June 2023
SHEDDING LIGHT ON INVERTER DERATING
ISOLITE
SHEDDING LIGHT ON INVERTER DERATING
Chalk Talk
Derating In This Context
NEC/NFPA 70
Run Time
Recommendations
How to Get More Information
SHEDDING LIGHT ON INVERTER DERATING
OVERVIEW
BACKGROUND
HOW TO DERATE
FOLLOW UP
Power Factor
Crest Factor & Inrush
Motor Loads
Storage Temperature
Altitude
- To improve some other specification point
- To accommodate a site related factor
- To extend the runtime of the inverter
Anything that makes a 1000W inverter have less than 1000W of load connected to it
DERATING, WHAT ARE WE TALKING ABOUT
BACKGROUND
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SHEDDING LIGHT ON INVERTER DERATING
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NEC mandates derating on the breaker side for lighting circuits
NFPA 70 - THE NATIONAL ELECTRICAL CODE
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SHEDDING LIGHT ON INVERTER DERATING
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2.10.20(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.
"The 80% Rule"
Still applies to branch circuit breakers within the inverter
This isn't the focus of today...
BACKGROUND
Inverter run time is a special case...
INVERTER RUN TIME
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SHEDDING LIGHT ON INVERTER DERATING
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Important Recurring Theme: Batteries aren't rated in watts! They're rated in volt-amps
(Volt-amp-hours to be specific)
1000W Inverter
1000VA Inverter
1500 VAh Inverter
This makes it easy to calculate an expected runtime
1500 VAh / 500VA = 3h = 180 minutes
We actually do better than this approximation...
- Call us if you need to get hyper accurate
BACKGROUND
BATTERY DERATING CHART
BATTERY VOLTAGE
RUN TIME
- We recommend only loading the Inverter to 90% of load wattage.
So what does this line in the cut sheet mean???
THE RECOMMENDATION
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SHEDDING LIGHT ON INVERTER DERATING
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Inverters are rated to 100% of their "VA" rating
UL tests 1000VA inverter at 1000VA for the entire 90 minute runtime.
BACKGROUND
Watts are not Volt-Amps
Watts are "True" Power
Volt-Amps are Total Power
POWER FACTOR: THE MAJOR ISSUE
HOW TO DERATE
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SHEDDING LIGHT ON INVERTER DERATING
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Reactive Power (VAR)
Real Power (Watts)
Apparent Power (VA)
LED Drivers
- Generally promote > 0.9 PF
- Generally get worse as they dim
Determines how much current may be required for a short burst at initial LED illumination
They are related only in that they refer to "current" in some way.
Both relate to the characteristics of the downstream driver and control circuitry.
CREST FACTOR & INRUSH
Inrush Current
Characterized by NEMA 410, which our inverters are tested to and pass
Generally no derating required
Determines the characteristic "peakiness" of the waveform
Generally only becomes a concern with 2-wire forward-phase dimming
Derating of about 25% for most applications, or use a reverse phase dimmer
Crest Factor
HOW TO DERATE
Not "derating" but understanding of how the ratings work.
MOTOR LOADS
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SHEDDING LIGHT ON INVERTER DERATING
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Requirements for success
Horsepower * Power Factor * Efficiency < Inverter Amperage
Locked Rotor Current < Inverter Amperage * Crest Factor
Information available on the rating label or use best practice numbers:
Power Factor: 0.6
Efficiency: 0.8
HOW TO DERATE
- Only here because it's a common question
- High storage temperatures shorten inverter life; they don't (within reason) reduce capacity
- You can't under-load an inverter to compensate for a high storage temperature
- Inverters must be kept between 68°F and 86°F, ideally below 77°F
STORAGE TEMPERATURE
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SHEDDING LIGHT ON INVERTER DERATING
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HOW TO DERATE
65º
70º
75º
80º
85º
- Often forgotten, rarely needed derating point.
- Inverters utilize convection cooling; thus they rely on the flow of air over heatsinks to stay cool
- Higher altitudes result in less air, thus less capacity for cooling
- Above 1 mile, derate capacity by 2% per 400 feet. Above 8250, call us for guidance.
ALTITUDE
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SHEDDING LIGHT ON INVERTER DERATING
Chalk Talk
HOW TO DERATE
- Specs Sheets & Drawings
- Boilerplate Specifications
- Chalk talks on Motor Loads and Runtime Extension
- Continuing Education via The Continuing Architect
Available on the Website
- Training Video Link
- Sales Presentation PDF
Available Within Follow-Up Sales Packet
SUPPORTING MATERIALS
FOLLOW-UP
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SHEDDING LIGHT ON INVERTER DERATING
Chalk Talk
- Schedule a Webinar for Advanced Sales & Engineering Training
Team of Experts
NEED FURTHER ASSISTANCE?
FOLLOW-UP
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SHEDDING LIGHT ON INVERTER DERATING
Chalk Talk
For Additional Training, Please Contact Your
Local Sales Representative
THANK YOU