250MCM for 21.7 amps? Voltage drop calc must be wrong?
- Thread starter Bri22
- Start date
- Status
JFletcher
Senior Member
- Location
- Williamsburg, VA
Yeah, especially if:
Correct. Sleeving is technically not code compliant. I'm ok with violating that one.
the raceway would be one long sleeve and not really capable of having more conductors pulled thru it in the future. That said, a quarter mile db is a long way to have the chance of improper backfill ruining the cables. The customer is already ok with raceway costs, might as well run a proper one. Maybe even a chance to upsell other receptacles/lighting along the way. 2 or 3 pullboxes would make pulling cable a piece of cake.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
Personally, and with the soils/rocks around here, I am pretty uncomfortable with direct bury cables and conductors, but I agree sleeving UF or USE conductors is a way around 300.18. Im not scared of long pulls by any means, but you would have to increase the pipe size quite a bit to make that feasible - sometimes it just gets not worth the extra expense and hassle IMO.
kwired
Electron manager
- Location
- NE Nebraska
You always pull all conductors out of all raceways if changing say a panelboard/cabinet so that you are in compliance with that section in those type of instances?
JFletcher
Senior Member
- Location
- Williamsburg, VA
You always pull all conductors out of all raceways if changing say a panelboard/cabinet so that you are in compliance with that section in those type of instances?
The raceway should be complete before conductors are installed. In the case of a panelboard change, it is complete. Making it temporarily incomplete to affect a parts change/upgrade would imho only necessitate the removal of conductors insofar as to complete the work.
Off topic a second; I found this thread here re: 300.18(A). I imagine the rule comes from building a raceway that must be "pullable", rather than building a raceway around the conductors for protection only. If we were going to do that, we could use plumbing 90s, have nearly infinite bend w/o j-boxes, etc.
ptonsparky
Tom
- Occupation
- EC - retired
1300' = cablecon
conductors already in in the raceway. Trench it or plow it.
conductors already in in the raceway. Trench it or plow it.
wjfawb0
New member
- Location
- McDonald, TN, USA
My utility has many 50A loads at 240/120 that are often 1000+ feet from the the main load centers. The utility uses two pole 480V breakers to run two legs to a 480 to 240/120 dry type transformer at the load. These transformers usually can accept 480 or 240 input so they can also be used at locations without 480V. Sizes of the transformers range from 5kVA to 12kVA depending on the load. Often it's 45A of staggered start motors, 60W lights, 300W heaters, and a 15A convenience outlet.
Correct. Sleeving is technically not code compliant. I'm ok with violating that one.
LOL
Definitely going to have a few pull boxes!
I'm thinking thats what we are probably going to do. We can run 480 out to the guard house which is in between the two far gates. The difference in wire size from 480v to 600v doesn't seem to justify adding another transformer to bump it to 600v.
A few people here have recommended using UF cable but for what ever reason I didn't consider it as an option. But now that I am thinking about it, it would make life a lot easier. I'll have to check out prices and see if that would be a good option.
Are you referring to a splice kit with no J-box? I'm searching now...
Found them. They only go to #8 from what I have found so far. The engineer still wants to plan on future use so he has calculated 6100va so I'll need a splice kit for #6 at 480v.
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ptonsparky
Tom
- Occupation
- EC - retired
Butt splices and heat shrink if you have to splice it and do not want to consider Cable con.
Genearally you can get a pretty good price on larger spools of wire. They will custom cut to length with all of the conductors on one spool. Saves a lot of labor for the bigger stuff. Maybe not for #6.
Do do not skimp on conduit size if you end up pulling it in. Not a good choice
Genearally you can get a pretty good price on larger spools of wire. They will custom cut to length with all of the conductors on one spool. Saves a lot of labor for the bigger stuff. Maybe not for #6.
Do do not skimp on conduit size if you end up pulling it in. Not a good choice
I went to the cable con website and did't see anything there that would match my needs. Everything on there site seemed to be for communication/data. If I'm missing something please fill me in.
Thanks!
JFletcher
Senior Member
- Location
- Williamsburg, VA
You need the Ideal db splices:
http://www.idealind.com/products/wire_processing/heat_guns/thermo-shrink_splices.jsp
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If Bri22 goes with 50A feed, I dont suppose a 480V L-N MWBC would be kosher/possible here would it? Or would he need 2 sets of xfmrs to accomplish that?
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
Maybe ask this guy what he would do if HE was paying for it
Ill bet he would order it and amp clamp it to see what it ACTUALLY draws - its probably way under 1000 watts.
ptonsparky
Tom
- Occupation
- EC - retired
Bad calculator
Bad calculator
Your voltage drop calculator is wrong. Most of the calculators you can download are wrong when calculating phase to neutral loads. They incorrectly double the distance from the source to the load when calculating phase to neutral voltage drops. The definition of voltage drop is the drop from the source to the load, not the drop from the source to the load and then back again to the source. If you have access to an Eaton Consulting Application Guide, run your voltage drop calculation using their published voltage drop tables and you'll find you can do your circuit with #1/0 at 90% power factor. Then do it again with double the length of the circuit and it requires #250 kcmil just like the downloadable calculators show. Unfortunately, these calculators are prevalent and many engineers and electricians are putting in conductors much larger than required for phase to neutral single phase circuits.
Stephen W. Nelson, PE, RCDD
Leo A Daly
Bad calculator
Your voltage drop calculator is wrong. Most of the calculators you can download are wrong when calculating phase to neutral loads. They incorrectly double the distance from the source to the load when calculating phase to neutral voltage drops. The definition of voltage drop is the drop from the source to the load, not the drop from the source to the load and then back again to the source. If you have access to an Eaton Consulting Application Guide, run your voltage drop calculation using their published voltage drop tables and you'll find you can do your circuit with #1/0 at 90% power factor. Then do it again with double the length of the circuit and it requires #250 kcmil just like the downloadable calculators show. Unfortunately, these calculators are prevalent and many engineers and electricians are putting in conductors much larger than required for phase to neutral single phase circuits.
Stephen W. Nelson, PE, RCDD
Leo A Daly
- Status