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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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NEC mandates derating on the breaker side for lighting circuits

NFPA 70 - THE NATIONAL ELECTRICAL CODE

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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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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

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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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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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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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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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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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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- Schedule a Webinar for Advanced Sales & Engineering Training

Team of Experts

NEED FURTHER ASSISTANCE?

FOLLOW-UP

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