When to use parallel runs.

[Lifetimelearner]

Hello All:

I am designing a retrofit for distribution system and am currently selecting the cable sizes for the schedule.
I do not have a code question but would like your input as electricians/engineers.

What size of cables do you generally start specifying parallel runs?

Context:
-I have a need for a cable run with a rating of 250A
-My options are
1) 3 Phase + Neutral of 250 kcmil (75°C) in a conduit (255A rated)
2) 2 Parallel runs of 1 AWG (75°C) for each 3 Phase + Neutral in two conduits (260A rated)

What is the wire size cutoff that you find too hard to pull 4 conductors in commercial situations?

Cheers!

 

[luckylerado]

Parallel conductors must be 1/0 or larger. 310.10(H)(1). Depending on the length 250s are not terribly difficult to pull in a properly sized conduit.


Edit. Sorry, I just noticed you are North of the Border. IDK how it works in Canada

 

[310 BLAZE IT]

You see ampacity diminishing returns after 750kcmil and pulling becomes difficult to impossible depending on the existence of bends after 500kcmil

Cannot paralell les than 1/0 like said above

 

[iwire]

You see ampacity diminishing returns after 750kcmil and pulling becomes difficult to impossible depending on the existence of bends after 500kcmil

Cannot paralell les than 1/0 like said above

If we are talking copper I would put it about 500 kcmil before I parrelel.

 

[luckylerado]

Parallel conductors must be 1/0 or larger. 310.10(H)(1)

Same for you folks in Canada

12-108

 

[electrofelon]

Hello All:

I am designing a retrofit for distribution system and am currently selecting the cable sizes for the schedule.
I do not have a code question but would like your input as electricians/engineers.

What size of cables do you generally start specifying parallel runs?

Context:
-I have a need for a cable run with a rating of 250A
-My options are
1) 3 Phase + Neutral of 250 kcmil (75°C) in a conduit (255A rated)
2) 2 Parallel runs of 1 AWG (75°C) for each 3 Phase + Neutral in two conduits (260A rated)

What is the wire size cutoff that you find too hard to pull 4 conductors in commercial situations?

Cheers!

Without getting into the copper aluminum debate, with the type of work I do, I am nearly always the decider on the type and size of wire and I use aluminum so my answer is based on that. For copper I may be inclined to go parallel sooner. Probably around/over 500 is when I would think about parallel. Multiples of 500 are good for 1200 amp services. For 600 amps, you could use 3 250's or 2 500's, but with 600 amp equipment you often find you only get 2 lugs per phase.

 

[Lifetimelearner]

Thanks for all your responses, you are all beauts!

Go parallel at or around 500kcmil is the general consensus.

Cheers
LL