100% branch rating on PDU enclosure with standard (80%) breakers

[Bob F.]

I'm reviewing a data center PDU that claims fully rated 20A breakers and has UL listing at 20A on that branch. However, the breaker itself is a standard 20A breaker without 100% ratings. The only thing I can figure is that somehow they have exploited the exception under NEC 210.20(A). Searching around the web, I only see statements that interpret that exception as requiring 100% breakers. Can anyone confirm that the PDU (being an assembly that includes standard 80% breakers) can be listed at 100% because of this exception?

 

[Dennis Alwon]

I don't understand. The exception states that you can use a special breaker that is listed as a 100% breaker. a standard 20 amp breaker is not listed for 20 amps of continuous loads. They are listed for 80% of a continuous load. This exception allows you to use a breaker listed at 100% of continuous load. I have not seen a small breaker rated 100% however I believe there are some breakers used in the solar industry rated at 100%

 

[infinity]

I'm reviewing a data center PDU that claims fully rated 20A breakers and has UL listing at 20A on that branch. However, the breaker itself is a standard 20A breaker without 100% ratings. The only thing I can figure is that somehow they have exploited the exception under NEC 210.20(A). Searching around the web, I only see statements that interpret that exception as requiring 100% breakers. Can anyone confirm that the PDU (being an assembly that includes standard 80% breakers) can be listed at 100% because of this exception?

What's the make and model number?

Welcome to the forum.

 

[ron]

the 100% rating requires the breaker to be listed as such and the PDU to be tested for heat disapation with 100% rated breakers as an assembly.

So the PDU might be rated for 100% breakers to be used, but the breakers need to be 100% rated and on the label.

 

[jim dungar]

the 100% rating requires the breaker to be listed as such and the PDU to be tested for heat disapation with 100% rated breakers as an assembly.

So the PDU might be rated for 100% breakers to be used, but the breakers need to be 100% rated and on the label.

A standard breaker is rated for 40C ambient. I am pretty sure this is much hotter than most locations this PDU is intended to be used.
Almost every manufacturer of thermal style protective devices provides 'rerating' procedures for when the device is in ambient different than its listing.
Maybe the PDU manufacturer got their product 100% listed based on a more realistic computer room ambient of 25C?

 

[kwired]

Maybe the PDU manufacturer got their product 100% listed based on a more realistic computer room ambient of 25C?

That was my thoughts, breaker was tested/listed as a component of the PDU even though it already has a listing for it's "normal" applications. As long as used within the listing of the PDU, it's "stand alone" listing doesn't mean anything.

 

[Smart $]

I'm reviewing a data center PDU that claims fully rated 20A breakers and has UL listing at 20A on that branch. However, the breaker itself is a standard 20A breaker without 100% ratings. The only thing I can figure is that somehow they have exploited the exception under NEC 210.20(A). ...

That's just it. If the assembly is UL listed for 100% operation, the NEC has no say on what is inside the unit.

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.

This assumes the breakers are not replaceable in the same fashion as a panelboard.

 

[Bob F.]

What's the make and model number?

Welcome to the forum.

It is Raritan PX3-5830I2U-G1V2A1K201, the certification label states 20A rated branch circuits, and the breaker is an Airpax LELBX1-37804-20-V. This breaker has no indication of 100% rating. In fact, I see no indication that any breakers below maybe 250A are made by anyone with 100% rating. Thanks for the help!

 

[petersonra]

It is Raritan PX3-5830I2U-G1V2A1K201, the certification label states 20A rated branch circuits, and the breaker is an Airpax LELBX1-37804-20-V. This breaker has no indication of 100% rating. In fact, I see no indication that any breakers below maybe 250A are made by anyone with 100% rating. Thanks for the help!

IIRC, Airpax CBs are not listed at all. They are only recognized.

 

[Bob F.]

That's just it. If the assembly is UL listed for 100% operation, the NEC has no say on what is inside the unit.

This assumes the breakers are not replaceable in the same fashion as a panelboard.

Thanks, Smart. That was the only thing that made sense to me.

 

[ron]

That's just it. If the assembly is UL listed for 100% operation, the NEC has no say on what is inside the unit.

This assumes the breakers are not replaceable in the same fashion as a panelboard.

Most of the time they are easily field replaceable. Especially the output breakers are often something like an Square D I Line panel

 

[Smart $]

Most of the time they are easily field replaceable. Especially the output breakers are often something like an Square D I Line panel

I suppose I should have stated that differently. The breakers, if replaced in the field, must be listed replacements for the PDU.