I am getting mixed messages from different licenced electricians. Run length 100ft. 60 amp sub-panel in 1" conduit. Wire size according to NEC??

2 electricians have stated #6
1 electrician has stated #4
I have also verbally talked with another electrician that said you have to rate the wire based at 60deg not 90deg because the breaker says 60deg and that is the weakest link:eek:

I am starting to get confused. I don't get why there is grey in the above picture. At 1st I was thinking voltage drop, but after looking into it further this should not be a problem.
Any feedback would be good.

Chuck

That 60 Amp subpanel is going to have a hard time fitting inside a 1" conduit. <G>.

I believe you mentioned a lot of motor loads, but I'm not sure. Motor loads may increase requirements.

Are we talking apples (copper) or oranges (Aluminum)?

What is the continuous load (multiply amps by 1.25) (on for more than 3 hrs) and non-continuous loads?

Type of wire?

Did you do voltage drop calcs based on 240 or 120 V? The sizing to the box should be based on 120V and 3 wires, even though it's 240 and 4 wires.

There is lots of grey.

You are correct about he Grey. I apologize for that. Let me clarify this a bit better---
This would be for a wood work shop. Most of the major draw will be for 30 minutes or less.
->The biggest draw I see at one time would be--
24 amps 5hp motor---220
18 amps-3hp motor--220
8 amps---120 Continuous
10 amps--120 Continuous
->All the wire I would be using is copper--thhn
->I was planning on 1" EMT for the raceway
->Main Box 200amp Bryant
->Planned sub-panel Square D

I think that should help see things a little bit better

I was under the impression that 4(2 black, 1 white, 1 green) #6 thhn was fine in 1" EMT. Am I missing something here?:eek:

Let's do voltage drop calculations backwards:

60 A breaker, means 48 Amps continuous (Maximize service), 100' away

#6 Cu would yield 3.9% drop at 120 V and 48A
# 4 Cu would yield 2.5% drop at 120 V and 48 A

OK, now for some intuative stuff because of the 120 stuff.

It could be a) 24+18+8+10 or 60 amps or it could be:
b) 24+18+2 or 48 Amps depending on how things are wired.

If the loads were calculated, you would end up as (24+18)+(8+10)*1.25 or a circuit rating of 63.6 and you would have to round up to the next breaker size.
You could sustain 60A without tripping, but you have a continuous load of 18 A derated by multiplying by 1.25.

In b, you would have a circuit of (24+18)+(2*1.25) or 44.5 A, you would have to round up to a 50 A breaker.

You probably want to keep the drops to within 3% especially because of the motor loads. There will be a starting current. I see you did use FLA (Full Load Amps). In the US, there isn't 220 V anymore. It's 240/120. Continuous loads are multiplied by 1.25 to get the OCPD (Overcurrent Protection Device). 120 volt loads can be carried as the sum or the difference depending on if they are distributed between the hots. Doing the voltage drop calculations based on 240V seems to be a mistake people make. Now when sizing wire to the 240 V motors, you would use 240 V because there is no neutral to the equipment. The neutral carries the difference of the currents on the hots.

My vote is for #4 Cu with the two 120 V circuits split - One on L1 and 1 on L2.

KeepItSimpleStupid: Wow, then out of the 3 licenced electricians only one was right. That is kinda of scary. It will be interesting to see what the 4th electrician says, as I have a final quote tommorrow.
Two final questions--
What size emt would I use for #6? What size emt would I use for #4?
So far all quotes have included 1". But the one who quoted #4 also said 1".

I think 1" is fine for #6, but for #4 it would be tight and out of code. Am I correct. I didn't say anything to the electrcian because I am not one to tell someone how to do there job.

Last question--Off the subject, but I have always wanted to know--When can the plastic conduit be use in place of EMT? I always have believed that plastic was used only for underground, but when at HD the clerk said people use it in attic all the time and it is fine. I couldn't debate his statement because I am not familiar with the plastic. I think there are 2 types, but I am not even sure on that. Anyway, a few quick comment on plastic would be helpful for me to know. Type and Usages?
Thanks a lot for your feedback. I think I will use the electrian who is using #4.

For #4's won't fit in 1 EMT, but the ground conductor can be smaller, so therefore it COULD be OK with a smaller gage ground wire.

1-1/4" EMT will fit four #4's or 4 #6's.

I'll refer you here: Electrical Wiring in the Home: Wire Size for Subpanel, amp breaker, gfi outlet

Conduits:

There are a number of types such as EMT, ENT, IMC, LFNC, RMC, PVC and HDPE

With the plastic conduits, the wall is thicker and therefore less wire can be run in the space. So, there is a disadvantage. You can't disassemble them. They are inherently water tight.

You have flexible conduits which can be watertight.

And you have rigid and non-ridged conduits.

So, the bottom line is you have to use plastic conduits underground and for above ground applications you might have to bump up the size compared to EMT.

1" EMT may be OK with 3 ea #6 and 1 ea #? which would be a smaller ground conductor which is permissible. I did not determine the ground size.

Grounds handle fault currents and therefore do not have to sized as the current carrying conductors. Take a look at the ground wire in a standard 14-2 w/ground Romex or NM-B cable.

Here is some info on PVC and HDPE matherials:

Thermoplastics

KeepItSmpleStupid--Question about something I have never heard of in one of the abover links.Electrical Wiring in the Home: Wire Size for Subpanel, amp breaker, gfi outlet

Also a relatively new code requirement, when installing a subpanel you have to use the fourth ground wire, in this case the #8, and also drive a ground rod and bond it to the ground bar of the sub panel.

I understand ground rod because this is not an attached garage. But what I don't get is the extra ground wire. This box is for an outside of the garage. Does it matter if it inside or outside an unatttached garage?
I would think you would need 2 hots, 1 neutral, and 1 ground making the total wires 4. In the article I understand it to be 2 hots, 1 neutral and 2 grounds.

Please explain this to me.

Let's ask a question. What is ground?

1. It is a zero volt reference
2. It's a place where faults go and the fault should not disturb the zero volt reference.

So, let's examine #1. This means that CATV and telephone and the power ground should all be at zero volts.

Now, we add a sub-panel. In order to maintain that 0 volt reference, the ground to the sub must not be bonded to the neutral. So, we have satisfied the requirement that the neutral current from the sub will not disturb the ground reference.

Thunderstrorms/Lightning

A couple of things can happen. During a thunderstorm the Earth's potential can change over a hundred feet or so, hence the necessity to again have a ground at a single point.

Now suppose we get a lightning strike at the unattched structure.
What might happen? That lightning strike will likely dissapate through the ground of the sub back to the main panel. Well, that ground will likely melt. What we would like happen is that the lightning strike be diverted to Earth and it will take the path through the ground rod of the sub panel.

GROUND LOOPS

These are differences in potential in so called "grounds". These loops are a real pain to eliminate in electronics and you may have to make some compromises along the way. Very little difference in potential can damage electronics. In many cases that ground is common to electrical communication so isolation and differential transmission techniques are used to help elimiinate the problem. (Lots of stuff can go here)

We used to just be concerned with "protective ground". If there was a break down in the insulation of a piece of grounded equipment, the fuse would pop. When power was first generated, we probably only had lamps in the home, so two wires were sufficient. Then there were motors (washing machines) and drills and protective ground came into play. Then came plastics and the idea of "double-insulated" came into play. Now we have GFCI and AFCI's because people don't inspect their electrical wiring and/or don't know what to look for. Incidentally, GFCI's don't require a ground to work. 10 mA or so across the heart muscle is enough to stop the heart.

Ethernet is transformer isolated. USB is not. Telephone is an isolated entity. CATV is a grounded entity.

In extremely sensitive buildings, there actually will be two different grounds. One being a clean ground used for communication and another one being a dirty ground used as protective ground. There are also orange colored outlets which have an isolated or independent ground. These are very rare.

I guess a couple of asides:
1) The guy's main breaker box and service entrance was located on the exterior of the building. This is entirely possible.
2) Conduit is used as protective ground. You cannot rely on its integrity.

KeepItSimpleStupid

That is the best explanation I have ever had given to me. You should write books. I hope this site references back to this link because it is very clear to understand. Wow:)

Thanks for spending the extra effort. I really do appreciate the feedback and definition.

Thanks!! :) :) :)

I know KISS and I differ on this subject, but for a feeder you DO NOT use 120v for your voltage drop calculations. It is assumed that the loads are at least mostly balanced. You would have to go out of your way to unbalance them. ESPECIALLY with such large 240v loads as you have.
I mean how can you even consider using 120v when right off the bat you have 42A worth of 240v motors??

Also, I doubt ANY of the loads you have would be considered continuous. There is NO 48A max in a 60A panel. A 60A panel can have a 60A load. In a residence I SERIOUSLY doubt you'd even come close to 48A for more than three hours. And it is not even that you would for more than three hours, it is if it is expected to last more than three hours. This precludes forgetting to turn something off.

A FULL 60A load @ 100' @ 240v is LESS than 3% with #6cu.

Using your own numbers there would be a 2A imbalance. 2A @ 120v is not worth even thinking about @ 100'. :rolleyes:

I think KISS might be right.:D I have been doing some research on my own and have learned a few things. I am in no way as talented and educated as you and KISS but let me take a stab at this.
Let do Voltage Drop 1st--
I am using Copper thus k=12.9 If I have #6 THHN on a 240 ling for 130 feet these are my numbers--
60 amps=7.67 Voltage drop, Voltage at load at end of circuit 232.33 Voltage Drop %= 3.2
50 amps=6.39 Voltage drop, Voltage at load at end of circuit 233.61 Voltage Drop %=2.66
I don't think the NEC has a requirement for Voltage Drop, but <3 to 5 is good. My 60 amp circuit is at 3.2 which is getting close.:(

Now my #4
60 amps=4.82 Voltage Drop, Voltage at End of circuit 235.18, Voltage Drop %=2.01
50 amps=4.02 Voltage Drop, Voltage at End of circuit 235.98, Voltage Drop%=1.67
Both of these circuit are good.:D

So in theory with the above data I could run #6 for 60 amps, but I would be starting to push things a little. The other problem that derates things even more is Temperature. I live in Southern California--This run will be in EMT through the attic. I estimate the high temperature of the attic to be around 140-158 degrees F. Thus, I will use 70C for my high Ambient Temperature.

#6, 60 amps, 240 Volts @ 70C(158F) for 130feet would calculate out to Exceeding NEC Table 310.16 limit. The Max Amps under this condition would come in at about 46 amps which is far from the 60 amps I want.
#4, 60 amps 240 Volts @ 70C(158F) for 130 feet would calculate out to within range and give me number of Voltage Drop 5.1, Voltage at load end 234.9, with a Voltage Drop % of 2.1. Thus within specs.

Thus #4 would actually be code. Thus, I think KISS is correct or my lack of experience is incorrect.:cool:

As you know, VD is a suggestion, NOT a code requirement. Even though I do not typically wire to code minimums, in my experience, 100'-120' is not enough to justify over sizing wire, even in So-Cal.
You are talking about less than 5% drop, in fact you are very close to 3%. IMO this is not even worth thinking about.

I understand and see your point about the voltage drop. What you opinion about the tempature being that the EMT will be run in the attic of the house?:o

I think your temp numbers are a bit high.
I don't generally worry about temp adjustments in a residential setting.

Will it appears that you thinking is in line with the other electricians. I had my final quote on Friday and 3 out of 4 agree in the #6 wire would be acceptable.
I am starting to believe that KISS is doing things a little over kill. Anyway, thanks for your feedback and have a nice day.

No problem. You too.

cc4digital:

Do your voltage drop calculations for 120 V. Doesn't the panel also supply 120 V?

Assume all your 240 V loads are at maximum and either add both your 120 V loads or the difference in current of the 120 V loads.

What would be the % voltage drop under these two conditions using #4 and #6?

I totally agree that when using the 240 method #4 is fine. I'm saying that since the panel also supplies 120 V, the Vd calcs need to be done with that voltage. The 120 V load may or may not be within 3%.

Also see: https://www.askmehelpdesk.com/electr...t=voltage+drop

https://www.askmehelpdesk.com/electr...t=voltage+drop

THIS I can understand, although I still don't agree.
HOW do you know what the actual difference will be at any given time, if any at all?

Just because the panel provides 120v circuits is not justification to use 120v in figuring VD.

While it is true that the panel does provide 120v loads, it is also VERY likely (and definitely assumed) that the load will be mostly balanced.
Like I said, you would have to go WAY out of your way to have an unbalanced load in a residential panel.

I really do think this is a case of agree to disagree. We can just link these threads when this comes up and let folks decide for themselves.