- Location
- Massachusetts
Re: sercvice conductor size
I still suggest you take a look at Georges link it may help you out.
OK
I still suggest you take a look at Georges link it may help you out.
sercvice conductor size
- Thread starter tim
- Start date
- Status
Minuteman
Senior Member
- Location
- The Sooner Nation
Re: sercvice conductor size
If the 75* column is used in 310.16 than use 600kcmil = 420amps. So the parallel 3" GRC would handle the 600kcmil as well.
BTW thanks George, I will print that out and read it later today. Perhaps whilst upon the throne.
If the 75* column is used in 310.16 than use 600kcmil = 420amps. So the parallel 3" GRC would handle the 600kcmil as well.
BTW thanks George, I will print that out and read it later today. Perhaps whilst upon the throne.
- Location
- Massachusetts
Re: sercvice conductor size
310.16, 500 CU @ 75C = 380 amps x 2 = 760 amps.
240.4(B)
I agree he can do that, but it is likely he can use the 500 and save some money if the load is less than 760 amps.
310.16, 500 CU @ 75C = 380 amps x 2 = 760 amps.
240.4(B)
A great place to do important reading.Originally posted by Minuteman:
I will print that out and read it later today. Perhaps whilst upon the throne.
- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
Re: sercvice conductor size
Is it too early for me to be doing math, or could be use parallel 350 AL, 700 amp fuses, and be fine?
- Location
- Massachusetts
Re: sercvice conductor size
I think you misread 310.16 as two sets of 350 AL at best results in a total ampacity of 500 amps.
In AL you would need two sets of 600 kcmil minimum for the 625 amps of load.
Going back to copper two sets of 400 CU would provide a capacity of 670 amps and could be fused at 700 amps.
George I know you are not using Table 310.15(B)(6) as an ampacity chart right?
I think you misread 310.16 as two sets of 350 AL at best results in a total ampacity of 500 amps.
In AL you would need two sets of 600 kcmil minimum for the 625 amps of load.
Going back to copper two sets of 400 CU would provide a capacity of 670 amps and could be fused at 700 amps.
- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
Re: sercvice conductor size
I mistakenly typed 350, I meant 250.
My wife was rushing me off, I goofed. I also didn't have time to show my math.
I've got 205 amps on 250 MCM AL per 310.16.
I've got 6 conductors per pipe (4 hot, 2 neu).
I've got 2 conduits.
205 x 4 = 820 amps
I've got to derate that:
205 x .8 = 164 amps per ungrounded conductor
164 x 4 = 656 amps
700 amp fuse.
I mistakenly typed 350, I meant 250.
My wife was rushing me off, I goofed. I also didn't have time to show my math.
I've got 205 amps on 250 MCM AL per 310.16.
I've got 6 conductors per pipe (4 hot, 2 neu).
I've got 2 conduits.
205 x 4 = 820 amps
I've got to derate that:
205 x .8 = 164 amps per ungrounded conductor
164 x 4 = 656 amps
700 amp fuse.
- Location
- Massachusetts
Re: sercvice conductor size
Ah, that makes more sense.
I mistakenly assumed you meant two sets not four sets.
Ah, that makes more sense.
I mistakenly assumed you meant two sets not four sets.
- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
Re: sercvice conductor size
But actually, he'd be over on pipe fill unless he used a smaller neutral in each parallel run.
If all the conductors were the same size, in 2.5" RMC, then his only option would be 3/0 CU, which would squeak into the fill tables and give him 640 amps to use.
edit to correct "640" - typed from memory
[ January 05, 2006, 08:45 AM: Message edited by: georgestolz ]
But actually, he'd be over on pipe fill unless he used a smaller neutral in each parallel run.
If all the conductors were the same size, in 2.5" RMC, then his only option would be 3/0 CU, which would squeak into the fill tables and give him 640 amps to use.
edit to correct "640" - typed from memory
[ January 05, 2006, 08:45 AM: Message edited by: georgestolz ]
Re: sercvice conductor size
I'll try: How about using the 800 amp load 3phase, using three 2 1/2" conduits with four 400 Kcmil 75 degree Celsius column (table 310.16) thhn,in each conduit.The GEC will be 3/o. Man that Iwire is fast on the draw. Single phase OK: Load 625 amps, two 2 1/2" conduits w/three 400Kcmil in each conduit.GEC 2/o
[ January 05, 2006, 06:53 PM: Message edited by: Jhr ]
I'll try: How about using the 800 amp load 3phase, using three 2 1/2" conduits with four 400 Kcmil 75 degree Celsius column (table 310.16) thhn,in each conduit.The GEC will be 3/o. Man that Iwire is fast on the draw. Single phase OK: Load 625 amps, two 2 1/2" conduits w/three 400Kcmil in each conduit.GEC 2/o
[ January 05, 2006, 06:53 PM: Message edited by: Jhr ]
- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
Re: sercvice conductor size
Copper is expensive but commands respect among many here.
It's up to you.
In that case, the four parallel runs of 250 MCM AL would fit, if you were so inclined.
Copper is expensive but commands respect among many here.
It's up to you.
frenchelectrican
Senior Member
- Location
- Nord'est Wisconsin et Paris France
Re: sercvice conductor size
now now hold on a min please i was reading thru this part did someone say going fromsingle phase to three phase delta ?? if so. you have to watch out the single phase load vs 3 phase load because slecting the wires will get very tricky here.
I went thru that headache before
Tim is this installment is single phase if so i might miss this other wise if 3 phase service to the place you are wiring it most POCO will not hook up delta service anymore unless specal approval have to run in wye format
please let us know excat answer
if there please excuse moi for this one
Merci , Marc
now now hold on a min please i was reading thru this part did someone say going fromsingle phase to three phase delta ?? if so. you have to watch out the single phase load vs 3 phase load because slecting the wires will get very tricky here.
I went thru that headache before
Tim is this installment is single phase if so i might miss this other wise if 3 phase service to the place you are wiring it most POCO will not hook up delta service anymore unless specal approval have to run in wye format
please let us know excat answer
if there please excuse moi for this one
Merci , Marc
- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
Re: sercvice conductor size
It's so easy to get lost in this one!
It's so easy to get lost in this one!
frenchelectrican
Senior Member
- Location
- Nord'est Wisconsin et Paris France
Re: sercvice conductor size
thanks George for head up with the oringal question i know i got little lost here with so much feedback and alot of good info here.
Tim:
I can see what you mean being a single phase service for 12 plex apt set up but one question how you can come up with load demand for each apt ???
i know there is a " magic number " but i really can't point where i did see it but for myself i came up some figures for ave figures for small to med size apt i use 50 amp per apt and came up with 600 amp but you were wise to go little bigger service there. i will stick to 800 amp service if possible
for 600 amp service you can use 350KCM wires [X 2 ] in parallel set up with 3.5 inch rigid pipe the reason i slect slightly bigger than it should because it is easier to snake the wires in the same time you can bump up to 500 KCM if need to go to 800 amp service but really for 800 amp serivce it is wise to go with 4 inch conducts
merci , Marc
thanks George for head up with the oringal question i know i got little lost here with so much feedback and alot of good info here.
Tim:
I can see what you mean being a single phase service for 12 plex apt set up but one question how you can come up with load demand for each apt ???
i know there is a " magic number " but i really can't point where i did see it but for myself i came up some figures for ave figures for small to med size apt i use 50 amp per apt and came up with 600 amp but you were wise to go little bigger service there. i will stick to 800 amp service if possible
for 600 amp service you can use 350KCM wires [X 2 ] in parallel set up with 3.5 inch rigid pipe the reason i slect slightly bigger than it should because it is easier to snake the wires in the same time you can bump up to 500 KCM if need to go to 800 amp service but really for 800 amp serivce it is wise to go with 4 inch conducts
merci , Marc
- Location
- Massachusetts
Re: sercvice conductor size
Both have advantages and disadvantages.
For better or worse almost all jobs we take on have specifications that require all copper conductors.
I used copper SE on my own homes service for one reason only. The copper cable is smaller than its AL equal so it is less obtrusive.
For me it is just habit like I imagine AL is habit for you. I have nothing against AL other than it's lower scrap value.Originally posted by georgestolz:
Copper is expensive but commands respect among many here.
Both have advantages and disadvantages.
For better or worse almost all jobs we take on have specifications that require all copper conductors.
I used copper SE on my own homes service for one reason only. The copper cable is smaller than its AL equal so it is less obtrusive.
Re: sercvice conductor size
Specs require all copper conductors. Also, I did not do the load calculations. The engineer did all that for me. The reason the load might seem a little high for each unit is that they are heated with three baseboard heaters and have a small electric water heater. No laundry.
Specs require all copper conductors. Also, I did not do the load calculations. The engineer did all that for me. The reason the load might seem a little high for each unit is that they are heated with three baseboard heaters and have a small electric water heater. No laundry.
- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
Re: sercvice conductor size
A load calculation is such a one-time, involved process, that trying to find a magic number would waste time, IMO. There's no safe, practical purpose for such a number, unless you're guessing at what size conduit to install for future use.
In many cases even the conduit size is spec'd in the plans.
Marc, I don't think there really is.
A load calculation is such a one-time, involved process, that trying to find a magic number would waste time, IMO. There's no safe, practical purpose for such a number, unless you're guessing at what size conduit to install for future use.
In many cases even the conduit size is spec'd in the plans.
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