4160V MV-90 Conductor size

4160 is way to dangerous to be played with. Get a pro...

There are seemingly more questions on cable sizing in this section than any other topic!

At what point does British Standard 7671 become 'standing orders'?

Hello kplee4 : Assuming that the 600hp approx = 600kva, I = 83 amp. The minimum conductor size would be 83 amp x 125% = 104 amp or 3cond # 2awg 5kv cable.

volt drop(v.d.) = I x Z ... v.d. = 83 amp x ( 0.19416 ohms/1000ft ) x 600ft = 9.7 volts . Therefore, negligible.

Thank you Brudo, will I size conduit the same as 480V?

Hi Kplee4 : No ! The 4160 V ( 5 KV class ) cable has a much bigger diameter ( because of the insulation, guess about 8 times bigger). So you have to get diameter of cable from a manufacturer ; the next most important data is the type of cable--- I'm assuming that you will be using one cable with 3 conductors ? the next most important data is deciding whether to have a 5 KV cable with a Shield or without ? This depends on your system/client/reliability needs; a cable with a shield is better if your conduit is nonmettalic; if the conduit is metallic, then you don't have to have a shield. Why all this? because it affects the diameter a little bit. ( a shield provides reduced voltage stress on the cable insulation ) . So, once you have the diameter of the cable, you calculate the conduit size by using a maximum conduit fill of 40% of the cross-sectional area of the conduit.

Thanks again for your detail and information, appreciated. I wanted to use the MV-90 refer to NEC 2008, table 310.73, my issue is that I can not find the sq. in or Dia. data on these type of conductor in the Ugly or NEC. Will some one direct me to the right location please. Your response appreciated very much.

Hello KPLEE4 : My source is Okonite.com ; I would select three single conductors ( instead of three conductors in one cable, for pulling into a conduit ) ; this is specified as " 3-1/c #2awg Copper"; from Okonite's list of cables , I would pick the following : Okoguard Type MV-105 / shielded 5 KV . The diameter of one conductor is 0.80 inches, so three conductors = 2.40 inches. Cross-section of three cond = 1.51 in. sq. ; cross-section of 3 inch conduit = 7 in.sq. x 40 % = 2.8 in.sq. So, a 3 inch conduit is okay, especially if you have a couple of bends in it.

Thank you, you are the best, have a good day.

Hello Ovide Brudo, I need to ask you about (ground or neutral) conductor, should I pull (1) 1/0 awg (MV-105/ 5KV conductor) per phase alone with the other cable per conduit or (1) 1/0 in a seperate conduit? This is the service from 4160V 2500KVA Xfr to 4160 MCC (A.B). Thank you, your advise appreciated.

Hi KPLEE4 : 1st : Does this Xfr feed only this MCC ? 2nd : Is your Xfr a "wye -grounded neutral" secondary ? 3rd : Does the MCC have or will have any single phase loads ( 2400 V to Neut ) ?

Thanks for your inputs, this is what I have: This Xrf feed only this 4160 MCC, the Xfr Wye-grounded neutral secondary and the MCC will service to (2) 600 hp motors. What I don't understand is the grounding neutral conductor, do I need to pull (1) 1/0 per phase or ?? Thank you, your advise are very important to me and appreciated.

KPLEE4 : I'm assuming that the main circuit breaker for the Xfr secondary ( probably a 600 or 800amp frame with a 450 amp trip @ 4160V ) is in the MCC?! Therefore, you should bring the neutral from the Xfr to the MCC. Since you don't need it for any loads, it can be 1/3 the capacity of the phase conductors. The phase conductors need to be a minimum of 125% of Ifl ( amps Xfr secondary at full load) or 125% x 347amp = 434amp minimum; I would suggest two parallel feeders, each in a conduit, containing 3 - 1/c # 250 kcm( this is about 500amps total) or # 4/0 ( about 460amp total). The neutral conductor has to be in each of the two conduits, so your suggestion of a #1/0 is okay, as long as there is one for each conduit! As for a ground equipment conductor, it could be the conduit , if it is metallic; but if not , then add a bare stranded copper conductor, in each conduit; it can be a #1.

Thank you, due to the distance, this is what I'm consider using: (2) 4/0 per phase and (1) 1/0 per phase for neutral in (1) 3" conduit. I'm spec. out the MV-90 nonshielded power cable and the distance aprox. 150+ feet. Will this be fine, thank you very much I feel better after reading your inputs and have a good day.

KPLEE4 : Yes, that will be fine; I noticed that you have decided to spec 5KV unshielded cable; are you comfortable with that? are you using metal conduit?are you limited by budget? Well, it's good to talk to you and let me know where you're located; I'm in Canada.

Ovide Brudo: Thanks, I used to live in Michigan and been to Canada so many time, as now I move to Oklahoma. Yes I am limited in budget, also these medium voltage are new to me that's why I'm not confortable with size cable..etc, appreciated