30 amp receptacle for Krell 700cx

Mclsound,

The Full Power Balanced 700cx,
750Mcx, 400cx, and 450Mcx amplifiers need to
be operated from a dedicated AC power line
rated at a minimum of 20 amps.
Please contact your authorized Krell dealer, distributor,
or Krell before using any devices
designed to alter or stabilize the AC power for
Full Power Balanced amplifiers.

http://www.krellonline.com/assets/support/0162_020_MAN.pdf

I assume the unit uses a NEMA 5-20P plug. Thus you will need a NEMA 5-20R receptacle. A NEMA 5-20R 20 amp receptacle can only be installed on a 20 amp branch circuit per UL, NEC, and most importantly the manufacture of the receptacle.

Krell should of incorporated soft start circuitry in the amp but instead, and I am only guessing here, is telling their dealers to tell their customers to use a 30 amp breaker if nuisance tripping occurs. Bad call....

Subject: Breaker nuisance tripping>http://www.lyntec.com/body_faq-msp.htm
Subject: Breaker nuisance tripping

Do all 20 amp circuit breakers respond to inrush surges the same way?
NO! Circuit breakers have widely varying trip responses depending on their intended use. For most audio power amplifiers you need breakers with a HM rating. The High Magnetic rating allows a substantial inrush current, about double, for the first 100 milliseconds to eliminate nuisance trips. Nuisance trips are common on circuit breakers not rated for High Magnetic duty.

For instance, a standard Square D QO120 breaker will trip with as little as 120 amps in the first cycle compared to 240 amps for a QO120HM.

In Square D, the HM rating is only available for 15 and 20 amp breakers.

The 30 amp QO breakers sustain inrush currents of 300 amps for the first 10 cycles @ 60 Hz, sufficient to light up most of the largest power amplifiers without nuisance tripping.

Instead of using a 30 amp breaker I suggest you ask the electrician who will be installing the dedicated circuit for the Krell to see if the electrical panel manufacture makes a HM 20 amp breaker for the panel.
I would still have #10 awg solid core wire installed for the branch circuit wiring.

Example of an HM 20 amp breaker.
http://ecatalog.squared.com/fulldetail.cfm?partnumber=QO120HM

Something else I would suggest if you will not be leaving the amp on 24/7 and will be turning on and off the amp daily you may want to use a heavy duty UL listed 20 amp receptacle. Hubbell manufactures a highly respected heavy duty recept. The Porter Port is a Hubbell heavy duty recept.

I believe Wattgate also uses a Hubbell. Maybe others....

How does Krell define a 30-amp circuit? By the circuit breaker or the wire size?

If you install a 30-amp breaker, an inspector will look for 30-amp wire (#10 or fatter) and for 30-amp rated receptacles. Those receptacles will not fit the standard 15-amp power cord plug with parallel blades pointing up and down. Installing a 30-amp breaker on a circuit with standard receptacles is a code violation.

If you install the standard receptacles - parallel blades up and down - you can only install a maximum of a 20-amp breaker. That's because the power cord plug will limit the circuit to 15-amps.

A 20-amp circuit has a 20 amp breaker that feeds two to ten 15-amp receptacle/plugs for a total steady load of 16-amps. Or a single 20-amp receptacle (blades are perpendicular) feeding a 16-amp appliance.

A 30-amp circuit feeds either a dedicated 30-amp receptacle or multiple 30-A receptacles with no more that 24-amp appliance power draw total.

So when you get your amp, look at the plug. If it is a standard plug, you can use 30-amp wire in the wall (the Krell power cord is probably 10/3, which is 30-amp rated) but you can only use a 15-amp receptacle (or a combo 15/20-amp). But you cannot use a 30-amp breaker in most places. Check with your local BD.

Now you may ask why do amps with 15-amp plugs say in their specs that they draw a maximum power of, say, 6000 Watts -- which is 50-amps single phase. Won't that melt the 15-A plug and/or receptacle? No, because that is not a steady power draw. The over current is not greater than one half the power cycle and the 20-amp breaker lets that 50-amps pass since that breaker will have a 10,000 amp withstand rating for that time period. The danger is a fault within the equipment that draws a steady, say, 24 amps. A 30-A CB will happily let that pass but a 20-A CB will thermal trip and protect your property.

Correct Link for error link in my last post.

http://www.lyntec.com/body_faq-msp.htm
For example of a 20 amp standard breaker verses a HM breaker, lag time / inrush current.

thanks guys
Seems like most are using a 20amp rec. with 10awg wire and 30amp breaker.

I am picking up my new 700cx today(excited)and maybe some 10awg and will see where it leads me.