Can I safely replace a B-Curve breaker with a D-Curve breaker?

[michaelm]

Hello,

I am an American living in Germany. I have some US appliances (120v) that I want to use, so I bought a 5000 Watt step down transformer.

Unfortunately, plugging in the transformer usually trips the breaker. More than 1/2 of the time, but less than 3/4. When the breaker does not trip, nothing I use with the transformer causes the breaker to trip later. My searching tells me this is a symptom of an inrush current problem.

The circuit I am using it on was originally on a 16amp breaker with a B curve. With the B curve breaker, the transformer tripped the breaker 100% of the time. Online advice recommended changing a B curve breaker for a C curve breaker to handle the inrush and indicated that this was safe. So, I replaced the 16 amp B curve breaker with a 16 amp C curve breaker.

Does it sound like this is an inrush current issue, and that installing a D curve breaker might resolve it? Should I be able to safely install a D curve breaker (sticking with 16 amps, of course) on the circuit that originally had a B curve breaker?

If it's not that black and white, what other info would I need to know, in order to determine if it is safe to install a D curve breaker?

Many thanks!

 

[James]

Not sure about German regs
however in the U.K. the thing that might stop you using a D curve breaker is ensuring you get a suitable disconnection time in the event of a fault to earth on that circuit.
you should not change a B to a C and then to a D without ensuring that it will still do its job and disconnect in a suitable time in the event of a fault.

 

[michaelm]

Not sure about German regs
however in the U.K. the thing that might stop you using a D curve breaker is ensuring you get a suitable disconnection time in the event of a fault to earth on that circuit.
you should not change a B to a C and then to a D without ensuring that it will still do its job and disconnect in a suitable time in the event of a fault.

Hi James, thanks for the reply.

I'm not an expert, so please correct if I'm misunderstanding.

I thought that the difference between A,B,C and D curve breakers was the amount of current-out-of-spec that was briefly allowed? I thought that they have time-out-of-spec settings (for equivalent breakers).

So, a replacement D curve should break in just as much time as the B, but it would allow a higher current during that time before breaking.

Happy to be corrected, doubly so if you can point me at some good reading so I can better understand.

 

[James]

B curve 3 to 5 times rated current for a 16A that would be 48 to 80A

D curve 10 to 14 times rated current that would be for a 16A breaker 160 to 224A

you have to consider if the circuit can handle over 200A for a few seconds.