Is rule R56 and the accompanying table 8-3 saying you can have only one “CUSTOM CIRCUIT” on a PDP branch circuit and it has to be a 40A circuit? So for example if I have a raspberry pi and an axis camera, each device has to be connected to its own 40A circuit on the PDP? Since there are only eight 40A circuits on a PDP you’d have only 6 circuits left. Am I reading this right?
Further down the table it lists “Additional VRM” and up to 3 of them can be connected to a 20A circuit, so if I powered the raspberry pi and camera off of one or more VRMs I’d be in compliance with the rule using only one 20A circuit. Is that right?
Thanks for the clarification on the breaker sizes.
I gave some bad examples with the pi and the camera…if I had two 12 volt devices, and each one drew about 4A, is R56 saying I would have to power each of them off their own separate branch circuit and couldn’t run them in parallel off a single 20A circuit?
Yea I had the same reaction to the “single” custom circuit bit.
Seems like an arbitrary line to draw. As you said, what constitutes a single circuit? I could have a coprocessor, a camera, LEDs, a bunch of sensors, etc… In “one” circuit.
If you power them directly from the PDP, then you are correct.
However, you don’t want to do that. Voltage from the PDP is NOT reliable. In brown out conditions (when you are driving the motors hard and they stall - such as in a robot pushing battle), your voltage can dip as low as 7-8 volts.
Thus the purpose of the VRM. It maintains stable 5v and 12v in brownout conditions.
You can power multiple devices off a single VRM, and can attach up to 3 VRMs to a single 20A branch circuit.
My understanding of the rules is that you can put as many devices/components in a “single” CUSTOM CIRCUIT as you desire, provided each and every one of them fits the definition of a CUSTOM CIRCUIT.