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The All Channels Driven (ACD) Amplifier Test - page 2

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Power Limitations of Power Receptacles & Consumer Devices

An Interview with Michael Schenck of APC AV

 

When I asked our friends at APC AV (one of the leading authorities on power, filtering and surge suppression in the PC and AV marketplace) to elaborate about the standard IEC connector on the back of most receiver/amplifiers being limited to 15A, here is what they had to say.

APC AV: The standard IEC connector (as used in the US) is approved for use on products 12A of CONTINUOUS LOAD. Please note that the connector itself is rated for 15A, but the products are rated for 12A. The connector is limited to this amount mostly for heating and arcing. The mating surface limits the amount of current. The spacing between conductors and the hood limit the possibility of arcing,

If products are designed to be UL (or NRTL) approved, the products must not draw more than 80% of the branch circuit's current rating. This stems from a National Electric Code requirement that states a loads may not continuously draw more than 80% of the rated breaker (with some exceptions) to provide a margin of safety and headroom. The 'standard IEC connector' is commonly called a '15A - connector' because it is intended for use on 15A branch rated circuits. The '15A' IEC connector is typically coupled with a NEMA 5-15P, also a '15A plug'. In practice though, the connector should not be used with products greater than 12A.

 

IEC 13 & 14 are the most common IEC connectors used in consumer AV gear. There are notable examples where some power conditioners manufacturers' equip their products with mixed amperage receptacles. In other words, a '15A' IEC 13/14 inlet style power cord is used on a product with '20A' NEMA 5-20 receptacles. This allows the user to plug a '20A' load into a '15A' circuit. It is OK to use a '15A' plug on a '20A' branch circuit, but not a '20A' receptacle on a '15A' branch circuit. I guess somehow they think providing a '20A' IEC or NEMA receptacle with a '15A' plug gives them more power. In reality, it creates a dangerous overload condition. But that is a conversation for another myth destroying article!

 

Power strips, surge protectors, and Relocatable Power Taps (RPT) are one expectation to the 80% derating rule - they are simply meant to be an extension of the wall. An RPT is rated for 15A - but it must not consume significant power on its own. Some irresponsible manufacturers will classify power hungry power conditioners as RPTs, exploiting a loophole in the system.

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Note: IEC 13 & 14 are the most commonly used in consumer AV gear

 

Companies can circumvent the power draw derating requirements of the Standards during 'non-standard' or 'non-continuous' use. Voltage regulators by their nature will operate with increased current during non-standard conditions. APC automatic voltage regulator units will provide 120V @ 12A OUTPUT. This means, we will have to draw more input current at 110V in order to sustain the user's load. At 120V, we cannot pull more than 'rated current' - 12A - from the wall continuously. However, our peak current draw can exceed this by a few amps for short periods of time under transient usage.

 

Can you confirm and provide a standard that references this?

 

APC AV: The National Electric Code (NEC) is very clear: Article 110 plainly states any product connected to the electrical supply in the U.S. must have a National Recognized Testing Laboratory (NRTL) safety agency Listing mark, or be specially approved by an onsite electrical inspector. For the most part, Underwriters Laboratories (UL) and other NRTLs follow NEC guidelines. Article 210 specifies the 20% derating factor - as specified in a table from the 2002 NFPA NEC Handbook.

Table 210.21(B)(2)
Maximum Cord-and Plug- Connected Load to Receptacle

 

 

Circuit Rating (Amps)

Receptacle Rating (Amps)

Maximum Load (Amps)

15 or 20

15

12

20

20

16

30

30

24

 

The NEC also states that branch circuits are sized according to the VA (Volts x Amp) requirement of the loads. It is NOT correct to assume Watts = VA. It is very possible a 1575W load will need 20A of current, necessitating a 30A branch rated circuit.

According to Crown Audio: "The amperage capacity of the power cord is determined by the amount of current drawn by the amplifier from the AC mains when measured according to CSA/CAN E60065, IEC60065 and UL 6500 standards, which all relate to audio/video and musical instrument apparatus for household, commercial, and similar general use."

 

Refer to: http://www.crownaudio.com/pdf/amps/137331.pdf

 

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