Amp and preamp on same outlet?

John, yes your math is of course correct. And the 700cx does indeed have a max power consumption spec of 6000 watts, which if anything seems a bit low in relation to its specified output power rating of 2800 watts/channel into a 2 ohm load (the 8 ohm and 4 ohm ratings being 700 and 1400 watts respectively).

But it seems safe to assume that it would be an unusual occurrence for the amp to be used in a manner that would require it to draw more than 20 amps x 120 volts = 2400 watts for a long enough time to cause a 20 amp breaker to trip.

Best regards,
-- Al

50 amps is correct.

But we should keep in mind that the amp is likely never going to produce such power, as it would only be possible if the load were one ohm. I remember the Apogee Full-Range speaker approached that value, but the speaker cables used in such an installation would add to the load impedance and limit the possibility of such power.

On most 4 ohm loads the output power is about 1500 watts.

In addition if I recall correctly, its the power transformer in that amp that has that rating, not the amp itself. The transformer would current-limit the amp even if the output section was capable of delivering such power.

Line voltage sag can cause some amps to heat up as the bias point can shift somewhat depending on the design so I can see that reducing the sag with a higher current breaker might have an effect. But installing such a breaker without upgrading the associated wiring would be foolhardy and would not meet code in any state in the country.

"But installing such a breaker without upgrading the associated wiring would be foolhardy and would not meet code in any state in the country."

Well said.

Jim, you do not understand, Krell runs 30 amp braker on every krell 700cx, 750mcx amp there at the factory, BTW, I have 4 fuses, well with-in the current capability useing a 30 amp breaker, as I said befor, I am not useing all the 30 amps!,however, This amp in particular spikes well above 20 amps while in use, maybe you should call krell, then you will get all the theory as to why this works properly you want, remeber, this amp at full power is 6,000 watts!

Audiolabyrinth,

IF, Krell is indeed telling customers the amp was designed to be connected to a 120V 30 amp branch circuit for use in the USA or Canada. Again IF!!!

You are the one that that does not understand what Krell is actually up to. If Krell is having to connect the amp to a 120V 30 amp circuit for the amp to operate properly as designed as well as to achive the amps reported specs then Krell should be using a captive power cord and a NEMA 125V 30 amp plug on the end of the cord. The user, customer, would then be required, per NEC Code, to install a 120V 30 amp branch circuit with the correct NEMA 125V 30 amp receptacle for the Krell amp plug. Per NEC Code a 30 amp branch circuit requires #10AWG minimum wire and shall be connected to a 30 amp branch circuit breaker, period. The receptacle must be a NEMA rated 125V 30 amp receptacle, period. No exceptions.

Instead Krell is apparently more interested in building a product that violates NEC code safety standards for the USA by using a 20 amp max rated IEC inlet connector on the amp where by the user can use a power cord that has a NEMA 5-15P or a NEMA 5-20P plug. Then Krell has the gull to tell a customer that bought the amp to change out the breaker at the electrical panel from a 20 amp to a 30 amp, which I believe the real reason is, because the Krell amp is nuisance tripping the 20 amp breaker on startup in rush current.

So because Krell was too tight to design/incorporate a soft start circuit to limit inrush current to solve the customer's problem of the 20 amp breaker nuisance tripping they tell the customer to change out the 20 amp breaker to a 30 amp breaker. What they should be telling the customer is to change out the 20 amp breaker to a 20 amp HM, High Magnetic, breaker that has a longer delay time for startup inrush current. Problem solved.

I wonder how many Krell users have followed the advice of krell? How many users who changed out the 20 amp breaker to a 30 amp on a 20 amp dedicated branch circuit that has #12AWG 20 amp rated wire?

As I have pointed out earlier in this thread the current carrying contacts as well as the other current carrying metal parts of a 20 amp breaker are identical to that of a 30 amp breaker. Had an EE at Krell done his/her homework he/she would know this as well. They would also know as well a typical TM, thermal magnetic, breaker will easily pass short bursts of current of 120 amps all day long. More than enough for their amp but not enough apparently for startup inrush current. A 30 amp TM breaker will pass short bursts of 300 amps. Hell you can arc weld with 120V at 30 amps. And if the branch circuit wire is of any length and #12AWG copper once I get the #12 branch circuit wire cooking I won't have to worry about tripping the 30 amp breaker.

I have looked at every article in NEC Code that pertains to the code violations and nowhere in the NEC Code book is an exception given for Krell inc.

Audiolabyrinth , did you know?

NEWS from CPSC

U.S. Consumer Product Safety Commission

Office of Information and Public Affairs Washington, DC 20207

August 19, 2009
Release # 09-312
Firm's Recall Hotline: (888) 436-6055
CPSC Recall Hotline: (800) 638-2772
CPSC Media Contact: (301) 504-7908

Amplifiers Recalled by Krell Industries Recalled Due to Fire Hazard
WASHINGTON, D.C. - The U.S. Consumer Product Safety Commission, in cooperation with the firm named below, today announced a voluntary recall of the following consumer product. Consumers should stop using recalled products immediately unless otherwise instructed. Units:
Distributor: Krell Industries LLC, of Orange, Conn.

Hazard: The amplifiers were designed to operate at a temperature warm to the touch. However, a component input device can fail and cause the amplifiers to overheat, posing burn and fire hazards to consumers.

Incidents/Injuries: Krell has received 50 reports of the amplifiers overheating including reports of smoke and electrical fire. No injuries have been reported.

Description: This recall involves Krell power amplifiers with model numbers KAV-250a, KAV-250a/3, KAV-500i and KAV-1500. The amplifiers are used to provide power to a loudspeaker in a home audio playback system. The Krell logo is printed on the front of the amplifier.

Sold by: Authorized dealers and distributors of audio equipment nationwide from January 1997 through February 2001 for between $3,000 and $8,000.

Manufactured in: USA

Remedy: Consumers should immediately stop using the amplifiers, and contact Krell to schedule the free installation of replacement fuses.

Consumer Contact: For additional information contact Krell at (888) 436-6055 between 9 a.m. and 4:30 p.m. ET Monday through Friday, or visit the firm's Web site at www.krellonline.com. Consumers can also email the firm at service@krellonline.com

Krell recall

I would bet that no owner of the Krell amp mentioned in this thread has anything in writing from a representative of Krell inc. stating Krell recommends changing the breaker on a 20 amp branch circuit from a 20 amp to a 30 amp breaker. All a user/customer has is a verbal conversation that is worthless in a court of law.

So who is in violation of State, and local governing body safety electrical codes and electrical safety standards when a 20 amp breaker is changed out to a 30 amp breaker on a 20 amp branch circuit? ……. The person/home owner that changes it out of course.

I suggest you call you insurance agent and ask him/her if you are covered by your home owners insurance policy in the event of an electrical fire if it is found a 30 amp breaker is installed on a 20 amp branch circuit.

Then call the governing electrical inspection department in your city and ask them about changing the 20 amp breaker to a 30 amp breaker on a 20 amp branch circuit.

NEC Code
210.21 (B)(3) Receptacle Rating.
Where connected to a branch circuit supplying two or more receptacles or outlets, receptacles ratings shall conform to the values listed in table 210.21(B)(3), ...........

NEC Table 210.21(B)(3) Receptacle Ratings for Various Size Circuits.

Circuit Rating ..... Receptacle Rating
(Amperes) .............. (Amperes)
15 ............................ 15
20 ....................... 15 or 20
30 ............................ 30

Minimum wire size #10awg. Breaker size 30 amp.

*No exception given for Krell Inc.

Circuit Breaker Myths

Siemens Breakers

Electrical-forensics
.

See page #5

Full Power Balanced
X Series Power Amplifiers

AC POWER GUIDELINES
The Full Power Balanced 300cx and 350Mcx
amplifiers need to be operated from a dedicated
AC power line rated at a minimum of 15
amps. 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.

Note the word [minimum] used for the "750Mcx, 400cx, and 450Mcx amplifiers need to be operated from a dedicated AC power line rated at a minimum of 20 amps."

If the equipment is manufactured for use in the USA with the intent of using a power cord with a NEMA 5-20P 125V 20 amp plug then the max branch circuit ampacity rating is 20 amps. Period! The minimum branch circuit ampacity rating because of the NEMA 5-20P plug is 20 amps. Period!

Minimum wire size #12AWG copper.
Branch circuit breaker size, 20 amp. Period!
Receptacle, if the Krell power cord plug is a NEMA 5-20P plug then a NEMA 5-20R 125V 20 amp receptacle for the plug to fit it is required.

All the above are NEC Code minimum electrical safety standard requirements.

Krell can spec #10 AWG copper wire, which I would recommend. For long branch circuit runs maybe even #8 AWG Cu.
They can spec an HM, High Magnetic, 20 amp breaker must be used to help prevent nuisance breaker tripping.
They should spec that only power cords that has a NEMA 5-20P plug can be used with a minimum cord conductor wire size of #10AWG.
They can spec only a NEMA 5-20R 125V 20 amp heavy duty commercial/industrial rated receptacle be used.
The bigger wire and heavy duty receptacle will help reduce voltage sag on the branch circuit wiring, receptacle contacts to plug blades, and power cord wire right up to that 20 amp IEC inlet connector mounted on the back of the unit caused by the Krell amp's dynamic power connected load.

They cannot spec a 30 amp circuit breaker be used on a 20 amp branch though. You will notice in the owner manual a 30 amp branch circuit was not mentioned. Everybody reading this thread by now should know the reason why.

.