MCB Question

[wreck-it-steve]

In what case would a shunt trip or under voltage accessory be used on the side of an MCB?

Just seen some for Merlin breakers and could not figure out what they would be used for.

 

[JohnW2]

In what case would a shunt trip or under voltage accessory be used on the side of an MCB? ... Just seen some for Merlin breakers and could not figure out what they would be used for.

AIUI ....

The undervoltage one does just what it says - causes the device to trip as a result of undervoltage (including 'no voltage') as well as overcurrent. I imagine that one common reason for using such a device would be to ensure that a manual reset was required after a power loss, which could be an important safety issue when various machines/tool were connected (analogous to an active RCD) ... as well, of course, in any situations in which a low supply voltage could be problematical or dangerous.

A shunt trip is a device which, when supplied with power (which may be AC or DC, and a range of voltages), causes the attached MCB to trip. I think that this is used in conjunction with emergency stop buttons, sensors detecting dangerous states etc. Again, manual resetting of the MCB is required before power is restored.

Kind Regards, John

 

[wreck-it-steve]

so you could put a shunt trip on the side of a single or double pole mcb and use it as a sort of emergency stop that requires manual reset of the breaker?

 

[JohnW2]

so you could put a shunt trip on the side of a single or double pole mcb and use it as a sort of emergency stop that requires manual reset of the breaker?

Exactly. As for whether "you" (or I) could do it is a different matter - my understanding is that, with at least some makes/models of MCBs for which shunt trips are available, they have to be factory-fitted (rather than user-/field-fitted).

Kind Regards, John

 

[wreck-it-steve]

so you could put a shunt trip on the side of a single or double pole mcb and use it as a sort of emergency stop that requires manual reset of the breaker?

Exactly. As for whether "you" (or I) could do it is a different matter - my understanding is that, with at least some makes/models of MCBs for which shunt trips are available, they have to be factory-fitted (rather than user-/field-fitted).

Kind Regards, John

Ahh, there are some available "addons" for Merlin / Schneider breakers

 

[JohnW2]

Ahh, there are some available "addons" for Merlin / Schneider breakers

There are, but (including their typo!) ....

Some circuit breakers allow field installlation of a shunt trip kit, however others require factory installation when the breaker is ordered. Check the specific breaker type for available ac and dc shunt trip voltage ratings and for the method of installation.

Kind Regards, John

 

[333rocky333]

I recall some mcbs had little plastic covered windows in the side, you took the plastic cover bit off and this is where the sort of protruding peg on the accesory poked into the mechanism once clipped on the side.

Early Merlin and Bill, sold rcds that did that, thus making possibly the first ever Rcbo, though it took up 2 modules