Inrush current

Farmelectrics · Aug 9, 2012

Can anyone give me a simple example of inrush current

Bobster · Aug 9, 2012

Motor starting, or is that to brief?

plugsandsparks · Aug 9, 2012

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 · Aug 9, 2012

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 · Aug 9, 2012

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

Knobhead · Aug 9, 2012

The two dials are thermal and magnetic overload settings.

Farmelectrics · Aug 9, 2012

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

Deleted member 26818 · Aug 9, 2012

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 · Aug 9, 2012

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 · Aug 9, 2012

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

plugsandsparks · Aug 10, 2012

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

AS mentioned, could do with a photo of the switch in question. Or the make and model no. Some of the adjustable ones have setting for various Ix, and sometimes time. They allow you to tune the breaker. Some of these breakers may say they are 140/200 amp breakers, with a setting to tune them down from 200 amp. Some have inrush settings which are " XN " i.e. X the setting of the breaker, i.e. X5 maybe in your case. Some also have a time characteristic to shorten or lengthen the tripping times, a bit like an adjustable MCB.
If you think about it, you have to sometimes energise this breaker on load.
They use terms like In, Ir and Im, i have to look them up everytime.
Hope this helps.
The data should be available online, is most of the time.
I am forever reducing Ir as they always appear to be set at max, i.e. 1

Farmelectrics · Aug 10, 2012

Will try today to upload photo how do I get it on to the forumn from my I phone can't remember

plugsandsparks · Aug 10, 2012

Dont have i-phone but on my samsung i connect phone to pc, then i can see all the files from my laptop. I just click image in the reply box and browse to the phone and upload. My laptop uses a programme called Kiers to enable comms to phone.