Creaking MCBs

[Steve]

At work we have a lot of discharge lighting, in the form of 12 metal halide canopy lights and two halide lamp posts. All 250w. The canopy lights are grouped in 3 lots of 4. Now, when any of these circuits are powered on, the mcbs creak as though they want to trip. I have noticed the same when the chiller powers up too. All obviously inductive loads with high startup so i understand the mcbs are under plenty of load on startup, but should a correctly sized mcb creak under high load? They are merlin gerin multi9 in various ratings.

One of the lamp posts does occasionally trip on startup.

Bizarrely, all the lighting above and the fluorescent lighting in the building are on one 30mA RCD. Amazed it never trips.

 

[bhm1712]

I've never heard a creaking MCB.

Why would you think an RCD would trip if there's no fault though?

 

[333rocky333]

seen this before in arcadia stores with highbay lights, 4 - 250w fittings seemed to be the limit on 10 amp breakers , the breakers settled down after about a minute,
these were on 10 amp breakers and some had to be uprated to 16 amp, wiring permitting, sometimes changing from B type to C type overcomes it, if permissable to do so.
Its usually because hi bays and 250watts tend to use magnetic ballasts rather than high frequency

 

[RF Lighting]

I've heard breakers humming when powering large inductive loads.

 

[stillp]

Is the creaking from the breakers, or are the conductors shifting under the magnetic forces from the inrush current?

 

[securespark]

I've heard breakers humming when powering large inductive loads.

Which tune do they hum?

 

[oldbutnotdead]

You might be hearing some arcing- best get a responsible competent etc. person to check all the terminals are tight in the DB.