Loop current

What is the method for calculating loop current? Say the per loop current limit for Fire Alarm panel is 400mA.
Now of total stand by current for smoke, heat and multi detectors are 5 micro ampere and Alarm current is 5 mA. Input and output module alarm current is 1 mA. 100 Smoke detectors are connected along with 15 modules per loop.
Now my question is, how do I calculate the loop current?
If I consider only stand by current the max loop current limit doesn’t exceed. But the alarm current is calcuated then the loop cilurrent limit exceeds very easily. Please guide me in this regard.

Moved to Fire Alarm Help

Why would you need the loop current? Most addressable panels already have specific guidelines with regards to how many devices you can have on one loop. For example, a Kidde VS4, its 250 Addressable devices per loop. Modules controlling conventional heats or smokes already need 24VDC power along with the SLC loop. There is no way to overload a loop because you can only add a certain amount of devices.

It’s not like a conventional circuit where you need a different wire per zone and can only go a certain amount of feet, and can only add a certain amount of devices. An SLC loop can cover many, many floors with just 2 wires. Most highrises I do usually have around 4 loops total. Of course you need additional devices like Isolators and such, but it is far more efficient. I notice almost all new builds I see are all addressable systems now, I rarely see a new conventional system being installed anywhere. Even with retrofits, you are basically using an SLC loop to control monitor modules for zones instead of having phsyical zones on the FACP panel.

You are correct on the VS4 for conventional smoke but when you use 2 wire smoke on a siga-um your device capability drops this is where your current comes into play there are also other type of module that range in current that will effect the loop it is always wise to keep track of your current on all circuits.

True, but if using a SIGA-UM with smokes, you would automatically need a SMK module, which provides power and current to the smokes so that the loop doesn’t have to. The SMK is powered by auxillary power from the FACP. I guess that’s where I’m getting confused.

To my understanding, all the loop is doing is talking to each addressable device. When it comes to modules that need extra power, like a UM module with 2 wire smokes, you always need another source of power, and that’s where the SMK comes into play. Or if you have an RZI board and have 2 wire smokes on the circuits, same deal. The power is usually taken from the auxillary power on the FACP, which is where you take your amperage into play.