Hi Guys,
I'm doing my Level 3 C&G design project and just have a few design related queries which i am so far struggling to find clarity on either in the text books/guides or online.
- Main issue is circuit lengths for lighting for calculation volt drop and ZS:
With power its seemingly quite simple, Just the length of line to the end of the for a radial, and the entire length of the line from out and back into the DB for a ring.
However, for lighting circuits, I'm a bit unsure what is measured to determine the maximum length, especially when 2 way and 2 way + intermediate switches are used.
Would you include the entire potential maximum length of the line through the strappers? Some of the floor areas in question are quite large so with switches on opposite ends of the room, you are talking a potential length of 20m+ between just between switches (making it 40m there are back for a 2 way and intermediate). So would you add that length to the furthest point in the circuit?
So for example, you have a bank of lights all controlled by one 2 way + int switching set up and that is all that is on the circuit. Would you therefore say the circuit length (for purposes of the voltage drop calculation) is the entire run from the DB, through to the furthest switch and back and then all the way to the last/furthest away light on the circuit?
Or would you only need to combine the length to the last light + one way length to the furthest switch, because as I understand it, the voltage drop figures given in the OSG table take into account an equally sized return/neutral (so already account for a "there and back" as such)? If that is the case though, would I not need to calculate/give a different length for R1 + R2 (taking into account the whole potential maximum length of the line conductor (including through the switching) to the load)?
-Second issue/query:
The brief says power must be provided to a 13A unswitched fused connection unit for a fire repeater panel. There is no further explanation or express criteria beyond that.
My first instinct was to put it on its own circuit to satisfy the regs requirement for fire safety circuits to not be affected by a fault on another circuit, but i'm not completely sure RE the best way to go about it. Would it just be a simple radial to the FCU and due to it being a 13A fuse, would i use the next rating up for the In of the CB (, so 16 Amps)?
Doing this feels a bit odd though to me but I'm not sure how else to do it, beyond having the FCU as part of one of the ring socket circuits. However, if i did that then, a fault on that circuit would take out the fire repeater panel which i assume would not be satisfactory.
Thanks in advance for any help you can contribute. I have tried to seek clarity on these two points, but i have struggled to get a definitive answer from anywhere.
I'm doing my Level 3 C&G design project and just have a few design related queries which i am so far struggling to find clarity on either in the text books/guides or online.
- Main issue is circuit lengths for lighting for calculation volt drop and ZS:
With power its seemingly quite simple, Just the length of line to the end of the for a radial, and the entire length of the line from out and back into the DB for a ring.
However, for lighting circuits, I'm a bit unsure what is measured to determine the maximum length, especially when 2 way and 2 way + intermediate switches are used.
Would you include the entire potential maximum length of the line through the strappers? Some of the floor areas in question are quite large so with switches on opposite ends of the room, you are talking a potential length of 20m+ between just between switches (making it 40m there are back for a 2 way and intermediate). So would you add that length to the furthest point in the circuit?
So for example, you have a bank of lights all controlled by one 2 way + int switching set up and that is all that is on the circuit. Would you therefore say the circuit length (for purposes of the voltage drop calculation) is the entire run from the DB, through to the furthest switch and back and then all the way to the last/furthest away light on the circuit?
Or would you only need to combine the length to the last light + one way length to the furthest switch, because as I understand it, the voltage drop figures given in the OSG table take into account an equally sized return/neutral (so already account for a "there and back" as such)? If that is the case though, would I not need to calculate/give a different length for R1 + R2 (taking into account the whole potential maximum length of the line conductor (including through the switching) to the load)?
-Second issue/query:
The brief says power must be provided to a 13A unswitched fused connection unit for a fire repeater panel. There is no further explanation or express criteria beyond that.
My first instinct was to put it on its own circuit to satisfy the regs requirement for fire safety circuits to not be affected by a fault on another circuit, but i'm not completely sure RE the best way to go about it. Would it just be a simple radial to the FCU and due to it being a 13A fuse, would i use the next rating up for the In of the CB (, so 16 Amps)?
Doing this feels a bit odd though to me but I'm not sure how else to do it, beyond having the FCU as part of one of the ring socket circuits. However, if i did that then, a fault on that circuit would take out the fire repeater panel which i assume would not be satisfactory.
Thanks in advance for any help you can contribute. I have tried to seek clarity on these two points, but i have struggled to get a definitive answer from anywhere.
- TL;DR
- How do you measure the max circuit length of a lighting circuit with 2 way or 2 way + int switches for the purposes of Volt drop/ZS + how do you wire up a FCU for a fire repeater panel
