Make-Before-Break

Make-Before-Break (MBB) is a term “Denoting a switch or other device in which a new electrical connection is made before the existing one is broken”. In short, it simply means, shorting the circuit before disconnecting it.

You may know about MBB when purchasing a relay. But do you know there are terminal blocks designed with MBB in mind too? These MBB terminal blocks can usually be found in power industry applications.

For those who are familiar, you may have come across this term (MBB) during a Current Transformer (CT) testing on a protection relay. However, do you know the importance of ensuring MBB when conducting a CT test with your Terminal? Or what the consequences will be of not having a terminal blocks that comes with a MBB feature during the test?

A CT will certainly be at risk of being destroyed or even worse (Explosion!) if the secondary is left open circuit while the primary current is present. This is due to the insulation failing from the “higher than rated” voltage that occurs. Therefore it is extremely important to ensure MBB before conducting a live testing. A good terminal block with MBB feature will definitely help you provide the extra mile in ensuring safety.

How does the MBB terminal blocks function and what does it look like?  Here are some good examples of a good MBB terminal block.

1. A good MBB terminal block must have the feature where shorting is always present first before you are able to break the circuit. It would be best if the terminal blocks are able to automatically perform the short circuit for you whenever it is being disconnected during the CT test.
   
2. Clear indication of Short Circuit and disconnection must be visible and this allows your engineers to have an ease of mind during testing.
   
3. Good MBB terminal blocks should have safe and easy to operate features. Having said that, these features can help to cut short the time while testing (shorten the risk) and ensuring the safety of the person that is conducting the CT test.
   

So where can you find good MBB terminal blocks for your applications? Phoenix Contact, of course!

With 94 years of experience manufacturing and designing terminal blocks for the Power Industry. Phoenix Contact has never stopped developing new innovative testing terminal blocks that will suits your application, at the same time ensuring safety and quality.

For more info, check out this video of our PTME terminal blocks or visit our website!

If you have more inquiries, feel free to contact us at marketing@phoenixcontact.com.sg and we will get back to you as soon as possible.