Square D breaker adjustment

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Volta

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Location
Columbus, Ohio
I'm working in a 480v panel with a 600v, 400a, 3p main breaker. I think it is a LH36400. The AIC at this voltage is 35 kA.

The breaker has an adjustment that I can't figure out. It is a slider, marked min and max in the plastic, with five hash marks. It is now set near the lower end. There is a sticker next to it that says 2000 A at the min and 4000 A at the max.

What is this for? Overcurrent adjustment with a typo? Ability to allow (or disallow) large inrush?:confused:
 
J

jim dungar

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Wisconsin
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PE (Retired) - Power Systems
This is an adjustment for the magnetic trip (instantaneous function) of the breaker. You are correct that the typical reason to make an adjustment is to accommodate inrush currents. The other reason is to coordinate with downstream devices.

My suggestion is to leave this set at the minimum unless you have a very good reason to turn it up. In general, the sooner the breaker trips the lower the arc flash incident energy.
 
zog

zog

Senior Member
Location
Charlotte, NC
Many times the min and max are used to designate delays for LT, ST, and GF. But those current ranges are indeed INST values for this breaker so Jim must have nailed it, I dont work with breakers this small very often so I would need to look that one up.
 
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Volta

Senior Member
Location
Columbus, Ohio
zog said:
Many times the min and max are used to designate delays for LT, ST, and GF.
Click to expand...
Oh, so many things I don't know! Um, Long time, Short time, Ground fault?

Thanks for all the responses. I surely wasn't going to move it, but with the loads I'm adding, I wanted to be sure it was not a simple OC adjusment that would trip at some low setting.
 
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