Q & A of the day: We have a JCB generator fitted with a Schneider Electric circuit breaker of 1600A.

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Question: We have a JCB generator fitted with a Schneider Electric circuit breaker of 1600A. 

This circuit breaker trips at once and very fast when we load the units to more than 30kW. What is the reason for this problem and do you have any suggestions?

We think that the main reason is in the setting of the circuit breaker. You can see the setting knobs on the attached picture. To see this picture – and that of the genset, please use the links below.

Answer: As you have not provided the trip unit details and settings, and since the details in the attached picture are limited, it is difficult to provide precise information.

However, the NS1600 A circuit breaker with Micrologic 2 or 5 trip, has a long time current setting in the range 640A to 1,600A. Short time settings are in the range Isd = Ir x 1.5 to x10 the long time setting.

The setting must be above the load current and inrush value, but also below the maximum earth fault current determined by the circuit Zs value.

You can gain far more information on Micrologic trip settings by using the third link below (PDF doc – 116kB file size).

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Attachments

• A chart showing Micrologic trip settings (PDF - 116kB).

  © Schneider Electric

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