MCB's Tripping more often than not

[shieldssecurity]

Hi,

I wonder if you can help.

I've got 3 rows of 6 400watt metal halide fittings

They are wired in lots of 3 using 1.5 singles and go back to 3 contactors which are controlled with a timer.

Each row is on its own 16amp MCB

When the timer kicks in sometimes one of the MCB's will trip. this happens quite a bit and its not any MCB in particular.

Anyone shed some light on this problem

Thanks

 

[matt.leung]

are they on a 'B' type MCB? if so i would upgrade it to a 'C' type due to the high start up current...

 

[PC Electrics]

In rush current at start up.

Is the mcb a B type? If so change to C type if Zs is okay.

Your in rush current spike is obviously just touching the trip curve of the mcb, so sometimes it trips sometimes not. IIRC the derating factor for this type of lighting is 70% - you're just on that. Would have been better to put 5 (or even 4) lights per MCB or else use 20A MCBs (which would have required 2.5 cable).

 

[Apache]

I was talking ballcocks, ignore me...............

 

[Evans Electric]

Almost certainly due to inrush current , use type C .

 

[Evans Electric]

Patch , you are talking ballcocks No offence infered need I say. I'd say it was the opposite as MCBs are thermal and magnetic. Could be problematical in a hot boiler room . Had a job this summer , rows of lighting started to trip in the afternoons, place was baking hot . Lighting MCBs were in an enclosure with a contactor, three of them , 10A , always the middle one. Moved them apart on the dinrail ,problem solved.

Deke

 

[Apache]

Patch , you are talking ballcocks I'd say it was the opposite as MCBs are thermal and magnetic. Could be problematical in a hot boiler room . Had a job this summer , rows of lighting started to trip in the afternoons, place was baking hot . Lighting MCBs were in an enclosure with a contactor, three of them , 10A , always the middle one. Moved them apart on the dinrail ,problem solved.

ah - temperature sensitive. Is it fuses (plug top type) that are more likely to blow when cold?

 

[Evans Electric]

Not that I know of, Patch. Not sure where you are thinking of. Fluorescent tubes didn't like striking in the cold years ago , used to have a thin metal strip along them to assist striking.

I don't like getting out of bed on cold mornings.

 

[Andy™]

ah - temperature sensitive. Is it fuses (plug top type) that are more likely to blow when cold?

no. they work by melting, the the hotter they are before loading, the more likely they are to melt

 

[kme]

However, if they`re running close to tolerance, the filament can become "stressed" when repeatedly asked to rapidly heat up from a very cold state, so I would tend to follow `pache`s argument here - I`m sure I`ve heard of it before.

Similar issue with the HT fuses on magnetrons (microwave). They tend to "wear out" and need replacing; not due to a fault, simply the regular instantaneous pulsing nature of the mag supply.