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If ther are more than conductors in the raceway the ampacity of the conductors must be derated?
Wiki User
∙ 14y ago
Ampacity must be derated depending on the number of conductors and the ambient temperature. In the Canadian Electrical Code Table 5C denotes derating for the number of conductors.
1-3 conductors = 100% load
4-6 conductors = 80%
7-24 conductors = 70%
25-42 conductors = 60%
43 or more conductors = 50%
Wiki User
∙ 14y ago
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How can we calculate cable size for 800A breaker?
Wire sizing is based on the load that the conductors carry. The breaker is then sized to protect the wire. To get to an amperage the wires are going to have to be paralleled. The calculations are already sized in the electrical code books, CEC and NEC. These are code books used by North America electricians. A 500 MCM conductor with an insulation factor of 90 degrees C is rated at 430 amps. Four 500 MCM conductors paralleled will give you an ampacity of 1720 amps. The breaker will need to have a 500 MCM 4 barrel lug to receive the conductors. The same thing with the load end, it will also need a four barrel 500 MCM lug.
What is the current carrying capacity of a 18 awg stranded wire rated to 105 deg c 600 volts with PVC insulation?
The 2005 NEC allows 14 amps for 18 AWG wire in conduit, 18 amps in free air. Solid or stranded does not matter. There is no table that allows more current with higher insulation temperature rating. These values are good only up to 86 deg F ambient temperature, and must be derated according to table 310.16 or 310.17 if the ambient temp is above 86. You must also derate for more than 3 conductors in a raceway. I have not seen a PVC insulated wire rated to 105C. Is there such a thing?
What is zip cord?
Zip cord is a type of plastic insulated wire having 2 or more conductors. These conductors can be easily separated by manually "unzipping" the cord along a molded indentation between conductors. Zip cord with a large number of conductors is usually called ribbon cable.
How to reduce tower footing resistance?
1. Use of short length radial conductors bonded at the injection point. rather than a single long length conductor. This produces the effect of having a number of conductors in parallel. 2. Terminating radial conductors with vertical electrodes. This measure is more effective in low to medium soil resistivity. 3. Using large bending radii when changing the direction of horizontal conductors. Sharp bends tend to increase the inductance. 4. The use of earth enhancing compounds to improve the soil resistivity in the proximity of the conductors which will reduce the tower footing resistance
How long does it take to splice a cable?
It depends on how many wires are in the cable. The more conductors in the cable set the longer it will take to splice them.
You have 3 sets of conduits with 6 500MCM conductors in each one what is your ampacity?
The ampacity of 500 MCM R 90 degree wire is 395 amps. Don't forget to de-rate the wire as there are more that three conductors in a raceway.
Five 8 aluminum conductors with THHN insulation are to be routed through a conduit found in a boiler room with an ambient temperature of 75 degree C. What would be the ampacity of each conductor?
#8 aluminum thhn 90 degree wire is rated at 30 amps. Remember to de-rate the wire for more that three conductors in a raceway and the second de-rate for the ambient temperature. Most students miss the de-rate for more that three conductors in a raceway.
How can you know cable size for a given current?
NEC code book table 310.15. Find the current you want to send through the conductor, look up which size conductor can handle that amperage. If you are pulling more than three current carrying conductors (hots and neutrals) in the same pipe you need to derate the listed ampacity of the wire. The percentages that you derate to are listed a couple pages before in the code. 4-6 current carrying conductors in the same raceway i believe is derated to 80% and i can't remember right off the top of my head the others.
Do you derate for a three phase line and load conductors in the same conduit?
Yes, there will be a de-rate applied to this type of installation. In the electrical code book the amperage rating of conductors is for allowable ampacities for not more than three copperconductors in raceway or cable. This is based on an ambient temperature of 30 degrees C. If the ambient temperature of the conductors where the raceway is installed is over 30 degrees C the conductor amperages have to be reduced. Where the number of conductors are from 4 to 6 conductors in a raceway, the conductors amperage has to be reduced by .8
How do you determine the number of conductors per phase?
The number of conductors is simply the service amperage divided by the desired wire size's ampacity rounded up if there is a remainder. Example: 1000A service, using 300kcmil conductors at 75 deg C: 300kcmil ampacity in this situation is 285. 1000/285=3.5 Since you can't have 3.5 conductors, you must round up to 4. This would give you a total ampacity of 285A x 4, or 1140A. If you're rounding farther than necessary, such as in this case, you can try using the next smallest conductor and adding another set to closer match your required ampacity. 250kcmil ampacity is 255. 1000/255=3.92 We will also round this up to 4, but we aren't rounding as far as the earlier example. The total ampacity is now 1020. 250kcmil x 4 sets is probably the best arrangement for this 1000A service. You could use larger wire and fewer sets, but smaller wire is more cost effective for both ampacity per pound and labor costs for installation.
DoesCode permit connecting receptacles to a 20ampere branch circuit using short lengths of 14AWG conductors as the pigtail between the receptacle terminals and the 12AWG branch-circuit conductors?
No. This practice is a violation of Article 210.19 (A) of the NEC. "Conductors of branch circuits supplying more than one receptacle for cord-and-plug-connected portable loads shall have an ampacity of not less than the rating of the branch circuit."
Can a three phase circuit be installed in the same conduit or in different conduits?
The conductors of any three phase circuit must be run in the same conduit. If the circuit requires a neutral, it must also run with the conductors in the same conduit. (If they were to be run in more than one conduit or raceway, the circuit would not operate properly.)
How can we calculate cable size for 800A breaker?
Wire sizing is based on the load that the conductors carry. The breaker is then sized to protect the wire. To get to an amperage the wires are going to have to be paralleled. The calculations are already sized in the electrical code books, CEC and NEC. These are code books used by North America electricians. A 500 MCM conductor with an insulation factor of 90 degrees C is rated at 430 amps. Four 500 MCM conductors paralleled will give you an ampacity of 1720 amps. The breaker will need to have a 500 MCM 4 barrel lug to receive the conductors. The same thing with the load end, it will also need a four barrel 500 MCM lug.
What is the current carrying capacity of a 18 awg stranded wire rated to 105 deg c 600 volts with PVC insulation?
The 2005 NEC allows 14 amps for 18 AWG wire in conduit, 18 amps in free air. Solid or stranded does not matter. There is no table that allows more current with higher insulation temperature rating. These values are good only up to 86 deg F ambient temperature, and must be derated according to table 310.16 or 310.17 if the ambient temp is above 86. You must also derate for more than 3 conductors in a raceway. I have not seen a PVC insulated wire rated to 105C. Is there such a thing?
Where is Yonkers Raceway located?
Tonkers Raceway is located near the town of Yonkers in New York. You can find more information by visiting the Yonkers official website online, where an agent will help you.
What is the purpose of a tone generator and tone probe?
They are used to trace wiring. There may be multiple conductors in a bundle that are unmarked, or perhaps unmarked wires that go to different locations. The tone generator is connected to a pair of conductors (or one conductor and ground), and the probe is used to find the same conductor on the opposite end. The probe is used to look for the conductor that is carrying the tone. In a bundle of conductors, or several conductors in a raceway, the tone may be induced, or "bleed" into other conductors. In this case, the desired wire has the strongest tone. Connecting the generator to one conductor and ground tends to induce the signal into other conductors. Toning a pair, with neither one grounded, is the most selective, making identification more sure.
WHY STRANDED CONDUCTERS ARE USED IN POWER CABLES?
Stranded conductors are more flexible than solid conductors.
