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Use of AC MCCB as DC MCCB
- Thread starter varyspeed
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Most electrical components primarily designed for AC service have a limited DC rating, eg the 600VAC / 250VDC markings. The major limitations on MCCBs in DC service are: they're usually confined to loads with little or no inductance; their DC voltage rating is much lower than for AC duty - you may need multiple poles in series; and only true thermal-mag or pure mag MCCBs will work correctly. Self-powered electronic tripping modules don't work on DC.
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- Location
- Wisconsin
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- PE (Retired) - Power Systems
varyspeed said:Can we use TP 200 Amp AC MCCB in 200A DC CIRCUIT?
If we can use AC MCB or MCCB in DC circuit how much higher rating has to be considered?
IS it advisable to use ac mccb / mcb in dc circuit?
kindly give feedback with technical data
Most circuit breaker manufacturers have DC ratings for their equipment. You need to contact the manufacturer.
To understand the challenge of breaking DC current one has to appreciate the fact the 60hz AC goes through zero 2 times each cycle which is zero volts. When the moving contact moves away from the stationary contact to interrupt the current this aids in interrupting the current flow. As the arc is pulled up through the arc chutes the arc is spit up deionized and cooled.
The problem with DC the current does not go through zero volts so the potential persists between the moving and stationery contacts as the contacts open. When the DC arc is struck what clears it. It's the what ever resistance that can overcome the voltage between the contacts which is air and the arc chute ability to deionize the DC arc. As indicated in one of the other posts the dc voltage is usually limited to 250v or even 125v as I recall depending upon the breaker.
Another means of applying a breaker on DC is series connecting the poles. For example, a 3p breaker can be connected such that the line is connected to the line end of the pole on the far left, then from the load end of that pole the load end of the center pole, from the line of the center pole to the line of the right pole and the load end of the right pole to the load. The contacts are placed in series, which adds to the contact gap and increases the interrupting capability on DC. This can be done on either the positive or negative line. Often time 2poles are series on the positive line to the load and the negative is run from the load back through the third pole of the breaker which accomplishes the same thing.
Also, the I2t inverse time current curve will not be the same as AC as far as I can recall.
As a side note electronic trip breaker don?t respond to DC current.
The problem with DC the current does not go through zero volts so the potential persists between the moving and stationery contacts as the contacts open. When the DC arc is struck what clears it. It's the what ever resistance that can overcome the voltage between the contacts which is air and the arc chute ability to deionize the DC arc. As indicated in one of the other posts the dc voltage is usually limited to 250v or even 125v as I recall depending upon the breaker.
Another means of applying a breaker on DC is series connecting the poles. For example, a 3p breaker can be connected such that the line is connected to the line end of the pole on the far left, then from the load end of that pole the load end of the center pole, from the line of the center pole to the line of the right pole and the load end of the right pole to the load. The contacts are placed in series, which adds to the contact gap and increases the interrupting capability on DC. This can be done on either the positive or negative line. Often time 2poles are series on the positive line to the load and the negative is run from the load back through the third pole of the breaker which accomplishes the same thing.
Also, the I2t inverse time current curve will not be the same as AC as far as I can recall.
As a side note electronic trip breaker don?t respond to DC current.
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