breakers are rated for 100% continuous duty. MidNite’s breakers are rated to break the full rated load at the rated voltage repeatedly, with NO DAMAGE. Always use a properly sized breaker for disconnecting.
Nothing about this is incorrect, just misleading. ALL UL489 listed BREAKERS can make this statement as it is worded.

All MidNite circuit breakers can be used at 100% rated current when mounted in a MidNite enclosure.
Ah, THERE'S the rub right there. ONLY in THEIR enclosures. Then if you look a little deeper into that, their enclosure packages are NOT listed by UL, they are listed by ETL. I know that ETL is a perfectly acceptable NRTL, but I also know from direct experience that it is a lot easier to get something through them than it is with UL. I'm not saying anyone deliberately pulled a Volkswagon here, but it's possible that in the listing process with ETL, the Midnite Solar people may not have told them the complete story as to how many breakers might be in the box, how close they would be to each other, what size and type of wire would be used in the field, etc. etc. etc., and the ETL people may not have known to question it the way UL would have, who deals with that issue day in and day out. Even if I'm wrong about that, the only boxes they sell hold a maximum of 4 breakers, so not too hard to get that to pass.
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Don't get me wrong here, what they are saying it likely all true, but it may not mean what you THINK it means.
 
Thanks so much for the info. I am a bit confused here

However, ALL UL listed breakers are tested for use at 100% current, the "80% rating" is kind of an urban myth. UL489 testing of the breakers themselves says absolutely NOTHING about only loading them to 80%, the continuous rating of a UL489 listed branch circuit breaker is officially 100% of the rating under the breaker test procedure, which is all by itself in free air. The so-called "80% rule" for a breaker is based on how they are MOUNTED and terminated as part of a SYSTEM that includes the box you put them in. If you want to USE the breakers at 100% rated current continuously, the way they are mounted and wired is part of that listing.
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Are you saying that all breakers not just dim rail are rated 100% continuous???
 
He is saying, I think, that all breakers are tested for 100% of their nominal current, but the NEC does not allow them to be used at that rating in a normal panel.
 
GoldDigger said:
He is saying, I think, that all breakers are tested for 100% of their nominal current, but the NEC does not allow them to be used at that rating in a normal panel.
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So its the enclosures that are not listed at 100%

Exception: Where the assembly, including the overcurrent
devices protecting the branch circuit(s), is listed for operation
at 100 percent of its rating, the ampere rating of the
overcurrent device shall be permitted to be not less than the
sum of the continuous load plus the noncontinuous load.
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Dennis Alwon said:
So its the enclosures that are not listed at 100%
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Even with the so-called 100% rated breaker, the entire assembly (enclosure, panel, breaker, etc) must be listed for 100% operation in order for the breaker to have any advantage over the "not" breaker.
 
GoldDigger said:
He is saying, I think, that all breakers are tested for 100% of their nominal current, but the NEC does not allow them to be used at that rating in a normal panel.
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Correct

Dennis Alwon said:
So its the enclosures that are not listed at 100%
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GoldDigger said:
You could look at it that way, yes. :)
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Well, sort of. It's the breakers IN the enclosure that is rated for 100% use. You still have to purchase the breaker that SAYS it is 100% rated, and when you do, you will have restrictions on how it can be used based on the way it is mounted (and wired).

For example;
I can buy a 400A Siemens/ITE breaker that says it has a continuous rating of 400A at 40degC. But if I put that breaker in a panelboard as a Branch Feeder Breaker, I can only USE that breaker on a circuit that can be loaded to 360A continuous, or 400A if some of it is non-continuous, defined as 3 hours or more. It's all lined out for you in 210.20(A).
“Where a branch circuit supplies continuous loads or any combination of continuous and noncontinuous loads, the rating of the overcurrent device shall not be less than the noncontinuous load plus 125 percent of the continuous load.
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The inverse of 125% is 80%, that's where the "80% rated breaker" idea comes from.

If I pay 10% more for that breaker, I can get a label on it that says it is RATED as a 100% breaker, meaning I can put 400A on it any time I like. But to do so, I have to use 90C rated conductors, SIZED at the 75C column, and I have to use lugs rated for 90C (which in Siemens world are copper lugs, so copper conductors only). Then the NEC will tell me, in the exception to this and 215.2(A) that I have to use it in an enclosure that is suitable for using the breaker at this 100% rating.
Exception: Where the assembly, including the overcurrent devices protecting the feeder(s), is listed for operation at 100 percent of its rating, the
ampacity of the feeder conductors shall be permitted to be not less than the sum of the continuous load plus the noncontinuous load.
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That by the way will NOT be that panelboard enclosure (unless, in a few cases, you use it as the main CB), it will be a separate enclosure, i.e. an "Enclosed Circuit Breaker", or used in another assembly, such as a control panel or MCC or Switchboard, where THAT entire enclosed assembly is listed WITH that 100% breaker in it.

Simple, eh?

:?
 
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Now I am more confused...:D

Let me see if I have at least the basic concept here. You are saying all breakers are tested at 100% but they are not marketed or sold with the sticker that states they are rated 100% continuous. Even if you had a breaker that was MARKED 100% Continuous the entire assembly would still need to be rated 100% continuous.

Is that close enough???:D
 
Dennis Alwon said:
Are you saying that all breakers not just dim rail are rated 100% continuous???
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Yes. All breakers are 100% rated by themselves. In fact trip curves start around 125% for most breakers and can legally hold 134% indefinitely.

The 80% rule comes in place to reduce nuisance tripping in panel boards from heat build up. 80% is a code rule rather then a UL thing.
 
mbrooke said:
The 80% rule comes in place to reduce nuisance tripping in panel boards from heat build up. 80% is a code rule rather then a UL thing.
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It is as much a 'UL thing' as a code rule.

Look in the UL general directory and you find the exact same restrictions as the NEC.
 
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