MCB Operating Voltage

[Anonymous user]

Hi. 

I'm having a 230v ac / 24v ac Transformer of 2kVA rating.

The secondary side 24v ac is used for hand lamp (Inspection lamp).

Can I use a conventional MCB (the one we use for 230V ac) for 24V ac hand lamp circuit for protection against short circuit. 

Or should I a buy a different MCB

[RHH · Accepted solution]

Hello Seekau,

Our experience with 24Vac is mostly with 24Vac relais behind an transformer (most commonly 160VA).
So in this instance much smaller in comparisson.

To protect the relais (24Vac side) we use a small glass fuse.

Perhaps you could use the same thing but then in a bigger format.

The 230Vac side can be protected by a normal MCB, like a iDPNN or any other product.

Hope this is of any help to you.

[Anonymous user]

Hi @RHH 

Thank you for the answer. Very useful. 

My doubt is that whether an MCB (example Acti 9 XC60, C2 rated i.e., 2 amp) used in 230V ac will work in 24V ac circuit also when installed?

or

In simple terms, are MCBs voltage dependent or only current matters as long as the voltage is not exceeding rated operating voltage?

[RHH · Accepted solution]

Hey @Anonymous user ,

Thats a very good question, I think I can't fully answer that. Maybe a product manager of Schneider can.

However I can tell that; 

breaking capacity

6000 A Icn at 230 V AC 50/60 Hz conforming to EN/IEC 60898-1

for instance

breakers have been tested on 230 Vac at 50/60 Hz to have several guarantee's on capacities the breaker has.

Also it does say in the complementary of the breakers; 

[Ue] rated operational voltage

230 V AC 50/60 Hz between phase and neutral

This is vague and it doesn't tell it doesn't work with 24Vac, but it does give the information that its not tested/designed for 24Vac.

I suggest using a (small) fuse as well to protect the 24Vac side.

[Gregoire_Brun]

Hello Seekau

For mccb side, we test them between 110 V to 690 V on AC curent.

As I know and after discussion with some other experts, voltage effect is to increase energy during short circuit and difficulties to cut the arc, so with 24V AC, any troubles to cut the current, just needed to choose the righ rating.

[J_Travostino]

Thanks @Gregoire_Brun  for your contribution.

However, do you think it would be the same situation for MCB (vs. MCCB)?

[Gregoire_Brun]

Yes I think so, product achitecture is quit similar