Connecting 2 different wire sizes

Status
Not open for further replies.
S

sergiyny

Member
Location
Brooklyn, NY
I have (2) 100 amp, 3ph, 480V outlets installed in floor. From each outlet there is 1" conduit concrete encased running to each it's own junction box. Those 1" conduits can take only 3#3 awg wires. The panelboard from which (2) 100 amp outlets will be powered, it is 400 ft away. Because of the voltage drop I need to go with bigger wire size, in this case its 2/0 and it cannot be installed in 1" conduit. Now here is my question, I want to install 2" conduit and run 3#2/0 in it to the junction box and from there I need to go with 1" conduit and 3#3. Can I connect #3 and #2/0 together? If it's not allowed, what are my other options?
 
sergiyny said:
I have (2) 100 amp, 3ph, 480V outlets installed in floor. From each outlet there is 1" conduit concrete encased running to each it's own junction box. Those 1" conduits can take only 3#3 awg wires. The panelboard from which (2) 100 amp outlets will be powered, it is 400 ft away. Because of the voltage drop I need to go with bigger wire size, in this case its 2/0 and it cannot be installed in 1" conduit. Now here is my question, I want to install 2" conduit and run 3#2/0 in it to the junction box and from there I need to go with 1" conduit and 3#3. Can I connect #3 and #2/0 together? If it's not allowed, what are my other options?
Click to expand...

It is allowed, but you may have a problem finding a crimped butt splice rated for that size difference. Other options include split bolts and Polaris terminals.
 
jumper said:
Am I gonna look like a moron for asking why this would be a factor?

Pretty common to have one welder using one of two receptacles, convenient locations.
Click to expand...

No. The reason I ask is that welders can use OCPD much higher than wire size and that duty cycle would have a fair amount of impact on wire size. In other words, does he have an actual 100A load at the receptacle?. OP asked if he had any other options; using #2 CU (Still can get 3 in a 1" conduit, using conduit as EGC) back to the panel may be viable.

Using this calculator:

http://www.encorewire.com/wp-content/uploads/Voltage_Drop.html

and the values 480V, Copper, 3ph, 400', and 100A, I get #2 wire is needed.

Southwire's calculator is not working at the moment as it isnt correctly figuring inputted allowable voltage drop. Using the same specs there I get #1 wire, but at 2.15% VD. I dont see why #2 Cu wouldnt work for his application.
 
Status
Not open for further replies.
Top