c1 drafted · lead AC circuit breaker proposed
- CPS 3Phs Inverter Site Design Guidelines
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AC breaker thermal nuisance tripping
The AC breaker trips below its nominal current because it is too hot to shed heat, even though there is no real overcurrent. Common causes are a hot enclosure from sun and conductor heat, and breakers mounted close together while several inverters feed at full current. The temperature inside the enclosure can be well above the outside air temperature, especially in enclosures with large east- or west-facing surfaces. To confirm, measure the load current through the breaker against its rating and check the temperature inside the enclosure. Also check that the breaker rating is not below what the inverter manufacturer recommends. To fix it, size the breaker with the temperature derate applied, or space the breakers further apart. Other options are cooling or reorienting the enclosure, or using electronic trip or 100% rated breakers.
<!-- review notes
- sentence 1: support check: partial - Tripping below nominal current from heat is stated, but 'even though there is no real overcurrent' is not explicit.
- sentence 4: support check: partial - Passages mention verifying current against rating and enclosure temperature vs OSAT, but don't explicitly prescribe checking enclosure temperature as a confirmation step.
- sentence 4: review: partial - Solis supports checking the load current against the breaker rating, but the passages only describe the enclosure temperature as a design factor and never name measuring it as a confirmation step. -->
Claims
affects
presents_as
c2 drafted · lead AC circuit breaker tripping
Breaker trips below its nominal current when it cannot shed heat.
- 275587
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caused_by
c3 drafted · lead High operating temperature
High temperature inside the breaker enclosure means less heat can leave the breaker. The enclosure temperature is not the same as the outside air temperature.
- CPS 3Phs Inverter Site Design Guidelines
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c4 drafted · lead Solar heat gain proposed
How much the enclosure heats up depends on its color and which way it faces. Large east- and west-facing surfaces pick up the most heat in the evening.
- CPS 3Phs Inverter Site Design Guidelines
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c5 drafted · lead Mutual breaker heating proposed
Breakers mounted close together, with inverters all feeding at full current, heat each other and trip early.
c6 drafted · lead Undersized component
A breaker that is rated too low or was not derated for temperature.
- CPS 3Phs Inverter Site Design Guidelines
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review note: support check: partial - Derating for temperature and MCB rating below recommended are mentioned, but the passages don't directly say an undersized or non-derated breaker causes thermal nuisance tripping (u15 is a general MCB tripping checklist).
detected_by
c7 drafted · lead Phase current measurement
Check that the total current through the breaker stays within its rating.
- 44001815757-ac-breaker-trips-steps-to-diagnose-and-resolve-issues
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review note: support check: partial - Passage says to confirm total current doesn't exceed rating, but doesn't tie it to detecting thermal nuisance tripping or call it phase current measurement.
c8 drafted · lead Ambient temperature check
Measure the temperature inside the AC enclosure, not the outside air temperature.
- CPS 3Phs Inverter Site Design Guidelines
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review note: support check: partial - Passage distinguishes enclosure temperature from OSAT, but doesn't explicitly say to measure it as a detection method.
mitigated_by
c9 drafted · lead AC protective device sizing
Derate the breaker for enclosure temperature and use the breaker size the manufacturer specifies.
- CPS 3Phs Inverter Site Design Guidelines
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sec=h3h=ed1216ee4475 - PVI 25TL-208 36TL-V2 50-60TL IOM DOCR-071086-C
sec=h120h=c0cdd47c085a - CPS 25kW User Manual Rev 2.1
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c10 drafted · lead Increased breaker spacing proposed
Leave more space between breakers so heat can dissipate, or apply the grouping correction factor when sizing.
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c11 drafted · lead Enclosure cooling proposed
Use active or passive cooling and choose the enclosure's orientation to keep its temperature down.
- CPS 3Phs Inverter Site Design Guidelines
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c12 verified · fact Electronic trip breaker proposed
Electronic trip breakers often tolerate higher temperatures.
- CPS 3Phs Inverter Site Design Guidelines
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verified by: review-workflowverified on: 2026-10-24
c13 drafted · lead 100% rated circuit breaker proposed
- CPS 3Phs Inverter Site Design Guidelines
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review note: review: partial - The passage lists 100% rated breakers as a design option to control (lower) breaker rating and wire size, but does not say they reduce thermal nuisance tripping.
temperature_rise
c14 verified · fact nominal 28 K
Conditions: Temperature inside the AC breaker enclosure above outside air temperature, recorded at one typical site in Florida in July
At that site the inside of the enclosure reached 60 °C, which gave a worst-case breaker derate of 81%.
- CPS 3Phs Inverter Site Design Guidelines
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verified by: review-workflowverified on: 2026-10-24