What’s the differences between AC and DC circuit breaker? Can AC circuit breakers be used for DC? Many users want to ask such questions.
Firstly, we need to know more about Alternating Current and Direct Current:
According to above photo, we can see that for Direct Current, the voltage is very stable and won’t change when the time goes through. The Direct Curent voltage will never be zero.
While for the Alternating Current, the voltage will change as sine wave when the time goes through. The Alternating Current voltage will change to zero two times each cycle.
Due to the different characteristics of AC and DC, we can find out that AC arc is easier to be disconnected, the DC arc is more difficult to be disconnected because the voltage never reaches zero.
After we understand the difference between AC and DC, we will understand that the AC breaker can’t be used as DC breaker, because the arc extinguishing ability of DC breaker should be better than AC breaker.
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As we all know there’re many different brands and types of DC circuit breakers in the market, how can we choose the correct DC circuit breakers?
Compare with AC circuit breaker, the DC circuit breaker must have a strong arc extinguishing ability and in order to get a strong arc extinguish ability, the DC breakers should:
1)Add a bigger arc extinguish chamber .
2)Expand the distance of the moving contact and fixed contact.
3)Design with UL94 V-0 flame retardant shell.
4)Meet the IEC 60898-1 standard if the max voltage is below DC440V and meet the IEC 60947-2 standard if the voltage exceed DC440.
The above two DC MCB shape are well sold in the market because for these types, the price are very cheap. Usually we call them C45 type and we can distinguish them with the handle located in the bottom.
The above photo is the inside structure of the C45 type circuit breaker. The plastic material of C45 series is PC material and the flame retardant is UL94 HB, some brand maybe better with UL94 V-2.
One of the most important part of the breaker is the green circle: arc extinguish chamber. In this breaker, the arc extinguish chamber is exactly the same as the AC arc extinguish chamber, total 9 pieces of arc extinguish plates.
Another important part of the C45 breaker is the red circle: distance between moving contact and fixed contact: 4mm which is the same as AC breaker.
The only difference between AC and DC is that the manufacture add two magnets at the blue circle position.
The magnets will also make the circuit breaker become a polarity type which means you should connect the DC wire in the correct direction, otherwise it will be burnt.
For the C45 series circuit breakers with two magnets may be ok below DC440V 2Pole. It is certainly unacceptable for more than DC500V.
In summary, we call the C45 series fake DC circuit breaker if they decare the voltage exceed DC440V.
The above MCBs with metal handle, rectangle indicator window and plastic handle, triangle indicator window, we call them L7 type. We can distinguish them based on the handle in the middle position.
The left structure belongs to the one with metal handle and rectangle indicator window. The right structure belongs to plastic handle, triangle indicator window.
According to this photo we can see that the L7 structure is better than C45 structure. Especially the arc extinguish chamber, there’re 13 pieces of arc extinguish plates while C45 type only have 9 pieces, see yellow line above.
The L7 type is usually for AC application and if we use better materials for example using the silver plated moving contact instead of copper moving contact, see blue line above. it can work for DC. Most of the manufactures just add magnets to strengthen the arc extinguish performance, see the red line above.
The distance of L7 type between moving contact and fixed contact is also about 4mm.
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So what’s DC circuit breaker can be called as a real DC circuit breaker?
YRO electric YRL7-63DC Series DC circuit breaker:
1)Designed the DC maze arc-extinguish room instead of the regular AC arc-extinguish chamber and add two extra arc-extinguish plates to make it total 15 pieces of arc extinguish plates. See the green circle above.
2)Strengthen the thickness of the moving contact and plated the silver.
3)Choose AgC4 fixed contact.
4)Expand the distance of moving contact8&fixed contact to 7mm instead of 4mm.
5)Use PA66 material shell and ensure the UL94 V-0 flame retardant level.
Regarding this, 2Pole 1000V is still impossible for the L7 type MCBs， not to mention the C45 type MCBs.
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If you read all the words and photos, I believe you already know how to distinguish a real DC circuit breaker and fake circuit breaker. Also you know the differences between DC circuit breaker and AC circuit breaker.
Any further questions please feel free to contact YRO electric: [email protected]