Inrush current

[Farmelectrics]

Can anyone give me a simple example of inrush current

 

[Bobster]

Motor starting, or is that to brief?

 

[plugsandsparks]

do you mean with values ?

Typical example are transformers, big inrush until the field gets established.
Often worse than motors size for size and they dont care whether there is any load.

Manufacturers give the data for inrush curves so you can match it to a breaker

 

[Farmelectrics]

No rob what it is a Madrix main switch with different settings on its a 200a switch set at 1 which is 200a but another dial next to it is set at 5 Madrix tech people said this is for your inrush current I'm awaiting an email of them explaining in better detail

 

[plugsandsparks]

would that not be 1000A then ? - sounds about right

 

[Knobhead]

The two dials are thermal and magnetic overload settings.

 

[Farmelectrics]

Plug is that what it would trip at 1000a seems very high to me tony explain a bit more

 

[Deleted member 26818]

In-rush or start up current is the extra current drawn to start certain items of equipment, such as flourescent lights, discharge lighting, DOL motors, welders, etc.
A setting of 5X the overload current seems rather extreme.
I'd expect 1.5X - 2X, hence type C and D MCBs.

 

[Knobhead]

Thermal O/L has a time curve the same as you would find on a domestic MCB.
Magnetic O/L is for short circuit protection. It needs to operate fast in the case of a S/C but must allow the magnetising “inrush” current for inductive loads without tripping. It’s a juggling act between sensitivity to short circuit and the let through for inrush.

Several years back I changed a burnt out 300Hp motor, the company policy was that any replacement had to be a high efficiency motor. High efficiency = higher inrush. First test run (direction check) with no belts on the pulleys, all OK. once the belts were put on, Oh dear, the 400A MCCB tripped immediately on instantaneous O/L. We had to fit a new MCCB that could withstand 8X current.
Final settings were I-th .95, I-in 7X. So I-in = 2800A

 

[Bobster]

As tony has already stated. It sounds like an overload with short circuit protection. Could you upload a photo?