M
Hey guys,
I see a lot 250mA fuses put inline with each Analog 4-20mA I/O. The thing is I don't know why they use 250mA. My thought is if you have 4-20mA loop, the highest continuous current will be 20mA. Per NEC, the fuse size is 125% of continuous current plus 100% of noncontinuous current. So fuse size will be 20mA * 1.25 = 25mA (don't know noncontinuous current).
So where the 250mA fuse came from?
Also related to this topic, I have a client saying they have a standard to have 250mA for inputs (Analog or Digital/PLC relay outputs) and 500mA fuses for outputs (Analog or Digital) and I don't why either. To me Analog Outputs should be the same as Analog Inputs and Digital inputs consume about 10mA which is less than 20mA (10mA * 1.25= 12.5 mA) and Relay output depends on load which might be solenoid with 1-2A consumption.
Can somebody clear my confusion?
Sorry for the long text. that's what happened when you are confused
Mohamad Ashour
I see a lot 250mA fuses put inline with each Analog 4-20mA I/O. The thing is I don't know why they use 250mA. My thought is if you have 4-20mA loop, the highest continuous current will be 20mA. Per NEC, the fuse size is 125% of continuous current plus 100% of noncontinuous current. So fuse size will be 20mA * 1.25 = 25mA (don't know noncontinuous current).
So where the 250mA fuse came from?
Also related to this topic, I have a client saying they have a standard to have 250mA for inputs (Analog or Digital/PLC relay outputs) and 500mA fuses for outputs (Analog or Digital) and I don't why either. To me Analog Outputs should be the same as Analog Inputs and Digital inputs consume about 10mA which is less than 20mA (10mA * 1.25= 12.5 mA) and Relay output depends on load which might be solenoid with 1-2A consumption.
Can somebody clear my confusion?
Sorry for the long text. that's what happened when you are confused
Mohamad Ashour