KA rating versus Voltage rating

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CCDTHOMAS

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OK here it is Im in Afghanstan we have alot of previous install QO panel that are reated 120/240V panels, the common voltages that are used are 230/380V. What are the potentional hazards with using these 240V 22KA rated breakers on this system? I do realize that it is a code voilation, that not what im concerned with right now, just the reaction time of the breaker to clear a fault and to protect the end user.
 

cpal

Senior Member
Location
MA
If your concerned with protecting the end user than I would certainly discourage using a slash rated breaker on the 230/380 system. The mfg will not stand behind the breaker if the voltage to ground exceeds 120V. And a 230 V fault phase to ground could result in catastrophic failure.

Be Safe!!
 

CCDTHOMAS

Member
I understand what you are saying, I guess what Im asking is there any evidence to the fact, I'm on a military post and most of this was thrown together mission critical get it running, Now what you have is the government wanting us to address the accual potentional in writen form. The only thing I have is the UL 489 test result, the problem there is they were only tested under the voltage rating of the breaker. I have deemed it as an LHS issue, Im needing some evidence that this could cause damage to person if not rectified. Im looking for of an educated responce thats not just is not UL rated and a NEC code voilation.
 

cpal

Senior Member
Location
MA
Some multiple-pole, mechanical overcurrent protective devices, such as circuit
breakers, self-protected starters, and manual motor controllers, have a slash
voltage rating rather than a straight voltage rating. A slash voltage rated
overcurrent protective device is one with two voltage ratings separated by a
slash and is marked such as 480Y/277V or 480/277V. Contrast this to a
straight voltage rated overcurrent protective device that does not have a slash
voltage rating limitation, such as 480V. With a slash rated device, the lower of
the two ratings is for overcurrents at line-to-ground voltages, intended to be
cleared by one pole of the device. The higher of the two ratings is for
overcurrents at line-to-line voltages, intended to be cleared by two or three
poles of the circuit breaker or other mechanical overcurrent device.
Slash voltage rated overcurrent protective devices are not intended to open
phase-to-phase voltages across only one pole. Where it is possible for full
phase-to-phase voltage to appear across only one pole, a full or straight rated
overcurrent protective device must be utilized. For example, a 480V circuit
breaker may have to open an overcurrent at 480V with only one pole, such as
might occur when Phase A goes to ground on a 480V, B-phase, corner
grounded delta system.
The NEC​
? addresses slash voltage ratings for circuit breakers in 240.86
restricting their use to solidly grounded systems where the line to ground
voltage does not exceed the lower of the two values and the line voltage does

not exceed the higher value.
 

CCDTHOMAS

Member
Charlie,

You have been most helpful, in the fact that you are responding to my questions. The point that im trying to make and not to clearly and that is my fault is that the breakers are rated 240v at 22 ka, so in essence it will clear a line to neutral fault that potentional would only be 230v, it would not clear a phase to phase fault. So are there any results that state the potentional and the hazards that would result from a phase to phase fault on a breaker that is not rated for the voltage. And thanks for the information so far.
 

charlie b

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Location
Lockport, IL
Occupation
Retired Electrical Engineer
I doubt that you will find any tests that demonstrate any component's performance in an installation that exceeds its rating. The purpose of a manufacturer's test is to obtain the UL listing that states that the component has been tested at its rated conditions, and has passed the test. If a manufacturer has no intention to list an item at 400 volts, they are not going to pay to have it tested at 400 volts.

If a two-pole breaker's phase-to-phase rated voltage is 240, and if you install it in a system for which the phase-to-phase rated voltage is 380, and if it has a fault current rating of 22kA, and if it experiences a fault at or below that current level, I suspect it might open properly. The things that make a breaker go open are related to current, not to voltage.

That said, any component's voltage rating is based on the ability of its insulation system to prevent current from leaking from the current-carrying metal parts, through the insulation, to other current-carrying metal parts, or to the outside world. If a breaker is installed in a system that has a voltage higher than its rating, there could be leakage current, resulting ultimately in failure, even if you never experience a fault. It could (and eventually will, I believe) fail under normal operations.

The point is not so much that a test was once performed to prove that it could fail. Rather, the point is that no test was ever performed to prove that it won't fail.
 

charlie b

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Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
By the way, on an "almost related" topic, I once read of a simple thermostatic control device that was installed in a system (specifically, an oxygen tank) for which the voltage exceeded its rating. It was a matter of incorrectly choosing which device to install, and nobody noticed the mistake. Later, they ran a routine procedure to remove moisture from the tank by heating it. The thermostat failed, since it was being operated at too high a voltage. As a result, the temperature in the tank got too high. That caused the insulation in other wires installed inside the tank to overheat, and to melt away. Nobody noticed that either. Still later, when the tank was in actual use in a real mission, the operator tried to perform a routine stirring of the oxygen within the tank. The wires chose that moment to short circuit, and the oxygen tank exploded.

The book in which I read this story was called, ?Lost Moon,? and was written by the commander of that particular mission. His name is Jim Lovell. They gave him a 5 second ?bit part? at the very end of the movie they made from the book. The name of the movie was ?Apollo 13.?

What is my point? When something eventually fails, somebody is going to find out how and why. At that time, they are going to ask why, when someone knew the breaker was being operated beyond its rated voltage, that someone didn?t do something about it. A simple action taken early enough would have prevented the failure, and the injury/fatality (heaven forbid it comes to that), and nobody took that action.
 

Hameedulla-Ekhlas

Senior Member
Location
AFG
Charlie,

You have been most helpful, in the fact that you are responding to my questions. The point that im trying to make and not to clearly and that is my fault is that the breakers are rated 240v at 22 ka, so in essence it will clear a line to neutral fault that potentional would only be 230v, it would not clear a phase to phase fault. So are there any results that state the potentional and the hazards that would result from a phase to phase fault on a breaker that is not rated for the voltage. And thanks for the information so far.

Nice to hear you from Afghanistan. By the way, I am trying to get you but your question is very complicated. In Afghanistan there is 380 V 3ph and 240 volt 1ph. To know all steps please do a shortcircuit calculation. I have done some projects shortcircuit calculation and as long as military projects concerned, they are all barracks and buildings. On fault system analysis or shortcircuit calculation in each node or terminal with 22 kA is enough i think.

First you should calculate the shortcircuit MVA and you can find fault ampere in each terminal. Voltage is only used for finding the current.
Per military Scope of works, the minimum breaker size is 20 Amp which contains 6kA per legrand catalog.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
Not saying you have these but, Square D sells a QOXD breaker (they used to be called QOX) for international applications. These look like US QO breakers but are intended for use in the UK, among other locations. They are rated 416Y/240.
 

Cmdr_Suds

Member
That said, any component's voltage rating is based on the ability of its insulation system to prevent current from leaking from the current-carrying metal parts, through the insulation, to other current-carrying metal parts, or to the outside world. If a breaker is installed in a system that has a voltage higher than its rating, there could be leakage current, resulting ultimately in failure, even if you never experience a fault. It could (and eventually will, I believe) fail under normal operations.


Besides internal insulation capabilities, the voltage also plays a factor in the separation of the contacts when breaking the current. If they do not separate by enough distance, the arcing could continue and not effectively stop the current flow. Also, voltage higher then they are rated for will significantly shorten the life of the contacts.
 
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