Low Voltage Power Breaker 30 Cycle Rating

[corvalan]

A LVPCB can be set or purchased without INST setting and according to IEEE C37 test, it can hold the short circuit for 30 cycles. What happens after the 30 cycles if the short circuit current is still present? Will the LVPCB open instantaneously, like an override? Or will still remain closed?

 

[Zogzog]

It will eventually trip, when depends on the fault level and the protective device installed on the LVPCB.

 

[Mila15]

The 30 cycle rating means the CB can withstand SC for 30 cycles. If there is no trip setting based on time and current to trip the CB, its contacts can last 30 cycles before they melt closed.

 

[corvalan]

Thanks for the answer.

So that means that there is not an override built (open instantly) in the LVPCB's after the 30 cycles similar to the ICCB's that have a built in override?

Is there any manufacturer literature (from a specific LVPCB) I can read that explains what happens after the 30 cycles?

Thanks.

 

[Hoxton]

I don't know this standard or have access to reAd it, but this is one of those reverse working things.

One could design the device to work with a short circuit for an indefinite period of time. It doesn't matter what the device is, this attitude would make it expensive, large, consume too much of the earths precious resources etc etc.

So clever people who sit on these committees have to decide standard design criteria.

In tHis case, they have decided on a 30 cycle withstand.

This must assume that your prime and backup protection will operate within this time.

So the manufacturers do not have to explain what happens after 30 cycles, that has been established as a design criteria. The world of standardization is full of examples like this.

To give you an example closer to home, your heating / air conditioning will have been designed to maintain a room temperature of say 21C with an external temperature of say -5 C, so your installer does not have to explain what happens if the extErnal temperature falls to -10C. Your rooms will not be at 21C.

Welcome to the weird world of standardization.

 

[dpc]

If no instantaneous, the breaker MUST have a short time trip that will open before 30 cycles, at least in the US. Some breaker/trip units do have an override instantaneous, but this is generally only operates for extremely high levels of fault current.

The 30 cycle rating is at the maximum rated fault current. For lower fault current levels (long-time trip range), obviously the brekaer will not open in 30 cycles.