in the real world, do we really need to do the voltage drop calculation? - Page 2 - Electrician Talk - Professional Electrical Contractors Forum
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Old 08-07-2017, 10:24 AM   #21
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Voltage drop has never been enforced by AHJ that I know of.
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Old 08-07-2017, 11:03 AM   #22
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I wonder if in the original posters case they were instructed to install per plans.
And as said for some reason his superior(s) said they didn't know how to do a VD calc.

But in reality it was designed by an electrical engineer when the plans were drawn.
With VD factored in.
Then the plans were submitted to the local inspection department for review that may or may not look at the VD on the feeders.
When submitted for bid the company estimator may have looked at it.
Or someone in the office when the job was being planned and mobilized may have looked at it.

By the time a job like that get to the install stage many eyes should have already looked at it. While it's good for the installer to use their experience to question something that does not seem right. Such as why would they call for 3/0 but only a 1.5" EMT. It's not the place for a journeyman to be 2nd guessing the engineers calculations or design. By that point there is a contract in place to install per the engineered drawings. Yes there has been a 1000 times I wished I could do something different.

Point is your supervisor probably wont be happy if your sitting with the plans, pad of paper, and calculator. Your job is to install. I've had guys not far in the trade that learned a few things that wanted to basically do that. While I don't mind helping them learn, after a few minutes we both have a job to do. At that point they can study on their break, not on the clock.

Don't see condos with 200a panels much until you get into the luxury. Such as a 400a but they have most of the floor. Or (2) 100a as they were 2 condos merged together. But I see boilers or central plants. Perhaps electric heat up North 200a is more common?

Back to the calc.
A 200a 208v 1p service with 300' 3/0 cu
With an extreme calculated load at 80% = 160a load
The VD = 4% or 8.4v

Somewhere in the plans it should have what the calculated panel load is.
It's probably not even close to 200a. There may be other reasons for choosing the 200a panel by the EE. Such as a local code, customer request, or more cost effective than something between 100 and 200.

Perhaps your thinking the units closer to the electrical distribution could use a smaller and the farther ones a larger conductor. It's just goes back to the EE, and how he draws it. From a foremans view it's much easier to use 1 size conduit and conductor for everything. Maybe the EC would get better pricing.
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Old 08-07-2017, 11:22 AM   #23
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Quote:
Originally Posted by mike883 View Post

please focus on the voltage drop topic
thanks
Gee, mom. Thanks for the reminder.

The load on the panels is exactly relevant to the voltage drop.
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Old 08-07-2017, 11:29 AM   #24
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Quote:
Originally Posted by cdslotz View Post
Voltage drop has never been enforced by AHJ that I know of.
That is because it has nothing to do with code.
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Old 08-07-2017, 11:34 AM   #25
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Quote:
in the real world, do we really need to do the voltage drop calculation?
When it comes to wiring in a building, maybe, it depends on the length and the calculated load.

But when it comes to outdoor stuff like Cow's agricultural stuff, or roadway lighting where the cable runs can be several thousand feet, the answer is absolutely yes they are necessary.
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Old 08-07-2017, 11:50 AM   #26
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With the apps available now that you can download to you phone, its pretty simple. Do them if in doubt. I do some long runs on heavy continuous loads and its cheap insurance for me.
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Old 08-07-2017, 11:53 AM   #27
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Not doing voltage drop calcs on every circuit is like not meggering every circuit. You are all a bunch of hacks.
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Old 08-07-2017, 12:08 PM   #28
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Quote:
Originally Posted by HackWork View Post
Not doing voltage drop calcs on every circuit is like not meggering every circuit. You are all a bunch of hacks.
I've used a megger once. It was awhile ago. If memory serves it looked similar to this guy...



Did a service calc a few years back. Tell the guy he needs to upgrade for his new air conditioner. He just finds somebody else to hook it up.

Voltage drop calc in school. I don't know 1968-72. One of those years.
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Old 08-07-2017, 12:19 PM   #29
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CHOO-CHOO!!!!

I have an app on my phone and iPad. I think it's by SouthWire.

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Old 08-07-2017, 12:29 PM   #30
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Quote:
Originally Posted by mike883 View Post
not for the suite,
for the heat trace, snow melt, common area lighting or whatever panel
and by the way ,not I said 80% or 100%
it shows on the drawing line diagram

please focus on the voltage drop topic
thanks
We are, the first sentence in the voltage drop rule says to use the calculated load.
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Old 08-07-2017, 12:46 PM   #31
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Originally Posted by HackWork View Post
Not doing voltage drop calcs on every circuit is like not meggering every circuit. You are all a bunch of hacks.
My point was for feeders on a large project the VD is not done by the installer in the field. You got the conduit done and a container of wire spools delivered and you want the guy pulling the wire check and correct the stamped plan set?

Like to hear that conversation.
"Hey boss, we need to send back all those pre-cut spools of 3/0 and get some 4/0 instead. When I calculated the units with the standard method, then figured in a VD of 2% I got came up with 250's. Think the 2" EMT might be an issue also. I checked each unit twice on my cell phone app.
We need 250cu for half the condos, 2/0 on unit 101, and 4/0 for the 3rd floor".

I would give that person their 2 checks and the door.
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Old 08-07-2017, 12:54 PM   #32
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I was joking, active1. I wasn't replying to your post.
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Old 08-07-2017, 01:03 PM   #33
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Quote:
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I was joking, active1. I wasn't replying to your post.
You were joking? You mean you don't really do voltage drop calculations for every single run of Romex ? Do you really mean that?
You are not allowed at Mike Holt's forum ever...............
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Old 08-07-2017, 01:19 PM   #34
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In Canada, voltage drop is code-enforceable.
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Old 08-07-2017, 01:29 PM   #35
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On Friday I put in two multi gang switch boxes at a door , mounted back to back. I ran a nine inch piece of 14-2 between the boxes and put all the switches on the same circuit. I forgot to do a voltage drop calc for the nine inch piece. Should I go back there and rip it out and put in a larger cable now since it didn't get a vd calculation?
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Old 08-07-2017, 01:33 PM   #36
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On Friday I put in two multi gang switch boxes at a door , mounted back to back. I ran a nine inch piece of 14-2 between the boxes and put all the switches on the same circuit. I forgot to do a voltage drop calc for the nine inch piece. Should I go back there and rip it out and put in a larger cable now since it didn't get a vd calculation?
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Old 08-07-2017, 01:35 PM   #37
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I always check my 9 inches for VD ... but that's just me
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Old 08-07-2017, 01:38 PM   #38
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I always check my 9 inches for VD ... but that's just me
You better spit it out so you can get a good look at it.
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Old 08-07-2017, 01:42 PM   #39
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This thread delivers.
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Old 08-07-2017, 01:55 PM   #40
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Originally Posted by RePhase277 View Post
You better spit it out so you can get a good look at it.




Good advice from the experienced Master
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