derating for voltage drop

[georgeswe]

So I have multiple panels feeding line power to feed line contacts in a Musco lighting panel. The guy actually installing the lighting and connecting to the load side of the musco panel is supposed to install #4 wire to his fixtures. My question is since Im feeding the module in the musco panel with a 20 amp circuit breaker, do I have to install #4 from my 20 amp breaker to the line side of the lighting control panel. This whole question is compounded by the fact that I have to create all of my wire since I'm running all wire thru a gutter with over 30 conductors. The way it stands if I had to derate for Voltage drop and on top of having to derate the gutter my 20 amp load would have to be fed with a 3/0 wire while in the gutter. If I didn't have to derate for voltage drop my wire size would be #6. The panel to the lighting panel is about 25' feet apart.

 

[GoldDigger]

Is the #4 required because it is low voltage lighting? Or incredibly long wire runs?
Either way you size your conductors based on the input voltage and current to the panel.

Tapatalk!

 

[Smart $]

Will the derating for over 30 conductors in the gutter be because your wires will put it over 30 or because there are already over 30 in the gutter?

If your wires take the count to over 30, not just your added conductors need to be derated, but all the other conductors have to be derated where there are over 30 at any cross section.

May be more prudent to run your conductors in a separate raceway.

 

[GoldDigger]

29 conductors in each of two gutters is a lot more forgiving than 58 in one.
And if you are already oversizing for voltage drop derating may not hurt you at all.

Tapatalk!

 

[kingpb]

You do not have to derate a derated value, if that makes sense. You also get to start with the 90 deg C column as well. The final ampacity just can't be greater than the 75 deg C ampacity after the derating is done.

Step 1: What size conductor do you need for your current carrying capacity based on the number of conductors in the raceway? (Start with 90 deg C column)

Step 2: Is the derated ampacity of the cable less than or equal to the rated ampacity listed in the 75 deg C Column? If so, go to Step 3, if greater than you have to jump up one size.

Step 3: With the cable selected for current based on Step 1 and 2, perform VD calc. If the VD is reasonable, you are done, if it is too high, than select larger cable. No need to go back to Step 1 and 2 since the current in the cable did not change.

 

[GoldDigger]

And if you have only 25' of wire in your input or output circuit, there may be no need for you to upsize for VD just because a longer run of wire in the same lighting system needs VD adjustment.