2 Pole Breaker for Load Between Two Phases

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david.mullins

david.mullins

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We have a system built for us (control panel) that has a 480VAC Y power with no neutral. It has a pilot light on the 480 in, wired between two phases. It has a two pole breaker with one pole of between each phase and the light. The breaker is rated at 415VAC. Is this ok, since when it trips, in theory, each pole will only see half of the 480?
 
If the breaker is rated 415V then it isn't ok.

However you should dig deeper, since the breaker might have alternate ratings with different restrictions. For example it might have a 'slash rating ' permitting it to be used on grounded wye systems with no more than a given l-n voltage, eg in addition to the 415V rating it might have a 277/480V rating.

Unfortunately I suspect that what you are calling a 415V rating is really a 240/415V rating.

the highest voltage this breaker is likely to see is no half of 480V, but rather the 277V to ground.

Jon
 
winnie said:
If the breaker is rated 415V then it isn't ok.

However you should dig deeper, since the breaker might have alternate ratings with different restrictions. For example it might have a 'slash rating ' permitting it to be used on grounded wye systems with no more than a given l-n voltage, eg in addition to the 415V rating it might have a 277/480V rating.

Unfortunately I suspect that what you are calling a 415V rating is really a 240/415V rating.

the highest voltage this breaker is likely to see is no half of 480V, but rather the 277V to ground.

Jon
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True, but it doesn't matter. If the breaker does not specifically SAY it is rated for 480V P-to-P, then it is not suitable for the intended use and is a 110.3 violation.

Also, from the description this sounds as though it is most likely what's called an "MCB", Mini Circuit Breaker. Many of those are NOT listed under UL489 as a circuit breaker even if listed as 480/277, they are sometimes listed under UL1077 as "suplementary protectors", meaning they cannot be used unless there is ANOTHER branch OCPD ahead of them (rendering them mostly useless). Then even if they DID happen to use a version that is UL489 listed, you have to contend with the SCCR (Short Circuit Current Rating). Most MCBs are rated for no more than 18kAIC, some as low as 10kAIC and on equipment that will be connected to 480V, that is usually not high enough, meaning your entire PANEL may be in violation of NEC Article 409.

Details matter. If you want further help, post the mfr and model number of your breaker.
 
david.mullins said:
It is a Square D M9F42102, which is UL489 and it is a mini CB. Schneider M9F4102

3KAIC but it is right behind a Schneider 600A main breaker. Almost qualifies for the tap rule.
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That's a 1 pole breaker, so 277V max. If you meant a 2 pole version of that same breaker, it IS rated for 480/277V, so if your 480 is oming from a solidly grounded Wye secondary, that's acceptable. 10kAIC is still pretty low though, especially for something capable of feeding a 600A Main. I doubt you will find that the Available Fault Current is 10kA or under.
 
Currently we're running from a generator with a Wye output but all loads are line to line. Neutral of the Wye is not even connected to the panel. Also, someone updated the panel and not the schematic: it is an Eaton FAZ-D2/2-NA breaker which is UL489 and dual rated for 277/480VAC.

But we digress. My original question is does the code allow for two or more poles to be wired in series to work at a higher AC line voltage, assuming all other aspects of the device are appropriate for that voltage (such as case insulation good for 500V, etc)? I know that is done for arc suppression on breakers used in DC systems.
 
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