Relay Panels
Relay Panels
(OP)
I am working on a lighting design involving a relay panel. The fixtures are located 150'-300' away from the relay panel and the source panel. The relay panel is fed from three (3) 20A,1P breakers from a 120/208V,3ph,4w panelboard. There are 6 relays coming out of the relay panel. I am having trouble figuring out how to size the wires from the source panel to the relay panel and then from the relay panel to the lighting fixtures including the voltage drop. I understand that only the hot wire goes to the relay panel. I've added up the loads for each relay and also designated relays to one of the three input circuits. Do I size each individual relay for the load on the relay (taking into account voltage drop)? Do I size each circuit from the source panel for the entire load (all associated relays) and take into account voltage drop? Since the neutral and ground do not go through the relay panel and sized of the entire circuit load, won't these be too large for the associated relay?
Example: circuit number 1 consists of relay r1 r2 and r3. r1=500W, r2=250W, r3=350W. Total load =1100W. So the conductors (H,N &G) from the source panel to the relay panel will be sized for 1100W? On the other side of the relay panel, the hot wire for r1 is sized off of 500W, r2 for 250W and r3 for 350W? Or should the conductors be sized off of 1100W for everything?
I am sorry if my post is confusing, but any help would be much appreciated.
Thanks!
Example:
Example: circuit number 1 consists of relay r1 r2 and r3. r1=500W, r2=250W, r3=350W. Total load =1100W. So the conductors (H,N &G) from the source panel to the relay panel will be sized for 1100W? On the other side of the relay panel, the hot wire for r1 is sized off of 500W, r2 for 250W and r3 for 350W? Or should the conductors be sized off of 1100W for everything?
I am sorry if my post is confusing, but any help would be much appreciated.
Thanks!
Example:





RE: Relay Panels
You need to add up the current needed for one relay circuit.
The chosen relay must be rated for that current or more and for that type of load. Tungsten requires larger relays.
The breaker feeding that relay must be rated to handle that load.
The wire from the breaker to the relay must be sized according to the breaker protecting it.
Then the wire from the relay to the lights must be at least the size protected by the breaker. In reality it must be up-sized because you need to reduce the voltage drop on that long line.
The neutrals need to sized to handle the return current and also be over-sized to reduce the drop.
Of course the grounds SHALL NOT BE BROKEN.
I suggest you find a local electrician to help you out. There are lots of little disasters waiting for you on this project. It would be good to have two sets of eyes on the job.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Relay Panels
You can calculate the voltage drop for each relay controlled branch of the circuit and calculate the voltage drop from the source panel to the relay panel for the total load on the circuit, which will give you a close approximation of the total voltage drop for each leg of the control circuit.
RE: Relay Panels
RE: Relay Panels