class of circuit

[lquadros]

1. We typically use 3KVA and above transformers rated 110VAC to 24VDC voltage for all our control circuits. We use regulated power supply to accomplish this. What class of circuit would this be and why?
2. How to determine the circuit loading on these during design? Is there a set demand factor?
(We use these circuits to PLC power, inputs, outputs, Relay coils etc.)
3. What is the allowabe voltage drop to solenoid and other 24VDCloads? Use the manufactureres recommendations or is there any rule to go by?
4. What are the grounding requirements for these circuits? We have positive grounded systems.
Thanks for all your replies in advance.

 

[Ed MacLaren]

Re: class of circuit

lquadros,
You indicated in an earlier thread that you are in Canada. Are you looking for NEC or CEC answers to these questions?

Ed

 

[lquadros]

Re: class of circuit

Ed,
I would like Canadian Electric Code answers. At the same time, any NEC info. can be of help, for crosscheck and to find out if someone can help with explaining the intent of any of these rules that exist on the above subject.

 

[Ed MacLaren]

Re: class of circuit

1. They would be Class 1 extra-low voltage power circuits if the source was rated 1000 va (1kva) or less. 16-100(1)
They would be Class 1 remote control and signal circuits if they did not supply loads, such as solenoids, motorized valves, etc. 16-100(2)
As you've described them, I don't think they are covered by Section 16.

2. There is no rule specific to this. Total the loads, and multiply any that will be in use for more than 1 hour in any 2 hour period by 1.25. 8-104(3)

3. There is no rule specific to this. Voltage drop cannot exceed 3% in any feeder or branch circuit. 8-102

4. DC circuits under 50 volts only have to be grounded if the primary of the supply transformer is over 150 volts-to-ground, or if it is ungrounded. 10-114

Ed