CH digitrip 520M Short time too fast!

[tem1234]

Hi,

We were testing low Voltage CB with digitrip 520 M trip unit.

The short time delay setting is .5 sec, but when we test it with primary injection, the tripping delay is 60 ms. The flag really show ST trip, not inst. When we test the inst., the delay was 50 ms.

All the 3 breaker tested were the same. We really were in the ST range for current. We tried to change setting, different current, but always the same.

Does anybody experencied the same with this trip unit.

Thanks

 

[tem1234]

Forget my question, i found the answer:

Zone interlocking

 

[Zogzog]

Digitrips will default to the lowest setting, in this case STD. A common failure is dirt in the pots. We repair these often with the same issues.

Or, ZSI can get you.

 

[unclebob]

Sorry for the late post.
520's need a jumper between B8 and B9 secondary terminals to defeat the zone interlock. Without this jumper, the time delay setting is overrided.

 

[alehman]

I've seen problems with misalignment of the ZSI connectors on the DS-II breakers.

Alan
“The engineer's first problem in any design situation is to discover what the problem really is.” Unk.

 

[tem1234]

Thank you for your replies

As i said, i found the solution, and it was as unclebob said.

The jumper was there on the craddle terminal, but when we unracked the breaker for primary injection testing, the breaker wasn't connected anymore to the craddle, so the jumper wasn't there also.

It was the first time we tested this trip unit and i tried to find a quick answer when i was on the field.