Does table 310.16 apply to utility feeds

[bwise863]

I'm setting a 200 amp panel on a work shop and wiring in a few plugs and lights. The work shop is on a residential property and it is proposed to have it's own meter. According to the utility company it is automatically considered commercial. Which translates to the owner runs conduit and wires from the panel to the utility box at the street. Left for utility to connect. The utility will not size this and says the county inspector will approve/disapprove the installation.

The issue is it is a 375' run. Calculating the voltage drop to be below 3% I'm coming up with 3" PVC sch. 40 and 3 - 750 kcmil wires. Does Table 310.16 and a 3% minimum drop apply to primary wires.

Any suggestions would be appreciated.

Thanks

 

[raider1]

The 3% voltage drop you refer to is located in 215.2(A)(4) Informational Note No.2 and 210.19(A)(1) Informational Note No.4. Informational Notes are not enforceable and are just there for informational purposes.

Chris

 

[raider1]

Also 310.16 would apply if you are installing the conductors.

Chris

 

[Smart $]

I didn't check your numbers for voltage drop sizing, but it seems you are calculating for the whole 200 amps. You mentioned a few plugs [I assume you meant receptacles] and lights... but unless it is a super large shop, these would not total 200 amps. Did you calculate the load? Voltage drop has many considerations that can be included or omitted, but the first should always be the typical load current versus the calculated load current... and only on occasion, full service-rated current.

 

[bwise863]

Yes, I'll be putting in the service lateral conductors (750 kcmil). That size is quite a chore and what I'm looking for is whether I did the calculation right or not.

thanks

 

[bwise863]

The largest calculated load is 131 amps on one leg. That is a future load that is not part of this phase of the work but we want to plan for. When I talked to the county they said the service lateral they don't even look at. It seems someone needs to verify the load and voltage drop numbers.

thx

I didn't check your numbers for voltage drop sizing, but it seems you are calculating for the whole 200 amps. You mentioned a few plugs [I assume you meant receptacles] and lights... but unless it is a super large shop, these would not total 200 amps. Did you calculate the load? Voltage drop has many considerations that can be included or omitted, but the first should always be the typical load current versus the calculated load current... and only on occasion, full service-rated current.

 

[iceworm]

The largest calculated load is 131 amps on one leg. That is a future load that is not part of this phase of the work but we want to plan for. When I talked to the county they said the service lateral they don't even look at. It seems someone needs to verify the load and voltage drop numbers.

I don't know how you came up with 750. Maybe you meant 3 - 350 AL

Using round numbers, 240V at 3% = 7.2 volts. for a 150A load, that's about .05 ohms over 2 x 375 = 750 feet. Ohms/1000 = (.05/750) x 1000 = .067 ohms/1000.

So I would highly consider parallel 3/0 AL - which should fit in 3" PVC sch 80. Or 3 - 350AL

ice

 

[augie47]

My calculator shows with a 4/0 Cu (or 300 AL), 131 amp load, 375' you would still be within a 3% range.
I agree with Iceworm, I'd go for (3) 350 AL in a 3"

 

[Smart $]

I don't know how you came up with 750. Maybe you meant 3 - 350 AL

Using round numbers, 240V at 3% = 7.2 volts. for a 150A load, that's about .05 ohms over 2 x 375 = 750 feet. Ohms/1000 = (.05/750) x 1000 = .067 ohms/1000.

So I would highly consider parallel 3/0 AL - which should fit in 3" PVC sch 80. Or 3 - 350AL

ice

I hope you mean 3 conductors and not 3 sets.

And that's assuming 120/240V 1? 3W system. OP did not specify.

I got slightly higher number: 7.2V ? 2 ? 131A ? 375' ? 1000 = 0.073ohms/kft

...which is exactly what Table 9 shows for 350AL at Effective Z of 0.85PF in PVC conduit.

Getting back to 3 conductors, may need only 2 at 350kcmil-AL. The neutral can be smaller if the maximum calculated unbalanced neutral current is lower than 131.

Actually, the ungrounded conductors could be smaller too if the typical load current is lower than 131. For example, if the typical load is 100A, and only on occasion would it get up to 131A, we could calculate the V-drop at 100A... though slight dimming of lights could occur if that occasional high load current is a result of a motor load.

Should also point out that many times when people state calculated load, they include the extra 25% for continuous loads... and calculated load does not actually include that extra 25% and neither should V-drop calculations.

 

[bwise863]

Smart $ you're right it is single phase 3 wire 120/240. So, then can I still breaker the panel out at 200 amps if I did go with 3 350 mcm conductors? I think I'm missing some logic behind this.

thx

 

[hurk27]

With all the math aside, would it not be better to upgrade the houses meter to a 320 meter base with double lugs and feed this shop off the extra set of lugs if the house is much closer? then the customer would be billed at the residential rate and the conductor length would be shorter?

I mean you would have to find out if this would be acceptable by the utility and inspector but might be worth looking into?

 

[Smart $]

Smart $ you're right it is single phase 3 wire 120/240. So, then can I still breaker the panel out at 200 amps if I did go with 3 350 mcm conductors? I think I'm missing some logic behind this.

thx

Yes, you can use a 200A main circuit breaker. 350kcmil AL is good for 250A. The downside is if the (actual) connected load goes over 131A (at an assumed power factor of 0.85), the voltage drop will exceed 3%. If 131A is the calculated max' future load, shouldn't be a problem. Now if you (or customer) can foresee a future load going beyond 131A, the customer may opt to go larger or use parallel sets.

Also, as I said, your neutral conductor may be able to be smaller (and not affect voltage drop). Just subtract any 240V load currents from the 131A calculated load, and that should be your calculated max' unbalanced neutral current. You can calculate for voltage drop at that current for the neutral... or a simpler way is to just subtract the 240V load current from the 250A rating of 350kcmil AL. Say you have 50A of 240V loads. 250A – 50A = 200A. A 250kcmil AL rated 205A should be good for the neutral and its voltage drop considerations (for this example).

 

[Smart $]

With all the math aside, would it not be better to upgrade the houses meter to a 320 meter base with double lugs and feed this shop off the extra set of lugs if the house is much closer? then the customer would be billed at the residential rate and the conductor length would be shorter?

I mean you would have to find out if this would be acceptable by the utility and inspector but might be worth looking into?

Upgrading just the house meter base may not cut it. Would likely require upgrading service conductor size too for accomodating the additional load. Don't know the physical layout, so it may or may not be shorter... but doing so to get the resi' rate is a good point.